Should I Change or Should I Go? Phenotypic Plasticity and Matching Habitat Choice in the Adaptation to Environmental Heterogeneity

Matching Habitat Choice and the Evolution of a Species' Range

Natural selection is not the only mechanism that promotes adaptation of an organism to its environment. Another mechanism is matching habitat choice, in which individuals sense and disperse toward habitat best suited to their phenotype. This can in principle facilitate rapid adaptation, enhance range expansion, and promote genetic differentiation, reproductive isolation, and speciation. However, empirical evidence that confirms the evolution of matching habitat choice in nature is limited. Here we obtain theoretical evidence that phenotype-optimal dispersal, a particular form of matching habitat choice, is likely to evolve only in the presence of a steep environmental gradient. Such a gradient may be steeper than the gradient the majority of species typically experience in nature, adding to the collection of possible explanations for the scarcity of evidence for matching habitat choice. We draw this conclusion from numerical solutions of a system of deterministic partial differential equations for a population's density along with the mean and variance of a fitness-related quantitative phenotypic trait such as body size. In steep gradients, we find that phenotype-optimal dispersal facilitates rapid adaptation on single-generation time scales, reduces within-population trait variation, increases range expansion speed, and enhances the chance of survival in rapidly changing environments. Moreover, it creates a directed gene flow that compensates for the maladaptive core-to-edge effects of random gene flow caused by random movements. These results suggest that adaptive gene flow to range margins, together with substantially reduced trait variation at central populations, may be hallmarks of phenotype-optimal dispersal in natural populations. Further, slowly-growing species under strong natural selection may particularly benefit from evolving phenotype-optimal dispersal.

Phenotypic and dispersal plasticity are not alternative strategies for organisms to face thermal changes

To buffer the effects of local environmental changes, organisms may modify their phenotypic traits (i.e. phenotypic plasticity) or disperse towards other potential habitats (i.e. dispersal plasticity). Despite extensive work studying either 'local phenotypic plasticity' or 'dispersal plasticity' independently, little is known about their potential covariation and interplay. These strategies are classically viewed as alternatives. However, this expectation has been challenged by theoretical work suggesting that they may instead evolve together under some environmental contexts. Here, we experimentally quantified morphological, movement and dispersal plasticity in response to thermal changes in 12 strains of the ciliate Tetrahymena thermophila. We showed that phenotypic and dispersal plasticity are not alternative strategies, with half of the strains expressing simultaneously all dimensions of plasticity in response to thermal changes. Furthermore, the extent of morphological and movement plasticity weakly but significantly differed between residents and dispersers. Interestingly, we found no covariation between these different plasticity dimensions, suggesting that they may evolve independently, which pleads for studying which environmental contexts favour the evolution of each. The fact that phenotypic and dispersal plasticity are not alternative strategies and may affect the expression of one another opens interesting perspectives about their joint evolution and the potential consequences of their interplay.

Conceptualising research environments using biological niche concepts

Several philosophers of science have taken inspiration from biological research on niches to conceptualise scientific practice. We systematise and extend three niche-based theories of scientific practice: conceptual ecology, cognitive niche construction, and scientific niche construction. We argue that research niches are a promising conceptual tool for understanding complex and dynamic research environments, which helps to investigate relevant forms of agency and material and social interdependencies, while also highlighting their historical and dynamic nature. To illustrate this, we develop a six-point framework for conceptualising research niches. Within this framework, research niches incorporate multiple and heterogenous material, social and conceptual factors (multi-dimensionality); research outputs arise, persist and differentiate through interactions between researchers and research niches (processes); researchers actively respond to and construct research niches (agency); research niches enable certain interactions and processes and not others (capability); and research niches are defined in relation to particular entities, such as individual researchers, disciplines, or concepts (relationality), and in relation to goals, such as understanding, solving problems, intervention, or the persistence of concepts or instruments (normativity).

The role of evolving niche choice in herbivore adaptation to host plants

Individuals living in heterogeneous environments often choose microenvironments that provide benefits to their fitness. Theory predicts that such niche choice can promote rapid adaptation to novel environments and help maintain genetic diversity. An open question of large applied importance is how niche choice and niche choice evolution affect the evolution of insecticide resistance in phytophagous insects. We, therefore, developed an individual-based model based on phytophagous insects to examine the evolution of insecticide resistance and niche choice via oviposition preferences. To find biologically realistic parameter ranges, we performed an empirical literature survey on insecticide resistance in major agricultural pests and also conducted a density-dependent survival experiment using potato beetles. We find that, in comparison to a scenario where individuals randomly oviposit eggs on toxic or non-toxic plants, the evolution of niche choice generally leads to slower evolution of resistance and facilitates the coexistence of different phenotypes. Our simulations also reveal that recombination rate and dominance effects can influence the evolution of both niche choice and resistance. Thus, this study provides new insights into the effects of niche choice on resistance evolution and highlights the need for more studies on the genetic basis of resistance and choice.

Effect of Different Temperatures on Herbicide Efficacy for the Management of the Invasive Weed Solanum rostratum Dunal (Family: Solanaceae)

Solanum rostratum Dunal, an invasive weed first recorded in Israel in the 1950s, undergoes multiple germination waves from early spring to late summer. Recently, its distribution has significantly expanded, with new populations reported throughout the country. This study assessed the efficacy of various herbicides for controlling S. rostratum populations under two distinct temperature regimes, focusing on temperature-dependent variations in herbicide performance. The results demonstrated that fluroxypyr and tembotrione consistently achieved high levels of control across all temperature conditions. Conversely, oxyfluorfen exhibited low performance under elevated temperatures and showed greater population-specific variability, while metribuzin proved more effective at higher temperatures across all S. rostratum populations. These findings emphasize the pivotal role of post-application temperature in influencing herbicide efficacy and underscore the importance of a precise application timing to optimize the control outcomes. Temperature-optimized herbicide strategies could play a critical role in limiting the spread and establishment of S. rostratum in agricultural systems, contributing to a sustainable and effective weed management.

Performance-based habitat choice can drive rapid adaptive divergence and reproductive isolation

Theory predicts that performance-based habitat choice1,2,3-where individuals select environments based on their local performance-should be widespread in nature and significantly influence ecological and evolutionary processes, including local adaptation, population divergence, reproductive isolation, and speciation.2,4,5,6,7,8,9 However, experimental evidence supporting these predictions has been largely lacking. In this study, we addressed this by inducing performance-based habitat choice in wild tree sparrows (Passer montanus) through the manipulation of differential access to transponder-operated feeders in two adjacent woodland areas. Sparrows overwhelmingly chose to move to and breed in the area where their feeding performance was highest, leading to local adaptation and increased reproductive success. Moreover, this non-random movement led to a high degree of assortative mating for transponder type and to reproductive isolation with respect to this ecological trait-all within a single generation. Our findings provide an empirical proof of principle that performance-based habitat choice can drive adaptive population divergence, even in the absence of divergent natural selection, underscoring its potential role as a key mechanism in ecological and evolutionary dynamics. This highlights the importance of integrating performance-based habitat choice into broader frameworks of adaptation and speciation, especially in the context of rapidly changing environments.

Climate mediates the trade-offs associated with phenotypic plasticity in an amphibian polyphenism

Polyphenisms occur when phenotypic plasticity produces morphologically distinct phenotypes from the same genotype. Plasticity is maintained through fitness trade-offs which are conferred to different phenotypes under specific environmental contexts. Predicting the impacts of contemporary climate change on phenotypic plasticity is critical for climate-sensitive animals like amphibians, but elucidating the selective pressures maintaining polyphenisms requires a framework to control for all mechanistic drivers of plasticity. Using a 32-year dataset documenting the larval and adult histories of 717 Arizona tiger salamanders (Ambystoma mavortium nebulosum), we determined how annual variation in climate and density dependence explained the maintenance of two distinct morphs (terrestrial metamorph vs. aquatic paedomorph) in a high-elevation polyphenism. The effects of climate and conspecific density on morph development were evaluated with piecewise structural equation models (SEM) to tease apart the direct and indirect pathways by which these two mechanisms affect phenotypic plasticity. Climate had a direct effect on morph outcome whereby longer growing seasons favoured metamorphic outcomes. Also, climate had indirect effects on morph outcome as mediated through density-dependent effects, such as long overwintering coldspells corresponding to high cannibal densities and light snowpacks corresponding to high larval densities, both of which promoted paedomorphic outcomes. Both climate and density dependence serve as important proxies for growth and resource limitation, which are important underlying drivers of the phenotypic plasticity in animal polyphenisms. Our findings motivate new studies to determine how contemporary climate change will alter the selective pressures maintaining phenotypic plasticity and polyphenisms.

Early-life variation in migration is subject to strong fluctuating survival selection in a partially migratory bird

Population dynamic and eco-evolutionary responses to environmental variation and change fundamentally depend on combinations of within- and among-cohort variation in the phenotypic expression of key life-history traits, and on corresponding variation in selection on those traits. Specifically, in partially migratory populations, spatio-seasonal dynamics depend on the degree of adaptive phenotypic expression of seasonal migration versus residence, where more individuals migrate when selection favours migration. Opportunity for adaptive (or, conversely, maladaptive) expression could be particularly substantial in early life, through the initial development of migration versus residence. However, within- and among-cohort dynamics of early-life migration, and of associated survival selection, have not been quantified in any system, preventing any inference on adaptive early-life expression. Such analyses have been precluded because data on seasonal movements and survival of sufficient young individuals, across multiple cohorts, have not been collected. We undertook extensive year-round field resightings of 9359 colour-ringed juvenile European shags Gulosus aristotelis from 11 successive cohorts in a partially migratory population. We fitted Bayesian multi-state capture-mark-recapture models to quantify early-life variation in migration versus residence and associated survival across short temporal occasions through each cohort's first year from fledging, thereby quantifying the degree of adaptive phenotypic expression of migration within and across years. All cohorts were substantially partially migratory, but the degree and timing of migration varied considerably within and among cohorts. Episodes of strong survival selection on migration versus residence occurred both on short timeframes within years, and cumulatively across entire first years, generating instances of instantaneous and cumulative net selection that would be obscured at coarser temporal resolutions. Further, the magnitude and direction of selection varied among years, generating strong fluctuating survival selection on early-life migration across cohorts, as rarely evidenced in nature. Yet, the degree of migration did not strongly covary with the direction of selection, indicating limited early-life adaptive phenotypic expression. These results reveal how dynamic early-life expression of and selection on a key life-history trait, seasonal migration, can emerge across seasonal, annual, and multi-year timeframes, yet be substantially decoupled. This restricts the potential for adaptive phenotypic, microevolutionary, and population dynamic responses to changing seasonal environments.

Testing the evolutionary potential of an alpine plant: phenotypic plasticity in response to growth temperature outweighs parental environmental effects and other genetic causes of variation

Phenotypic plasticity and rapid evolution are fundamental processes by which organisms can maintain their function and fitness in the face of environmental changes. Here we quantified the plasticity and evolutionary potential of an alpine herb Wahlenbergia ceracea. Utilizing its mixed-mating system, we generated outcrossed and self-pollinated families that were grown in either cool or warm environments, and that had parents that had also been grown in either cool or warm environments. We then analysed the contribution of environmental and genetic factors to variation in a range of phenotypic traits including phenology, leaf mass per area, photosynthetic function, thermal tolerance, and reproductive fitness. The strongest effect was that of current growth temperature, indicating strong phenotypic plasticity. All traits except thermal tolerance were plastic, whereby warm-grown plants flowered earlier, grew larger, and produced more reproductive stems compared with cool-grown plants. Flowering onset and biomass were heritable and under selection, with early flowering and larger plants having higher relative fitness. There was little evidence for transgenerational plasticity, maternal effects, or genotype×environment interactions. Inbreeding delayed flowering and reduced reproductive fitness and biomass. Overall, we found that W. ceracea has the capacity to respond rapidly to climate warming via plasticity, and the potential for evolutionary change.

Microevolutionary change in wild stickleback: Using integrative time-series data to infer responses to selection

A central goal in evolutionary biology is to understand how different evolutionary processes cause trait change in wild populations. However, quantifying evolutionary change in the wild requires linking trait change to shifts in allele frequencies at causal loci. Nevertheless, datasets that allow for such tests are extremely rare and existing theoretical approaches poorly account for the evolutionary dynamics that likely occur in ecological settings. Using a decade-long integrative phenome-to-genome time-series dataset on wild threespine stickleback (Gasterosteus aculeatus), we identified how different modes of selection (directional, episodic, and balancing) drive microevolutionary change in correlated traits over time. Most strikingly, we show that feeding traits changed by as much 25% across 10 generations which was driven by changes in the genetic architecture (i.e., in both genomic breeding values and allele frequencies at genetic loci for feeding traits). Importantly, allele frequencies at genetic loci related to feeding traits changed at a rate greater than expected under drift, suggesting that the observed change was a result of directional selection. Allele frequency dynamics of loci related to swimming traits appeared to be under fluctuating selection evident in periodic population crashes in this system. Our results show that microevolutionary change in a wild population is characterized by different modes of selection acting simultaneously on different traits, which likely has important consequences for the evolution of correlated traits. Our study provides one of the most thorough descriptions to date of how microevolutionary processes result in trait change in a natural population.

Chasing the fitness optimum: temporal variation in the genetic and environmental expression of life-history traits for a perennial plant

BACKGROUND AND AIMS

The ability of plants to track shifting fitness optima is crucial within the context of global change, where increasing environmental extremes may have dramatic consequences for life history, fitness, and ultimately population persistence. However, tracking changing conditions relies on the relationship between genetic and environmental variance, where selection may favour plasticity, the evolution of genetic differences, or both depending on the spatial and temporal scale of environmental heterogeneity.

METHODS

Over three years, we compared the genetic and environmental components of phenological and life-history variation in a common environment for the spring perennial Geum triflorum. Populations were sourced from alvar habitats that exhibit extreme but predictable annual flood-desiccation cycles and prairie habitats that exhibit similar but less predictable variation in water availability.

KEY RESULTS

Heritability was generally higher for early life-history (emergence probability) relative to later life-history traits (total seed mass), indicating that traits associated with establishment are under stronger genetic control relative to later life-history fitness expressions, where plasticity may play a larger role. This pattern was particularly notable in seeds sourced from environmentally extreme but predictable alvar habitats relative to less predictable prairie environments. Fitness landscapes based on seed source origin, largely characterized by varying water availability and flower production, described selection as the degree of maladaptation of seed source environment relative to the prairie common garden environment. Plants from alvar populations were consistently closer to the fitness optimum across all years. Annually, the breadth of the fitness optimum expanded primarily along a moisture gradient, with inclusion of more populations onto the expanding optimum.

CONCLUSIONS

These results highlight the importance of temporally and spatially varying selection in life-history evolution, indicating plasticity may become a primary mechanism needed to track fitness for later life-history events within perennial systems.

Ecomorphological convergence in the walking leg dactyli of two clades of ascidian- and mollusc-associated shrimps (Decapoda: Caridea: Palaemonidae)

Symbiotic species, living within or on the surface of host organisms, may evolve a wide range of adaptations as a result of various selection pressures, host specificity of the symbiont and the nature of the symbiosis. In tropical marine coral reef ecosystems, palaemonid shrimps (Crustacea: Decapoda: Caridea) live in association with at least five different invertebrate phyla. Host switches between (distantly) related host groups, and the thereby associated selection pressures were found to play a major role in the diversification of these shrimp lineages, giving rise to various host-specific adaptations. Two lineages of palaemonid shrimp, which have switched from an ectosymbiotic association towards endosymbiosis, are studied for their morphological diversification and possible convergence. Special attention is given to the between-phyla host switches involving ascidian and bivalve hosts, which are characteristic for these lineages. Using landmark-based (phylo)morphospace analyses and Scanning Electron Microscopy, the walking leg dactylus shape and the microstructures on these dactyli are studied. No specific bivalve- or ascidian-associated morphotypes were found, but morphological convergence in dactylus morphology was found in various species within the two studied clades with similar host groups. In addition, multiple lineages of bivalve-associated species appear to be morphologically diverging more than their ascidian-associated relatives, with 'intermediate' morphotypes found near host-switching events.

Niche construction and the environmental term of the price equation: How natural selection changes when organisms alter their environments

Organisms construct their own environments and phenotypes through the adaptive processes of habitat choice, habitat construction, and phenotypic plasticity. We examine how these processes affect the dynamics of mean fitness change through the environmental change term of the Price Equation. This tends to be ignored in evolutionary theory, owing to the emphasis on the first term describing the effect of natural selection on mean fitness (the additive genetic variance for fitness of Fisher's Fundamental Theorem). Using population genetic models and the Price Equation, we show how adaptive niche constructing traits favorably alter the distribution of environments that organisms encounter and thereby increase population mean fitness. Because niche-constructing traits increase the frequency of higher-fitness environments, selection favors their evolution. Furthermore, their alteration of the actual or experienced environmental distribution creates selective feedback between niche constructing traits and other traits, especially those with genotype-by-environment interaction for fitness. By altering the distribution of experienced environments, niche constructing traits can increase the additive genetic variance for such traits. This effect accelerates the process of overall adaption to the niche-constructed environmental distribution and can contribute to the rapid refinement of alternative phenotypic adaptations to different environments. Our findings suggest that evolutionary biologists revisit and reevaluate the environmental term of the Price Equation: owing to adaptive niche construction, it contributes directly to positive change in mean fitness; its magnitude can be comparable to that of natural selection; and, when there is fitness G × E, it increases the additive genetic variance for fitness, the much-celebrated first term.

Plasticity in growth is genetically variable and highly conserved across spatial scales in a Mediterranean pine

Phenotypic plasticity is a main mechanism for sessile organisms to cope with changing environments. Plasticity is genetically based and can evolve under natural selection so that populations within a species show distinct phenotypic responses to environment. An important question that remains elusive is whether the intraspecific variation in plasticity at different spatial scales is independent from each other. To test whether variation in plasticity to macro- and micro-environmental variation is related among each other, we used growth data of 25 Pinus pinaster populations established in seven field common gardens in NW Spain. Phenotypic plasticity to macro-environmental variation was estimated across test sites while plasticity to micro-environmental variation was estimated by using semivariography and kriging for modeling within-site heterogeneity. We provide empirical evidence of among-population variation in the magnitude of plastic responses to both micro- and macro-environmental variation. Importantly, we found that such responses were positively correlated across spatial scales. Selection for plasticity at one scale of environmental variation may impact the expression of plasticity at other scales, having important consequences on the ability of populations to buffer climate change. These results improve our understanding of the ecological drivers underlying the expression of phenotypic plasticity.

Intraspecific trait variation and adaptability of Stipa krylovii: Insight from a common garden experiment with two soil moisture treatments

Understanding patterns of intraspecific trait variation can help us understand plant adaptability to environmental changes. To explore the underlying adaptation mechanisms of zonal plant species, we selected seven populations of Stipa krylovii, a dominant species in the Inner Mongolia Steppe of China, and evaluated the effects of phenotypic plasticity and genetic differentiation, the effects of climate variables on population trait differentiation, and traits coordinated patterns under each soil moisture treatment. We selected seeds from seven populations of S. krylovii in the Inner Mongolia Steppe, China, and carried out a soil moisture (2) × population origin (7) common garden experiment at Tianjin City, China, and measured ten plant traits of S. krylovii. General linear analyses were used to analyze how soil moisture and population origin affected each trait variation, Mantel tests were used to analyze population trait differentiation-geographic distance (or climatic difference) relationships, regression analyses were used to evaluate trait-climatic variable relationships, and plant trait networks (PTNs) were used to evaluate traits coordinated patterns. Both soil moisture and population origin showed significant effects on most of traits. Aboveground biomass, root-shoot ratio, leaf width, specific leaf area, and leaf nitrogen (N) content were significantly correlated with climate variables under the control condition. Specific leaf area and leaf N content were significantly correlated with climate variables under the drought condition. By PTNs, the hub trait(s) was plant height under the control condition and were aboveground biomass, root length, and specific leaf area under the drought condition. This study indicates that both phenotypic plasticity and genetic differentiation can significantly affect the adaptability of S. krylovii. In addition, soil moisture treatments show significant effects on trait-climate relationships and traits coordinated patterns. These findings provide new insights into the adaptive mechanisms of zonal species in the semiarid grassland region.

Simulating plasticity as a framework for understanding habitat selection and its role in adaptive capacity and extinction risk through an expansion of CDMetaPOP

Adaptive capacity can present challenges for modelling as it encompasses multiple ecological and evolutionary processes such as natural selection, genetic drift, gene flow and phenotypic plasticity. Spatially explicit, individual-based models provide an outlet for simulating these complex interacting eco-evolutionary processes. We expanded the existing Cost-Distance Meta-POPulation (CDMetaPOP) framework with inducible plasticity modelled as a habitat selection behaviour, using temperature or habitat quality variables, with a genetically based selection threshold conditioned on past individual experience. To demonstrate expected results in the new module, we simulated hypothetical populations and then evaluated model performance in populations of redband trout (Oncorhynchus mykiss gairdneri) across three watersheds where temperatures induce physiological stress in parts of the stream network. We ran simulations using projected warming stream temperature data under four scenarios for alleles that: (1) confer thermal tolerance, (2) bestow plastic habitat selection, (3) give both thermal tolerance and habitat selection preference and (4) do not provide either thermal tolerance or habitat selection. Inclusion of an adaptive allele decreased declines in population sizes, but this impact was greatly reduced in the relatively cool stream networks. As anticipated with the new module, high-temperature patches remained unoccupied by individuals with the allele operating plastically after exposure to warm temperatures. Using complete habitat avoidance above the stressful temperature threshold, habitat selection reduced the overall population size due to the opportunity cost of avoiding areas with increased, but not guaranteed, mortality. Inclusion of plasticity within CDMetaPOP will provide the potential for genetic or plastic traits and 'rescue' to affect eco-evolutionary dynamics for research questions and conservation applications.

Bet-hedging via dispersal aids the evolution of plastic responses to unreliable cues

Adaptive plasticity is expected to evolve when informative cues predict environmental variation. However, plastic responses can be maladaptive even when those cues are informative, if prediction mistakes are shared across members of a generation. These fitness costs can constrain the evolution of plasticity when initial plastic mutants use of cues of only moderate reliability. Here, we model the barriers to the evolution of plasticity produced by these constraints and show that dispersal across a metapopulation can overcome them. Constraints are also lessened, though not eliminated, when plastic responses are free to evolve gradually and in concert with increased reliability. Each of these factors be viewed as a form of bet-hedging: by lessening correlations in the fates of relatives, dispersal acts as diversifying bet-hedging, while producing submaximal responses to a cue can be understood as a conservative bet-hedging strategy. While poor information may constrain the evolution of plasticity, the opportunity for bet-hedging may predict when that constraint can be overcome.

Contrasting effects of experiencing temporally heterogeneous light availability versus homogenous shading on plant subsequent responses to light conditions

Temporally heterogeneous environments is hypothesized to correlate with greater plasticity of plants, which has rarely been supported by direct evidence. To address this issue, we subjected three species from different ranges of habitats to a first round of alternating full light and heavy shading (temporally heterogeneous light experience), constant moderate shading and full light conditions (temporally homogeneous light experiences, control) and a second round of light-gradient treatments. We measured plant performance in a series of morphological, biomass, physiological and biochemical traits at the end of each round. Compared to constant full light experience, temporally heterogeneous light conditions induced immediate active biochemical responses (in the first round) with improved late growth in biomass (during the second round); constant moderate shading experience increased photosynthetic physiological and biomass performances of plants in early response, and decreased their late growth in biomass. The karst endemic species of Kmeria septentrionalis showed greater improvement in late growth of biomass and lower decrease in biochemical performance, due to early heterogeneous experience, compared to the non-karst species of Lithocarpus glaber and the karst adaptable species of Celtis sinensis. Results suggested plants will prefer to produce morphological and physiological responses that are less reversible and more costly in the face of more reliable environmental cues at early stage in spite of decreased future growth potential, but to produce immediate biochemical responses for higher late growth potential when early environmental cues are less reliable, to avoid the loss of high costs and low profits. Typical karst species should be more able to benefit from early temporally heterogeneous experience, due to long-term adaptation to karst habitats of high environmental heterogeneity and low resource availability.

Plant Species' Capacity for Range Shifts at the Habitat and Geographic Scales: A Trade-Off-Based Framework

Climate change is causing rapid shifts in the abiotic and biotic environmental conditions experienced by plant populations, but we lack generalizable frameworks for predicting the consequences for species. These changes may cause individuals to become poorly matched to their environments, potentially inducing shifts in the distributions of populations and altering species' habitat and geographic ranges. We present a trade-off-based framework for understanding and predicting whether plant species may undergo range shifts, based on ecological strategies defined by functional trait variation. We define a species' capacity for undergoing range shifts as the product of its colonization ability and the ability to express a phenotype well-suited to the environment across life stages (phenotype-environment matching), which are both strongly influenced by a species' ecological strategy and unavoidable trade-offs in function. While numerous strategies may be successful in an environment, severe phenotype-environment mismatches result in habitat filtering: propagules reach a site but cannot establish there. Operating within individuals and populations, these processes will affect species' habitat ranges at small scales, and aggregated across populations, will determine whether species track climatic changes and undergo geographic range shifts. This trade-off-based framework can provide a conceptual basis for species distribution models that are generalizable across plant species, aiding in the prediction of shifts in plant species' ranges in response to climate change.

Herbivory selects for tolerance and constitutive defence across stages of community succession

Plants defend themselves from herbivory by either reducing damage (resistance) or minimizing its negative fitness effects with compensatory growth (tolerance). Herbivore pressure can fluctuate from year to year in an early secondary successional community, which can create temporal variation in selection for defence traits. We manipulated insect herbivory and successional age of the community as agents of natural selection in replicated common gardens with the perennial herb Solidago altissima. In these genotypic selection experiments, herbivory consistently selected for better defended plants in both successional communities. Herbivore suppression increased plant survival and the probability of flowering only in mid-succession. Despite these substantial differences in the effects of herbivory between early and mid-succession, the selection on defence traits did not change. Succession affected selection only on aboveground biomass, with positive selection in early but not mid-succession, suggesting an important role of competition in the selective environment. These results demonstrate that changes in the community that affect key life-history traits in an individual species can occur over very short timescales in a dynamic secondary successional environment. The resulting community context-driven variation in natural selection may be an important, yet overlooked, contributor to adaptive mosaics across populations.

Experimental and theoretical support for costs of plasticity and phenotype in a nematode cannibalistic trait

Developmental plasticity is the ability of a genotype to express multiple phenotypes under different environmental conditions and has been shown to facilitate the evolution of novel traits. However, while the associated cost of plasticity, i.e., the loss in fitness due to the ability to express plasticity in response to environmental change, and the cost of phenotype, i.e., the loss of fitness due to expressing a fixed phenotype across environments, have been theoretically predicted, empirically such costs remain poorly documented and little understood. Here, we use a plasticity model system, hermaphroditic nematode Pristionchus pacificus, to experimentally measure these costs in wild isolates under controlled laboratory conditions. P. pacificus can develop either a bacterial feeding or predatory mouth morph in response to different external stimuli, with natural variation of mouth-morph ratios between strains. We first demonstrated the cost of phenotype by analyzing fecundity and developmental speed in relation to mouth morphs across the P. pacificus phylogenetic tree. Then, we exposed P. pacificus strains to two distinct microbial diets that induce strain-specific mouth-form ratios. Our results indicate that the plastic strain does shoulder a cost of plasticity, i.e., the diet-induced predatory mouth morph is associated with reduced fecundity and slower developmental speed. In contrast, the non-plastic strain suffers from the cost of phenotype since its phenotype does not change to match the unfavorable bacterial diet but shows increased fitness and higher developmental speed on the favorable diet. Furthermore, using a stage-structured population model based on empirically derived life history parameters, we show how population structure can alleviate the cost of plasticity in P. pacificus. The results of the model illustrate the extent to which the costs associated with plasticity and its effect on competition depend on ecological factors. This study provides support for costs of plasticity and phenotype based on empirical and modeling approaches.

A generalised approach to the study and understanding of adaptive evolution

Evolutionary theory has made large impacts on our understanding and management of the world, in part because it has been able to incorporate new data and new insights successfully. Nonetheless, there is currently a tension between certain biological phenomena and mainstream evolutionary theory. For example, how does the inheritance of molecular epigenetic changes fit into mainstream evolutionary theory? Is niche construction an evolutionary process? Is local adaptation via habitat choice also adaptive evolution? These examples suggest there is scope (and perhaps even a need) to broaden our views on evolution. We identify three aspects whose incorporation into a single framework would enable a more generalised approach to the understanding and study of adaptive evolution: (i) a broadened view of extended phenotypes; (ii) that traits can respond to each other; and (iii) that inheritance can be non-genetic. We use causal modelling to integrate these three aspects with established views on the variables and mechanisms that drive and allow for adaptive evolution. Our causal model identifies natural selection and non-genetic inheritance of adaptive parental responses as two complementary yet distinct and independent drivers of adaptive evolution. Both drivers are compatible with the Price equation; specifically, non-genetic inheritance of parental responses is captured by an often-neglected component of the Price equation. Our causal model is general and simplified, but can be adjusted flexibly in terms of variables and causal connections, depending on the research question and/or biological system. By revisiting the three examples given above, we show how to use it as a heuristic tool to clarify conceptual issues and to help design empirical research. In contrast to a gene-centric view defining evolution only in terms of genetic change, our generalised approach allows us to see evolution as a change in the whole causal structure, consisting not just of genetic but also of phenotypic and environmental variables.

Genome-phenotype-environment associations identify signatures of selection in a panmictic population of threespine stickleback

Adaptive genetic divergence occurs when selection imposed by the environment causes the genomic component of the phenotype to differentiate. However, genomic signatures of natural selection are usually identified without information on which trait is responding to selection by which selective agent(s). Here, we integrate whole-genome sequencing with phenomics and measures of putative selective agents to assess the extent of adaptive divergence in threespine stickleback occupying the highly heterogeneous lake Mývatn, NE Iceland. We find negligible genome wide divergence, yet multiple traits (body size, gill raker structure and defence traits) were divergent along known ecological gradients (temperature, predatory bird densities and water depth). SNP based heritability of all measured traits was high (h²  = 0.42-0.65), indicating adaptive potential for all traits. Environment-association analyses further identified thousands of loci putatively involved in selection, related to genes linked to, for instance, neuron development and protein phosphorylation. Finally, we found that loci linked to water depth were concurrently associated with pelvic spine length variation - supporting the conclusion that divergence in pelvic spine length occurred in the face of gene flow. Our results suggest that whilst there is substantial genetic variation in the traits measured, phenotypic divergence of Mývatn stickleback is mostly weakly associated with environmental gradients, potentially as a result of substantial gene flow. Our study illustrates the value of integrative studies that combine genomic assays of multivariate trait variation with landscape genomics.

Social phenotype-dependent selection of social environment in wild great and blue tits: an experimental study

There is growing evidence that individuals actively assess the match between their phenotype and their environment when making habitat choice decisions (so-called matching habitat choice). However, to our knowledge, no studies have considered how the social environment may interact with social phenotype in determining habitat choice, despite habitat choice being an inherently social process and growing evidence for individual variation in sociability. We conducted an experiment using wild great and blue tits to understand how birds integrate their social phenotype and social environment when choosing where and how to feed. We used programmable feeders to (i) record social interactions and estimate social phenotype, and (ii) experimentally manipulate the local density experienced by birds of differing social phenotype. By tracking feeder usage, we estimated how social environment and social phenotype predicted feeder choice and feeding behaviour. Both social environment and social phenotype predicted feeder usage, but a bird's decision to remain in a particular social environment did not depend on their social phenotype. By contrast, for feeding behaviour, responses to the social environment depended on social phenotype. Our results provide rare evidence of matching habitat choice and shed light on the dependence of habitat choice on between-individual differences in social phenotype.

Dispersal plasticity driven by variation in fitness across species and environmental gradients

Dispersal plasticity, when organisms adjust their dispersal decisions depending on their environment, can play a major role in ecological and evolutionary dynamics, but how it relates to fitness remains scarcely explored. Theory predicts that high dispersal plasticity should evolve when environmental gradients have a strong impact on fitness. Using microcosms, we tested in five species of the genus Tetrahymena whether dispersal plasticity relates to differences in fitness sensitivity along three environmental gradients. Dispersal plasticity was species- and environment-dependent. As expected, dispersal plasticity was generally related to fitness sensitivity, with higher dispersal plasticity when fitness is more affected by environmental gradients. Individuals often preferentially disperse out of low fitness environments, but leaving environments that should yield high fitness was also commonly observed. We provide empirical support for a fundamental, but largely untested, assumption in dispersal theory: the extent of dispersal plasticity correlates with fitness sensitivity to the environment.

Phenotypic Diversity Analysis and Superior Family Selection of Industrial Raw Material Forest Species-Pinus yunnanensis Franch

Pinus yunnanensis Franch is a major forest species in southwest China as a source of timber and industrial raw materials. The genetic quality of the species is declining and the differentiation of offspring is strong as affected by environmental change and improper management measures. To assess the phenotypic diversity of natural populations, the evaluation of twelve phenotypic traits in nine populations from its whole distribution was performed. Studies revealed plentiful phenotypic variations within and among populations. The phenotypic variation within the population was 4.03%, and was lower than that among populations (21.04%), indicating that the phenotypic variation among populations was the main source. The mean differentiation coefficient was 91.23%, and the mean coefficient of variation of twelve traits was 28.27%, ranging from 14.18% (length of needles) to 70.11% (height under the branches). No significant correlation between plant height and environmental factors was found. Mean annual temperature, mean temperature of the driest quarter, mean temperature of the wettest quarter, and latitude were significantly correlated to diameter breast height, respectively. Temperature is the most important factor affecting the diameter of breast height. Three principal components that represent plant shape, needle, and lateral branch trait, respectively, were obtained while the cumulative contribution rate reached 74.40%. According to the unweighted pair-group method with arithmetic means (UPGMA) cluster analysis, nine populations were divided into three clusters. However, populations were not clustered strictly according to geographic distance, implying that there is a discontinuity in the variation of phenotypic traits. Compared with other populations, the Lufeng population contains obvious advantages in plant height, diameter breast height, crown diameter, and needle length and width, whereas the Yongren population has the worst performance in plant height, crown diameter, and the number of lateral branches. Moreover, for selecting superior families, both the comprehensive scoring method and principal component analysis were combined. By comparing trait values from 258 families, eleven superior families with an actual gain of each trait ranging from 0.02% to 32.23% were successfully screened out. This study provides a certain reference significance for the breeding of improved varieties and plantation management of P. yunnanensis.

Birds of a Feather Flock Together: Extent of Long-Term Consistency of Colony-Size Choice in Cliff Swallows

Explaining why animal groups vary in size is a fundamental problem in behavioral ecology. One hypothesis is that life-history differences among individuals lead to sorting of phenotypes into groups of different sizes where each individual does best. This hypothesis predicts that individuals should be relatively consistent in their use of particular group sizes across time. Little is known about whether animals’ choice of group size is repeatable across their lives, especially in long-lived species. We studied consistency in choice of breeding-colony size in colonially nesting cliff swallows (Petrochelidon pyrrhonota) in western Nebraska, United States, over a 32-year period, following 6,296 birds for at least four breeding seasons. Formal repeatability of size choice for the population was about 0.41. About 45% of individuals were relatively consistent in choice of colony size, while about 40% varied widely in the colony size they occupied. Birds using the smaller and larger colonies appeared more consistent in size use than birds occupying more intermediate sized colonies. Consistency in colony size was also influenced by whether a bird used the same physical colony site each year and whether the site had been fumigated to remove ectoparasites. The difference between the final and initial colony sizes for an individual, a measure of the net change in its colony size over its life, did not significantly depart from 0 for the dataset as a whole. However, different year-cohorts did show significant net change in colony size, both positive and negative, that may have reflected fluctuating selection on colony size among years based on climatic conditions. The results support phenotypic sorting as an explanation for group size variation, although cliff swallows also likely use past experience at a given site and the extent of ectoparasitism to select breeding colonies.

Habitat choice promotes and constrains phenotypic plasticity

Habitat choice can either speed up or slow rates of phenotypic evolution, depending on which trait is measured. We suggest that habitat choice plays an analogous, and generally overlooked, role in shaping patterns of phenotypic plasticity. Using our work with an amphibious fish, we discuss two case studies that demonstrate how habitat choice can both promote and constrain expression of plasticity. First, habitat choice during the dry season accentuates adaptive metabolic plasticity and minimizes maladaptive changes to muscle, ultimately increasing survival time out of water. Second, a trade-off between water- and air-breathing drives matching habitat choice, resulting in positive feedback that reinforces respiratory specialization and environmental preference. Overall, these case studies demonstrate that we must consider the interactions between plasticity and habitat choice to fully understand how animals survive in the face of environmental change. Without considering both processes simultaneously, the performance of animals in challenging conditions can be either under- or over-estimated. Finally, because habitat choice shapes the frequency and predictability of environmental changes that animals experience, feedback between habitat choice and expressions of phenotypic plasticity may be an important factor that influences how plasticity evolves.

Does genetic differentiation underlie behavioral divergence in response to migration barriers in sticklebacks? A common garden experiment

Abstract

Water management measures in the 1970s in the Netherlands have produced a large number of “resident” populations of three-spined sticklebacks that are no longer able to migrate to the sea. This may be viewed as a replicated field experiment, allowing us to study how the resident populations are coping with human-induced barriers to migration. We have previously shown that residents are smaller, bolder, more exploratory, more active, and more aggressive and exhibited lower shoaling and lower migratory tendencies compared to their ancestral “migrant” counterparts. However, it is not clear if these differences in wild-caught residents and migrants reflect genetic differentiation, rather than different developmental conditions. To investigate this, we raised offspring of four crosses (migrant ♂ × migrant ♀, resident ♂ × resident ♀, migrant ♂ × resident ♀, resident ♂ × migrant ♀) under similar controlled conditions and tested for differences in morphology and behavior as adults. We found that lab-raised resident sticklebacks exhibited lower shoaling and migratory tendencies as compared to lab-raised migrants, retaining the differences in their wild-caught parents. This indicates genetic differentiation of these traits. For all other traits, the lab-raised sticklebacks of the various crosses did not differ significantly, suggesting that the earlier-found contrast between wild-caught fish reflects differences in their environment. Our study shows that barriers to migration can lead to rapid differentiation in behavioral tendencies over contemporary timescales (~ 50 generations) and that part of these differences reflects genetic differentiation.

Significance statement

Many organisms face changes to their habitats due to human activities. Much research is therefore dedicated to the question whether and how organisms are able to adapt to novel conditions. We address this question in three-spined sticklebacks, where water management measures cut off some populations, prohibiting their seasonal migration to the North Sea. In a previous study, we showed that wild-caught “resident” fish exhibited markedly different behavior than migrants. To disentangle whether these differences reflect genetic differentiation or differences in the conditions under which the wild-caught fish grew up, we conducted crosses, raising the F1 offspring under identical conditions. As their wild-caught parents, the F1 of resident × resident crosses exhibited lower migratory and shoaling tendencies than the F1 of migrant × migrant crosses, while the F1 of hybrid crosses were intermediate. This suggests that ~ 50 years of isolation are sufficient to induce behaviorally relevant genetic differentiation.

Building on 150 Years of Knowledge: The Freshwater Isopod Asellus aquaticus as an Integrative Eco-Evolutionary Model System

Interactions between organisms and their environments are central to how biological diversity arises and how natural populations and ecosystems respond to environmental change. These interactions involve processes by which phenotypes are affected by or respond to external conditions (e.g., via phenotypic plasticity or natural selection) as well as processes by which organisms reciprocally interact with the environment (e.g., via eco-evolutionary feedbacks). Organism-environment interactions can be highly dynamic and operate on different hierarchical levels, from genes and phenotypes to populations, communities, and ecosystems. Therefore, the study of organism-environment interactions requires integrative approaches and model systems that are suitable for studies across different hierarchical levels. Here, we introduce the freshwater isopod Asellus aquaticus, a keystone species and an emerging invertebrate model system, as a prime candidate to address fundamental questions in ecology and evolution, and the interfaces therein. We review relevant fields of research that have used A. aquaticus and draft a set of specific scientific questions that can be answered using this species. Specifically, we propose that studies on A. aquaticus can help understanding (i) the influence of host-microbiome interactions on organismal and ecosystem function, (ii) the relevance of biotic interactions in ecosystem processes, and (iii) how ecological conditions and evolutionary forces facilitate phenotypic diversification.

A neglected conceptual problem regarding phenotypic plasticity's role in adaptive evolution: The importance of genetic covariance and social drive

There is tantalizing evidence that phenotypic plasticity can buffer novel, adaptive genetic variants long enough to permit their evolutionary spread, and this process is often invoked in explanations for rapid adaptive evolution. However, the strength and generality of evidence for it is controversial. We identify a conceptual problem affecting this debate: recombination, segregation, and independent assortment are expected to quickly sever associations between genes controlling novel adaptations and genes contributing to trait plasticity that facilitates the novel adaptations by reducing their indirect fitness costs. To make clearer predictions about this role of plasticity in facilitating genetic adaptation, we describe a testable genetic mechanism that resolves the problem: genetic covariance between new adaptive variants and trait plasticity that facilitates their persistence within populations. We identify genetic architectures that might lead to such a covariance, including genetic coupling via physical linkage and pleiotropy, and illustrate the consequences for adaptation rates using numerical simulations. Such genetic covariances may also arise from the social environment, and we suggest the indirect genetic effects that result could further accentuate the process of adaptation. We call the latter mechanism of adaptation social drive, and identify methods to test it. We suggest that genetic coupling of plasticity and adaptations could promote unusually rapid ‘runaway’ evolution of novel adaptations. The resultant dynamics could facilitate evolutionary rescue, adaptive radiations, the origin of novelties, and other commonly studied processes.

Should dispersers be fast learners? Modeling the role of cognition in dispersal syndromes

Both cognitive abilities and dispersal tendencies can vary strongly between individuals. Since cognitive abilities may help dealing with unknown circumstances, it is conceivable that dispersers may rely more heavily on learning abilities than residents. However, cognitive abilities are costly and leaving a familiar place might result in losing the advantage of having learned to deal with local conditions. Thus, individuals which invested in learning to cope with local conditions may be better off staying at their natal place. In order to disentangle the complex relationship between dispersal and learning abilities, we implemented individual-based simulations. By allowing for developmental plasticity, individuals could either become a 'resident' or 'dispersal' cognitive phenotype. The model showed that in general residents have higher learning abilities than dispersers. Dispersers evolve higher learning ability than residents when dispersers have long life spans and when dispersal occurs either early or late in life, thereby maximizing the time in one habitat patch. Time is crucial here, because the longer an individual resides in a location where it can use its learned knowledge or behavior, the more often it profits from it and thus eventually obtains a net benefit from its investment into learning. Both, longevity and the timing of dispersal within lifecycles determine the time individuals have to recoup that investment and thus crucially influence this correlation. We therefore suggest that species' life history will strongly impact the expected cognitive abilities of dispersers, relative to their resident conspecifics, and that cognitive abilities might be an integral part of dispersal syndromes.

Do I build or do I move? Adaptation by habitat construction versus habitat choice

Trait adaptation to a heterogeneous environment can occur through six modes: genetic differentiation of those traits, a jack-of-all-trades phenotypic uniformity, diversified bet-hedging, phenotypic plasticity, habitat choice, and habitat construction. A key question is what circumstances favor one mode over another, and how they might interact if a system can express more than one mode at a time. We examined the joint evolution of habitat choice and habitat construction using individual-based simulations. We manipulated when during the life cycle construction occurred and the fitness value of construction. We found that for our model habitat construction was nearly always favored over habitat choice, especially if construction happened after dispersal. Because of the ways that the various modes of adaptation interact with each other, there is no simple answer as to which will be favored; it depends on details of the biology and ecology of a given system.

Environmental heterogeneity promotes individual specialisation in habitat selection in a widely distributed seabird

Individual specialisations in behaviour are predicted to arise where divergence benefits fitness. Such specialisations are more likely in heterogeneous environments where there is both greater ecological opportunity and competition-driven frequency dependent selection. Such an effect could explain observed differences in rates of individual specialisation in habitat selection, as it offers individuals an opportunity to select for habitat types that maximise resource gain while minimising competition; however, this mechanism has not been tested before. Here, we use habitat selection functions to quantify individual specialisations while foraging by black-legged kittiwakes Rissa tridactyla, a marine top predator, at 15 colonies around the United Kingdom and Ireland, along a gradient of environmental heterogeneity. We find support for the hypothesis that individual specialisations in habitat selection while foraging are more prevalent in heterogeneous environments. This trend was significant across multiple dynamic habitat variables that change over short time-scales and did not arise through site fidelity, which highlights the importance of environmental processes in facilitating behavioural adaptation by predators. Individual differences may drive evolutionary processes, and therefore these results suggest that there is broad scope for the degree of environmental heterogeneity to determine current and future population, species and community dynamics.

The association between personalities, alternative breeding strategies and reproductive success in dunnocks

Although consistent between-individual differences in behaviour (i.e. animal personality) are ubiquitous in natural populations, relatively few studies have examined how personalities influence the formation of social relationships. Yet, behavioural characteristics of both sexes might be key when it comes to pair-bond formation, and cooperation with partners to successfully rear offspring. We here use a wild population of dunnocks (Prunella modularis) to first investigate whether individuals mate nonrandomly (i.e. assortative mating) with regard to four behavioural traits-flight-initiation distance (FID), provisioning, activity and vigilance-that differ in repeatability and have previously been associated with mating patterns and fitness in other species. Second, we test whether an individual's FID is associated with variability in the dunnocks' mating system (i.e. monogamous pairs vs. polygamous groups). Finally, we determine whether FID and provisioning of males and females associate with their reproductive success. We found no statistical support for assortative mating in FID between males and females. Interestingly, in polygamous groups, co-breeding males differed in their FIDs with dominant alpha males having significantly shorter FIDs compared with subordinate beta-males. Moreover, there was evidence for assortative mating in provisioning for alpha males and females in polygamous groups. We also found that male provisioning influenced reproductive success of both sexes, whereas female provisioning rates only positively correlated with her own but not their partner(s) reproductive output. Our results suggest that personality differences may have important implications for social relationships, the emergence of different mating patterns and ultimately reproductive success within populations.

Specialist versus Generalist at the Intraspecific Level: Functional Morphology and Substrate Preference of Mediodactylus kotschyi Geckos

Populations of the same species occupying different microhabitats can either exhibit generalized traits across them or display intraspecific variability, adapting to each microhabitat in order to maximize performance. Intraspecific variability contributes to the generation of diversity, following selection and adaptation, and understanding such variability is important for comprehending how individuals choose their microhabitats. Compared with interspecific variability, however, intraspecific variability in functional morphology and its relationship with microhabitat preference and use have been relatively little studied. Here we examined whether populations of the gecko Mediodactylus kotschyi that differ in the substrates they occupy display habitat-specific behaviors and differing morphologies associated with functional adaptation to their microhabitats. We collected 207 geckos from under or on rocks or on trees from seven populations in Greece. On large islands individuals occupy both substrates; whereas small islets are devoid of trees and the geckos are restricted to rocks, while on the mainland they are only found on trees. We determined gecko substrate preferences in the laboratory, together with their clinging abilities to the different substrates. We measured their limbs, digits, and claws and assessed how these measurements relate to clinging ability. Geckos from all populations preferred the tree made available to them, but this preference was not statistically significant. Geckos from both large and small islands clung better to the tree than to the rock in the laboratory, while those from the mainland clung similarly to both substrates. Geckos collected from trees had longer manual digits and hind limbs. Geckos collected from large and small islands had taller (longer on the dorso-ventral axis; henceforth "deeper") claws. Longer digits and deeper but shorter claws were associated with a better ability to cling to rocks. Our findings suggest that while M. kotschyi is potentially preferentially arboreal, due to the great variation and plasticity it possesses, it can successfully also exploit the habitats available on the smallest, treeless islets in the Aegean Sea. Our study suggests that the dichotomous use of generalist versus specialist in describing species' habitat use is oversimplified, and we suggest the use of a generalist-specialist gradient instead.

The interaction of resource use and gene flow on the phenotypic divergence of benthic and pelagic morphs of Icelandic Arctic charr (Salvelinus alpinus)

Conceptual models of adaptive divergence and ecological speciation in sympatry predict differential resource use, phenotype-environment correlations, and reduced gene flow among diverging phenotypes. While these predictions have been assessed in past studies, connections among them have rarely been assessed collectively. We examined relationships among phenotypic, ecological, and genetic variation in Arctic charr (Salvelinus alpinus) from six Icelandic localities that have undergone varying degrees of divergence into sympatric benthic and pelagic morphs. We characterized morphological variation with geometric morphometrics, tested for differential resource use between morphs using stable isotopes, and inferred the amount of gene flow from single nucleotide polymorphisms. Analysis of stable isotopic signatures indicated that sympatric morphs showed similar difference in resource use across populations, likely arising from the common utilization of niche space within each population. Carbon isotopic signature was also a significant predictor of individual variation in body shape and size, suggesting that variation in benthic and pelagic resource use is associated with phenotypic variation. The estimated percentage of hybrids between sympatric morphs varied across populations (from 0% to 15.6%) but the majority of fish had genotypes (ancestry coefficients) characteristic of pure morphs. Despite evidence of reduced gene flow between sympatric morphs, we did not detect the expected negative relationship between divergence in resource use and gene flow. Three lakes showed the expected pattern, but morphs in the fourth showed no detectable hybridization and had relatively low differences in resource use between them. This coupled with the finding that resource use and genetic differentiation had differential effects on body shape variation across populations suggests that reproductive isolation maintains phenotypic divergence between benthic and pelagic morphs when the effects of resource use are relatively low. Our ability to assess relationships between phenotype, ecology, and genetics deepens our understanding of the processes underlying adaptive divergence in sympatry.

Predator-specific responses and emergent multi-predator effects on oviposition site choice in grey treefrogs, Hyla chrysoscelis

Predators affect prey through both consumptive and non-consumptive effects (NCEs), and prey typically face threats from multiple simultaneous predators. While different predators have a variety of NCEs on prey, little is known regarding effects of simultaneous multiple predators on demographic habitat selection. Demographic habitat selection is unique among NCEs, especially in discrete habitat patches; decisions directly affect both distribution and abundance of species across habitat patches, rather than simply abundance and performance within patches. Our goal was to determine strength of avoidance responses to multiple species/species combinations of predatory fish, and responses to predator richness. We assessed responses of ovipositing grey treefrogs (Hyla chrysoscelis) to three predatory fish species and substitutive combination of species. In single-species treatments, treefrogs avoided only one species, Notemigonus crysoleucas. All two-species combinations, and the three-species combination, were avoided, including the Fundulus chrysotus × Noturus phaeus combination, of which neither were avoided alone. This suggests emergent properties of multiple predators, with potential interactive effects among cues themselves or in the perception of cues by treefrogs. Our results indicate effects of multiple predators are not predictable based on individual effects, and illustrate the importance and complexity of effects of demographic habitat selection on distribution and abundance.

Dietary-based developmental plasticity affects juvenile survival in an aquatic detritivore

Developmental plasticity is ubiquitous in natural populations, but the underlying causes and fitness consequences are poorly understood. For consumers, nutritional variation of juvenile diets is probably associated with plasticity in developmental rates, but little is known about how diet quality can affect phenotypic trajectories in ways that might influence survival to maturity and lifetime reproductive output. Here, we tested how the diet quality of a freshwater detritivorous isopod (Asellus aquaticus), in terms of elemental ratios of diet (i.e. carbon : nitrogen : phosphorus; C : N : P), can affect (i) developmental rates of body size and pigmentation and (ii) variation in juvenile survival. We reared 1047 individuals, in a full-sib split-family design (29 families), on either a high- (low C : P, C : N) or low-quality (high C : P, C : N) diet, and quantified developmental trajectories of body size and pigmentation for every individual over 12 weeks. Our diet contrast caused strong divergence in the developmental rates of pigmentation but not growth, culminating in a distribution of adult pigmentation spanning the broad range of phenotypes observed both within and among natural populations. Under low-quality diet, we found highest survival at intermediate growth and pigmentation rates. By contrast, survival under high-quality diet survival increased continuously with pigmentation rate, with longest lifespans at intermediate growth rates and high pigmentation rates. Building on previous work which suggests that visual predation mediates the evolution of cryptic pigmentation in A. aquaticus, our study shows how diet quality and composition can generate substantial phenotypic variation by affecting rates of growth and pigmentation during development in the absence of predation.

Adaptation to elevation but limited local adaptation in an amphibian

We performed a reciprocal transplant experiment to estimate "parallel" adaptation to elevation and "unique" adaptation to local sites at the same elevation, using the frog Rana temporaria in the Swiss Alps. It is important to distinguish these two processes because they have different implications for population structure and ecological specialization. Larvae were reared from hatching to metamorphosis within enclosures installed in their pond of origin, in three foreign ponds at the same elevation, and in four ponds at different elevation (1500-2000 m higher or lower). There were two source populations from each elevation, and adults were held in a common environment for 1 year before they were crossed to produce offspring for the experiment. Fitness was a measure that integrated larval survival, development rate, and body size. Parallel adaptation to elevation was indicated by an advantage at the home elevation (11.5% fitness difference at low elevation and 47% at high elevation). This effect was stronger than that observed in most other studies, according to a survey of previous transplant experiments across elevation (N = 8 animal species and 71 plants). Unique local adaptation within elevational zones was only 0.3-0.7 times as strong as parallel adaptation, probably because gene flow is comparatively high among nearby wetlands at the same elevation. The home-elevation advantage may reduce gene flow across the elevational gradient and enable the evolution of habitat races specialized on elevation.