Stand Alone Conference of the American Society of Naturalists
Asilomar Conference Grounds, Pacific Grove, California, 5-9 January 2018
Saturday morning, 6 January 2018
Adaptation | Chapel
|C1||8:30||Jesse Czekanski-Moir||Modeling adaptive and nonadaptive radiations|
|C2||8:50||James Peniston||The role of pulsed migration events in the adaptation to harsh sink environments|
|C3||9:10||Matthew Schrader||Adaptation to a novel family environment involves both apparent and cryptic phenotypic changes|
|C4||9:30||Samuel Scheiner||The role of multiple traits and trait interactions in the evolution of plasticity: a simulation|
|C5||9:50||Stephen Proulx||Experimental evolution of transgenerational plasticity in fluctuating environments|
|10:10||Coffee Break - Refreshments in Chapel|
|C6||10:40||Ryan Greenway||Transcriptomic analyses of convergent evolution in sulfide spring fishes|
|C7||11:00||Courtney Van Den Elzen||Dispersal trait evolution correlates with microhabitat adaptation in wind-dispersed vernal pool congeners|
|C8||11:20||Aaron Comeault||Evolution of the thermal niche in three species of Drosophila from equatorial Africa.|
|C9||11:40||Jannice Friedman||Loss of colour pigmentation is maintained at high frequency in a monkey flower population|
Macroecology & Macroevolution | Sanderling
|C10||8:30||Holly Kindsvater||Linking individual behavior to macroevolutionary life history variation in tunas|
|C11||8:50||David Hembry||Mutualism breakdown and ecological opportunity in leafflower-moth interactions|
|C12||9:10||Eliot Miller||Macroevolutionary drivers of plumage convergence: quantitative tests and new insights|
|C13||9:30||Joseph Tobias||Convergent evolution connects form to function in the world’s birds|
|C14||9:50||David Reznick||Mode of maternal provisioning builds a bridge between microevolution and macroevolution|
|10:10||Coffee Break - Refreshments in Chapel|
|C15||10:40||Hannah Frank||Signatures of ecology and biogeography on pathogen-interacting genes in bats|
|C16||11:00||Rui P B Diogo||Evolution driven by organismal behavior: A new, unifying view of life, function, form, mismatches and trends|
|C17||11:20||Molly Hetherington-Rauth||Island biogeography and the evolution of floral traits|
Niches | Marlin
|C19||8:30||Ari Martinez||Fear-based niche shifts in Neotropical birds|
|C20||8:50||Luke Frishkoff||Past niche evolution and its manifestations in an Anthropogenic biosphere|
|C21||9:10||Kelly Carscadden||Niche breadth measures yield different estimates: Classifying and comparing measures from across ecology and evolutionary biology|
|C22||9:30||Parris Humphrey||Sex increases the rate and predictability of adaptation while decreasing its pleiotropic costs|
|C23||9:50||Kinsey Brock||Beyond sexual selection: a role for ecological niche breadth in the evolution of sexual dichromatism|
|10:10||Coffee Break - Refreshments in Chapel|
|C24||10:40||Travis Ingram||The dimensionality of individual niche variation|
|C25||11:00||Nicholas Kortessis||Character displacementin a temporally varying environment: evolution of differential use of a fluctuating environment|
|C26||11:20||Robert Holt||Spatial scale and ecological niche concepts|
|C27||11:40||Kaitlyn Brown||Pollinator-mediated facilitation explains asymmetric neighborhood effects in experimental plant communities|
Host-Parasite Dynamics | Scripps
|C28||8:30||Jeremy Draghi||Red Queen dynamics oppose host-range generalists in an eco-evolutionary model of parasites and hosts|
|C29||8:50||Patrick Clay||The impact of within-host priority effects on multi-pathogen epidemics|
|C30||9:10||Yun Tao||The Art of Outbreak Control: transient models of movement and disease management|
|C31||9:30||Ryosuke Iritani||Horizontal transmission of parasites can favour conditional host dispersal|
|C32||9:50||Jessica Hite||Parasite-induced anorexia: consequences for the evolution of parasite and host traits|
|10:10||Coffee Break - Refreshments in Chapel|
|C33||10:40||Amanda Hund||Divergent sexual traits evolve independently with local parasites to signal relevant information to females|
|C34||11:00||Ben Wasserman||The effect of intraspecific variation in predator defense traits on parasite infection within and across generations|
|C35||11:20||Emlyn Resetarits||How interspecific competition influences eusociality across a guild of body-snatching trematodes|
|C36||11:40||Camille Wendlandt||Host and symbiont contributions to nodule occupancy in the legume-rhizobium symbiosis|
Mutualisms | Curlew
|C37||8:30||Kane Keller||Rhizobium mutualists alter competitive interactions|
|C38||8:50||Katherine Eisen||The effects of community context and wet-year vs. dry-year dynamics on pollinator-mediated selection inClarkia (Onagraceae) in the southern Sierra foothills (Kern County, CA)|
|C39||9:10||Gordon Smith||Intraspecific variation in nectar use by foraging hawkmoths|
|C40||9:30||Judith Bronstein||The behavioral ecology of nectar-robbing: how alluring is "the temptation to cheat"?|
|C41||9:50||Jeremy Yoder||Sanctions, partner recognition, and variation in mutualism|
|10:10||Coffee Break - Refreshments in Chapel|
|C42||10:40||Jacob Heiling||Balancing costs and benefits when a gamete is also a pollinator reward|
|C43||11:00||Sarah Richman||Evidence for asymmetric competition between mutualists of varying quality|
|C44||11:20||Kenji Quides||Optimizing fitness benefits in the legume-rhizobium symbiosis|
|C45||11:40||Emily Hudson||Does early heterospecific song exposure affect species recognition in wild nestling birds?|
Sunday morning, 7 January 2018
Rapid Evolution & Environmental Effects | Chapel
|C46||8:30||Ron Bassar||The evolution of coexistence: theoretical and empirical studies in a simple community|
|C47||8:50||Anne Panetta||Selection in a warmer world: insights from a climate warming experiment|
|C48||9:10||Kiyoko Gotanda||You are what you eat: urbanization erodes niche segregation in Darwin’s Finches|
|C49||9:30||Eben Gering||Two tickets to paradise: rapid evolution of feral fowl from Kauai and Bermuda|
|C50||9:50||Michelle Tseng||Rapid evolution of resources and consumers to temperature change|
|10:10||Coffee Break - Refreshments in Chapel|
|C51||10:40||Susan Magnoli||Rapid evolution in ecological restorations|
|C52||11:00||Axel Meyer||Genomics of parallel adaptations and speciation in repeated species flocks of cichlid fishes|
|C53||11:20||Carol Boggs||Temporal scale and timing of environmental variation: effects on insect life history and populations|
|C54||11:40||Elena Litchman||Rapid evolution of thermal reaction norms in marine phytoplankton reveals constraints and trade-offs|
Consumer-Resource Dynamics | Sanderling
|C55||8:30||Benjamin Toscano||Long-term dynamics of life-history intraguild predation|
|C56||8:50||Benjamin Van Allen||Thrift, gluttony and death: Population responses to resource availability in a tide pool copepod|
|C57||9:10||André de Roos||When life history matters: Somatic maintenance costs and juvenile-adult stage-structure jointly overturn ecological rules-of-thumb|
|C58||9:30||Shannon Beston||The evolution of vertebrate eye size across an environmental gradient in Trinidadian killifish|
|C59||9:50||Candace Low||Optimal control and cold war dynamics between plant and herbivore|
|10:10||Coffee Break - Refreshments in Chapel|
|C60||10:40||Michael McCoy||Pulsed dynamics: A top down perspective|
|C61||11:00||Megan Sabal||Trade-offs between migration speed and predator evasion with hatchery and wild salmon|
|C62||11:20||Grant Haines||Integration of swimming kinematics and ram suspension feeding in American paddlefish|
|C63||11:40||Carina Baskett||Traits contributing to stronger anti-herbivore defense at lower latitudes in a temperate herb|
Method Development & Application | Marlin
|C64||8:30||Carl Boettiger||Resolving an uncertainty paradox in ecological management|
|C65||8:50||Kevin Gross||Funding science in an era of scarce funds: Would a modified lottery help?|
|C66||9:10||Silas Tittes||A novel Bayesian inference method to model tolerance curves|
|C67||9:30||Erica Newman||Revealing biases in the sampling of species interaction networks|
|C68||9:50||Shane DuBay||Bird specimens track 135 years of atmospheric soot and environmental policy|
|10:10||Coffee Break - Refreshments in Chapel|
|C69||10:40||Jonathan Davies||Reconciling phenological observations with flowering records in herbaria|
|C70||11:00||Kyle Coblentz||The neglected numerical response of consumers|
|C71||11:20||Charles Goodnight||The phenotypic perspective: A post-modern synthesis|
|C72||11:40||Donald Waller||Phantom species: Can we estimate pseudo-turnover?|
Behavior & Mating Systems | Scripps
|C73||8:30||Helen McCreery||Does individual persistence promote group coordination? A comparative approach to cooperative transport in ants|
|C74||8:50||Ryan Germain||The consequences of polyandry for sibship structures, distributions of relatedness, and potential for inbreeding in a wild population|
|C75||9:10||Denon Start||Causes and consequences of animal personality in larval dragonflies: individuals to ecosystems|
|C76||9:30||Sonya Auer||Nutrients from salmon parents relax selection pressures on their offspring|
|C77||9:50||Jeremy Van Cleve||Stags, hawks, and doves: Individual variation in helping in social evolution theory|
|10:10||Coffee Break - Refreshments in Chapel|
|C78||10:40||William Fagan||Intruder alert! How communication behaviors influence territory maintenance, expansion, and the persistence of local populations|
|C79||11:00||Michael Moore||Thermoregulatory effects and the geographic diversification of sexual coloration in a North American dragonfly|
|C80||11:20||Heather Briggs||Variation in context dependent foraging behavior across pollinators|
|C81||11:40||Gina Calabrese||Diversity in mate preferences and signals in Spadefoot toads: causes and consequences|
Environmental Change | Curlew
|C82||8:30||Susana Wadgymar||Maternal effect mitigate maladaptation to climate change|
|C83||8:50||Christopher Johnson||How climate warming affects plant phenology and reproduction|
|C84||9:10||Molly Albecker||Adaptation to environmental change in species with complex life cycles: The influence of stage specific selection and density dependence|
|C85||9:30||Volker Rudolf||Linking phenological shifts to species interactions in a changing world|
|C86||9:50||Hilary Rollins||How do climate-change induced phenological shifts alter terrestrial competition between two amphibians?|
|10:10||Coffee Break - Refreshments in Chapel|
|C87||10:40||Na Wei||Functional traits and plasticity confer polyploid advantage in changing environments|
|C88||11:00||Johanna Schmitt||Mechanisms of life history variation and climate adaptation in a native wildflower|
|C89||11:20||Melis Akman||Species persistence under climate change: interplay between adaptation, plasticity and migration in common sugarbush (Protea repens) of South Africa|
|C90||11:40||Shannon Carter||Linking phenological synchrony to species interactions|
Monday morning, 8 January 2018
Lightning Talks | Chapel
|L1||8:30||Holly Moeller||Acquired metabolism as an evolutionary path to mixotrophy|
|L2||8:40||Simone Des Roches||Ecological effects of variation within species|
|L3||8:50||Becky Fuller||Using human vision to detect variation in avian coloration: How bad is it?|
|L4||9:00||Thomas Miller||Quantifying resource niches in microbial communities|
|L5||9:10||Sharon Strauss||Stature drought & rarity|
|L6||9:20||Andrius Jonas Dagilis||Gene interactions and the location of genes|
|L7||9:30||Abigail Pastore||Higher order interactions regulated by drought result in selection in semi-arid annual plants|
|L8||9:40||Raffica La Rosa||Plasticity, specialization, and species distributions across environmental gradients|
|L9||9:50||Kelly Thomasson||Long-term evolution of S. cerevisiae subjected to frequent dispersal by insect gut-vectoring.|
|10:10||Coffee Break - Refreshments in Chapel|
|L10||10:40||Maren Friesen||Why fix nitrogen?|
|L11||10:50||Mauro Toshiro Caiuby Sugawara||Subspecies richness and diversity gradients: a case study with birds|
|L12||11:00||Lesley Kim||Stages of diversification for Neotropical electric fish Apteronotidae|
|L13||11:10||Léa Blondel||Evidence for contemporary and historical gene flow between guppies in different watersheds|
|L14||11:20||Lotte Skovmand||Keystone genes: how can single genes have large ecological effects?|
|L15||11:30||Jennifer Lau||Restoration in a changing world: Can genetic diversity buffer restorations from climate change?|
Phylogenetics & Genomics | Sanderling
|C91||8:30||Kira Delmore||Comparative genomic analysis reveals repeatability in patterns of genomic divergence across birds|
|C92||8:50||David Rasmussen||Recoupling adaptive molecular evolution to phylogenetics using a fitness-dependent birth-death model|
|C93||9:10||Rachael Bay||Genomic signals of selection predict climate-driven population declines in a migratory bird|
|C94||9:30||Kathleen Donohue||Pleiotropy across the life cycle: environmental regulation of germination and flowering|
|C95||9:50||Elizabeth Scordato||A continent-spanning migratory divide reduces interbreeding across multiple barn swallow contact zones|
|10:10||Coffee Break - Refreshments in Chapel|
|C96||10:40||Lawrence Uricchio||Modulation of adaptation rate by background selection in the human genome|
|C97||11:00||Nathan Muchhala||Genomic signature of asymmetric pollen transfer among Burmeistera|
|C98||11:20||Orlando Schwery||Unveiling the factors behind the diversification of dung beetles (Scarabaeinae)|
|C99||11:40||Rachel Steward||Genomic signatures of divergent host plant use in the context of an evolutionary trap|
Demography & Dispersal | Marlin
|C100||8:30||Charlotte Lee||Elasticity of population growth with respect to the intensity of biotic or abiotic driving factors|
|C101||8:50||Gideon Bradburd||Isolation by distance as a null hypothesis of population structure|
|C102||9:10||Marc Mangel||Blue whales in variable and disturbed environments: working in Pasteur's quadrant|
|C103||9:30||Mario Pesendorfer||Declining seed production before death in a long-lived tree: senescence, not terminal investment?|
|C104||9:50||Bo Zhang||Carrying capacity in a heterogeneous environment with habitat connectivity|
|10:10||Coffee Break - Refreshments in Chapel|
|C105||10:40||Allison Shaw||The evolution of marine larval dispersal kernels in spatially structured habitats|
|C106||11:00||Adrian Stier||Environment, harvest, and the erosion of a population portfolio|
|C107||11:20||Joseph Travis||Thinking realistically about density dependence|
|C108||11:40||Katrina Catalano||Annually variable connectivity in yellowtail clownfish|
Community Patterns & Coexistence | Scripps
|C110||8:50||Trevor Price||Assembly of Himalayan bird communities|
|C111||9:10||Alexander White||Himalayan bird communities reveal the integration of tropical, temperate and arid biomes|
|C112||9:30||Chad Brassil||Ecological communities in pursuit of an elusive equilibrium|
|C113||9:50||Malyon Bimler||Assessing how microclimate impacts coexistence dynamics: a case study of Western Australian annual plants|
|10:10||Coffee Break - Refreshments in Chapel|
|C114||10:40||Elizabeth Miller||Extinction and time help drive the marine-terrestrial biodiversity gradient: Is the ocean a deathtrap?|
|C115||11:00||Margaret Mayfield||Climate effects on coexistence outcomes.|
|C116||11:20||Rachel Germain||The spatial scaling of plant diversity and its ecological correlates: experimental evidence from a global biodiversity hotspot|
|C117||11:40||Sara Jackrel||The microbiome is associated with accelerated aquatic ecosystem function in response to intraspecific variation in a terrestrial ecosystem subsidy.|
Social Networks & Invasion Ecology | Curlew
|C118||8:30||Samuel Scarpino||On the predictability of infectious disease outbreaks|
|C119||8:50||Theadora Block||Familiarity breeds contempt for badge plumage experiments in sparrows|
|C120||9:10||Erol Akcay||Evolution of cooperation on dynamic social networks|
|C121||9:30||Daizaburo Shizuka||Demographic processes and social network dynamics in animal populations|
|C122||9:50||Casey terHorst||Evolution to overcome biotic resistance to invasion is limited by multiple species interactions|
|10:10||Coffee Break - Refreshments in Chapel|
|C123||10:40||Priyanga Amarasekare||Latitudinal variation in ectotherm invasion success|
|C124||11:00||Matthew Walsh||Rapid evolution mitigates the ecological consequences of an invasive species (Bythotrephes longimanus) in lakes in Wisconsin|
|C125||11:20||Po-Ju Ke||The effect of soil cultivation length on plant-soil microbe interaction|
|C126||11:40||Sahas Barve||Big larders but skinny helpers: territory quality and density dependence in a highly social bird|
A guide for presenters to format their presentations can be found here.
Contributed Papers Abstracts
Modeling adaptive and nonadaptive radiations
Although adaptive radiations continue to contribute immensely to our understanding of evolution, there are some clades of organisms which appear minimally divergent in morphology or niche. For some of these cases, it may turn out that we simply have not found that axis along which niche partitioning and divergent selection have occurred, but they highlight the fact that we lack null models of what a nonadaptive radiation would look like in the absence of strong stabilizing selection. In this modeling approach, I assume lineages require some barrier to reproduction for speciation to take place, and compare simulations in which competitive exclusion is more or less important. I find that nonadaptive radiations generate significantly more species, with a higher proportion of closely related taxa. I discuss remaining hurdles for making these findings applicable to actual organisms, and suggest a clade of land snails to which these results might usefully be applied.
The role of pulsed migration events in the adaptation to harsh sink environments
When organisms are colonizing new habitats they are often forced to adapt to novel environmental conditions. The rate of immigration to new environments plays a complicated role in the ability of species to adapt to these novel conditions. Increased immigration rates lead to larger population sizes and increased genetic variation, which can aid in adaptation. However, higher immigration rates also increases gene flow, which can constrain selection. Here we examine how pulsed migration events affect the adaptation of species to harsh sink environments, using two complementary models: a continuous state quantitative genetics model and an individual based model. We show that in certain cases pulsed migration events allow organisms to adapt to environments they could not adapt to with constant migration.
Adaptation to a novel family environment involves both apparent and cryptic phenotypic changes
Matthew Schrader, Benjamin J. M. Jarrett, Darren Rebar, and Rebecca M. Kilner
Cryptic evolution occurs when evolutionary change is masked by concurrent environmental change. In most cases, evolutionary changes in the phenotype are masked by changing abiotic factors. However, evolutionary change in one trait might also be masked by evolutionary change in another trait, a phenomenon referred to as evolutionary environmental deterioration. Nevertheless, detecting this second type of cryptic evolution is challenging and there are few compelling examples. Here we describe a likely case of evolutionary environmental deterioration occurring in experimental burying beetle (Nicrophorus vespilloides) populations that are adapting to a novel social environment that lacks post-hatching parental care. We found that populations rapidly adapted to the removal of post-hatching parental care. This adaptation involved clear increases in breeding success and larval density (number of dispersing larvae produced per gram of breeding carcass), which in turn masked a concurrent increase in mean larval mass across generations. This cryptic increase in larval mass was accomplished through a change in the reaction norm that relates mean larval mass to larval density. Our results suggest that cryptic evolution might be commonplace in animal families, because evolving trophic and social interactions can potentially mask evolutionary change in other traits, like body size.
The role of multiple traits and trait interactions in the evolution of plasticity: a simulation
A models of the evolution of trait plasticity are based on just a single trait. Yet traits are embedded within a network of other traits. I present the results of an individual-based simulation model that explores the effect of trait architecture on selection for trait plasticity. I examine evolution when two traits independently affect fitness, when the phenotype of one trait is dependent on the phenotype of the second trait, and when the phenotype of only one or both traits are affected by the environment. These results may help explain why phenotypic plasticity is much less common that expected.
Experimental evolution of transgenerational plasticity in fluctuating environments
Stephen Proulx and Henrique Teotonio
Transcriptomic analyses of convergent evolution in sulfide spring fishes
Ryan Greenway, Joanna L. Kelley, and Michael Tobler
Understanding when evolution by natural selection produces predictable and repeatable adaptations (convergence) remains a challenge in evolutionary biology. Environments characterized by the presence of physiochemical stressors provide excellent opportunities to investigate the predictability and repeatability of evolution because – unlike many biotic sources of selection – physiochemical stressors create consistent selective regimes with well-characterized biochemical targets and physiological consequences. Hydrogen sulfide (H2S) is a natural toxicant lethal to most organisms, yet at least 12 evolutionarily independent colonizations of H2S-rich freshwater springs have occurred within the fish family Poeciliidae. Using transcriptome wide analyses of molecular evolution and gene expression, we are investigating patterns of convergent evolution in sulfide spring fishes using a phylogenetically explicit framework. We expect to find repeated changes in the expression and the protein sequences of genes associated with H2S toxicity as well as those responsible for mediating the detoxification process.
Dispersal trait evolution correlates with microhabitat adaptation in wind-dispersed vernal pool congeners
Courtney Van Den Elzen and Nancy C. Emery
For many species, environmental heterogeneity may impose selection on traits that influence dispersal (i.e. dispersal traits). Plants exhibit a diversity of dispersal traits, such as the hair-like structures attached to the achene (i.e. the pappus) in Asteraceae, which influences dispersal distance by wind. Due to potential fitness costs of dispersing into less-suitable habitats, we expect dispersal traits to evolve in response to environmental heterogeneity. In this study, we identified traits that influence dispersal distance in three closely related species of Lasthenia (Asteraceae) that occupy different microhabitats within vernal pool landscapes, where dispersal distance is known to have large fitness consequences. Specifically, using wind-tunnel trials we found that diaspore (i.e. achene + pappus) traits varied both within species and between species that occupy different microhabitats, and these traits influenced dispersal distance. This suggests habitat characteristics may indeed cause selection on dispersal. A field experiment is currently underway to test this hypothesis.
Evolution of the thermal niche in three species of Drosophila from equatorial Africa.
Aaron Comeault and Daniel Matute
The genetic basis of hygrosensation (the ability to detect different ambient relative humidity) has been well characterized in Drosophila melanogaster; however, Drosophila is a diverse and globally distributed genus whose species occupy many niches. How humidity preferences evolve across ecologically diverse species of Drosophila remains unknown. Here we use genomic and genetic approaches to explore the role of protein changing substitutions and gene duplication in the evolution of humidity preferences across the geographically widespread and ecologically diverse Drosophila yakuba species complex. Our results shed light on the evolutionary processes and traits underlying adaptation to different climatic niches.
Loss of colour pigmentation is maintained at high frequency in a monkey flower population
Jannice Friedman and Alex D. Twyford
Colour polymorphisms have long been of evolutionary interest for their diverse roles including mate choice, predator avoidance, and pollinator attraction. While colour variation is often under strong selection, some taxa demonstrate unexpectedly high frequencies of presumed deleterious colour forms. Here we show a genetic variant underlying complete loss of anthocyanin pigmentation has risen to an unexpectedly high frequency of >0.2 in a natural population of the plant Mimulus guttatus. Decreased expression of MYB5 transcription factor is associated with unpigmented morphs. While the allele was only found in heterozygote adults in the wild, suggesting negative selection, experiments were unable to demonstrate a fitness cost for unpigmented plants, suggesting a cryptic selection pressure in the wild. However, life history differences among morphs suggests unpigmented individuals benefit from later flowering and clonal growth. Overall, our study highlights the complex interplay of factors maintaining variation in nature, even for genes of major effect.
Linking individual behavior to macroevolutionary life history variation in tunas
Holly Kindsvater and Marc Mangel
Understanding the remarkable diversity of fish life histories is key to predicting their population dynamics and informing their conservation and management. Among the vertebrates, fishes stand out for the wide ranges of body sizes, fecundities, and offspring sizes that are represented in extant taxa. Using stochastic dynamic programming, I developed a model of foraging behavior that incorporates variation in metabolic requirements and temperature. From this model, body size, maturation age and lifespan evolve as a consequence of trade-offs between mortality associated with foraging and metabolic requirements for growth. Using this framework, mechanistically-based predictions for mortality and fecundity rates - central to demographic models of population dynamics - emerge. These evolutionary insights can be used to predict the trajectories of tunas and their relatives where time series of abundance are incomplete. Understanding these sources of life history diversity is one way that evolution can be used to conserve and manage tunas and their relatives.
Mutualism breakdown and ecological opportunity in leafflower-moth interactions
David Hembry, Noah K. Whiteman, and Katrina M. Dlugosch
Although mutualism is thought to be inherently unstable, few macroevolutionary transitions from mutualism to parasitism have been reported. Leafflower moths (Lepidoptera: Epicephala) are distributed throughout (sub)tropical regions of the Old World, where most are specialized pollinating seed predators of their host leafflower plants (Phyllanthaceae: Phyllanthus s. l.). Through phylogenetic inference, we examine the evolution of mutualistic and parasitic leafflower moths worldwide and use this comparative framework to ask questions about this repeated transition. This analysis includes the first reported non-pollinating leafflower moths from the US. We find that some losses of mutualism are associated with transitions among distantly related host lineages and colonization of new continents, suggesting that mutualism breakdown may in some cases offer novel ecological opportunity. Our results also suggest that co-occurrence of mutualists and non-mutualists on the same host may be unstable. Finally, I discuss the implications of these results for our understanding of mutualism loss generally.
Macroevolutionary drivers of plumage convergence: quantitative tests and new insights
Eliot Miller, Gavin M. Leighton, Alexander C. Lees, Benjamin G. Freeman, and Russell A. Ligon
What are the ecological, geographical, and life-history parameters that govern the evolution of animal coloration? Are broad-scale patterns, such as apparent convergences in appearance among distantly-related species, the consequence of drift and limited color palettes, or does adaptation to specific habitats or climates drive these processes? Alternatively, do biotic interactions among species play an important, and largely as-yet-unquantified role in convergences? To address these possibilities, we employed a novel method to quantify plumage similarity across the global radiation of woodpeckers. We then used habitat, climate, range, and genetic similarity in a partial Mantel test framework to quantify the relative contribution of each of these elements to global woodpecker plumage evolution.
Convergent evolution connects form to function in the world’s birds
Joseph Tobias, Alex Pigot, and Catherine Sheard
The link between morphological form and ecological function is a central organizing principle in nature, but a lack of data has prevented a general understanding of how organismal traits are connected to ecological function. Using comprehensive beak and body measurements for >98% of bird species, we demonstrate that phenotypes map onto niche axes with remarkable fidelity, predicting variation in resource use and foraging strategy with over 70% accuracy. We also show that this fundamental association arises through the independent convergence of ecologically similar lineages toward the same regions of phenotypic space. Our analyses suggest that ecological adaptation generates a universal structure to biodiversity, which in turn can provide information about ecological function at a range of spatial scales. We briefly outline case studies to illustrate how phenotypic traits provide a quantitative niche-based framework for use in macroevolution, community ecology and ecosystem science.
Mode of maternal provisioning builds a bridge between microevolution and macroevolution
David Reznick, Andrew Furness, Bart Pollux, Robert Meredith, and Mark Springer
The evolution of a placenta incites conflict between mothers and offspring over control of maternal provisioning because the optimal quantity of resources for offspring to obtain from mothers is larger than is in the best interest of mothers to provide to offspring. Three predicted consequences of this conflict are a shift from pre-copulatory to post-copulatory mate choice, accelerated evolution of post-zygotic reproductive isolation and hence accelerated speciation. However, the shift from pre- to post-zygotic RI also means weakened sexual selection, which would slow speciation if sexual selection is the primary driver. We present tests of the first and third predictions in fish the family Poeciliidae, in which there have been 9 or more independent origins of placentation plus remarkable interspecific diversity in the development of traits associated with sexual selection. Sexually selected traits, including dichromatism, ornamentation, and courtship, only evolved in lecithotrophhic lineages. Such traits tend to be lost after the evolution of placentation. The evolution of male sexually selected traits, but not matrotrophy, is associated with accelerated speciation, suggesting that prezygotic RI dominates in governing the rate of speciation.
Signatures of ecology and biogeography on pathogen-interacting genes in bats
Bats are widely distributed, ecologically diverse and also the reservoirs of a number of lethal emerging infectious zoonotic diseases. They are therefore an ideal system in which to investigate the impact of ecology and biogeography on the macroevolution of pathogen-interacting genes. Using available genomes and newly generated data, we analyzed positive selection in the genes for 200 pathogen-interacting proteins from 70 species of bats, the largest study of the macroevolution of pathogen-interacting genes in a single group to date. We found strong selection in bats whose ranges overlap more other bat species and also in Toll-like receptors that sense single-stranded RNA (ssRNA), suggesting that viral sharing and ssRNA viruses have been particularly important for the evolution of pathogen-interacting genes. Investigations of specific proteins in these lineages may yield insights into the unique bat-virus relationship, which may aid in disease prevention or treatment.
Evolution driven by organismal behavior: A new, unifying view of life, function, form, mismatches and trends
Rui P B Diogo
In this talk I will summarize a new way to think about evolution and life. I will bring together evidence from diverse fields of science to bridge the gaps between many different - and usually seen as conflicting -ideas, Specifically, I will present an integrative theory named ONCE, which stands for Organic Nonoptimal Constrained Evolution. I argue that evolution is mainly driven by the behavioral choices and persistence of organisms themselves, in a process in which Darwinian natural selection is mainly a secondary - but still crucial - evolutionary player. Within ONCE, evolution is therefore generally made of mistakes and mismatches and trial-and-error situations, and is not a process where organisms engage in an incessant, suffocating struggle in which they can't thrive if they are not optimally adapted to their habitats and the external environment. Therefore, this unifying view incorporates a more comprehensive view of the diversity and complexity of life by stressing that organisms are not merely passive evolutionary players under the rule of external factors. The argument will be based on numerous fascinating case studies from a wide range of organisms, including bacteria, plants, insects and diverse examples from the evolution of our own species. Therefore the talk will have an appeal to researchers, students, teachers, and those with an interest in the history and philosophy of science, as well as to the broader public, as it brings life back into biology by emphasizing that organisms, including humans, are the key active players in evolution and thus in the future of life on this wonderful planet.
Island biogeography and the evolution of floral traits
Molly Hetherington-Rauth and Marc T. J. Johnson
The theory of island biogeography predicts that smaller and more isolated islands should have a lower equilibrium number of species due to decreasing immigration and increasing extinction rates compared to larger and less isolated islands. As a result island pollinator communities are often simpler and less diverse than mainland communities and they frequently lack key pollinators present in mainland communities. Thus, the evolution of floral traits on islands is expected to differ from that on the mainland, whereby island taxa are predicted to exhibit reduced investment in floral traits used for pollinator attraction. To test this prediction we compared the flower size of island endemic angiosperms across eight Pacific islands to that of their mainland sister taxa using herbaria specimens. We tested for the effect of island biogeography on the strength and direction of floral evolution using phylogenetic generalized least-squares to fit a variety of evolutionary models.
Fear-based niche shifts in Neotropical birds
Ari Martinez, A.E. Martínez, E. Parra, O. Muellerklein, and V.T.V. Vredenburg
Predation is a strong ecological force that shapes animal communities through natural selection.Prey species have evolved multiple pathways to minimize predation risk including detection anduse of information about predators from other prey species. Amazonian stable mixed speciesflocks of birds are hypothesized to form around alarm-calling species (“sentinels”) that alertflock members to avian predators, allowing less-vigilant species to expand their niche into riskierhabitats. To test this, we removed sentinel species and found that flocks responded with shifts inhabitat use to lower risk, more densely vegetated areas, and flocks also exhibited lower flockcohesion. Our experiment provides evidence that association with sentinel species may reducepredation risk and increase the realized niche of less-vigilant species.
Past niche evolution and its manifestations in an Anthropogenic biosphere
In an era of rapid environmental change, habitat conversion and climate change chief among them, it is imperative that we understand how the long arm evolution shapes biological communities so we can explain why novel anthropogenic communities look the way they do. Here I examine bird communities along independently varying gradients in land-use and climate using phylogenetic community abundance models. I quantify how species niche placement along these environmental axes is distributed across the avian phylogeny, in order to understand (1) the mode of niche evolution, and (2) the distribution of organisms in anthropogenic habitats. Bird niche evolution to vegetation structure is strongly phylogenetically conserved, resulting in close relatives frequently co-occurring in vegetatively depauperate converted habitats. In contrast, niche evolution to climate is extremely labile, with closely related species frequently occupying contrasting climate zones. The niche offers predictive means to tie the evolutionary past to the ecological future.
Niche breadth measures yield different estimates: Classifying and comparing measures from across ecology and evolutionary biology
Kelly Carscadden, Carlos Arnillas, Nancy Emery, Marc Cadotte, Dominique Gravel, Michelle Afkhami, and Scott MacIvor
Numerous longstanding ecological questions draw upon the niche breadth concept (a description of species’ requirements or tolerances). The niche breadth literature is extremely diverse and diffuse, comprising contrasting sub-disciplines, study systems, and scales (from individual to clade-level and local to global). As a result, over 50 unique niche breadth measures have been published. These measures differ in the type and number of niche axes they consider, the response variable used (e.g., occurrence vs. growth rate), whether they consider the background availability of resources or conditions, and their mathematical approach to synthesizing this information. We outline a classification scheme based on these divisions and compare niche breadth estimates generated by different measures using several ecological datasets (e.g., bee-parasite interactions, experimental habitat breadth data). Lastly, we discuss implications for selecting appropriate measures given different data types or research questions. We aim to help guide users through the myriad measures available.
Sex increases the rate and predictability of adaptation while decreasing its pleiotropic costs
Parris Humphrey, Camille Simonet, Katya Kosheleva, and Michael M Desai
Adaptation can be local and lead to specialization, but we can’t yet predict how often, how quickly, or why. Beneficial mutations can impact fitness elsewhere (pleiotropy), but so can neutral and deleterious mutations that fix via genetic linkage. Specialization depends on how these mutations affect fitness across environments. Sex (i.e. recombination) increases the rate of adaptation by changing how many (and what types of) mutations fix during evolution and should therefore impact the dynamics of specialization. By experimentally evolving many haploid yeast populations sexually or asexually for 1000 generations, we found that sex increased adaptation locally while decreasing the magnitude and variance of its pleiotropic costs in alternate environments. Compared to sexuals, asexual populations fixed more, and a wider spectrum of mutations via linkage, and non-beneficial alleles disproportionately contributed to latent pleiotropic costs. Thus, mating system can drive the dynamics of local adaptation and specialization and shape its genetic basis.
Beyond sexual selection: a role for ecological niche breadth in the evolution of sexual dichromatism
Kinsey Brock, Dan Edwards, and Justin Yeager
The evolution of color and pattern is strongly influenced by the environmental conditions a species experiences. Species that vary in color and pattern between the sexes (sexually dichromatic), offer an interesting evolutionary framework to study the effects of ecology on the evolution of phenotype. We used phylogenetic comparative methods and ecological niche modelling to investigate the coevolution of sexual dichromatism and niche breadth in a widespread Australian agamid radiation, the Agamidae.
The dimensionality of individual niche variation
The inherently multidimensional nature of the niche has not been fully integrated into the investigation of individual niche specialization within populations. This can be done by modeling both the between- and within-individual components of the population niche as variance-covariance matrices, which can be inferred using multiple response mixed models. This presentation will describe this framework and give several examples of how it can inform our understanding of basic ecological and evolutionary processes. For example, the consequences of intraspecific variation for ecosystem processes (e.g. via Jensen’s inequality) or for the direction of niche shifts may be influenced by the extent and ‘shape’ of niche variation in multiple dimensions. Empirical investigations in freshwater fish will be used to illustrate some of the potential causes and consequences of multivariate individual specialization.
Character displacement in a temporally varying environment: evolution of differential use of a fluctuating environment
Character displacement is a foundational concept at the interface of ecology and evolutionary biology. Despite being an old concept, the theory of character displacement has been limited in scope, with little attention to competition in fluctuating environments. Because of the possibility of pervasive temporal niche partitioning, a evolutionary analysis of character displacement in fluctuating environments is necessary. Does character displacement extend to competition in fluctuating environments? What modifications of the theory are required to allow inclusion of a fluctuating environments?I will present a model of competition between annual plants to demonstrate character displacement with respect to germination rate that responds to a fluctuating environment and derive general conditions for evolution to strengthen and weaken coexistence. To extend the theory of character displacement, I also provide a analogy between evolution of competitive ability in varying environments with that in a constant environment. I will briefly discuss implications for community assembly.
Spatial scale and ecological niche concepts
G.E. Hutchinson's niche concept focused on population persistence as a function of environmental conditions, but did not explicitly consider issues of spatial scale and dispersal. Recent advances in spatial demography can be used to articulate a niche concept that incorporates spatial processes and dispersal, as well as local demography.
Pollinator-mediated facilitation explains asymmetric neighborhood effects in experimental plant communities
Kaitlyn Brown and Benjamin Gilbert
Can rare species invade and persist in communities? This fundamental question of population ecology has received considerable attention, especially among plant ecologists, who have largely ignored the neighborhood context in which these rare populations are found. Here, we ask how the surrounding plant community can influence rare species fitness and persistence via pollinator interactions; do common species outcompete rare species for pollinators, or do they share pollinators and facilitate rare species fitness? To test this, we created patches varying in the rarity of two plant species, then compared fitness through pollinator visitation rate and seed set. We found an asymmetric neighborhood effect dependent on pollinator specificity: the bumblebee specialist, Chamaecrista, was an effective pollinator magnet, facilitating the pollination and reproductive success of the rare generalist, Polanisia. However, Polanisia did not alter bumblebee visitation, and therefore had no effect on the success of rare Chamaecrista. These results suggest that neighborhood context and pollinator specialization play an important role in mediating rare species fitness and persistence in communities.
Red Queen dynamics oppose host-range generalists in an eco-evolutionary model of parasites and hosts
What factors prevent generalists from displacing specialists? Traditional explanations rely on trade-offs, positing that the jack-of-all-trades must also be the master of none. However, such trade-offs have been notoriously difficult to confirm in systems ranging from phytophagous insects to bacteriophage. Alternative theories focus instead on the consequences of niche breadth for evolvability, hypothesizing that a population whose members occupy different habitats experiences weakened selection for traits expressed only in some. Here I explore a model of competition and adaptation in a system with multiple hosts and parasites. This analysis dissects the several ways that host range impacts evolvability and charts the parameter space permitting more slowly evolving generalists to coexist with specialists. By integrating antagonistic pleiotropy, this model synthesizes both the ‘trade-offs’ and ‘relaxed selection’ arguments to show how they work in concert and to identify key variables to help infer how each contributes to biodiversity in natural systems.
The impact of within-host priority effects on multi-pathogen epidemics
In co-infected populations, within-host interactions between pathogens can scale up to alter pathogen prevalence and co-existence. However, within-host pathogen interactions are not homogenous across hosts- rather they are determined by the order in which pathogens infect hosts, a process known as within-host priority effects. Theory also predicts that the order in which pathogens infect a host should be correlated with the pathogen dose that hosts are exposed to, and that these two factors may interact. Thus, Pathogen exposure and order of arrival should jointly determine how pathogens interact within a host. Thus, by parameterizing a mathematical model with data from a co-infected zooplankton system, we ask (1) how do within host interactions between pathogens change with order and dose of pathogens? And (2) what are the implications of variation in within-host interactions for disease patterns at the host population scale? Overall, our results show that within-host priority effects can systematically change the course of epidemics, and should be taken into consideration in future disease modelling efforts.
The Art of Outbreak Control: transient models of movement and disease management
Yun Tao, Alan Hastings, Katriona Shea, Luca Borger, and Matt Ferrari
In disease ecology, effective control in the wake of an outbreak (e.g. H1N1 flu epidemic) presents a serious management challenge. In these settings, outbreak managers must distribute vaccine in a race against the advancing outbreak, analogous to competitors for susceptible hosts. We capture this interaction by modeling the deployment of vaccination resource as diffusive movement of medical personnel, which is then coupled to a spatially explicit, stochastic epidemic model. The results reveal the existence of optimal, “moderate tempo” vaccination strategies in densely populated environments.Our approach also underlines the importance of movement transients and offers a new way to integrate disease ecology and movement ecology. Its potential to incorporate complex and adaptive movement behavior is demonstrated using a related model of animal territorial formations. We finally consider how similarly adaptive human movement can be incorporated into a disease framework to improve future management strategies.
Horizontal transmission of parasites can favour conditional host dispersal
Ryosuke Iritani and Mike Boots
Any degree of localized dispersal indicates that parasite transmission tends to occur among relatives. Consequently, sickness-dependent dispersal, the differential dispersal between infected and uninfected individuals, might be favoured. There is considerable variation in nature in sickness-dependent dispersal with numerous cases where infected or uninfected individuals preferentially disperse more. Here, we study the evolution of sickness-dependent dispersal under parasite transmission among relatives. We show that selection may lead to either infected or uninfected individuals dispersing more and that these two endpoints can be bistable given similar extrinsic costs of dispersal, leading to variation in host dispersal depending on initial conditions. If horizontal transmission makes the apparent genetic structuring between uninfected and infected juveniles more pronounced, higher dispersal for infected individuals than that for uninfected individuals is more likely to evolve. Emigration of infected individuals can not only protect healthy relatives from local transmission, but also transmit their diseases towards non-relatives. Also, emigration of uninfected individuals can increase the local force of infection, thereby harming healthy immigrants. Our results suggest that selection on host dispersal, rather than the parasites themselves, can dramatically modify the spatial scale of infectious disease transmission.
Parasite-induced anorexia: consequences for the evolution of parasite and host traits
Jessica Hite and Clay Cressler
A common response to parasite infection (and mere exposure) is anorexia. This defense mechanism likely reduces further exposure to parasites and consequently, alters the flow of resources to both hosts and parasites. We use a combination of consumer-resource theory and adaptive dynamics to reveal the consequences of parasite-driven anorexia for the evolution of host and parasite traits. We also present results of our recent meta-analysis that reviews the propensity and potential population-level consequences of this rather common defense mechanism.
Divergent sexual traits evolve independently with local parasites to signal relevant information to females.
Amanda Hund, Joanna Hubbard, Pavel Munclinger, Yoni Vortman, Tomas Albrecht, and Rebecca Safran
Many related populations are distinguished by variation in sexual traits, yet little is known about how sexual traits diverge. Determining what females gain from sexual signals is important to understanding these questions. Parasites have been associated with sexual traits in single populations, but it remains unclear how parasites may drive sexual trait divergence. To test this, we used the barn swallow species complex, which is characterized by sexual trait divergence. We found that parasite communities, and their costs, vary across populations. Divergent sexual traits signaled information about the costliest parasite(s), thus giving adaptive and locally relevant information to females. Sexual traits were frequently associated with multiple parasites, suggesting that several mechanisms may act in concert within populations to shape sexual signals. Across populations, the same traits were often associated with different parasites, suggesting that these parasite-sexual trait links are quite flexible and can evolve relatively quickly even in closely-related groups.
The effect of intraspecific variation in predator defense traits on parasite infection within and across generations
Ben Wasserman and Eric Palkovacs
Investment in defenses against multiple natural enemies, such as predators and parasites may require evolutionary tradeoffs. We hypothesize that threespine stickleback individuals that are completely-plated are less well-defended against a parasitic copepod (Ergasilus) than low-plated stickleback. Further, we hypothesize that completely-plated stickleback therefore leave a larger population of parasites in the environment. Using an in-situ enclosure experiment, we assayed the response of different stickleback morphs to Ergasilus parasites. We found that completely-plated fish acquired more parasites than low-plated stickleback. However, they also survived better, suggesting that they tolerated infection better. This led to differences in the parasite populations associated with each morph at the end of the experiment, which may affect selection on morph in the following generation.
How interspecific competition influences eusociality across a guild of body-snatching trematodes
Emlyn Resetarits, Ryan Hechinger, and Mark Torchin
Although much work has been devoted to studying cooperation and sociality inorganisms, little work has explored the role of interspecific interactions in structuringthese behaviors. Previous work in eusocial systems has shown that interspecificcompetition can alter the caste ratio, but these studies have focused on a single species underlimited conditions. However, it is likely that eusocial species with different competitive abilitiesmay differentially alter their caste ratios under increased interspecific competition. Parasitictrematodes in California Horn Snails represent a novel system to test this possibility. Theseparasitic trematodes are diverse and specialized on the California Horn Snail, have highintraguild predation to defend individual snail hosts that follows a strict competitive hierarchy,and form soldier and reproductives castes.
Host and symbiont contributions to nodule occupancy in the legume-rhizobium symbiosis
Camille Wendlandt and Joel Sachs
Root-nodulating legumes encounter wide variation in symbiotic quality of N-fixing rhizobia. To maximize benefits from symbiosis, the sanctions hypothesis predicts that legume hosts exposed to multiple rhizobial partners will influence the fitness of the strains in planta so that nodules are dominated by the more beneficial partner. However, previous work shows that outcomes of symbiotic interactions are subject to strong GxG effects. Here, we tested the sanctions hypothesis in a native California system by examining whether symbiotic quality of rhizobia was consistently a good predictor of in planta fitness during coinoculations, using multiple genotypes of a legume host (Acmispon strigosus) and its Bradyrhizobium symbiont. Our data support the sanctions hypothesis and suggest that rhizobial fitness inside the nodule is largely a function of symbiotic quality.
Rhizobium mutualists alter competitive interactions
Resource mutualisms, such as between legumes and nitrogen-fixing rhizobia, have the potential to alter communities through inhibitive or facilitative processes. For example, rhizobia can provide their legume host a competitive advantage through increased growth, thereby reducing light availability for competitors. Alternatively, by increasing nitrogen availability, the legume-rhizobium mutualism could facilitate other species by reducing competition for a limiting resource. In fact, studies exploring the role of rhizobia on diversity have found a range of positive and negative effects. Differences in densities and dominance of focal legumes may explain some of this variation. Using a response surface design, I explore how rhizobia-mediated effects on competitive interactions between the legume Chamaecrista fasciculata and non-leguminous species may be density-dependent. These results provide insight into the variable responses of non-leguminous species to the presence of rhizobia by helping identify the mechanisms underlying the direct and indirect effects of this important mutualism on species interactions.
The effects of community context and wet-year vs. dry-year dynamics on pollinator-mediated selection in Clarkia (Onagraceae) in the southern Sierra foothills (Kern County, CA)
Katherine Eisen, Amy C. Wruck, and Monica A. Geber
Determining the causes of natural selection and how community context alters selection represent fundamental goals in evolutionary ecology. Where flowering plants share pollinators, these species interactions, whether competitive or facilitative, can lead to diffuse (co)evolution. Abiotic agents of selection (e.g. rainfall) also affect both bee and plant population sizes and thus influence the evolution of floral traits. To determine if community composition and winter rainfall alter selection on annual plants, we estimated selection on the pollination-related traits of Clarkia species in twenty-five communities that vary in species composition. During a dry year, we estimated selection, and we performed an experimental test of pollinator-mediated selection during a year that was two to three times wetter. During the dry year, selection on several species was stronger in communities with fewer congeners, while results from the wet year are forthcoming. These results suggest that community context may affect natural selection among pollinator-sharing plants.
Intraspecific variation in nectar use by foraging hawkmoths
Gordon Smith, Daniel Papaj, Ruben Alarcon, Goggy Davidowitz, and Judie Bronstein
As the reproduction of many plants hinges upon animal pollen vectors, variation in floral visitation behaviors by pollinators can affect plant fitness. To investigate how pollinators vary within species and how pollinator traits affect foraging patterns, we analyzed the pollen loads of hawkmoth individuals from three species: the generalist Hyles lineata, and the specialists Manduca sexta and M. quinquemaculata. Pollen loads were collected from wild moths in Arizona across four years, and the carried pollen was identified and counted. First, we found that individuals across species vary extensively in pollen load species richness and evenness. Second, the Manduca species carried loads that were less even but more species rich than Hyles, suggesting that Manduca individuals may visit more species than previously thought. Third, across all three species, female moths carried larger and more species rich loads than males. The sexes may therefore differ in their quality as pollinators across species.
The behavioral ecology of nectar-robbing: how alluring is "the Temptation to Cheat"?
Judith Bronstein, Jessica L. Barker, Elinor M. Lichtenberg, Leif L. Richardson, and Rebecca E. Irwin
Animals in variable environments often forage consistently for a single food type even when other suitable foods are available and accessible. Pollinating bees’ floral constancy (their tendency to persistently visit one of many available flower species) is one well-known example. Here we extend this framework to explore mutualistic vs. nonmutualistic handling tactics employed on individual flower species. Nectar robbers feed through holes bitten in flowers. Many robbers, however, can also obtain nectar by visiting flowers “legitimately,” a behavior that (unlike robbing) leads to pollination. Here we show that even though individuals of many bumblebee species can switch between these alternative tactics, they often do not: individuals generally remain constant to either a mutualistic or nonmutualistic feeding strategy. We extend hypotheses of floral constancy to understand why bees might exhibit tactic constancy. We argue that simple behavioral principles can illuminate why mutualists may rarely succumb to the expected “temptation to cheat.”
Sanctions, partner recognition, and variation in mutualism
Mutualism can be stabilized against invasion by non-cooperative individuals by putting such "cheaters" at a selective disadvantage. Selection against cheaters should eliminate variation in partner quality — yet such variation is often found in nature. One explanation for this paradox is that mutualism outcomes are determined not only by responses to partner performance, but also by partner signals. A model of coevolution in a mutualism in which the ability to sanction non-cooperative symbionts and recognition of partner signals are determined by separate loci can maintain variation without destabilizing the interaction, in part because coevolution of signals and recognition is altered by the coevolution of sanctions and cooperation, and vice-versa. The dual systems of sanctions and partner recognition converge toward conditions similar to some economic models of mutualistic symbiosis in which hosts offering the right incentives to potential symbionts can initiate symbiosis without screening for partner quality.
Balancing costs and benefits when a gamete is also a pollinator reward
Jacob Heiling, William Morris, and Rebecca Irwin
The benefits of animal meditated pollination must be balanced against the costs of floral rewards. Pollinator reward size preferences could constrain fitness for pollen-rewarding plants. We modeled optimal pollen presentation, accounting for pollen loss and reward size discrimination by pollinators to answer: How do pollen loss and visitor preferences affect optimal pollen package size? How does pollen package size impact fitness? And, can increased pollen production overcome pollen loss related fitness constraints? We found that: grooming and reward size discrimination interact to constrain fitness in pollen-rewarding plants; fitness fails to increase with pollen package size when grooming is high and visitors prefer larger rewards; and increasing pollen production without increasing pollen package number does not overcome fitness limits imposed by grooming when reward size discrimination is strong. We conclude that pollen foraging constrains fitness, and that a pollen rewarding strategy may confer fitness advantages to plants subject to pollen-foraging.
Evidence for asymmetric competition between mutualists of varying quality
In mutualism, negative density-dependence due to competition between mutualist guilds is thought to be a critical component of interaction persistence, as it prevents overpopulation that would otherwise occur in a pairwise interaction. However, empirical evidence of coexistence between mutualist guilds is rare. For instance, resource partitioning by pollinators is often invoked as a coexistence mechanism, although few studies provide data to support this hypothesis. I tested the hypothesis that pollinator partition resources by conducting a response-surface competition field experiment between two bumble bee species (Bombus appositus and Bombus flavifrons) that vary in the degree to which they provide mutualistic benefits for Corydalis caseana (Fumariaceae). I found that B. appositus, a high-quality mutualist, does not suffer reduced foraging efficiency in the presence of B. flavifrons, a low-quality mutualist. However, B. flavifrons experiences a significant decrease in foraging efficiency in the presence of B. appositus relative to foraging alone. Additionally, when given the choice to forage on other plant species in the presence of B. appositus, B. flavifrons will show a lower preference for Corydalis caseana, and will instead forage on different plant species. This study demonstrates a competitive hierarchy between mutualists of varying quality, and illuminates a mechanism by which mutualist guilds can coexist.
Optimizing fitness benefits in the legume-rhizobium symbiosis
Rhizobial bacteria substantially increase host fitness via nitrogen fixation, but legumes must regulate nodule number to minimize exploitation. One mechanism used by hosts is autoregulation of nodulation (AON) which limits nodulation when plants are satiated for nitrogen. To examine how variation in nodule number affects both partner’s fitness we inoculated three Lotus japonicus genotypes, a wildtype and two AON mutants (i.e., hypernodulating), with Mesorhizobium loti varying in nitrogen fixation capacity. In clonal infections with effective symbionts host fitness was unimodal with optimal growth when ~25 nodules were formed. For the rhizobia, the effective genotype gained the greatest fitness per nodule in the wildtype host, but at the whole plant level rhizobial fitness was highest in hypernodulators. In mixed inoculation experiments, we found biased in planta rhizobial fitness towards effective strains irrespective of host AON phenotype. Our results suggest that AON optimizes host fitness and hypernodulators retain adaptive host control traits.
Does early heterospecific song exposure affect species recognition in wild nestling birds?
For taxa in which species-recognition signals are learned, rather than innate, avoiding learning errors is critical. In songbirds, particularly the white-crowned sparrow, cognitive mechanisms that allow flexibility while preventing learning from heterospecifics have been well-described in what as known as the auditory template model. According to this model, birds begin memorizing conspecific sounds soon after fledging; sounds heard before this age do not appear in adult song. However, the extent to which heterospecific song exposure prior to the onset of learning affects young birds in the wild has not been explored. Using autonomous recording and playback experiments in the field, we tested whether species recognition in nestling golden-crowned sparrows was affected by the amount of heterospecific vs. conspecific song to which they were naturally exposed in the nest. The effects of early experience with closely-related heterospecifics on learned species recognition are important to understanding pre-mating barriers between recently diverged groups.
The evolution of coexistence: theoretical and empirical studies in a simple community
The coexistence of ecologically similar species is one of ecology’s oldest paradoxes. Traditional attempts to resolve this paradox address whether each species can invade a population of the other, but assume that species do not evolve fast enough to modify interactions. Although patterns like character displacement indicate that species coexistence has often been the result of evolutionary change, experimental demonstrations of reciprocal adaptation of species are rare. Here, I discuss how we are testing for a role for evolution in the coexistence of guppies and killifish in Trinidadian streams. I outline how our combined approach of mathematical modeling and experiments in laboratory, mesocosm, and natural settings are advancing our knowledge of how rapid evolutionary change influences species coexistence. Our efforts thus far have shown how the evolution of competitive asymmetries, resource use, and the life history combine in size-structured populations to influence coexistence
Selection in a warmer world: insights from a climate warming experiment
Anne Panetta and Maureen L. Stanton
How does climate warming alter patterns of selection? To investigate this question, we measured selection on traits of Androsace septentrionalis (Primulaceae), a wildflower that grows across wide local and global elevation gradients, as well as in a 27 year-old active warming experiment (Colorado, USA; elevation 2,920 m). In 2014, we introduced parental and recombinant lineages of A. septentrionalis into heated and control plots, as well as into two lower-elevation sites (~2,683 m). For three years, we followed each individual, documenting its timing of emergence, flowering, and fruit maturation, vegetative and floral traits, and lifetime reproductive success and survival across all life stages. Here, we report our findings, placing an emphasis on how experimental warming alters patterns of selection, and the extent to which these altered patterns i) mirror those found in naturally warmer microsites, and ii) explain observed trait shifts in natural populations in response to climate warming.
You are what you eat: urbanization erodes niche segregation in Darwin’s Finches
Darwin’s finches of the Galápagos Islands are an iconic example of adaptive radiation where each species has evolved different beak sizes and shapes that are adapted to exploit different food resources. Thus, finch beak morphology is highly dependent on the availability of native foods. However, humans appear to be changing the evolution of Darwin’s finches. Specifically, beak size variation and bite force of urban finches is altered in comparison with non-urban finches. We hypothesize that the availability of human foods has weakened the selective pressures maintaining beak morphology. Here, we experimentally test if this is due to a behavioural shift whereby urban finches actually prefer human foods over native foods. We found that urban finches preferentially fed on human foods over native foods, expanding their ecological feeding niche. This demonstrates that humans are affecting the evolution of Darwin’s finches and has important conservation implications.
Two tickets to paradise: rapid evolution of feral fowl from Kauai and Bermuda
Eben Gering, Dominic Wright, Thomas Getty, and Danielle Whittaker.
Escaping captivity abruptly changes selection regimes, but evolutionary responses to feralization have not been well characterized. In this talk, I will summarize comparative studies of the genomes and phenotypes of feral Kauai hybrids (originating from both chickens and Red Junglefowl), and feral Bermuda chickens (with purely domestic recent origins). Both populations show evidence of rapid evolution in ecological and sexual traits, suggesting that feral environments impose natural and social selection on colonizing, formerly domesticated organisms. However, their patterns of standing variation are also divergent, and reflective of the two population’s different recent ancestries. These findings have implications for the predictability of evolution in complex environments, and at the nexus between naturally- and artificially-selected systems. I will conclude with some emerging findings and potential utilities of ongoing research into the feralization process.
Rapid evolution of resources and consumers to temperature change
Michelle Tseng, J. R. Bernhardt, and A. E. Chila
An important wildcard in predicting evolutionary responses to changing environments is the effect of species interactions. Will species interactions accelerate, hamper, or have no effect on whether populations can adapt to changing environments? Here we investigate rapid evolution in a tri-trophic system (algae, Daphnia, predators) in response to warming, and document rapid evolution in both the resource and the consumer. Both algal cell size and Daphnia body size evolved, and fitness of Daphnia was higher when they were fed algae evolving at the same temperature. The presence of predators altered evolutionary responses of Daphnia to warming, and surprisingly vice versa as well - morphological changes due to temperature selection conferred protection against predation. Overall our study documents the rapid evolution of resources and consumers to temperature change, and shows the importance of species interactions in mediating evolutionary responses to changing environments.
Rapid evolution in ecological restorations
Colonizing populations likely encounter novel environmental conditions, which can act as strong selective agents and potentially lead to adaptation of a colonizing population. Understanding the evolutionary processes underlying successful colonization events is important as species increasingly colonize new habitats in response to anthropogenic forces. Although many studies have found evidence of evolutionary changes in colonizing populations, few have determined whether these changes are actually adaptive. I combined a reciprocal transplant experiment with a resurrection experiment to compare populations of the annual legume Chamaecrista fasciculata in replicated prairie restorations to each other and to their original source population. I examined whether evolutionary changes had occurred in these recently established populations, and whether these changes were predicted by estimates of selection. I found evidence of evolutionary changes, and that these changes were generally predicted by estimates of selection, suggesting this evolution was adaptive.
Genomics of parallel adaptations and speciation in repeated species flocks of cichlid fishes
Cichlid fishes are well-known for their extraordinary rapid divergence and conspicuous convergence in terms of coloration, body shape, and trophic morphologies – making them an excellent model for addressing questions about the genomics of convergent evolution. Analyses in a phylogenetic context suggests that there are certain biases in the repeated generation of adaptations. One of the most notable cases of parallelism among repeated cichlid species flocks including those of the three large East African radiations is the evolution of hypertrophied lips that are used for specialized feeding and also serve as a signal in sexual selection – a possible magic trait. In a multidisciplinary approach, using whole genome re-sequencing on hundreds of individuals, QTL mapping, population genomics, feeding performance, and mate-choice experiments we disentangle the genetic basis and the adaptive significance of hypertrophic lips in both African and Central American cichlids and found that the genetic architecture of hypertrophic lips differs strongly between both lineages of cichlids. Also, color patterns, such as stripes and bars, have evolved repeatedly in several adaptive radiations of cichlids. We identified the molecular mechanisms that led to the repeated evolution of this coloration pattern. The underlying mutations are not conserved across radiations suggesting independent evolution of different cis-regulatory modules that all result in similar phenotypes within very short evolutionary time spans.
Temporal scale and timing of environmental variation: effects on insect life history and populations
Rapid evolution of thermal reaction norms in marine phytoplankton reveals constraints and trade-offs
Long-term dynamics of life-history intraguild predation
Benjamin Toscano and Volker H.W. Rudolf
Life-history intraguild predation (LHIGP), where juvenile predators compete with the prey of adults, is common within natural communities. Theory posits that this mix of stage-specific predation and competition can lead to alternative stable states. In one state, prey exclude predators through competition, while in the alternative, adult predators control prey to limit competition and foster coexistence. Here, we report on long-term, multi-generational experiments with freshwater zooplankton designed to test these model predictions. We manipulated copepod predator starting densities and algae resource levels, with the expectation that predators would be more likely to coexist with their cladoceran prey when introduced at high density and high resource levels. Our results indicate that both competitive exclusion of the predator and coexistence are possible, with evidence for the mechanisms driving such states. Deviations from theoretical expectations could be used to further refine assumptions of LHIGP models, thereby improving predictive capacity for natural LHIGP dynamics.
Thrift, gluttony and death: Population responses to resource availability in a tide pool copepod
Benjamin Van Allen
The vast majority of organisms live in heterogeneous environments. Accordingly, most organisms have flexibility in their life history strategy to account for changing or stable environments. Rather than producing the same number of similar offspring in any current or predicted conditions, parental decisions and natal experiences can alter the traits and condition of offspring, with large effects on fitness and resulting population responses. Theory predicts only a few general forms of fitness “reaction norms” across varying environments, but despite recent advances, experiments lag behind in identifying and categorizing examples of theory. Here I examine the population response of a specialized tide pool copepod to varying environmental conditions and synthesize my results with expectations and examples from the responses of ecologically different taxa.
When life history matters: Somatic maintenance costs and juvenile-adult stage-structure jointly overturn ecological rules-of-thumb
André de Roos
Ecological theory about dynamics of interacting species is the basis for our understanding of the functioning of ecological communities and ecosystems and their responses to changing environmental conditions, natural disturbances and human impacts. The mathematical foundation of this theory emphasises changes in species abundances, ignoring unique aspects of biological organisms, in particular within-population variation due to individual development during life history and individual energetics. Here I show generally that two fundamental elements of life, a juvenile, non-reproductive stage and the energetic costs to maintain a living body, jointly overturn basic rules about the most elementary of all interactions, that between a consumer and its resource. This not only calls into question the validity of basic ecological theory but also has major, applied ramifications, for example, for the management of marine fish populations.
The evolution of vertebrate eye size across an environmental gradient in Trinidadian killifish
Shannon Beston and Matthew R. Walsh
Vertebrates exhibit substantial variation in eye size. Eye size correlates positively with visual capacity and predator avoidance capability. Such trends foreshadow a connection between predation and eye size evolution, but empirical tests are lacking. We tested the influence of increased predation on eye size evolution in Trinidadian killifish (Rivulus hartii). Rivulus are found in sites where they occur with and without large piscivores. Wild-caught fish from sites with predators exhibited a smaller eye size than sites without predators, but these differences were dependent upon river of origin. However, eye size was consistently smaller in Rivulus from sites with predators following two generations of common garden rearing. We next performed experiments that examined the influence of light and resources on eye size. Sites that differ in light or resource availability did not differ in eye size. We conclude that predators are a key selective force on the evolution of eye size.
Optimal control and cold war dynamics between plant and herbivore
Low et al. (2013)’s theoretical model predicts that the outcome of plant and herbivore interactions would result in a non-antagonistic ecological interaction, when you allow evolutionary optimization to occur. This work is based on game theory economics, applies optimal control theory, and solves for the strategies of defense induction (by the plant against herbivores) and egg hatching (by the insect herbivore) that would give each of the players the greatest fitness. The predicted Nash equilibrium suggests that the players arrive at an ecologically neutral state; hence, evolutionary stasis is expected. This result contradicts the generally assumed co-evolutionary arms race scenario that underlies most hypotheses on plant-herbivore radiations. American Naturalist 182: E25-E39.
Pulsed dynamics: A top down perspective
Michael McCoy and Elizabeth Hamman
Research on the effects of pulsed resource inputs has provided tremendous insights about food web dynamics and community structure and stability. However, much less work has considered pulsed dynamics from a top down perspective. This talk will present results from simple models of consumer pulses. Specifically, pulsed predation can lead to lower equilibrium density for prey and in some cases lead to extinction. These findings have important implications for fisheries management, biocontrol, invasion ecology, and for our basic understanding of predator-prey interactions.
Trade-offs between migration speed and predator evasion with hatchery and wild salmon
Evasive behavior in response to predators may affect prey migration speed. Juvenile Chinook salmon (Oncorhynchus tshawytscha) face high predation en route migrating from rivers to the ocean. These wild fish share river systems with supplemented hatchery salmon, also subject to predation. We used behavioral experiments to examine trade-offs in juvenile wild (floodplain vs. river) and hatchery salmon migration rates in the presence of a predator. Salmon were timed moving downstream in an experimental flume in the Mokelumne River, CA with and without a model predator. Hatchery salmon did not change speed with a predator present, while wild salmon slowed down. Wild salmon caught in the river reacted more strongly to the predator than salmon caught on the floodplain. Our results provide a mechanistic basis for trade-offs between migration speed and predator evasion. Further, they suggest behavioral differences between hatchery and wild salmon that may have implications for survival.
Integration of swimming kinematics and ram suspension feeding in American paddlefish
Grant Haines and S. Laurie Sanderson
To capture their prey, ram suspension feeding fishes force water through their oral cavities by swimming forward with an open mouth, filtering plankton from the water column. Previous work has demonstrated that flow through the oral cavity interacts with branchial arches and gill rakers, spatially structuring the filter mechanism. However, the process by which captured prey are manipulated prior to ingestion and the degree to which feeding systems are integrated with locomotion in ram suspension-feeding fish remain largely unknown. We used a 3-D printed model of a paddlefish oral cavity to conduct experiments examining the effects of swimming kinematics on intra-oral pressure and flow speed, the dynamics of spatially structured flow, and the transport of food particles. The results show that swimming kinematics result in a temporal structure to the spatial organization of the filter, and flow dynamics that repeatedly re-suspend food particles on the gill rakers concentrating them at the edges of the gill slots.
Traits contributing to stronger anti-herbivore defense at lower latitudes in a temperate herb
Carina Baskett, Douglas W. Schemske, and Marjorie G. Weber
Biotic interactions are hypothesized to play a greater role in driving adaptation at lower latitudes where abiotic selection pressures are weaker. We tested whether plants from lower latitudes are better defended against herbivores along a gradient from 27°N to 42°N in pokeweed (Phytolacca americana, Phytolaccaceae), an herbaceous, perennial pioneer species native to the eastern US. Previous results have found higher herbivory rates in the field in the southern half of its range. We conducted palatability experiments for 13 pokeweed populations in the lab using a naïve generalist Lepidopteran (Spodoptera exigua). Caterpillar biomass was greater at higher latitudes for both young and mature leaves, indicating that lower-latitude leaves are better defended, consistent with the biotic interactions hypothesis. Palatability in mature leaves may be driven by a negative correlation between toughness and latitude. Young leaves were less palatable than mature leaves, perhaps due to chemical defenses, which we are quantifying with LC-MS.
Resolving an uncertainty paradox in ecological management
We settle a long standing paradox in ecological management regarding the influence of measurement uncertainty. Previous work has frequently suggested that the optimal management of fisheries should respond to increased measurement uncertainty by increasing harvest effort, contrary to the intuition of the precautionary principle. Through the use of cutting-edge point-based POMDP methods, we demonstrate that the standard management theory which ignores measurement uncertainty may lead to over-exploitation of fisheries and increased probability of economic and ecological collapse. In contrast, POMDP solutions which account for measurement error are overall more conservative, avoiding over-exploitation while generating higher economic value.
Funding science in an era of scarce funds: Would a modified lottery help?
Kevin Gross and Carl T. Bergstrom
The current system of allocating funds for scientific research through peer evaluation of competitive proposals has its roots in an era when funding rates were substantially higher than they are today. Now that funds are more scarce, does the same model continue to make sense, or can it be improved? We draw from the theory of costly signaling in biology and the economic theory of contests to analyze the strengths and inefficiencies of the current system. We also analyze the merits of a recent suggestion to add explicit randomness to the award process via a modified lottery.
A novel Bayesian inference method to model tolerance curves
Silas Tittes and Nancy C. Emery
Tolerance curves are a description of fitness as a function of a continuous environmental axis.We present a novel Bayesian inference method to model tolerance curves using a fixed set of biologically interpretable parameters. We applied the method to a hydrological tolerance experiment using fourteen taxa from the genus, Lasthenia, whose co-occurrences are predictably arranged along vernal pool inundation gradients. Using floral biomass as a measure of fitness, our modeling approach finds evidence for variation in taxonomic tolerance breadth, hydrological tolerance extremes, hydrological optima, and absolute cumulative fitness. After correcting for phylogenetic history, only parameters that influence taxa’s absolute floral biomass are correlated with their expected position along the vernal pool inundation gradient. The lack of correlation between inundation and hydrological optima highlights the need to further investigate both interspecific competitive exclusion and other environmental axes in driving Lasthenia’s spatial composition of vernal pools.
Revealing biases in the sampling of species interaction networks
Erica Newman, Marcus A. M. de Aguiar, Marie-Josée Fortin, Mathias M. Pires, Justin D. Yeakel, Paulo R. Guimaraes Jr, Dominique Gravel, David H. Hembry, Laura Burkle, Timothée Poisot, and Jimmy O’Donnell
The structure of ecological interactions is commonly understood through analyses of interaction networks. These analyses are sensitive to sampling biases and detectability issues in both the interactors and interactions. We explored the properties of sampled ecological networks by simulating large-scale ecological networks with predetermined topologies, and sampling them with different mathematical procedures. For this, we developed open-source software scripts NetGen and NetSampler to construct and sample networks. We show that the sampling effort needed to accurately estimate underlying network properties depends both on the sampling design and on the underlying network topology. Overall, the structure of nested modules was the easiest to detect, regardless of sampling design. Sampling according to species degree was consistently found to be the most accurate strategy to estimate network structure.
Bird specimens track 135 years of atmospheric soot and environmental policy
Shane DuBay and Carl Fuldner
Emission inventories of major climate-forcing agents like soot (also known as black carbon) suffer high uncertainty for the early industrial era. Without reliable emissions estimates for this period, it has been difficult to accurately model the historical effects of soot on climate forcing. We identified bird specimens as incidental records of atmospheric soot, filling a major historical sampling gap. We analyzed a time series of >1300 bird specimens to reconstruct trends in atmospheric soot within the U.S. Manufacturing Belt between 1880 and 2015. We found that prevailing emission inventories underestimate atmospheric soot levels in the U.S. through the first decades of the twentieth century, suggesting that black carbon’s contribution to past climate forcing may also be underestimated. This study builds toward a robust, spatially dynamic inventory of atmospheric soot, highlighting the value of natural history collections as a resource for addressing present day environmental challenges.
Reconciling phenological observations with flowering records in herbaria
Jonathan Davies and William Pearse
Data from herbaria can vastly expand the temporal, spatial, and phylogenetic scope at which we can study ecological and evolutionary responses to global change. However, collection records are heavily biased by sampling practices, with different species and different regions having unequal representation. In addition, modelling the timing of a phenological event, such as first flower or leaf-out, is immensely difficult for sparsely sampled data. This is one example of a more general problem: how to determine the absolute limit of a distribution. We show how this problem can be circumvented using sampling theory more usually employed to determine the date a species went extinct. We demonstrate that such methods can resolve an ongoing debate about the relative timings of the onset and cessation of flowering, and allow us to reliably combine modern observations with the vast wealth of historical data that reside in herbaria, museum collections, and written records.
The neglected numerical response of consumers
Kyle Coblentz and Leah Segui
Consumers exhibit two fundamental responses to resources: the functional response and the numerical response. Functional responses determine how consumers' feeding rates change with resource and consumer densities. Numerical responses determine how consumers' reproductive rates change with the consumers' feeding rates. Decades of theoretical and empirical research have focused on determining the form of functional responses and their effects on consumer-resource dynamics. In contrast, consumer numerical responses have been relatively neglected and are often treated simply as a linear conversion efficiency of resources into consumers. Here we discuss several biological mechanisms leading to nonlinearities in consumer numerical responses and use simple mathematical models to explore their effects on consumer-resource dynamics. We use these models to argue that: 1) linear conversion efficiencies are likely oversimplified, 2) nonlinearities in numerical responses can have significant effects on population dynamics, and 3) empirical research on the forms of numerical responses is badly needed.
The phenotypic perspective: A post-modern synthesis
Genes are typically viewed as having fixed effects that form the basis for heritable variation. However, it is becoming clear that the effects of genes are not fixed and many factors other than DNA sequence affect heritable variation. This is an attempt to provide a framework for a general model of evolution that extends the modern synthesis to include variable genetic effects and alternative forms of inheritance.
Phantom species: Can we estimate pseudo-turnover?
Donald Waller and Jared Beck
We use field surveys to monitor ecological change, but finite sampling and rare species mean many species go unseen. We quantify how much these “phantom species” inflate observed rates of colonization and extirpation using a model based on binomial sampling. False absences decline predictably as species abundance and sampling intensity increase, allowing us to estimate pseudo-turnover. This model is robust to sampling scheme and clumped distributions. We apply the model to a 50-year resurvey of 337 species distributed over 83 sites. Naïve estimates of colonization and extinction suffice when species are abundant and well-sampled, but we must commonly adjust for pseudo-turnover to obtain reliable estimates. With rare species and/or limited sampling, pseudo-turnover increases. Adjusting for phantom species effects reduced estimates of colonization and extirpation by 54% and 20%, respectively, in our case study. Accounting for phantom species improves our ability to accurately infer community dynamics and monitor ecological change.
Does individual persistence promote group coordination? A comparative approach to cooperative transport in ants.
When groups of ants work together to carry large objects – called cooperative transport – they must form consensus on travel direction. In many species, groups fail at this decision. In other collective decisions, individuals’ enthusiasm (recruitment intensity), for a given option affects the selection process. Is there a similar mechanism for cooperative transport that accounts for coordination differences among species? Results from theoretical models suggest that individual persistence may promote coordination. I tested this hypothesis empirically, and found that ant species with more persistent individuals succeeded more often and formed more coordinated groups. I also manipulated persistence in one species, and found that adding two fake, infinitely persistent ants to transport groups moderately increased coordination. These results support the hypothesis that high individual persistence promotes group coordination during cooperative transport. This is the first quantitative comparison of cooperative transport among species, and this study informs the mechanisms of emergent collective behavior.
The consequences of polyandry for sibship structures, distributions of relatedness, and potential for inbreeding in a wild population
Ryan Germain, Peter Arcese, and Jane Reid
The evolutionary benefits of polyandry remain elusive. One potential benefit could arise if polyandry alters sibship structures and consequent relatedness among females’ descendants, thereby intrinsically reducing future inbreeding risk. However, such effects have not been quantified in naturally complex reproductive systems that also encompass iteroparity, overlapping generations, and polygyny. We used long-term social and genetic pedigree data from song sparrows to quantify cross-generational consequences of polyandry for offspring sibship structures and distributions of relatedness among all possible mates. Polyandry decreased full-sibships and increased half-sibships on average, but such effects varied among females and were smaller than would occur in the absence of polygyny. While polyandry decreased the overall frequencies of possible matings among full-sibs and other close relatives, it increased the frequencies of possible matings among half-sibs and more distant relatives. These results imply that the intrinsic consequences of polyandry for inbreeding risk could cause weak indirect selection on polyandry.
Causes and consequences of animal personality in larval dragonflies: Individuals to ecosystems
Denon Start and Benjamin Gilbert
Intraspecific variation and particularly animal personality are increasingly recognized as having important consequences for communities. However, we have a poor understanding of the biological scales at which intraspecific variation occurs, the consequences of these different scales of variation, and the ultimate causes of individual differences. We investigated these questions using a series of projects investigating activity rate in dragonfly larvae and co-occurring predators and prey. We show that intraspecific variation among species, populations, and individuals can have important consequences for community and ecosystem processes. We further show that the role of consistent individual differences is modified by ontogeny to produce complex patterns of intraguild predation. Finally, we demonstrate that animal personality is under selection by predators, causing indirect selection on underlying biochemical pathways. Overall, our work demonstrates that intraspecific variation is under selection, occurs over several levels of biological organization, and can have important consequences for individuals, populations, communities, and ecosystems.
Nutrients from salmon parents relax selection pressures on their offspring
Organisms can modify their surrounding environment, but whether these changes are large enough to feedback and alter their evolutionary trajectories is not well understood, particularly in the wild. Here we show that nutrient pulses from decomposing Atlantic salmon (Salmo salar) parents alter selection pressures on their offspring with important consequences for their phenotypic and genetic diversity. We found a strong survival advantage to larger eggs and faster juvenile metabolic rates in streams with low parental nutrients but not in streams with high parental nutrients. Differences in selection intensities led to significant phenotypic divergence in these two traits among stream types. Stronger selection in streams with low parental nutrient levels also decreased the number of surviving families compared to streams with high parental nutrients. Observed effects of parental nutrients on selection pressures provide experimental evidence for key components of eco-evolutionary feedbacks in wild populations.
Stags, hawks, and doves: Individual variation in helping in social evolution theory
Jeremy Van Cleve
Mechanisms for cooperation include, kin selection (measured by relatedness), reciprocity (measured by responsiveness), and direct benefits to cooperation that are often nonlinear (i.e., synergistic), and investigating the joint action of these mechanisms has been more difficult. Using kin selection and evolutionary game theory, I show how different combinations of these mechanisms produce directional selection for or against cooperation or variation in levels of cooperation via stabilizing or diversifying selection. Moreover, each of these outcomes maps uniquely to one of four classic games from evolutionary game theory, which means that modulating relatedness, responsiveness, and synergy effectively transforms the payoff matrix from one the evolutionary game to another. My results provide a general framework with which to generate comparative predictions that can be tested using quantitative genetic techniques and experimental techniques that manipulate investment in cooperation.
Intruder alert! How communication behaviors influence territory maintenance, expansion, and the persistence of local populations
The interface of spatially explicit movement with communication behaviors is a rich area for ecological and evolutionary research. For example, investigations of how communication behaviors influence the formation, maintenance, and dissolution of animals’ territories provide special insights into space use and habitat needs that can inform conservation planning. Many predators use scent marking to delineate territory boundaries and dissuade intrusion by neighbors. Such scent-marks are localized, but with reinforcement, can persist as durable signals. Other communication mechanisms, such as aggressive calling, extend spatially over a much greater range than scents, and may be used to temporarily expand territory size. However, such calls may be energetically costly (either directly, or by inducing aggressive encounters), and calls lack the temporal persistence of scents. Using spatially explicit state-space modeling, we explore how this interplay between long-lasting, but localized, scent marking and transient, but wide-ranging, aggressive calls sets limits on population persistence. For animals that do not use aggressive calls, opportunity costs (i.e., the inability to feed while spending time on territorial defense through scenting) prevent the persistence of populations under many conditions. However, we find that aggressive calls, despite their costs and transient nature, may greatly expand the range of conditions under which population persistence is feasible. These results illustrate how the interplay between different modes of communication may have important spatial consequences such as the establishment and persistence of territories. We develop these ideas in the context of the territorial behaviors of the Giant Otter (Pteronura brasiliensis) of the Brazilian Pantanal.
Thermoregulatory effects and the geographic diversification of sexual coloration in a North American dragonfly
Michael Moore, Cassandra Lis, Iulian Ghergel, and Ryan A. Martin
In addition to its widespread function in signaling, sexual coloration may commonly have pronounced, but often overlooked, thermoregulatory effects that could enhance or constrain ornament elaboration. The blue dasher dragonfly (Pachydiplax longipennis) produces intrasexually selected wing coloration in some, but not all, parts of its broad North American range. Here, we examined the potential for temperature to shape the geographic diversification of this sexually selected trait. Using geo-referenced photographs taken by citizen scientists, we found that males rarely produce any wing coloration in the warmest regions of their range. Additionally, we observed that the thoracic temperature of males with naturally greater coloration, and males with experimentally augmented coloration, increased faster and reached higher temperatures than for males with weaker coloration. As flight performance during territorial contests depends on thoracic temperature, thermoregulatory effects of sexual coloration likely drive diversification in P. longipennis, and could underlie similar patterns in other animals.
Variation in context dependent foraging behavior across pollinators
Heather Briggs, Robin Hopkins, Callin Switzer, and Stuart Graham
Pollinator foraging behavior has direct consequences for plant reproduction and has been implicated in driving floral trait evolution. Exploring the degree to which pollinators exhibit flexibility in foraging behavior will add to a mechanistic understanding of how pollinators can impact selection on plant traits. We examine flexibility in flower color preference of two groups of native butterfly pollinators under natural field conditions. We found that pipevine swallowtails and skippers display distinct patterns of color preferences across different contexts. Pipevine swallowtails exhibit highly flexible color preferences and likely utilize other floral traits to make foraging decisions. In contrast, skippers have consistent color preferences and likely use flower color as a primary cue for foraging. This variation in color preference flexibility likely imposes concordant selection on flower color in some contexts but discordant selection in other contexts. This variability could have profound implications for how flower traits respond to pollinator-mediated selection.
Diversity in mate preferences and signals in Spadefoot toads: causes and consequences
Gina Calabrese and Karin Pfennig
Mate preferences can diverge among populations that face different selection regimes. Diversity in mate preferences can drive diversity in mating signals, local adaptation, and even reproductive isolation between populations (important in incipient speciation). Thus, understanding what conditions are most favorable for populations to evolve different mate preferences can shed light on many ecological and evolutionary processes. Populations of the Mexican Spadefoot Toad (Spea multiplicata) in the southwestern United States face spatially-variable selection on female mate preferences, due to variable hybridization risk, variable relationships between male signals and aspects of mate quality, and variable ecological conditions for offspring. I use female preference assays, field recordings of male signals, and ecological data across populations to explain the causes and consequences of divergent mate preferences among spadefoot populations.
Maternal effect mitigate maladaptation to climate change
Susana Wadgymar and Jill T. Anderson
Contemporary changes in climate could generate widespread local maladaptation if local genotypes cannot maintain a fitness advantage over genotypes from historically warmer sites. Maternal effects (ME) have long been considered a confounding source of environmental noise in studies of evolution. However, ME have the potential to promote or diminish local adaptation, depending on whether the maternal environment is predictive of the offspring environment. We conducted a spatially replicated, manipulative field experiment across an elevational gradient and a complementary controlled, growth chamber experiment with the perennial plant Boechera stricta to ask whether ME (1) contribute to local adaptation and (2) produce adaptive or maladaptive responses to climate change. This talk dissects three-way interactions between the maternal environment, the offspring environment, and population elevation of origin on offspring emergence, survival, and growth. These results illustrate the contexts in which ME can be adaptive and yield important insights on the eco-evolutionary consequences of climate change.
How climate warming affects plant phenology and reproduction
Christopher Johnson, Sarah Richman, Laura Stefan, and Jonathan M. Levine
A fundamental challenge in ecology is to disentangle how species’ responses to changing environments affect their fitness. Phenology – the timing of biological events – is both highly sensitive to climate warming and intrinsically linked to species’ fitness. We investigate how warming climate affects species’ phenology and reproduction by quantifying the phenology and seed set of plants transplanted along an elevational gradient in the Swiss Alps. We hypothesize that plants in warmer (lower-elevation) habitats will flower earlier and suffer reduced reproduction than plants in their native habitat. We find that flowering phenology advances as climate warms (at lower-elevation sites), but that reproduction often peaks under intermediate climate warming (at mid-elevation sites) and then declines as climate warms further (at low-elevation sites). These results suggest that climate warming affects species’ fitness via phenological changes, but that the net outcome may be positive or negative depending on plant species and magnitude of environmental change.
Adaptation to environmental change in species with complex life cycles: The influence of stage specific selection and density dependence
Molly Albecker and Michael McCoy
For organisms with complex life cycles (CLC) that are being affected by environmental change, different life stages may be differentially impacted by shifts in habitat conditions. CLC species may also have different demographic processes during different life stages. Consequently, adaptive responses to environmental change in CLC species may be affected by dual constraints. We use individual based models to explore how stage-specific selection pressures affect adaptive potential in stage-structured populations across a range of demographic scenarios. Strong selection on egg stage survival can facilitate rapid rates of adaptation by modifying the impact of strong negative density dependence during the larval phase. When density dependence or selective pressure on the egg stage is relaxed, adaptation slows. Since most organisms have complex life cycles, understanding of how adaptive evolution occurs in stage-structured populations provides insights into our understanding of rapid adaptation generally, and informs effective management of stage-structured populations during climate change.
Linking phenological shifts to species interactions in a changing world
Climate change is altering the phenologies of species worldwide. While these shifts are now well documented we still have a limited understanding of when and how they will affect dynamics and structure of natural communities. Making this connection requires a detailed understanding of how shifts in the relative phenologies of interacting species affect the outcome of species interactions across a range of conditions and what the underlying mechanisms are. Using a combination of experiments and theory we show that phenological shifts typically have non-linear effect on most demographic rates of competing species and varied across environments. This variation could be explained by size-mediated priority effects and positive feedbacks between growth rates and competitive dominance. Importantly, this non-linear relationship indicates that changes in the inter-annual variation itself can modify species interactions even when mean phenologies remain unchanged across years.
How do climate-change induced phenological shifts alter terrestrial competition between two amphibians?
Hilary Rollins and Michael F. Benard
Climate change is creating warmer, earlier springs which shift phenology. Shifting phenology and climate change may affect interspecific interactions, by increasing body size similarity or altering order of emergence. Wood frogs are breeding earlier in response to climate change while American toads are not. Breeding date in turn affects timing of and size at metamorphosis. To simulate climate change’s effect on phenotype, we manipulated food and temperature in mesocosms to create variation in wood frog size and date of metamorphosis. To test if wood frog metamorphic phenotype affected interspecific competition, wood frogs were placed in terrestrial enclosures with juvenile toads. Toads paired with initially larger and later emerging wood frogs had decreased body condition. Both results indicate that toads would experience fewer negative effects of competition with wood frogs under climate change. Understanding size and timing based interactions will help us better predict effects of climate change across taxa.
Functional traits and plasticity confer polyploid advantage in changing environments
Na Wei, Richard Cronn, Aaron Liston, and Tia-Lynn Ashman
All flowering plants are ancient polyploids, making polyploidy a principal mechanism promoting biodiversity. While many of the genomic and morphological innovations associated with polyploidy have been elucidated, the ecological consequences remain largely unknown. It has been hypothesized that genomic redundancy and diversity in polyploids contribute to broader ecological breadth and greater ability to cope with rapid environmental changes than diploids. To evaluate this hypothesis, we established a large-scale common garden experiment, comprising 12 clones of 269 genotypes from 69 populations of six polyploid and five diploid Fragaria species, grown in three climatic gardens in Oregon. We address (1) whether polyploids have higher fitness relative to diploids across all environments; if so, (2) whether polyploid fitness advantage is conferred by greater phenotypic plasticity or mean trait values. Our results show that polyploids have a fitness advantage across environments, which is gained through both trait mean and adaptive plasticity.
Mechanisms of life history variation and climate adaptation in a native wildflower
Johanna Schmitt, Jennifer Gremer, Chenoa Wilcox, Elena Suglia, and Alec Chiono
Local life history adaptation to elevational gradients depends on plasticity to seasonal environmental cues that are rapidly changing with ongoing climate change. We examined mechanisms of life history variation within and among populations of the California native wildflower Streptanthus tortuosus, manipulating germination timing and winter chilling cues in common garden experiments. Populations from higher elevations, which germinate after spring snowmelt, had stronger chilling requirements for germination and flowering and were more likely to perennate after flowering than low elevation populations. Germination timing also affected life history expression within populations. Within a low elevation population, fall-germinating plants were more likely to flower in the first spring and less likely to perennate and flower the next year than spring germinants. This seasonal life history contingency may maintain annual, biennial, and iteroparous perennial life histories within low elevation populations. However, climate change will alter selection on life histories and potential for population persistence.
Species persistence under climate change: interplay between adaptation, plasticity and migration in common sugarbush (Protea repens) of South Africa
Melis Akman, Jane E. Carlson, and Andrew M. Latimer
Under rapidly changing climates, populations’ ability to persist will depend on their potential for adaptation and gene flow, and capacity to adjust via plasticity. We showed that populations of an evergreen shrub from the Cape Floristic Region (CFR) of South Africa, Protea repens, show ample variation in growth patterns, morphology, physiology and gene expression. This variation is associated with the climatic gradients along this species’ range. Climate also contributed to plasticity differentiation: plasticity in growth and several gene networks under drought declined with increasing altitude of the source sites. In addition, plasticity differentiation was associated with mortality differences among populations: high below-ground carbohydrate accumulation in some populations under drought led to higher mortality. Through gene sequence variation, we uncovered limited gene flow between eastern and western populations. Our results suggest that climatically shaped adaptation and plasticity, together with limited gene flow may leave this species particularly threatened by climate change.
Linking phenological synchrony to species interactions
Changes in the timing of species life cycle events (phenological shifts) can disrupt ecosystems by altering the timing and duration of species interactions. Most phenology research identifies phenological shifts by changes in the onset or mean of a phenological event, but these metrics ignore individual variation in timing (i.e., phenological synchrony), and therefore may be uninformative for predicting ecological effects of phenological shifts. Phenological synchrony should be ecologically important because it influences a population’s density through time, size structure, and temporal-numerical overlap with interacting populations. However, we currently know very little about phenological synchrony, how it changes across time and space, or how it contributes to population dynamics and species interactions. Therefore, we asked 1) does variation a species’ phenological synchrony significantly alter numerical overlap with co-occurring species? and 2) how does phenological synchrony in a predator population affect predator-prey dynamics? We answered question 1 by analyzing high temporal resolution anuran calling data representing 12 species, 15 years, and 8 sites. We answered question 2 with an agent based model that manipulated phenological synchrony and mean of a predator population in relation to its prey and measured outcomes on predator and prey survival and fitness Results from question 1 show that species’ phenological synchrony can vary dramatically across years and sites and fundamentally shapes numerical overlap of co-occurring species. Relative timing of single metrics (first, mean) between 2 species predicted shifts in their numerical overlap for only 9% (4/42) of species pairs considered. However, when we considered phenological synchrony, we were able to detect changes in numerical overlap for 26% (11/42) species pairs. Including synchrony gave more power to detect phenological shifts on a shorter time scale, and furthermore, more directly informed changes in numerical overlap, a proxy for species interactions. Therefore, it is critical to consider synchrony when measuring phenological shifts and predicting ecological outcomes. Addressing question 2, we found that predator phenological synchrony can influence predator-prey dynamics. High synchrony predator populations exhibited pulsed, high predation pressure, while low synchrony populations exerted a lighter predation pressure for a longer period of time. Therefore, synchrony changed both predator numerical and per capita effects on prey. With climate change rapidly altering species phenologies, it is increasingly important to be able to accurately track phenological shifts and predict the net effects. We demonstrate that this requires considering shifts in phenological synchrony.
Acquired metabolism as an evolutionary path to mixotrophy
Holly Moeller, Michael G. Neubert, and Matthew D. Johnson
Acquired metabolism--metabolism not encoded within an organism's genome, but which is acquired through interactions with other species--mediates species interactions that shape both community composition and function. One example of this is acquired phototrophy: the acquisition of photosynthetic abilities through the retention of prey chloroplasts or hosting of photosynthetic endosymbionts. Unicellular, planktonic acquired phototrophs range in the degree to which they rely on their acquired metabolism. For example, the marine ciliate genus Mesodinium contains sister species ranging from the bloom-forming phototroph M. rubrum, which obtains >95% of its carbon from photosynthesis, to the heterotroph M. pulex, which does not retain prey plastids at all. Using a combination of mathematical and empirical approaches, I explore what this genus can tell us about how acquired metabolism allows new lineages to emerge from a background of closely related competitors, ultimately providing insight into the evolution of the modern eukaryotic phytoplankton.
Ecological effects of variation within species
Simone Des Roches
Human activity is causing wild populations to experience rapid trait change and local extirpation. Resulting changes in intraspecific variation, which are occurring much faster than changes in species diversity, could have substantial consequences for ecological processes. Researchers have long established that variation among species influences ecological processes; yet, only recently has evidence accumulated for the ecological importance of variation within species. We conducted a meta-analysis comparing the ecological effects of variation within focal species (intraspecific effects) to the effects of replacement or removal of that species (species effects). We evaluated ecological responses including changes in abundance, rates of ecological processes, and composition of organisms and nutrients. Our results show that intraspecific effects are often comparable to species effects and are sometimes stronger. Species effects tend to be larger for direct ecological responses (e.g., through consumption), whereas intraspecific effects and species effects tend to be similar for indirect responses (e.g., through trophic cascades). Intraspecific effects are especially strong when indirect interactions alter community structure or nutrient composition. Intraspecific variation, therefore, affects not only population persistence but also entire communities and ecosystems.
Using human vision to detect variation in avian coloration: How bad is it?
Becky Fuller and Zachary Bergeron
Assessing variation in animal coloration is difficult as animals differ in their visual system properties. This has led some to propose that human vision can never be used to evaluate coloration, yet many studies have a long history of relying on human vision. To reconcile these views, we compared the reflectance spectra of preserved avian plumage elements with two measures that are humans biased: RGB values from digital photographs and the corresponding reflectance spectra from a field guide. We measured 73 plumage elements across 14 bird species. The field guide reflectance spectra were drastically different from that of the actual birds, particularly for blue elements. However, principal components analyses on all three data sets indicated remarkably similar data structure. We conclude that human vision can detect much of the variation in coloration in the visible range, providing fodder for subsequent studies in ecology, evolution, behavior, and visual ecology.
Quantifying resource niches in microbial communities
Thomas Miller, Olivia Mason, Abigail Pastore, Catalina Cuellar-Gempeler, and Erin Canter.
Community ecology faces novel challenges when dealing with the types of data available from high throughput analysis of microbial communities. We have used communities from the leaves of pitcher plants (Sarracenia purpurea) to quantify the effects of protozoa species on their diverse bacterial prey. The effects of different protozoa species are compared using several measures of resource overlap, then correlated with measures of the strength of competitive interactions among the protozoa. Some species of protozoa appear to be generalist, changing the cell density but not relative abundance of bacteria, while others appear to specialized on dominant bacteria, resulting in significantly different prey communities. Effects of combinations of protozoa are generally not intermediate, but reflect the presence of a specific protozoan species. Effects of protozoa species on the bacterial communities are not correlated with competitive ability, suggesting that the resource niche may not be the dominant factor determining competitive outcomes.
Stature drought & rarity
Drought adaptation may favor small size, which may promote rarity
Gene interactions and the location of genes
Andrius Jonas Dagilis
In 1930 Fisher made the prediction that recombination reduction between coevolving genes is generally favored. Expanding to a genome-wide view, recombination reduction between coevolving genes should result in informative patterns of gene distribution among chromosomes. I test whether this occurs using interaction networks as a proxy for coevultionary networks. I find that in humans and yeast chromosomes contain many more interactions than expected by random chance alone, and that in general interacting genes tend to be closer than expected.
Higher order interactions regulated by drought result in selection in semi-arid annual plants
Abigail Pastore, Abigail I. Pastore, Trace E. Martyn, and Margaret M. Mayfield
Species interactions are recognized to have non-linear effects on density, known as higher order interactions (HOIs). But HOIs are rarely quantified though they can have significant effects on population dynamics. In an annual plant system in Western Australia, HOIs affect the fecundity of many species, which could result in selection on populations. We quantified HOIs between individuals, and looked for selection on the traits of several plant species by using fecundity as a proxy for fitness. This experiment was performed in an extreme drought year, and a watering treatment was also implemented, allowing us to test how drought changes the selection regime experienced at the individual level. Here we show that HOIs between plants and drought interact to regulate selection on plant traits. This indicates that complex selection pressures are mediating community composition and extreme weather events will be important for the preservation of this diverse but threatened community.
Plasticity, specialization, and species distributions across environmental gradients
Raffica La Rosa and Nancy C. Emery
Species growing in variable environments may adapt to this variation by specializing on a subset of conditions or evolving plasticity to tolerate a broad range of conditions. In this study, we investigated the extent to which these different strategies explain plant distribution patterns across environmental gradients. We studied three annual Lasthenia (goldfield) species (Asteraceae) that occupy different microhabitats in California vernal pool landscapes that are characterized by different levels of hydrological variation during their winter growing season. To test the prediction that Lasthenia distribution patterns reflect their tolerance to patterns of temporal variation in their environment, we measured traits and fitness of three Lasthenia species in a greenhouse common garden experiment that manipulated the mean and variance in water table height. Using these data, we quantified the amount of phenotypic plasticity exhibited by each species in traits that can influence flood tolerance, and estimated each species’ tolerance to environmental variability.
Long-term evolution of S. cerevisiae subjected to frequent dispersal by insect gut-vectoring.
Insect- microbial phoresis is an established method of microbial dispersal. Not only do insects play a role in determining the composition of microbial communitie, they may also play a role in selecting for specific phenotypes of microbe and the evolution of individual species within a microbial community. We performed a long term evolution experiment in which we repeatedly subjected the yeast strain Saccharomyces cerevisiae to digestion within the gut of the fruit flyDrosophila melanogaster over thirty treatment generations. We then compared the ancestral and derived strains using both phenotypic characteristics and genetic sequencing. Results indicated effects from both yeast ancestral regionality and experimemtal treatment type with respect to both phenotypic and genetic changes. Results from this study impact our understanding of how different community members can play a role in the evolution of one species.
Why fix nitrogen?
Nitrogen-fixation has global importance on par with photosynthesis, with nitrogen-fixing symbioses playing key roles in agricultural sustainability. I will present research on legume-rhizobia and grass-associative nitrogen fixer interactions exploring the molecular, organismal, ecological, and evolutionary facets shaping this key process.
Subspecies richness and diversity gradients: a case study with birds
Mauro Toshiro Caiuby Sugawara and Matthew Pennell
Most macroevolutionary methods use species as their unit of analysis. One exception is the protracted birth-death model (PBD). The goal of this project was to develop a Bayesian version of the PBD and use it to investigate the processes that generated the variation of species richness in birds. Using simulated data, we show that the Bayesian version of the model has higher accuracy. To analyze the latitudinal diversity gradient (LDG), the species were divided into regions and we used the distribution of subspecies richness to build priors. The estimates of the speciation rates did not vary significantly across the regions. This lack of variability between tropical and temperate indicates that speciation is occurring at roughly the same pace, suggesting that rates have little effect on the difference in diversity and either "regional carrying capacities" or "time since origination" might be better explanations for the LDG in birds.
Stages of diversification for Neotropical electric fish Apteronotidae
Lesley Kim, Kory J. Evans, and James S. Albert
Neotropical freshwaters constitute the world’s largest continental aquatic biota with more than 8,000 fish species. Yet the ecological and evolutionary processes underlying the formation and maintenance of this exceptional ecosystem remain poorly understood. A widely-cited model of adaptive radiation in African rift-lake cichlids (Kocher, 2004) proposes diversification in three stages; habitat specialization (H), trophic specialization (T), and sexual communication (S). Here we explore adaptive diversification in the Neotropical electric fish Apteronotidae (Teleostei: Gymnotiformes). Species within Apteronotidae share similar functional traits, are distributed in allopatry, and differ on electric signal (i.e. sexual) phenotypes and karyotypes. We use a combination of morphological (osteological and morphometric), behavioral (electric signal), ecological (trophic positon, habitat), and phylogenetic datasets to test alternative hypotheses regarding the sequence of evolution of lineages and functional phenotypes. We propose these patterns of lineage and functional diversification arise in part from differences in rates of evolution of mouth size and positon.
Evidence for contemporary and historical gene flow between guppies in different watersheds
Population genetic structure is expected to be shaped by historical and contemporary patterns of gene flow; yet the relative importance of these two time frames is often hard to demonstrate. We made inroads into this uncertainty by examining patterns of neutral genetic variation and adaptive traits in wild guppies (Poecilia reticulata) distributed across two watersheds in northern Trinidad. Although we found expected signatures of within-watershed gene flow, we also inferred at least two likely examples of cross-watershed gene flow – one recent event (41 years ± 13) in the upstream reaches and an older one (577 years ± 265) further downstream. Despite these strong signatures of gene flow events, we could find no evidence that they influenced adaptive trait variation. Divergent selection in this systems seems to overpower most gene flow – at least on the spatiotemporal scales investigated here.
Keystone genes: how can single genes have large ecological effects?
The keystone species concept is used in ecology to describe individual species that have disproportionately large effects on their communities. We extend this idea to the level of genes that influence ecological processes in a measurable way. Such “keystone genes” underlie traits that are either strongly involved in species interactions or that cause noteworthy abiotic changes, which can then influence the behavior, abundance, diversity, and/or fitness of other species, as well as emergent ecosystem properties. In this article, we consider possible keystone genes and propose two general pathways through which a single gene might have important ecological effects. Although rare, keystone genes could dominate certain ecological processes and thus their discovery and study are important to gain deeper insights into eco-evolutionary dynamics.
Restoration in a changing world: Can genetic diversity buffer restorations from climate change?
Jennifer Lau, Lars Brudvig, and Emily Grman
Genetic diversity can be important to population, community, and ecosystem-level processes. Yet, the magnitude of genetic diversity effects may be underestimated, and several potential mechanisms of genetic diversity effects have not been fully investigated because most studies have been short-term and conducted over small spatial scales. In particular, how genetic diversity affects population growth or adaptation to novel environments and the context dependencies of these effects remain poorly explored. We combined a new global warming experiment with a long-term, large-scale genetic diversity manipulation to investigate how global warming will influence restoration success and how genetic diversity may buffer the effects of warming. We find substantial variation in the traits and success of different seed sources but also evidence that both warming and variation across space influences plant growth and reproduction of the various ecotypes (GxE). These data suggest that sowing more genetically diverge populations may facilitate prairie plant establishment across a wide range of environmental conditions.
Comparative genomic analysis reveals repeatability in patterns of genomic divergence across birds
Heterogeneous patterns of genomic differentiation are commonly documented between populations and there is considerable interest in identifying factors that generate them. Investigations into repeatable patterns of genomic differentiation across population pairs provide a powerful setting for this work and birds are especially well-suited, as genome structure is phylogenetically conserved and a considerable amount of sequencing data have been generated. We re-estimated genomic differentiation across 8 species pairs and our results suggest that 3-18% of the variation in genomic differentiation can be explained by correlations across pairs. Linked selection at shared genomic features (e.g., areas of reduced recombination) likely account for this pattern. Species pairs further that exhibited higher levels of differentiation also exhibited more consistent patterns. This result could implicate genomic hitchhiking, with each speciation event beginning at different loci and linkage disequilibrium between these loci eventually the effects of selection, permitting shared genomic factors to influence landscapes of differentiation.
Recoupling adaptive molecular evolution to phylogenetics using a fitness-dependent birth-death model
David Rasmussen and Tanja Stadler
Most phylogenetic models assume that molecular evolution at the sequence level occurs independently of the other evolutionary processes giving rise to a phylogeny. This assumption implies that mutations cannot feedback and alter the fitness of a lineage, such that lineages carrying highly deleterious mutations are just as likely to survive and leave behind descendants as lineages carrying beneficial mutations. To relax this unrealistic assumption, we propose a multi-type birth-death model that couples the fitness effects of mutations at multiple sites to the birth and/or death rate of a lineage and thereby its overall fitness. In doing so, the model takes into account how selection shapes molecular evolution at each site and how fitness effects at linked sites act together to shape the phylogeny. We show that this model can be used to estimate either site-specific fitness effects or the entire distribution of fitness effects across sites from viral sequence data.
Genomic signals of selection predict climate-driven population declines in a migratory bird
The ongoing loss of biodiversity caused by rapid climatic shifts necessitates accurate models for predicting species responses. Despite evidence that evolutionary adaptation can mitigate the climate change impacts, evolution is rarely integrated into predictive models. North American migratory birds, including Yellow warblers (Setophaga petechia), are vulnerable to climate change and despite high dispersal capacity some species have experienced climate-driven population declines. Integrating population genomics and environmental data, we found that genomic variation in Yellow warblers was strongly associated with climate. Recent population declines were more likely in areas requiring the most adaptation, suggesting that failure to adapt may have already negatively impacted populations. The strongest candidate variant associated with climate variant was upstream from DRD4, a gene linked to exploratory behavior and migration. Broadly, our study suggests that the integration of genomic adaptation can increase the accuracy of future species distribution models and ultimately guide more effective mitigation efforts.
Pleiotropy across the life cycle: environmental regulation of germination and flowering
A continent-spanning migratory divide reduces interbreeding across multiple barn swallow contact zones
Elizabeth Scordato, Chris Smith, Georgy Semenov, Liu Yu, Matt Wilkins, Wei Liang, Alex Rubtsov, Sundev Gombobaataar, Kazuo Koyama, Sheela Turbek, Craig Stricker, Mike Wunder, and Rebecca Safran
Migratory divides have been assumed to act as reproductive barriers in a variety of avian taxa, but the direct role of divergent migratory behavior in reducing gene flow has not been demonstrated. We found that restricted hybridization between two pairs of barn swallow (Hirundo rustica) subspecies coincides with a migratory divide around the Tibetan Plateau. By contrast, a third subspecies pair exhibits no variation in migratory phenotype and experiences extensive genomic admixture. We further find within-individual correlations between genomic ancestry and migratory phenotype and assortative mating by migratory phenotype, implicating a central role for migratory behavior in reducing gene flow between subspecies. The remarkable coincidence in the locations of migratory divides and genetic breaks among different subspecies pairs provides clear support for a longstanding hypothesis that the Tibetan Plateau functions as a significant geographic barrier contributing to the diversity of Siberian avifauna.
Modulation of adaptation rate by background selection in the human genome
Lawrence Uricchio and David Enard
Much recent debate in human evolutionary genetics has focused on the selection mechanisms that best explain diversity and divergence on the human lineage. Here, we develop analytical theory showing that a state-of-the-art procedure for estimating adaptation rate is downwardly biased in the presence of weakly adaptive alleles and background selection. We develop an Approximate Bayesian Computation framework for estimating adaptation rate that accounts for weak adaptation, human demography, and genome-wide background selection and apply it to human sequence data. We find strong evidence that the majority of human lineage adaptive substitutions provide only weak fitness gains, and that background selection has reduced the overall proportion of fitness-increasing fixed alleles by over a factor of 2 in portions of the human genome. Our results clarify the evolutionary mechanisms driving adaptation in humans, and may help explain why humans have an apparently lower adaptation rate than many other species.
Genomic signature of asymmetric pollen transfer among Burmeistera
Species boundaries are often porous for plants, and gene flow between species is often asymmetric. Various post-mating barriers have been shown to cause such asymmetry, including pollen competition, ploidy differences, or postygotic barriers, but only rarely have premating barriers been implicated. Burmeistera species vary widely in flower morphology in terms of the exsertion of reproductive parts outside the opening, which allows them to partition pollen placement on the heads of their bat pollinators. Experimental work shows that bats will pass some pollen long-exserted species to short-exserted species, but much less in the opposite direction. Phylogenetic work with >500 gene trees demonstrates that short-exserted species have less stable phylogenetic positions, i.e. lower congruency between gene trees, as would be expected if the asymmetric pollen flow induces asymmetric gene flow. Thus this study provides rare evidence of premating barriers contributing to asymmetric gene flow across a genus.
Unveiling the factors behind the diversification of dung beetles (Scarabaeinae)
Orlando Schwery, Kimberly Sheldon, and Brian C. O'Meara
Dung beetles are one of the most ecologically and economically important insect groups, with >5000 species worldwide. Several hypotheses have been posited to explain their diversification, but have only been explicitly tested for specific subclades or regions. Using the largest Scarabaeinae phylogeny to date, we are addressing this question for the whole subfamily and on a global scale. We are employing comparative phylogenetic methods to investigate the factors associated to dung beetle diversification, such as biogeography, evolution of feeding strategies and thermal tolerance breaths. The ability to use dung for food and reproduction is a crucial trait affecting their interaction with the environment and thus their potential to diversify. However, it is unlikely the single cause for the rise of this diverse and widespread group, and while dung feeding may be an important prerequisite or trigger, other factors should come into play to maintain and drive the ongoing diversification.
Genomic signatures of divergent host plant use in the context of an evolutionary trap
Pieris macdunnoughii, a North American butterfly, specializes on mustards. Female butterflies use glucosinolates and other secondary metabolites to identify host plants and larvae happily feed on many native mustards. Following this evolved recognition system, females also oviposit on nonnative mustards, including Thlaspi arvense. T. arvense is lethal to P. macdunnoughii larvae, generating an evolutionary trap wherein cues are no longer reliably linked to good host plants. Lethality of T. arvense is particularly puzzling because the closely-related Pieris napi oviposits and develops normally on T. arvense in their native Eurasian ranges. We crossed P. macdunnoughii and P. napi butterflies, finding survival on T. arvense followed standard patterns of Mendelian inheritance at a single locus. We used a pooled sequencing approach to search for regions of the Pieris genome associated with the ability to survive on T. arvense. We also assessed key genes for resistance to glucosinolate defenses for signs of divergence.
Elasticity of population growth with respect to the intensity of biotic or abiotic driving factors
Demographic analysis can elucidate how driving factors, such as climate or species interactions, affect populations. One important question is how growth would respond to future changes in the mean intensity of a driving factor or in its variability, such as might be expected in a fluctuating and shifting climate. Here I develop an approach to computing new stochastic elasticities to address this question. The linchpin of this novel approach is the multidimensional demographic difference that expresses how a population responds to change in the driving factor between two discrete levels of intensity. I use this difference to design a perturbation matrix that links data from common empirical sampling schemes with rigorous theory for stochastic elasticities. Although the starting point is a difference, the products of this synthesis are true derivatives: they are elasticity with respect to the mean intensity of a driving factor, and elasticity with respect to variability in a driving factor. Applying the methods to published data, I demonstrate how these new elasticities can shed light on growth rate response within and at the boundary of the previously observed range of the driving factor, thus helpfully indicating nonlinearity in the observed and in the potential future response. The stochastic approach simplifies in a fixed environment, yielding a compact formula for deterministic elasticity to a driving factor.
Isolation by distance as a null hypothesis of population structure
A fundemental quandary in the description of biological diversity isthe fact that diversity shows both discrete and continuous patterns. For example, there is disagreement on species concepts because theprocess of speciation is usually gradual, and so there is no set pointin the continuous divergence of populations when they become separate species.This issue extends below the species level as patterns of phenotypicand genetic diversity within and among populations are shapedby continuous migration and drift, as well as more discrete eventssuch as geograpihc barriers, rapid expansions, bottlenecks, and rarelong distance migration. Indeed even the use of the word population in the last sentence implies that we have some idea of a cohesive unit that is worthy of a label. Here, we present a novel statistical framework for the simultaneous inference of continuous and discrete patterns of population structure.The method estimates ancestry proportions for each sample from a set of discrete population layers, and, within each layer, estimates a rate at which relatedness decays with distance.This model explicitly addresses the ``clines vs. clusters" problem in modeling population genetic variation by jointly accommodating both continuous and discrete patterns of differentiation.
Blue whales in variable and disturbed environments: Working in Pasteur's quadrant
Marc Mangel, Enrico Pirotta, Daniel P. Costa, Bruce Mate, Jeremy Goldbogen, Daniel Palacios, Luis Huckstadt , Elizabeth A. McHuron, Lisa Schwarz, and Leslie New
I will describe a dynamic state model, implemented via stochastic dynamic programming and forward Monte Carlo simulations, to predict the effects of disturbances on the reproductive success of migratory baleen whales. We parameterised the framework by integrating the best available evidence on the behaviour, energetics, physiology and movement of eastern North Pacific blue whales and explored the effects of both anthropogenic and environmental perturbations. The model also shows that the long-term relevance of environmental changes will depend on how the whales adjust to the perturbed environment. We characterize the sensitivity of our predictions to parameter uncertainty, highlighting the key knowledge gaps that should be prioritized by future research. Our modeling effort provides a general approach to assess the consequences of disturbance on this and other migratory baleen whale populations. Therefore, it can support effective management decisions regarding marine developments and activities in the face of a rapidly changing environment.
Declining seed production before death in a long-lived tree: senescence, not terminal investment?
Mario Pesendorfer, Michał Bogdziewicz, Walter D. Koenig, Mateusz Ledwoń, and Magdalena Żywiec
Aging poses a fundamental challenge for long-lived organisms; as growth and maintenance decline, life history theory predicts that reproductive investment should increase with mortality to maximize lifetime reproductive success. This terminal investment hypothesis has received broad support in animal studies, but it is unclear whether it applies to plants. The scarce available evidence from plants suggests that their reproductive investment remains unchanged or declines with age, a signature of senescence. We investigated fruit production before death in rowan (Sorbus aucuparia) trees that live up to 150 years. We show that 79 trees produced up to 25% fewer fruits in the years before their demise compared to surviving trees of the same population (N = 198). These results fail to support the terminal investment hypothesis; rather, the pattern of reproductive investment in S. aucuparia is indicative of senescence, the age-related decline of whole-plant function
Carrying capacity in a heterogeneous environment with habitat connectivity
Bo Zhang, Alex Kula, Lu Zhai, Wei-Ming Ni, Donald L. DeAngelis, and J. David Van Dyken
A large body of theory predicts that populations diffusing in heterogeneous environments reach higher total size than if non-diffusing, and, paradoxically, higher size than in a corresponding homogeneous environment. However, this theory and its assumptions have not been rigorously tested. Here we extended previous theory to include exploitable resources, proving qualitatively novel results, which we tested experimentally using spatially diffusing laboratory populations of yeast. Consistent with previous theory, we predicted and experimentally observed that spatial diffusion increased total equilibrium population abundance in heterogeneous environments, with the effect size depending on the relationship between r and K. Refuting previous theory, however, we discovered that homogeneously distributed resources support higher total carrying capacity than heterogeneously distributed resources, even with species diffusion. Our results provide rigorous experimental tests of new and old theory, demonstrating how the traditional notion of carrying capacity is ambiguous for populations diffusing in spatially heterogeneous environments.
The evolution of marine larval dispersal kernels in spatially structured habitats
Understanding the causes of dispersal is a major goal of ecology. While most marine larval dispersal research only addresses proximate causes, here we investigate ultimate, evolutionary causes of dispersal variation. Building on Hamilton and May (1977), we determine the evolutionarily stable strategy (ESS) dispersal kernel in spatially structured habitats. In a world without edges, the ESS paradoxically allocates most offspring to the longest dispersal class. In a world with edges, the ESS allocates nearly all offspring to very short distances. In a patchy world with edges, most offspring disperse short distances with some dispersing longer distances. Finally, in a real seascape, we show that the ESS kernel matches an empirical reef fish kernel: both show a high level of short-distance dispersal and low levels of long-distance dispersal. This framework could be used to model dispersal evolution in other species and seascapes, providing new insights into variation in larval dispersal patterns.
Environment, harvest, and the erosion of a population portfolio
Adrian Stier, Adrian C. Stier, Andrew Olaf Shelton, Jameal F. Samhouri, Blake E. Feist, and Phillip S. Levin
A metapopulation portfolio of spatially asynchronous subpopulations connected by dispersal can minimize region-wide variability in resources and reduce extinction risk. However, portfolio properties are not static, and the erosion of a portfolio can fundamentally alter the population dynamics and services a species provides. A portfolio of spatially asynchronous herring populations has historically provided regional reliability of herring to mobile predators and fishermen. Here, we fit a mechanistic model to herring spawn and catch records to quantify how population growth, climate, and fishing have contributed to a shift in the portfolio over time. We document portfolio erosion and a severe decline in herring population growth. Commercial harvest historically played a key role in herring dynamics, with local harvest rates as high as 81%. Our results highlight how structured populations can undergo dramatic shifts following disturbance, and emphasize the limitations of assuming systems can always rapidly regenerate and provide services following disturbance.
Thinking realistically about density dependence
Density dependence is the cornerstone of population regulation and density-dependent selection has long been a provocative topic for ecologists and evolutionary biologists alike. While ecological studies have offered considerable insight into the mechanisms of density dependence, evolutionary studies, with some notable exceptions, remain phenomenological. Insight into the biological processes that generate density dependence can open new possibilities for understanding this central idea.
Annually variable connectivity in yellowtail clownfish
Katrina Catalano and Malin Pinsky
Metapopulation theory has postulated how connectivity can promote population persistence, yet no studies have empirically measured how that connectivity changes over time. Patterns of connectivity are likely to be highly variable in time and space, and the consequences of this variability remains unclear. In some cases, research suggests environmentally driven variation in connectivity can increase the likelihood of persistence, may also decrease the probability that a metapopulation will persist. Here, we measure annual connectivity between subpopulations in a metapopulation of yellowtail clownfish in the Philippines over four years. Surprisingly, we found that the distance and directionality of dispersal changed significantly year to year. The size of a subpopulation contributed to it's importance as a larval source, but physical oceanographic factors such as current directionality also contributed significantly. These results provide a valuable baseline for how connectivity may be variable over time, an important factor in population persistence.
Assembly of Himalayan bird communities
Himalayan bird communities reveal the integration of tropical, temperate and arid biomes
Local communities of species are assembled from one or more source pools, a process thought affect both the numbers and kinds of species present and hence many functional attributes, such as energy flow. We studied 38 Himalayan bird communities across entire elevational gradients separated by up to 2000 km, and developed methods to assign the number, location, and contribution of regional source pools to each community. We show that communities are primarily constructed from one of two source pools, temperate or tropical, with structuring by elevation, not geography, and a turnover between pool contributions that runs the length of the Himalayas at ~1700m, roughly corresponding to the freezing line. When regional sources are further partitioned, differences between the drier west and wetter east become apparent at low elevations, associated with colonization from peninsular India or southeast Asia. We extend the methods to assess functional diversity, as measured by species composition and their abundances, phylogenetic affinity, or morphological composition to show that these are largely concordant with regional sources. However, functional differences are reduced by convergence along at least one morphological axis, and local processes appear to be the main driver of species richness.
Ecological communities in pursuit of an elusive equilibrium
The paradigm for understanding species diversity in nature is that communities assemble over time as new species colonize, some existing species go extinct, and an equilibrium level of species richness is eventually achieved. Existing indirect evidence has been interpreted to suggest that plant communities are often below their species potential, or undersaturated. We utilize a 23-year time series of 1900 prairie quadrats and show that communities’ diversity is not stable but fluctuates between oversaturation and undersaturation. Both colonization and extinction vary over time, resulting in variation in the predicted long-term equilibrium species richness, and communities lag behind the equilibrium. Given predictions of greater environmental fluctuations under global climate change scenarios, communities may increasingly be in non-equilibrium states, leading to increased rates of extinctions and invasions.
Assessing how microclimate impacts coexistence dynamics: a case study of Western Australian annual plants
Malyon Bimler, Daniel Stouffer, Trace Martyn, and Margaret Mayfield
Though it is widely understood that coexistence among species depends on the environmental context, few studies have incorporated environmental variation into empirical studies of coexistence. This gap exists in part because of the complex experiments needed to assess coexistence in the field, but is also hindered by a lack of feasible approaches for determining how environmental factors alter coexistence dynamics.We apply a Chessonian coexistence model to annual plant communities from SW Western Australia, and present a simple framework for incorporating local environmental factors into the calculation of niche and fitness differences, and thus coexistence outcomes. We show that not only can we easily incorporate important environmental factors into coexistence calculations, but that we can also assess whether changes in coexistence across environmental gradients reflects environmental-mediated shifts in niche or fitness differences (or both). This allows for new insights into the factors impacting coexistence dynamics across naturally heterogeneous environments.
Extinction and time help drive the marine-terrestrial biodiversity gradient: Is the ocean a deathtrap?
The marine-terrestrial richness gradient is among Earth’s most dramatic biodiversity patterns, but its causes remain poorly understood. Here, we analyze detailed phylogenies of amniote clades, paleontological data, and simulations to reveal the mechanisms underlying low marine richness, emphasizing speciation, extinction, and colonization. We show that differences in diversification rates (speciation minus extinction) between habitats are often weak and inconsistent with observed richness patterns. Instead, the richness gradient is explained by limited time for speciation in marine habitats, since all extant marine clades are relatively young. Paleontological data show that older marine invasions have consistently ended in extinction. Simulations show that marine extinctions help drive the pattern of young, depauperate marine clades. This role for extinction is not discernible from molecular phylogenies alone, and not predicted by most previously hypothesized explanations for this gradient. Our results have important implications for the marine-terrestrial biodiversity gradient, and studies of biodiversity gradients in general.
Climate effects on coexistence outcomes.
Margaret Mayfield, Claire Wainwright, Malyon Bimler, Daniel Stouffer, and Janneke HilleRisLambers
Tests for coexistence between plant species in the field have largely occurred in relatively controlled or consistent environments. In order to scale up our understanding of coexistence to community patterns of diversity, it is important to understand how environmental heterogeneity impacts coexistence in natural communities. Using annual plant communities in SW Western Australia, we examined the coexistence dynamics of six plant species across experimentally modified moisture gradients and natural gradients of soil P and shade. We found that intrinsic fitness, niche differences, fitness differences and coexistence outcomes all varied across environmental gradients but generalizable patterns were not widely evident. Results indicate that coexistence outcomes are dependent on environmental context. More studies are needed, however, to understand how important this variance is to community-wide coexistence and diversity patterns.
The spatial scaling of plant diversity and its ecological correlates: experimental evidence from a global biodiversity hotspot
Ecological theory posits that dispersal among habitat patches links local communities and is a key ‘regional’ process that maintains biological diversity. In a Californian grassland, we used a seed vacuum to increase dispersal at spatial scales varying from 1m to 10km while maintaining realistic spatial structure of species pools and environmental conditions. Species richness doubled in plots that received seed from large (≥5km) compared to small (≤5m) scales. This increase in diversity corresponded to an increase in how well species distributions were explained by environmental conditions, from modest at small scales (R2=0.34) to strong at large scales (R2=0.52). Responses to the spatial scale of seed mixing were nonlinear, with no differences below 5m or above 5km. Our novel approach of manipulating natural communities at different spatial scales reveals (i) nonlinear transitions in the importance of environmental sorting and dispersal, and (ii) the negative effects of dispersal limitation on local diversity.
The microbiome is associated with accelerated aquatic ecosystem function in response to intraspecific variation in a terrestrial ecosystem subsidy
Geographic structuring of leaf defensive chemistry in a population of riparian red alder trees drives ecological matching patterns in which decomposers both on land and in rivers more quickly consume leaf litter derived from local versus more distant trees. The network of stream microorganisms, the microbiome, is an often over-looked aspect of stream function and likely contributes to these local ecosystem responses. We studied the colonization and succession of riverine microbial communities on red alder leaves through the decomposition process using a reciprocal transplant leaf pack experiment and 16S rRNA sequencing. We found local leaves had a greater relative abundance and diversity of generalist bacterial decomposers, while non-local leaves tended to contain a greater abundance and diversity of taxa known to degrade aromatic compounds, such as some herbivore defense compounds. Overall, these results may help unravel the mechanisms driving locally accelerated ecosystem function to intraspecific variation in cross-ecosystem subsidies.
On the predictability of infectious disease outbreaks
Infectious disease outbreaks recapitulate biology: they emerge from the multi-level interaction of hosts, pathogens, and their shared environment. As a result, forecasting disease dynamics requires an integrative approach to modeling. Recent studies have demonstrated that predicting different components of outbreaks is feasible. Therefore, advancing the science of disease forecasting now requires testing for the presence of fundamental limits to prediction. To investigate these limits, we study the information theoretic barriers to forecasting across a broad set of diseases using permutation entropy as a model independent measure of predictability. Studying the predictability of a collection of historical outbreaks--including, chlamydia, gonorrhea, hepatitis A, influenza, Zika, measles, polio, whooping cough, and mumps--we identify a fundamental entropy barrier for time series forecasting. We also find that the entropy horizon varies by disease and demonstrate that social network structure is the most likely mechanisms for the observed differences in predictability across contagions.
Familiarity breeds contempt for badge plumage experiments in sparrows
Conflict in nature is common and risky, and mechanisms like individual recognition or badges of status can reduce such costs. Badges of status and individual recognition are thought unlikely to coexist in the same population since badges are primarily useful in larger, fluid social groups whereas individual recognition requires smaller, stable groups. Social networks of winter flocks of golden-crowned sparrows (Zonotrichia atricapilla) exhibit intermediate levels of social community structure. We found that dominance mechanism depends on social context. Experiments showed that strangers use badges of status to determine dominance. Conversely, badge experiments with familiar flockmates had no effect on dominance, and these experiments showed decreased aggression relative to experiments with strangers. Our results provide among the first experimental evidence for coexistence of status signals and individual recognition, suggesting that variation in social context, and hence the feasibility of recognition, may help maintain coexistence of these two dominance resolution mechanisms.
Evolution of cooperation on dynamic social networks
The dynamic social structure of animal societies has myriad effects on ecological and evolutionary processes, including social behavior, disease transmission, and resource exploitation. Here, we present a model for the evolution of social traits on dynamically coevolving social networks. In our model, social behaviors such as cooperation determine individuals' fitnesses (i.e. birth or death rates), while social connectivity traits determine their connections in the social network. We find that while certain types of networks promote cooperative behaviors, cooperative behaviors, when established in the population, tend to disfavor such networks. We discuss mechanisms that can break this self-limiting feedback between cooperation and network structure.
Demographic processes and social network dynamics in animal populations
All social networks change membership over time through demographic processes: individuals are lost through death or dispersal, and new individuals join the social network through birth and immigration. Yet we know little about how the joint effects of social and demographic processes shape the structure of social networks, nor do we understand how social networks may or may not be resilient to turnover in membership. Here, we highlight a case of a winter social network of a migratory bird, the golden-crowned sparrow, to discuss how social processes such as preference for familiar flock mates and social integration of new recruits leads to resilience in social structure beyond the lifespan of individuals. We suggest that studying the effects of demography on social networks is a fruitful avenue for integrating population ecology, behavior and evolution.
Evolution to overcome biotic resistance to invasion is limited by multiple species interactions
A recent meta-analysis suggests that species interactions are not as effective as we thought in providing biotic resistance to invasion. Perhaps that is because we have not considered mutualisms or multiple interactions among species. Further, some invading genotypes may be less affected by such interactions. We investigated intraspecific variation within Medicago polymorpha, an invasive legume on six continents, in response to several biotic and abiotic factors. Genotypes varied in response to drought, disturbance, herbivory, mutualistic bacteria, and indirect effects. Invasive range genotypes tended to be less responsive to natural enemies and less reliant on mutualists, relative to native range genotypes. This suggests that species interactions have evolved on relatively short time scales in the invaded range and can have significant effects on their invasion success. Indirect effects among multiple species, including mutualists, affect the overall biotic resistance of the community and its susceptibility to invasion.
Latitudinal variation in ecothem invasion success
Rapid evolution mitigates the ecological consequences of an invasive species (Bythotrephes longimanus) in lakes in Wisconsin
Matthew Walsh and Mike Gillis
Invasive species have negative consequences for ecosystem health. Novel species also drive contemporary evolution in native species, which could mitigate or amplify their impacts on ecosystems. The predatory zooplankton Bythotrephes longimanus invaded lakes in Wisconsin in 2009. This invasion caused declines in zooplankton prey (Daphnia pulicaria), with cascading impacts on ecosystem services (water clarity). We tested the link between Bythotrephes invasion, evolution in Daphnia and post-invasion ecological dynamics using 15 years of long-term data in conjunction with experiments. Invasion by Bythotrephes is associated with increased Daphnia body size. Laboratory experiments revealed that such shifts are genetic; third-generation laboratory-reared Daphnia from ‘invaded’ lakes are significantly larger and exhibit greater reproductive effort than individuals from ‘uninvaded’ lakes. Such evolutionary changes should enhance Daphnia population growth. We tested this prediction by via analyses of long-term data and show that evolution in Daphnia is associated with increased population growth in invaded lakes.
The effect of soil cultivation length on plant-soil microbe interaction
Po-Ju Ke and Tadashi Fukami
Interactions between plants and soil microbes (plant–soil feedback, PSF) can structure plant communities. However, studies often treat a species’ PSF strength as a static parameter. To understand temporal changes in a soil microbial community with increasing plant cultivation time, we utilized a series of aerial photos at the Bodega Dunes to estimate individual plant age. We sampled soils from individuals of different ages for four plant species that are typical dominants of California coastal dunes, two of which are invasive, and characterize temporal changes in microbial communities. Results suggested that microbial communities became progressively different from bare sand with longer cultivation time, and microbial OTU abundance was best predicted by temporal changes in soil pH and maximum soil temperature. In addition, native plants gained more pathogenic fungi through time compared to the non-natives. This study highlights that PSF is a dynamic process and its temporal development should be considered.
Big larders but skinny helpers: territory quality and density dependence in a highly social bird
Sahas Barve, W.D. Koenig, and E.L. Walters
Acorn woodpeckers (ACWOs) are a cooperatively breeding species of the California oak savannah with breeders and helpers living in social groups. Despite their strong reliance on the annual acorn crop, the population of ACWOs at Hastings Natural History Reservation has been increasing over time. We studied if cooperative breeding facilitates species to live at high population densities by testing the “supersaturation hypothesis”. True to its predictions, the proportion of helpers in the population has increased with increase in population density. Nestling mass has also increased over time but only in good quality territories suggesting competition between helpers and chicks. We find that helpers are significantly lighter than breeders. We thus propose that having more, but leaner helpers might be a mechanism of living at high densities through social context dependent differences in body condition in cooperatively breeding species but discuss the importance of habitat quality in influencing this supersaturation.