Workshop 5: Coevolution and the Ecological Structure of Plant-insect Communities

(April 4,2011 - April 7,2011 )

Organizers


Scott Nuismer
Biological Sciences, University of Idaho
Sharon Strauss
Evolution and Ecology, University of California, Davis

Plant-insect interactions have played a pivotal role in the development of modern coevolutionary theory, beginning with Darwin's initial insights into reciprocal adaptation between plants and pollinators. When Ehrlich and Raven published their now classic study of coevolution between butterflies and plants in 1964, the link between the development of coevolutionary theory and plant-insect interactions was cemented. Since this time, numerous studies of plant-insect interactions have revealed an important role for coevolution, even as the perceived importance of coevolution for the overall structure of plant-insect communities has waxed and waned. Currently, much of the research on the ecology and evolution of plant-insect interactions, both mutualistic and antagonistic, is expanding from simpler two-species frameworks to consider coevoluton in the context of multispecies communities.

The Geographic Mosaic Theory: The geographic mosaic theory focuses on how spatial variability in the abiotic and biotic environment shapes ecological and evolutionary dynamics of interspecific interactions. The geographic mosaic theory explicitly identifies coevolution as the driving force underlying the ecological dynamics and structure of biological communities. Much of the empirical work motivated by the geographic mosaic theory has focused on quantifying patterns of trait matching or local adaptation in interacting species, with plant-insect interactions representing several of the best studied cases. A general result that has emerged from this work is that species interactions exhibit a complex mix of local adaptation, local maladaptation, trait matching, and trait mismatching as predicted by the verbal theory. A substantial body of mathematical theory has been developed to elucidate whether these patterns are consistent with a geographic mosaic process, and if so, whether such a process is more likely than other simpler processes. The development of a robust mathematical framework for the geographic mosaic is essential for interpreting existing data and designing future empirical studies.

Community Genetics: Community genetics focuses on the role the genetic structure of component species plays in shaping the ecological structure and dynamics of biological communities. Thus, community genetics represents a marriage of the traditional disciplines of quantitative genetics, population genetics, and community ecology. As it is usually articulated, community genetics does not explicitly integrate the process of coevolution, although its potential importance is generally acknowledged. Empirical studies of community genetics have relied heavily on interactions between insects and plants. For instance, the long running studies of interactions between cottonwoods and insects conducted by Thomas Whitham and colleagues have clearly demonstrated that host genetics strongly influence the community of associated insect species. A wide variety of other studies, conducted in a diverse array of taxa, support the basic argument of community genetics - that integrating the genetic structure of the interacting species is important for any cohesive theory of community ecology. From a theoretical perspective, work in community genetics has been somewhat piecemeal, although excellent models have been developed and analyzed to address particular topics (e.g., see Neuhauser et al. for a particularly nice collection of examples). The development of a general theoretical framework for community genetics is an important goal, and essential for interpreting rapidly accumulating empirical data.

The importance of evolutionary history: A third area receiving increased attention recently has been the exploration of the role of evolutionary history in the assembly of communities and in the evolution of plant defense against insects, and insect adaptations. To date, there have been a few studies examining co-diversification of plants and insects. (Futuyma, Becerra, Funk), and ants and fungi (Mueller). Another set of studies explores the role of host plants in sympatric speciation and host shifts (Nosil, Feder); yet a third group examines multivariate trait space to understand constraints and tradeoffs in the evolution of defense under different biotic and abiotic conditions. The degree to which phylogenetic history predicts host use by insects varies among systems, and may benefit from broader theoretical approaches to this question.

Synthesis: Neutral theory suggests that how communities are assembled is largely agnostic to evolutionary processes. In contrast, strong evidence for coevolution between interacting species flies in the face of such approaches. We seek to understand how complex biological communities are assembled, what factors contribute to their stability or instability, and why the structure of such communities is often spatially variable. Discussing profitable avenues for the development of a mathematical framework which unifies multiple approaches to understanding the interplay between coevolution and community assembly will be an important focus of this workshop. An additional focus will be the development of statistical tools that can be used to evaluate the importance of reciprocal selection and ongoing coevolution for the composition, structure, and stability of plant-insect communities.

Goals of the Workshop:

  1. To discuss metrics (e.g., network structure, local adaptation, community heritability) with robust theoretical/statistical underpinnings that can be used elucidate the importance of coevolutionary processes in structuring plant-insect communities at local and regional scales.
  2. To discuss statistical techniques (e.g., path analysis; selective source analysis, etc.) for evaluating the importance of ongoing coevolutionary selection in multispecies communities of plants and insects.
  3. To discuss profitable avenues for the development of a cohesive theoretical framework that incorporates coevolution, multiple interacting species, spatial structure, evolutionary history and variable abiotic environments. This framework will thus formally link several of these different empirical approaches to communities.

Accepted Speakers

Ulrich Mueller
Integrative Biology, University of Texas
Peter Abrams
Ecology and Evolutionary Biology, University of Toronto
Bruce Anderson
Department of Botany & Zoology, University of Stellenbosch
Judith Becerra
Biosphere 2, University of Arizona/ Museum of Natural History, Paris
Judith Bronstein
Department of Life Sciences, University of Arizona
Reinhard Burger
Department of Mathematics, University of Vienna
Claire de Mazancourt
Redpath Museum, McGill University
Jose Gomez
Departament of Ecology, University of Granada
Richard Gomulkiewicz
School of Biological Sciences, Washington State University
Paulo Guimaraes
Departamento de Ecologia, Universidade de Sao Paulo
Martin Heil
Departamento de Ingenieria Genetica, CINVESTAV Unidad Irapuato
Paul Hohenlohe
Ecology and Evolutionary, University of Oregon
Rebecca Irwin
Department of Biological Sciences, Dartmouth College
Franck Jabot
Centers for Disease Control and Prevention
Marc Johnson
Plant Biology, North Carolina State University
Emily Jones
Ecology and Evolutionary Biology, Rice University
Pedro Jordano
Estacion Biologica de Donana, Consejo Superior de Investigaciones Cientificos
Ben Ridenhour
Department of Biological Science, University of Notre Dame
Risa Sargent
Biology, University of Ottawa
Akira Sasaki
Department of Evolutionary Studies of Biosystems, The Graduate University for Advanced Studies
Jacqui Shykoff
Laboratory of Ecology, Evolution and Systematics, Universit'e de Paris XI (Paris-Sud)
Mike Wade
Biology, Indiana University
Thomas Whitham
Department of Biological Sciences, Northern Arizona University
Monday, April 4, 2011
Time Session
09:30 AM
10:30 AM
Sharon Strauss - Coevolution and community complexity
Our best examples of coevolution come from simplified interactions, but communities are rarely simple. Are complex communities less coevolved, or is coevolution just harder to recognize? I discuss coevolution and community complexity in light of both natural and invaded systems.
11:15 AM
12:15 PM
Claire de Mazancourt - Red King predators, evolution of mutualistic antagonists and coevolution patterns between mutualists and antagonists
In this talk I will present several theories related to co-evolution between plants and insects. First I will present a model of predator-prey coevolution, showing that rapid evolution in the predator can lead to prey diversification and a decrease in the number of preys available to the predator. This correspond to a "Red King" scenario, where rapid evolution leads to an ecological disadvantage. Second I will present the evolution from an antagonistic to a mutualistic interaction. Finally I will contrast expected patterns of coevolution in mutualistic and antagonistic networks.
01:30 PM
02:30 PM
Marc Johnson - Exploring the interplay between ecology and evolution of plant-herbivore interactions
(Co)evolutionary ecologists have long appreciated that ecology drives evolution, and that evolution ultimately shapes the ecological processes and patterns of populations and communities over long periods of time. However, it remains unclear how these two processes interact to affects the ecology, evolution and coevolution of communities over short timescales (e.g. one to several generations). We address this problem by studying interactions between a native plant (common evening primrose, Oenothera biennis) and the diverse assemblage of arthropods that interact with this plant. Using a combination of field experiments and theory we address two related hypotheses: First, we examine if herbivory drives rapid evolution of life-history and plant defensive traits within plant populations. Second, we test whether standing genetic variation and rapid evolution within plant populations shape the structure and dynamics of arthropod communities over one to several generations. In support of the first hypothesis, we find that herbivores impose natural selection on many heritable plant traits. Using an experimental evolution approach in the field, we show that this selection causes rapid evolution within plant populations over just three generations. In support of the second hypothesis, we find that standing genetic variation in evening primrose is an important ecological factor affecting the abundance of many herbivore populations, as well as the composition and diversity of over 100 arthropod species in the community. Using quantitative genetics theory and simulations, we show that the observed natural selection and evolution within evening primrose is expected to drive rapid ecological changes in arthropod abundance and diversity. Therefore in this plant-herbivore system, ecological and evolutionary dynamics interact over very short time scales and using an eco-evolutionary approach provides greater insight into the factors that affect both the ecology and evolution of ecosystems.
02:30 PM
03:30 PM
Ben Ridenhour - Measuring coevolutionary selection in plant-insect interactions
No description available.
04:00 PM
05:00 PM
Mike Wade - The Plasticity Load: the cost of flexibility of defense in a variable environment
Plasticity can evolve when members of a population experience different environments, such as those with and without an herbivore, with a trade-off in fitness between environments. This G x E for fitness can favor genes which are conditionally expressed only in the environment in which they are adaptive. Thus, adaptive plasticity can be achieved by altering the expression pattern of a gene and allowing a gene's expression to be induced by the environment as can be the case for plant defenses against insect herbivores. However, such conditionally expressed or 'plasticity' genes have the property that every individual in a population carries and transmits the gene, but only a fraction expresses it and exposes it to natural selection. A consequence of this pattern of inheritance and expression is a weakening of the strength of natural selection, allowing deleterious mutations to accumulate within and between species and inhibiting the spread of beneficial mutations. Mutation accumulation diminishes the degree of adaptation of conditionally expressed genes to rare environments, and the mutational cost of phenotypic plasticity, 'the plasticity load,' is greater the more rarely expressed a gene is. Our theory connects gene-level relative polymorphism and sequence divergence between species with the spatial and temporal frequency of environments that induce plastic gene expression. Our theory suggests that null hypotheses for levels of standing genetic variation and sequence divergence for plasticity genes must be corrected to account for their frequency of expression. With conditional gene expression, selection may allow a species to be a 'jack of all trades', but mutation insures it will be master of none.
Tuesday, April 5, 2011
Time Session
09:00 AM
10:00 AM
Bruce Anderson - Trait Matching: What does it tell us?
Recently, several studies have used the geographic matching of morphological traits (e.g. proboscis versus corolla length) to infer that coevolution has taken place between two interacting organisms. However, geographic trait matching alone is not sound evidence for coevolution because it is not a mandatory end point for coevolutionary relationships, and nor is coevolution the only selective mechanism capable of giving rise to geographic trait matching. Here I demonstrate how both coevolved and non-coevolved relationships result in patterns of trait matching but that through selection studies and by a process of elimination, it is possible to determine what the mechanism is behind trait matching patterns. In addition, using data from several published studies, I suggest how the steepness of the slope and intercept may yield important information about the relative strength of selection acting on the morphological traits of interacting species. For example in plant-insect relationships, plants seem to consistently have more exaggerated morphological traits than insects at high trait magnitudes. This suggests that selection to exaggerate the magnitude of the plant trait is stronger than for insects to exaggerate the magnitude of their corresponding traits. Thus, when plant and insect morphological traits are coevolved, insects are the most likely to be the losers of the coevolutionary race.
10:30 AM
11:30 AM
Scott Nuismer - What do studies of local adaptation and trait matching reveal about the coevolutionary process?
No description available.
11:30 AM
12:30 PM
Ulrich Mueller - Frontier Mutualism and Community Genetics in Attine Ants and their Cultivated Fungi
I explore empirical approaches to elucidate community genetics and the geographic-mosaic of coevolution in fungus-growing ants, emphasizing computational and conceptual challenges that we encountered in our work. Fungus-growing ants propagate their cultivars as clonal monocultures within their nests, and in most cases clonally across many farmer generations as well. Long-term clonal monoculture presents special problems for disease control, but the ant farmers evolved diverse strategies to manage crop diseases, including management of an array of "auxiliary" microbes providing disease suppression and other services. Rather than growing a single cultivar solely for nutrition, insect farmers appear to cultivate, and possibly "artificially select" for, integrated crop-microbe consortia.

Ant-Fungus-Bacterial Community Genetics: In a collaboration with Tim Linksvayer (Univ. Pennsylvania), we use a quantitative-genetic approach to study how coevolution is affected by (a) the strength of reciprocal selection pressures; (b) the genetic architecture of the coevolving traits; and (c) the degree of co-transmission of the ants, their cultivated fungi, ant-associated microbes, and garden-associated microbes. Because it is easier to partition heritable components of phenotypic variance among clonal lineages, we developed an experimental system involving the clonal (asexual) ant Mycocepurus smithii, its clonal fungi, and associated microbial communities characterized with 16S-amplicon 454-sequencing.

Frontier Mutualisms within the Geographic Mosaic: Tropical leafcutter ants cultivate the fungus Attamyces bromatificus in a many-to-one, diffuse co-evolutionary relationship where ant and fungal partners re-associate frequently over time. To evaluate whether ant-Attamyces co-evolution is more specific (tighter) in peripheral populations, we characterized the host-specificities of Attamyces genotypes at their northern, subtropical range limits (southern USA, Mexico, Cuba). The northernmost leafcutter ant Atta texana sustains fungiculture during winter temperatures that would harm the cold-sensitive Attamyces cultivars of tropical leafcutter ants. Cold-tolerance of Attamyces cultivars increases with winter harshness along a south-to-north temperature gradient across the range of A. texana, indicating selection for cold-tolerant Attamyces variants along the temperature cline. Ecological niche modeling corroborates winter temperature as a key range-limiting factor impeding northward expansion of A. texana. Although the origin of leafcutter fungiculture was an evolutionary breakthrough that revolutionized the food niche of tropical fungus-growing ants, the original adaptations of this host-microbe symbiosis to tropical temperatures and the dependence on cold-sensitive fungal symbionts eventually constrained expansion into temperate habitats. Evolution of cold-tolerant fungi within the symbiosis relaxed constraints on winter fungiculture at the northern frontier of the leafcutter ant distribution, thereby expanding the ecological niche of an obligate host-microbe symbiosis. Studies of host-symbiont associations at their range limits are likely to inform models of co-extinctions of obligate mutualistic partners that are doubly stressed by habitat marginality and by environmental change.
01:45 PM
02:45 PM
Jose Gomez - Exploring selection mosaics and coevolution in multiespesific generalized systems
The geographic mosaic theory of coevolution (GMTC) considers that populations differ in evolutionary dynamics due to spatial variation in selective regimes. According to GMTC, three components of geographic structure drive the overall coevolutionary dynamics of such interactions: selection mosaics, coevolutionary hotspots, and trait remixing. Furthermore, the GMTC suggests the occurrence of a spatial pattern of interaction-mediated local adaptation and maladaptation. Empirical support to these theoretical predictions has come mostly from specialist antagonistic interactions. Contrasting with specialist interactions, free-living generalist interactions are formed by multispecies networks of interacting organisms that vary spatially in composition. Extreme reciprocal specialization between pairs of species is rare in these interactions. Consequently, multispecific selection and diffuse coevolution are prevalent in generalist interactions. Here I explore the possibilities of selection mosaic and interaction-mediated local adaptation in multiespecific generalized systems. To overcome the inherent difficulties of studying the interactions occurring among many species, I propose the combined use of structural equation modeling and individual-based network tools. This approach has allowed to detect that geographic mosaic of selections occur in generalist systems as well, and may be even a driver of the evolution of generalization in these types of multispecific systems.
02:45 PM
03:45 PM
Paul Hohenlohe - A coevolutionary resolution to the paradox of concave selection?
The adaptive landscape, long a useful metaphor, is also a rigorous tool for understanding evolution when it is linked to empirical measurements of fitness. However, empirical estimates of fitness surfaces are often concave, implying an evolutionarily unstable situation under general conditions in the short term, and untenable extrapolations to longer-term evolution under the traditional adaptive landscape model. Incorporating the multivariate genetic and ecological context of concave selection would lead to a more robust adaptive landscape model. The several non-exclusive hypotheses for the prevalence of concave selection fall roughly into two groups: static and dynamic. Coevolution lies at the heart of dynamic solutions and is thus critical to resolving the paradox of concave selection. In this talk I will discuss the basic hypotheses and empirical evidence for the prevalence of concave selection and explore its relationship to coevolution. I will propose a revised adaptive landscape model that can account for concave selection, yet maintain the adaptive landscape's heuristic value for understanding multivariate phenotypic evolution.
04:15 PM
05:15 PM
Judith Becerra - Bursera and Blepharida: The ecological play and the coevolutionary theatre
Coevolutionary theory proposes that the diversity of chemical structures found in plants is, in large part, the result of selection by herbivores. Because herbivores often feed on chemically similar plants, they should impose selective pressures on plants to diverge chemically or bias community assembly toward chemical divergence. Using a coevolved interaction between a group of chrysomelid beetles, the genus Blepharida and their host plants, the genus Bursera (Burseraceae), I tested whether coexisting plants of the Mexican tropical dry forest tend to be chemically more dissimilar than random. Results show that some of the communities are chemically overdispersed and that overdispersion is related to the tightness of the interaction between plants and herbivores and the spatial scale at which communities are measured. As coevolutionary specialization increases and spatial scale decreases, communities tend to be more chemically dissimilar. At fairly local scales and where herbivores have tight, one-to-one interactions with plants, communities have a strong pattern of chemical disparity. I use these results to propose a mechanism by which the coevolutionary interaction between plant defensive traits and specialized herbivorous insects promote stable coexistence and diversity for both tropical insects and plants.
Wednesday, April 6, 2011
Time Session
09:00 AM
10:00 AM
Franck Jabot - Coevolution in plant-pollinator networks: the impact of network properties
In many plant-pollinator systems, interactions present a high degree of generalism, so that coevolution should be studied at the community level. Indeed intraspecific trait variation in such systems may both lead to variation in the gains that individuals are drawing from their interactions, and to variation in their choice/attraction of interaction partners. In this contribution, I will study whether the structural properties of the network of interactions between plants and animals impact the magnitude of coevolution and the properties of coevolutionary outcomes through simulations. In these simulations, individuals interact following simple interaction rules based on a single trait, the interaction strength between two individuals being controlled by their trait values. The fitness of an individual is proportional to the sum of its interactions, and traits present a constant heritability. The distribution of trait values in every species as well as species abundances are monitored through time to capture the natural selection applying on each species as a function of its position in the simulated network of interactions.
10:30 AM
11:30 AM
Pedro Jordano - Complex networks of interactions and coevolution in multispecific assemblages of free-living species
Ecological interactions among plants and animals are the backbone of biodiversity. Interactions take a tremendous variety of forms in nature and have pervasive consequences for the population dynamics and evolution of species. Pollen and seed movement are the primary outcomes these interactions, yet we know very little of how these highly complex webs of mutualistic interactions coevolve and what are the consequences of these diversified mutualisms. A persistent challenge in evolutionary biology has been to understand how coevolution has produced complex webs of interacting species, where a large number of species interact through mutual dependences (e.g., mutualisms) or influences (e.g., predator-prey interactions in food webs). Recently, it has been shown that these interactions can form complex networks involving dozens and even hundreds of species. These coevolutionary networks are highly heterogeneous, with a core of super- generalists, nested, asymmetric, and contain multiple modules that act as the basic blocks of the complex web. I explore how the past evolutionary history conveyed in the phylogenies of plants and animals can explain these network patterns and the robustness of the network to species extinctions. Because phylogenetically similar species tend to play similar roles in the network, extinction events trigger non-random coextinction cascades. This implies that taxonomic diversity is lost faster than expected if there was no relationship between phylogeny and network structure. Zooming in the interaction pattern itself, I use examples of plant-animal mutualisms to show how the overall interaction pattern depicted in the network appears more influenced by the plant phylogeny, suggesting that the plant assemblage drives the interaction. Coevolved trends might thus depend on resource tracking by animals, so that each plant species 'filters out' subsets of mtualists given species-specific traits that constrain their interaction through trait matching and trait convergence. The overall network of interaction thus has a distinct signal marked by the plants phylogenetic history. These patterns suggest both precise ways on how coevolution goes on beyond simple pairwise interactions and scales up to whole communities. Network thinking applied to plant-animal mutualisms is helping us to understand the complex patterns of interactions involved in their evolution.
11:30 AM
12:30 PM
Akira Sasaki - Applying theories of arms races of plants and their parasites: Camellia-weevil system and rice blast disease
An eco-evolutionary model for the arms race of interacting quantitative traits, defensive measure of host/prey and countermeasure of parasite/predator, is applied to the correlated geographical clines of Japanese camellia and its facultative seed predator, camellia weevil. Both the thickness of fruit wall of plants to protect seeds and the length of mouthpart of weevil for boring the wall for oviposition co-varied latitudinally over the populations where both camellia and camellia weevils are found. Host productivity and the nonlinearity of cost for weevil mouthpart length are found to characterize the coevolutionary outcomes.

I next introduce a mathematical model for the coevolution of parasite virulence and host resistance under a multilocus gene-for-gene interaction (Sasaki 2000, PRSLB). The degrees of parasite virulence and host resistance show coevolutionary cycles for sufficiently small costs of virulence and resistance. If either the cost of virulence or the number of resistance loci is larger than a threshold, the host maintains the static polymorphism of singly (or doubly or more, depending on the cost of resistance) resistant genotypes and the parasite remains universally avirulent. The theory is applied to the 40 years race frequency changes of rice blast disease pathogen in response to the changes in the planting areas of resistant cultivars in Niigata prefecture, Japan. A model for accurately forecasting the race frequencies is proposed.
02:00 PM
03:00 PM
Thomas Whitham - Community genetics of foundation forest trees as drivers of community diversity, structure, stability, and evolution
The community phenotypes and genetic structure of foundation species are especially important to quantify as these species are by definition, "community and ecosystem drivers". Using observational and experimental studies of Populus and Pinus, our findings show that different tree genotypes support different communities of organisms (soil microbes, mycorrhizae, arthropods, vertebrates, understory plants, lichens, and pathogens) and that these differences can be quantified as heritable plant traits. Thus, genetic diversity in foundation tree species affects biodiversity and is very important to conserve even when these trees are common on the landscape. Using diverse examples, the community phenotypes of forest trees can be traced from the individuals possessing the trait, to the community, and to ecosystem processes such as leaf litter decomposition and N mineralization, which in turn can feed back to affect the fitness of the individual expressing the trait. Based on the concepts of community phenotype, community heritability, community feedbacks, and foundation species, our group is addressing issues including: 1. How many genes in a foundation species does it take to produce a community phenotype? 2. How important are the community phenotypes of transgenic species and should they be included in the evaluation process of crops that will soon account for over 200 million hectares? 3. How do communities associated with a foundation species interact (e.g., soil microbes and canopy arthropods) to affect the fitness of individual genotypes of a foundation species? 4. How many foundation species does a community have and how do their interactions predictably affect the rest of the community? 5. Since most species in a community are rare, do they individually or cumulatively play an important role in driving the community or are they tag-alongs that are defined by the interactions of foundation species? 6. Is coevolution among relatively few foundation species the driver of community evolution? 7. How will climate change affect the interactions of foundation species and the evolutionary trajectories of communities? 8. How can a community genetics perspective contribute to the controversial issue of assisted migration? 9. Are emergent properties such as biodiversity and stability under genetic control and thus subject to natural selection? We believe that answers to these questions have both basic and applied value, and have the potential to expand our knowledge of how complex communities and ecosystems evolve and function.
03:00 PM
04:00 PM
Jacqui Shykoff - Evolution of virulence and mixed infections
One very robust result of models of host-parasite co-evolution is that under regimes of mixed infection, where different strains of parasites compete for limiting host resources, parasites should evolve higher virulence strategies. This has wide reaching ramifications for optimal parasite strategies, since parasites are seldom alone in exploiting hosts. However, not all interactions between parasite strains within hosts are equal. When closely related parasite strains share hosts one might expect different evolutionary outcomes than when distantly related strains interact, particularly if the degree of relatedness between strains varies in nature such that parasites may be confronted with more or less related competitors. In addition to variation in the relatedness between interacting or competing parasite strains within hosts, the nature of the within-host interaction can vary greatly. Three types of within-host interactions have been identified, though this may not represent the whole range of the possibilities: competition for limiting host resources, production of public goods such as extra-cellular enzymes that promote infection success or efficient exploitation of the host and that can be used by all parasites within the same host, and spiteful interference between pathogen strains. Theoretical expectations differ for how virulence will change between single and mixed infections, and particularly for mixed infections of differing degree of relatedness between the parasite strains for these different types of interactions. I will discuss the outcome of experiments designed to examine how virulence differs among mixed infections that vary in degree of relatedness in the anther smut fungus Microbotryum violaceum, a Basidiomycete fungal pathogen of plants that is transmitted by insect vectors, with a small aside to examine the idea of relatedness and the applications of kin selection to microbial interactions. Individual strains, when involved in mixed infections, drew greater resources from their host plant and produced more spores per flower than did strains that infected on their own. Furthermore virulence, this time measured in terms of the degree of sterilisation of the host plant, varied among mixed infections that differed in genetic relatedness among strains. Individual strains interfered with each other's ability to colonise the plant, thereby reducing the virulence of mixed infections for this trait, but interfered less when strains were closely related, suggesting spiteful interactions. Thus for different traits of the infection genetic relatedness among interacting parasite strains differentially influence virulence.
Thursday, April 7, 2011
Time Session
09:00 AM
10:00 AM
Emily Jones - The consequences of exploitation for plant-pollinator mutualisms
Species exist in complex biotic environments, engaging in a variety of antagonistic and cooperative interactions that contribute to their population and evolutionary dynamics. However, studies tend to concentrate on each pairwise interaction in isolation. By doing so, they may overlook significant feedbacks between the interactions. In this talk, I will focus on plant-pollinator mutualisms, which are often beset by species that reduce the benefits of the mutualism by exploiting the plant, the pollinator, or both. Through a combination of theoretical and empirical results, I will demonstrate how predictions about the ecological stability of mutualisms and the level of cooperation between mutualistic partners are changed by consideration of exploiters such as non-pollinating seed predators and predators of pollinators.
10:30 AM
11:30 AM
Martin Heil - Reciprocal adapations as a key factor in the stabilization of a defensive ant-plant mutualism
Ant-plants are important structural elements in many disturbed tropical ecosystems and the mutualism between plants and their defending ant symbionts is increasingly being used as a model to study general factors that stabilize a horizontally transmitted mutualisms. As these mutualisms must be established anew in every consecutive generation they are particularly prone to the destabilization by cheaters (former mutualists that ceased the service provisioning) or parasites (non-reciprocating exploiters with no evolutionary history as a mutualist). Theoretical models predicted high exploitation rates for high-reward mutualisms. We empirically tested this prediction and found that sympatric Mexican Acacia myrmecophytes differ at the species level in the amount of food rewards and nesting space that they provide to their defending Pseudomyrmex ant mutualists. Several biochemical specializations help to exclude non-adapted potential consumers from feeding on the host-plant derived food rewards: food bodies and extrafloral nectar are biochemically protected from nectar-infecting microorganisms, nectar robbers and herbivores. Interestingly, the same adaptations appear to make the symbiotic ants fully dependent on these rewards. At the phenotypic level, hosts that produced more extrafloral nectar were more aggressively defended by their inhabitants. Genetically fixed, species-specific plant traits combine with phenotypic plasticity to create 'host sanction' mechanisms, which bind fitness-relevant traits of both partners to each other. This assumption is confirmed by the observation that two high-reward producing among four investigated host species were less commonly exploited by non-defending ant species. As reward production can be costly, this allows the diversification into 'low cost-high risk' versus 'high cost-low risk' strategies, and both strategies are indeed realized by sympatric and congeneric host species.
01:00 PM
02:00 PM
Peter Abrams - The Coevolution of Competitors in a Community Context
Most theoretical work on the evolution of competing species has used models having the minimum number of species (i.e. two), and has not represented either enemies or resources of those two consumer species. Empirical studies of character displacement involve species that share multiple resources, and usually multiple predators as well. Although some prominent experimental systems involve only two competitors, the natural communities where these species occur often have more. My talk will concentrate on two types of extension of the current body of theory. The first is models of the evolution of competitors in a community or food web context. This illustrates the importance of ecological interactions on other trophic levels when determining the response of one species to changes in a putative competitor on its own trophic level. The second is the study of multi-species coevolution under such a community context. It has long been known that the impact of one competitor on a second may be positive when the community contains many competitors; this occurs via indirect effects on other mutual competitors. However, the implications of such positive population-level interactions on predictions of character displacement have not been explored. If removal of one competitor causes niche shifts of similar competitors, will large magnitude shifts be propagated throughout the competitive community? These and other aspects of the coevolution of species on a given trophic level will be considered. Where possible, examples of relevant plant-insect systems will be discussed.
02:30 PM
04:00 PM
Scott Nuismer , Sharon Strauss, Sharon Strauss - What do studies of local adaptation and trait matching reveal about the coevolutionary process?
No description available.
Name Affiliation
Althoff, David dmalthof@syr.edu Biology, Syracuse University
Blanquart, François francois.blanquart@cefe.cnrs.fr CEFE - CNRS UMR5175, CNRS
Carter, Benjamin becarter@syr.edu Biology, Syracuse University
Duthie, Alexander aduthie@iastate.edu Ecology, Evolution, and Organismal Biology, Iowa State University
Emery, Nancy nemery@purdue.edu Biological Sciences and Botany and Plant Pathology, Purdue University
Fabina, Nicholas nsfabina@ucdavis.edu Department of Evolution & Ecology, University of California, Davis
Feng, Zhaosheng zsfeng@utpa.edu Department of Mathematics, University of Texas Pan American
Goodell, Karen goodell.18@osu.edu
Landry, Carol landry.26@osu.edu
McCall, Andrew mccalla@denison.edu Evolutionary ecologist, Denison University
Moe, Annika moex0125@umn.edu Ecology, Evolution and Behavior, University of Minnesota
Moffat, Chandra chandra.moffat@gmail.com Biology, University of British Columbia
Nakajima, Mifuyu mifuyu@stanford.edu Biology, Stanford University
Nonaka, Etsuko etsuko.nonaka@emg.umu.se
Nonaka, Etsuko etsuko.nonaka@emg.umu.se Department of Ecology and Environmental Science, University of Umeaa
Ponisio, Lauren lponisio@gmail.com Biology, Stanford University
Ryan, Sean sryan6@nd.edu Biology, University of Notre Dame
Sedio, Brian bsedio@umich.edu Department of Ecology and Evolutionary Biology, University of Michigan
Weiblen , George gweiblen@umn.edu Plant Biology, University of Minnesota
The Coevolution of Competitors in a Community Context
Most theoretical work on the evolution of competing species has used models having the minimum number of species (i.e. two), and has not represented either enemies or resources of those two consumer species. Empirical studies of character displacement involve species that share multiple resources, and usually multiple predators as well. Although some prominent experimental systems involve only two competitors, the natural communities where these species occur often have more. My talk will concentrate on two types of extension of the current body of theory. The first is models of the evolution of competitors in a community or food web context. This illustrates the importance of ecological interactions on other trophic levels when determining the response of one species to changes in a putative competitor on its own trophic level. The second is the study of multi-species coevolution under such a community context. It has long been known that the impact of one competitor on a second may be positive when the community contains many competitors; this occurs via indirect effects on other mutual competitors. However, the implications of such positive population-level interactions on predictions of character displacement have not been explored. If removal of one competitor causes niche shifts of similar competitors, will large magnitude shifts be propagated throughout the competitive community? These and other aspects of the coevolution of species on a given trophic level will be considered. Where possible, examples of relevant plant-insect systems will be discussed.
Trait Matching: What does it tell us?
Recently, several studies have used the geographic matching of morphological traits (e.g. proboscis versus corolla length) to infer that coevolution has taken place between two interacting organisms. However, geographic trait matching alone is not sound evidence for coevolution because it is not a mandatory end point for coevolutionary relationships, and nor is coevolution the only selective mechanism capable of giving rise to geographic trait matching. Here I demonstrate how both coevolved and non-coevolved relationships result in patterns of trait matching but that through selection studies and by a process of elimination, it is possible to determine what the mechanism is behind trait matching patterns. In addition, using data from several published studies, I suggest how the steepness of the slope and intercept may yield important information about the relative strength of selection acting on the morphological traits of interacting species. For example in plant-insect relationships, plants seem to consistently have more exaggerated morphological traits than insects at high trait magnitudes. This suggests that selection to exaggerate the magnitude of the plant trait is stronger than for insects to exaggerate the magnitude of their corresponding traits. Thus, when plant and insect morphological traits are coevolved, insects are the most likely to be the losers of the coevolutionary race.
Bursera and Blepharida: The ecological play and the coevolutionary theatre
Coevolutionary theory proposes that the diversity of chemical structures found in plants is, in large part, the result of selection by herbivores. Because herbivores often feed on chemically similar plants, they should impose selective pressures on plants to diverge chemically or bias community assembly toward chemical divergence. Using a coevolved interaction between a group of chrysomelid beetles, the genus Blepharida and their host plants, the genus Bursera (Burseraceae), I tested whether coexisting plants of the Mexican tropical dry forest tend to be chemically more dissimilar than random. Results show that some of the communities are chemically overdispersed and that overdispersion is related to the tightness of the interaction between plants and herbivores and the spatial scale at which communities are measured. As coevolutionary specialization increases and spatial scale decreases, communities tend to be more chemically dissimilar. At fairly local scales and where herbivores have tight, one-to-one interactions with plants, communities have a strong pattern of chemical disparity. I use these results to propose a mechanism by which the coevolutionary interaction between plant defensive traits and specialized herbivorous insects promote stable coexistence and diversity for both tropical insects and plants.
Red King predators, evolution of mutualistic antagonists and coevolution patterns between mutualists and antagonists
In this talk I will present several theories related to co-evolution between plants and insects. First I will present a model of predator-prey coevolution, showing that rapid evolution in the predator can lead to prey diversification and a decrease in the number of preys available to the predator. This correspond to a "Red King" scenario, where rapid evolution leads to an ecological disadvantage. Second I will present the evolution from an antagonistic to a mutualistic interaction. Finally I will contrast expected patterns of coevolution in mutualistic and antagonistic networks.
Exploring selection mosaics and coevolution in multiespesific generalized systems
The geographic mosaic theory of coevolution (GMTC) considers that populations differ in evolutionary dynamics due to spatial variation in selective regimes. According to GMTC, three components of geographic structure drive the overall coevolutionary dynamics of such interactions: selection mosaics, coevolutionary hotspots, and trait remixing. Furthermore, the GMTC suggests the occurrence of a spatial pattern of interaction-mediated local adaptation and maladaptation. Empirical support to these theoretical predictions has come mostly from specialist antagonistic interactions. Contrasting with specialist interactions, free-living generalist interactions are formed by multispecies networks of interacting organisms that vary spatially in composition. Extreme reciprocal specialization between pairs of species is rare in these interactions. Consequently, multispecific selection and diffuse coevolution are prevalent in generalist interactions. Here I explore the possibilities of selection mosaic and interaction-mediated local adaptation in multiespecific generalized systems. To overcome the inherent difficulties of studying the interactions occurring among many species, I propose the combined use of structural equation modeling and individual-based network tools. This approach has allowed to detect that geographic mosaic of selections occur in generalist systems as well, and may be even a driver of the evolution of generalization in these types of multispecific systems.
Reciprocal adapations as a key factor in the stabilization of a defensive ant-plant mutualism
Ant-plants are important structural elements in many disturbed tropical ecosystems and the mutualism between plants and their defending ant symbionts is increasingly being used as a model to study general factors that stabilize a horizontally transmitted mutualisms. As these mutualisms must be established anew in every consecutive generation they are particularly prone to the destabilization by cheaters (former mutualists that ceased the service provisioning) or parasites (non-reciprocating exploiters with no evolutionary history as a mutualist). Theoretical models predicted high exploitation rates for high-reward mutualisms. We empirically tested this prediction and found that sympatric Mexican Acacia myrmecophytes differ at the species level in the amount of food rewards and nesting space that they provide to their defending Pseudomyrmex ant mutualists. Several biochemical specializations help to exclude non-adapted potential consumers from feeding on the host-plant derived food rewards: food bodies and extrafloral nectar are biochemically protected from nectar-infecting microorganisms, nectar robbers and herbivores. Interestingly, the same adaptations appear to make the symbiotic ants fully dependent on these rewards. At the phenotypic level, hosts that produced more extrafloral nectar were more aggressively defended by their inhabitants. Genetically fixed, species-specific plant traits combine with phenotypic plasticity to create 'host sanction' mechanisms, which bind fitness-relevant traits of both partners to each other. This assumption is confirmed by the observation that two high-reward producing among four investigated host species were less commonly exploited by non-defending ant species. As reward production can be costly, this allows the diversification into 'low cost-high risk' versus 'high cost-low risk' strategies, and both strategies are indeed realized by sympatric and congeneric host species.
A coevolutionary resolution to the paradox of concave selection?
The adaptive landscape, long a useful metaphor, is also a rigorous tool for understanding evolution when it is linked to empirical measurements of fitness. However, empirical estimates of fitness surfaces are often concave, implying an evolutionarily unstable situation under general conditions in the short term, and untenable extrapolations to longer-term evolution under the traditional adaptive landscape model. Incorporating the multivariate genetic and ecological context of concave selection would lead to a more robust adaptive landscape model. The several non-exclusive hypotheses for the prevalence of concave selection fall roughly into two groups: static and dynamic. Coevolution lies at the heart of dynamic solutions and is thus critical to resolving the paradox of concave selection. In this talk I will discuss the basic hypotheses and empirical evidence for the prevalence of concave selection and explore its relationship to coevolution. I will propose a revised adaptive landscape model that can account for concave selection, yet maintain the adaptive landscape's heuristic value for understanding multivariate phenotypic evolution.
Coevolution in plant-pollinator networks: the impact of network properties
In many plant-pollinator systems, interactions present a high degree of generalism, so that coevolution should be studied at the community level. Indeed intraspecific trait variation in such systems may both lead to variation in the gains that individuals are drawing from their interactions, and to variation in their choice/attraction of interaction partners. In this contribution, I will study whether the structural properties of the network of interactions between plants and animals impact the magnitude of coevolution and the properties of coevolutionary outcomes through simulations. In these simulations, individuals interact following simple interaction rules based on a single trait, the interaction strength between two individuals being controlled by their trait values. The fitness of an individual is proportional to the sum of its interactions, and traits present a constant heritability. The distribution of trait values in every species as well as species abundances are monitored through time to capture the natural selection applying on each species as a function of its position in the simulated network of interactions.
Exploring the interplay between ecology and evolution of plant-herbivore interactions
(Co)evolutionary ecologists have long appreciated that ecology drives evolution, and that evolution ultimately shapes the ecological processes and patterns of populations and communities over long periods of time. However, it remains unclear how these two processes interact to affects the ecology, evolution and coevolution of communities over short timescales (e.g. one to several generations). We address this problem by studying interactions between a native plant (common evening primrose, Oenothera biennis) and the diverse assemblage of arthropods that interact with this plant. Using a combination of field experiments and theory we address two related hypotheses: First, we examine if herbivory drives rapid evolution of life-history and plant defensive traits within plant populations. Second, we test whether standing genetic variation and rapid evolution within plant populations shape the structure and dynamics of arthropod communities over one to several generations. In support of the first hypothesis, we find that herbivores impose natural selection on many heritable plant traits. Using an experimental evolution approach in the field, we show that this selection causes rapid evolution within plant populations over just three generations. In support of the second hypothesis, we find that standing genetic variation in evening primrose is an important ecological factor affecting the abundance of many herbivore populations, as well as the composition and diversity of over 100 arthropod species in the community. Using quantitative genetics theory and simulations, we show that the observed natural selection and evolution within evening primrose is expected to drive rapid ecological changes in arthropod abundance and diversity. Therefore in this plant-herbivore system, ecological and evolutionary dynamics interact over very short time scales and using an eco-evolutionary approach provides greater insight into the factors that affect both the ecology and evolution of ecosystems.
The consequences of exploitation for plant-pollinator mutualisms
Species exist in complex biotic environments, engaging in a variety of antagonistic and cooperative interactions that contribute to their population and evolutionary dynamics. However, studies tend to concentrate on each pairwise interaction in isolation. By doing so, they may overlook significant feedbacks between the interactions. In this talk, I will focus on plant-pollinator mutualisms, which are often beset by species that reduce the benefits of the mutualism by exploiting the plant, the pollinator, or both. Through a combination of theoretical and empirical results, I will demonstrate how predictions about the ecological stability of mutualisms and the level of cooperation between mutualistic partners are changed by consideration of exploiters such as non-pollinating seed predators and predators of pollinators.
Complex networks of interactions and coevolution in multispecific assemblages of free-living species
Ecological interactions among plants and animals are the backbone of biodiversity. Interactions take a tremendous variety of forms in nature and have pervasive consequences for the population dynamics and evolution of species. Pollen and seed movement are the primary outcomes these interactions, yet we know very little of how these highly complex webs of mutualistic interactions coevolve and what are the consequences of these diversified mutualisms. A persistent challenge in evolutionary biology has been to understand how coevolution has produced complex webs of interacting species, where a large number of species interact through mutual dependences (e.g., mutualisms) or influences (e.g., predator-prey interactions in food webs). Recently, it has been shown that these interactions can form complex networks involving dozens and even hundreds of species. These coevolutionary networks are highly heterogeneous, with a core of super- generalists, nested, asymmetric, and contain multiple modules that act as the basic blocks of the complex web. I explore how the past evolutionary history conveyed in the phylogenies of plants and animals can explain these network patterns and the robustness of the network to species extinctions. Because phylogenetically similar species tend to play similar roles in the network, extinction events trigger non-random coextinction cascades. This implies that taxonomic diversity is lost faster than expected if there was no relationship between phylogeny and network structure. Zooming in the interaction pattern itself, I use examples of plant-animal mutualisms to show how the overall interaction pattern depicted in the network appears more influenced by the plant phylogeny, suggesting that the plant assemblage drives the interaction. Coevolved trends might thus depend on resource tracking by animals, so that each plant species 'filters out' subsets of mtualists given species-specific traits that constrain their interaction through trait matching and trait convergence. The overall network of interaction thus has a distinct signal marked by the plants phylogenetic history. These patterns suggest both precise ways on how coevolution goes on beyond simple pairwise interactions and scales up to whole communities. Network thinking applied to plant-animal mutualisms is helping us to understand the complex patterns of interactions involved in their evolution.
Frontier Mutualism and Community Genetics in Attine Ants and their Cultivated Fungi
I explore empirical approaches to elucidate community genetics and the geographic-mosaic of coevolution in fungus-growing ants, emphasizing computational and conceptual challenges that we encountered in our work. Fungus-growing ants propagate their cultivars as clonal monocultures within their nests, and in most cases clonally across many farmer generations as well. Long-term clonal monoculture presents special problems for disease control, but the ant farmers evolved diverse strategies to manage crop diseases, including management of an array of "auxiliary" microbes providing disease suppression and other services. Rather than growing a single cultivar solely for nutrition, insect farmers appear to cultivate, and possibly "artificially select" for, integrated crop-microbe consortia.

Ant-Fungus-Bacterial Community Genetics: In a collaboration with Tim Linksvayer (Univ. Pennsylvania), we use a quantitative-genetic approach to study how coevolution is affected by (a) the strength of reciprocal selection pressures; (b) the genetic architecture of the coevolving traits; and (c) the degree of co-transmission of the ants, their cultivated fungi, ant-associated microbes, and garden-associated microbes. Because it is easier to partition heritable components of phenotypic variance among clonal lineages, we developed an experimental system involving the clonal (asexual) ant Mycocepurus smithii, its clonal fungi, and associated microbial communities characterized with 16S-amplicon 454-sequencing.

Frontier Mutualisms within the Geographic Mosaic: Tropical leafcutter ants cultivate the fungus Attamyces bromatificus in a many-to-one, diffuse co-evolutionary relationship where ant and fungal partners re-associate frequently over time. To evaluate whether ant-Attamyces co-evolution is more specific (tighter) in peripheral populations, we characterized the host-specificities of Attamyces genotypes at their northern, subtropical range limits (southern USA, Mexico, Cuba). The northernmost leafcutter ant Atta texana sustains fungiculture during winter temperatures that would harm the cold-sensitive Attamyces cultivars of tropical leafcutter ants. Cold-tolerance of Attamyces cultivars increases with winter harshness along a south-to-north temperature gradient across the range of A. texana, indicating selection for cold-tolerant Attamyces variants along the temperature cline. Ecological niche modeling corroborates winter temperature as a key range-limiting factor impeding northward expansion of A. texana. Although the origin of leafcutter fungiculture was an evolutionary breakthrough that revolutionized the food niche of tropical fungus-growing ants, the original adaptations of this host-microbe symbiosis to tropical temperatures and the dependence on cold-sensitive fungal symbionts eventually constrained expansion into temperate habitats. Evolution of cold-tolerant fungi within the symbiosis relaxed constraints on winter fungiculture at the northern frontier of the leafcutter ant distribution, thereby expanding the ecological niche of an obligate host-microbe symbiosis. Studies of host-symbiont associations at their range limits are likely to inform models of co-extinctions of obligate mutualistic partners that are doubly stressed by habitat marginality and by environmental change.
What do studies of local adaptation and trait matching reveal about the coevolutionary process?
No description available.
Panel discussion
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Measuring coevolutionary selection in plant-insect interactions
No description available.
Applying theories of arms races of plants and their parasites: Camellia-weevil system and rice blast disease
An eco-evolutionary model for the arms race of interacting quantitative traits, defensive measure of host/prey and countermeasure of parasite/predator, is applied to the correlated geographical clines of Japanese camellia and its facultative seed predator, camellia weevil. Both the thickness of fruit wall of plants to protect seeds and the length of mouthpart of weevil for boring the wall for oviposition co-varied latitudinally over the populations where both camellia and camellia weevils are found. Host productivity and the nonlinearity of cost for weevil mouthpart length are found to characterize the coevolutionary outcomes.

I next introduce a mathematical model for the coevolution of parasite virulence and host resistance under a multilocus gene-for-gene interaction (Sasaki 2000, PRSLB). The degrees of parasite virulence and host resistance show coevolutionary cycles for sufficiently small costs of virulence and resistance. If either the cost of virulence or the number of resistance loci is larger than a threshold, the host maintains the static polymorphism of singly (or doubly or more, depending on the cost of resistance) resistant genotypes and the parasite remains universally avirulent. The theory is applied to the 40 years race frequency changes of rice blast disease pathogen in response to the changes in the planting areas of resistant cultivars in Niigata prefecture, Japan. A model for accurately forecasting the race frequencies is proposed.
Evolution of virulence and mixed infections
One very robust result of models of host-parasite co-evolution is that under regimes of mixed infection, where different strains of parasites compete for limiting host resources, parasites should evolve higher virulence strategies. This has wide reaching ramifications for optimal parasite strategies, since parasites are seldom alone in exploiting hosts. However, not all interactions between parasite strains within hosts are equal. When closely related parasite strains share hosts one might expect different evolutionary outcomes than when distantly related strains interact, particularly if the degree of relatedness between strains varies in nature such that parasites may be confronted with more or less related competitors. In addition to variation in the relatedness between interacting or competing parasite strains within hosts, the nature of the within-host interaction can vary greatly. Three types of within-host interactions have been identified, though this may not represent the whole range of the possibilities: competition for limiting host resources, production of public goods such as extra-cellular enzymes that promote infection success or efficient exploitation of the host and that can be used by all parasites within the same host, and spiteful interference between pathogen strains. Theoretical expectations differ for how virulence will change between single and mixed infections, and particularly for mixed infections of differing degree of relatedness between the parasite strains for these different types of interactions. I will discuss the outcome of experiments designed to examine how virulence differs among mixed infections that vary in degree of relatedness in the anther smut fungus Microbotryum violaceum, a Basidiomycete fungal pathogen of plants that is transmitted by insect vectors, with a small aside to examine the idea of relatedness and the applications of kin selection to microbial interactions. Individual strains, when involved in mixed infections, drew greater resources from their host plant and produced more spores per flower than did strains that infected on their own. Furthermore virulence, this time measured in terms of the degree of sterilisation of the host plant, varied among mixed infections that differed in genetic relatedness among strains. Individual strains interfered with each other's ability to colonise the plant, thereby reducing the virulence of mixed infections for this trait, but interfered less when strains were closely related, suggesting spiteful interactions. Thus for different traits of the infection genetic relatedness among interacting parasite strains differentially influence virulence.
Coevolution and community complexity
Our best examples of coevolution come from simplified interactions, but communities are rarely simple. Are complex communities less coevolved, or is coevolution just harder to recognize? I discuss coevolution and community complexity in light of both natural and invaded systems.
Panel discussion
no description available
Panel discussion
no description available
The Plasticity Load: the cost of flexibility of defense in a variable environment
Plasticity can evolve when members of a population experience different environments, such as those with and without an herbivore, with a trade-off in fitness between environments. This G x E for fitness can favor genes which are conditionally expressed only in the environment in which they are adaptive. Thus, adaptive plasticity can be achieved by altering the expression pattern of a gene and allowing a gene's expression to be induced by the environment as can be the case for plant defenses against insect herbivores. However, such conditionally expressed or 'plasticity' genes have the property that every individual in a population carries and transmits the gene, but only a fraction expresses it and exposes it to natural selection. A consequence of this pattern of inheritance and expression is a weakening of the strength of natural selection, allowing deleterious mutations to accumulate within and between species and inhibiting the spread of beneficial mutations. Mutation accumulation diminishes the degree of adaptation of conditionally expressed genes to rare environments, and the mutational cost of phenotypic plasticity, 'the plasticity load,' is greater the more rarely expressed a gene is. Our theory connects gene-level relative polymorphism and sequence divergence between species with the spatial and temporal frequency of environments that induce plastic gene expression. Our theory suggests that null hypotheses for levels of standing genetic variation and sequence divergence for plasticity genes must be corrected to account for their frequency of expression. With conditional gene expression, selection may allow a species to be a 'jack of all trades', but mutation insures it will be master of none.
Community genetics of foundation forest trees as drivers of community diversity, structure, stability, and evolution
The community phenotypes and genetic structure of foundation species are especially important to quantify as these species are by definition, "community and ecosystem drivers". Using observational and experimental studies of Populus and Pinus, our findings show that different tree genotypes support different communities of organisms (soil microbes, mycorrhizae, arthropods, vertebrates, understory plants, lichens, and pathogens) and that these differences can be quantified as heritable plant traits. Thus, genetic diversity in foundation tree species affects biodiversity and is very important to conserve even when these trees are common on the landscape. Using diverse examples, the community phenotypes of forest trees can be traced from the individuals possessing the trait, to the community, and to ecosystem processes such as leaf litter decomposition and N mineralization, which in turn can feed back to affect the fitness of the individual expressing the trait. Based on the concepts of community phenotype, community heritability, community feedbacks, and foundation species, our group is addressing issues including: 1. How many genes in a foundation species does it take to produce a community phenotype? 2. How important are the community phenotypes of transgenic species and should they be included in the evaluation process of crops that will soon account for over 200 million hectares? 3. How do communities associated with a foundation species interact (e.g., soil microbes and canopy arthropods) to affect the fitness of individual genotypes of a foundation species? 4. How many foundation species does a community have and how do their interactions predictably affect the rest of the community? 5. Since most species in a community are rare, do they individually or cumulatively play an important role in driving the community or are they tag-alongs that are defined by the interactions of foundation species? 6. Is coevolution among relatively few foundation species the driver of community evolution? 7. How will climate change affect the interactions of foundation species and the evolutionary trajectories of communities? 8. How can a community genetics perspective contribute to the controversial issue of assisted migration? 9. Are emergent properties such as biodiversity and stability under genetic control and thus subject to natural selection? We believe that answers to these questions have both basic and applied value, and have the potential to expand our knowledge of how complex communities and ecosystems evolve and function.
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A coevolutionary resolution to the paradox of concave selection?
Paul Hohenlohe The adaptive landscape, long a useful metaphor, is also a rigorous tool for understanding evolution when it is linked to empirical measurements of fitness. However, empirical estimates of fitness surfaces are often concave, implying an evolutionarily

video image

Coevolution in plant-pollinator networks: the impact of network properties
Franck Jabot In many plant-pollinator systems, interactions present a high degree of generalism, so that coevolution should be studied at the community level. Indeed intraspecific trait variation in such systems may both lead to variation in the gains that indivi

video image

Evolution of virulence and mixed infections
Jacqui Shykoff One very robust result of models of host-parasite co-evolution is that under regimes of mixed infection, where different strains of parasites compete for limiting host resources, parasites should evolve higher virulence strategies. This has wide reac

video image

The consequences of exploitation for plant-pollinator mutualisms
Emily Jones Species exist in complex biotic environments, engaging in a variety of antagonistic and cooperative interactions that contribute to their population and evolutionary dynamics. However, studies tend to concentrate on each pairwise interaction in isola

video image

Reciprocal adapations as a key factor in the stabilization of a defensive ant-plant mutualism
Martin Heil Ant-plants are important structural elements in many disturbed tropical ecosystems and the mutualism between plants and their defending ant symbionts is increasingly being used as a model to study general factors that stabilize a horizontally transmi

video image

The Coevolution of Competitors in a Community Context
Peter Abrams Most theoretical work on the evolution of competing species has used models having the minimum number of species (i.e. two), and has not represented either enemies or resources of those two consumer species. Empirical studies of character displacemen

video image

Coevolution and community complexity
Sharon Strauss Our best examples of coevolution come from simplified interactions, but communities are rarely simple. Are complex communities less coevolved, or is coevolution just harder to recognize? I discuss coevolution and community complexity in light of both

video image

Red King predators, evolution of mutualistic antagonists and coevolution patterns between mutualists and antagonists
Claire de Mazancourt In this talk I will present several theories related to co-evolution between plants and insects. First I will present a model of predator-prey coevolution, showing that rapid evolution in the predator can lead to prey diversification and a decrease i

video image

Exploring the interplay between ecology and evolution of plant-herbivore interactions
Marc Johnson (Co)evolutionary ecologists have long appreciated that ecology drives evolution, and that evolution ultimately shapes the ecological processes and patterns of populations and communities over long periods of time. However, it remains unclear how thes

video image

Measuring coevolutionary selection in plant-insect interactions
Ben Ridenhour No description available.

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Trait Matching: What does it tell us?
Bruce Anderson Recently, several studies have used the geographic matching of morphological traits (e.g. proboscis versus corolla length) to infer that coevolution has taken place between two interacting organisms. However, geographic trait matching alone is not so

video image

Exploring selection mosaics and coevolution in multiespesific generalized systems
Jose Gomez The geographic mosaic theory of coevolution (GMTC) considers that populations differ in evolutionary dynamics due to spatial variation in selective regimes. According to GMTC, three components of geographic structure drive the overall coevolutionary