Behavioural responses to human‐induced environmental change

The initial response of individuals to human‐induced environmental change is often behavioural. This can improve the performance of individuals under sudden, large‐scale perturbations and maintain viable populations. The response can also give additional time for genetic changes to arise and, hence, facilitate adaptation to new conditions. On the other hand, maladaptive responses, which reduce individual fitness, may occur when individuals encounter conditions that the population has not experienced during its evolutionary history, which can decrease population viability. A growing number of studies find human disturbances to induce behavioural responses, both directly and by altering factors that influence fitness. Common causes of behavioural responses are changes in the transmission of information, the concentration of endocrine disrupters, the availability of resources, the possibility of dispersal, and the abundance of interacting species. Frequent responses are alterations in habitat choice, movements, foraging, social behaviour and reproductive behaviour. Behavioural responses depend on the genetically determined reaction norm of the individuals, which evolves over generations. Populations first respond with individual behavioural plasticity, whereafter changes may arise through innovations and the social transmission of behavioural patterns within and across generations, and, finally, by evolution of the behavioural response over generations. Only a restricted number of species show behavioural adaptations that make them thrive in severely disturbed environments. Hence, rapid human‐induced disturbances often decrease the diversity of native species, while facilitating the spread of invasive species with highly plastic behaviours. Consequently, behavioural responses to human‐induced environmental change can have profound effects on the distribution, adaptation, speciation and extinction of populations and, hence, on biodiversity. A better understanding of the mechanisms of behavioural responses and their causes and consequences could improve our ability to predict the effects of human‐induced environmental change on individual species and on biodiversity.     

Replicated evolution of integrated plastic responses during early adaptive divergence

Colonization of a novel environment is expected to result in adaptive divergence from the ancestral population when selection favors a new phenotypic optimum. Local adaptation in the new environment occurs through the accumulation and integration of character states that positively affect fitness. The role played by plastic traits in adaptation to a novel environment has generally been ignored, except for variable environments. We propose that if conditions in a relatively stable but novel environment induce phenotypically plastic responses in many traits, and if genetic variation exists in the form of those responses, then selection may initially favor the accumulation and integration of functionally useful plastic responses. Early divergence between ancestral and colonist forms will then occur with respect to their plastic responses across the gradient bounded by ancestral and novel environmental conditions. To test this, we compared the magnitude, integration, and pattern of plastic character responses in external body form induced by shallow versus open water conditions between two sunfish ecomorphs that coexist in four postglacial lakes. The novel sunfish ecomorph is present in the deeper open water habitat, whereas the ancestral ecomorph inhabits the shallow waters along the lake margin. Plastic responses by open water ecomorphs were more correlated than those of their local shallow water ecomorph in two of the populations, whereas equal levels of correlated plastic character responses occurred between ecomorphs in the other two populations. Small but persistent differences occurred between ecomorph pairs in the pattern of their character responses, suggesting a recent divergence. Open water ecomorphs shared some similarities in the covariance among plastic responses to rearing environment. Replication in the form of correlated plastic responses among populations of open water ecomorphs suggests that plastic character states may evolve under selection. Variation between ecomorphs and among lake populations in the covariance of plastic responses suggests the presence of genetic variation in plastic character responses. In three populations, open water ecomorphs also exhibited larger plastic responses to the environmental gradient than the local shallow water ecomorph. This could account for the greater integration of plastic responses in open water ecomorphs in two of the populations. This suggests that the plastic responses of local sunfish ecomorphs can diverge through changes in the magnitude and coordination of plastic responses. Although these results require further investigation, they suggest that early adaptive evolution in a novel environment can include changes to plastic character states. The genetic assimilation of coordinated plastic responses could result in the further, and possibly rapid, divergence of such populations and could also account for the evolution of genes of major effect that contribute to suites of phenotypic differences between divergent populations.     

Thermal tolerance in the keystone species Daphnia magna—a candidate gene and an outlier analysis approach

Changes in temperature have occurred throughout Earth's history. However, current warming trends exacerbated by human activities impose severe and rapid loss of biodiversity. Although understanding the mechanisms orchestrating organismal response to climate change is important, remarkably few studies document their role in nature. This is because only few systems enable the combined analysis of genetic and plastic responses to environmental change over long time spans. Here, we characterize genetic and plastic responses to temperature increase in the aquatic keystone grazer Daphnia magna combining a candidate gene and an outlier analysis approach. We capitalize on the short generation time of our species, facilitating experimental evolution, and the production of dormant eggs enabling the analysis of long‐term response to environmental change through a resurrection ecology approach. We quantify plasticity in the expression of 35 candidate genes in D. magna populations resurrected from a lake that experienced changes in average temperature over the past century and from experimental populations differing in thermal tolerance isolated from a selection experiment. By measuring expression in multiple genotypes from each of these populations in control and heat treatments, we assess plastic responses to extreme temperature events. By measuring evolutionary changes in gene expression between warm‐ and cold‐adapted populations, we assess evolutionary response to temperature changes. Evolutionary response to temperature increase is also assessed via an outlier analysis using EST‐linked microsatellite loci. This study provides the first insights into the role of plasticity and genetic adaptation in orchestrating adaptive responses to environmental change in D. magna.     

Facing change: forms and foundations of contemporary adaptation to biotic invasions

Ongoing adaptation in native populations to anthropogenic change both facilitates and challenges ecologically appropriate and sustainable management. Human disturbance promotes adaptive responses at the genomic, individual and population levels. Traits vary widely in whether adaptation occurs through plasticity or evolution, and these modes interact within and among traits. For example, plasticity in one trait may be adaptive because it permits homeostasis and lessens the intensity of selection in another. Both opportunity and catastrophe generate adaptive responses. Recently evolved adaptations characterize the responses of many native species to biotic invasions. Several well-known examples involve native phytophagous insects colonizing introduced plants. For example, our studies of North American and Australian soapberry bugs on nonindigenous plants demonstrate both diversifying and homogenizing contemporary evolution. Modes of adaptation differ among traits and populations and as a function of the host on which they develop. The genetic architecture of the evolving adaptations involves a substantial degree of nonadditive genetic variation. One important consequence of contemporary adaptation may be an enhanced capacity of native communities to provide adaptive biological control of invasive species. Conservation scientists may manipulate adaptation to achieve conservation goals, but must also decide how deeply they wish to attempt to control the phenotypes and genotypes of other species.     

Reconstructing changes in the genotype,phenotype, and climatic niche of an introduced species

An introduced species must contend with enormous environmental variation in its introduced range. In this study, we use niche models and ordination analyses to reconstruct changes in genotype, phenotype, and climatic niche of Johnsongrass Sorghum halepense, which is regarded as one of the world's most threatening invasive plants. In the United States, Johnsongrass has rapidly evolved within‐ and among‐population genetic diversity; our results show that genetic differentiation in expanding Johnsongrass populations has resulted in phenotypic variation that is consistent with habitat and climatic variation encountered during its expansion. Moreover, Johnsongrass expanded from agricultural to non‐agricultural habitat, and now, despite occupying overlapping ranges, extant agricultural and non‐agricultural populations are genetically and phenotypically distinct and manifest different plastic responses when encountering environmental variation. Non‐agricultural accessions are broadly distributed in climatic and geographic space and their fitness traits demonstrate plastic responses to common garden conditions that are consistent with local specialization. In contrast, agricultural accessions demonstrate ‘general purpose’ plastic responses and have more restricted climatic niches and geographic distributions. They also grow much larger than non‐agricultural accessions. If these differences are adaptive, our results suggest that adaptation to local habitat variation plays a crucial role in the ecology of this invader. Further, its success relates to its ability to succeed on dual fronts, by responding simultaneously to habitat and climate variability and by capitalizing on differential responses to these factors during its range expansion.     

A heuristic model on the role of plasticity in adaptive evolution: plasticity increases adaptation,population viability and genetic variation

An ongoing new synthesis in evolutionary theory is expanding our view of the sources of heritable variation beyond point mutations of fixed phenotypic effects to include environmentally sensitive changes in gene regulation. This expansion of the paradigm is necessary given ample evidence for a heritable ability to alter gene expression in response to environmental cues. In consequence, single genotypes are often capable of adaptively expressing different phenotypes in different environments, i.e. are adaptively plastic. We present an individual-based heuristic model to compare the adaptive dynamics of populations composed of plastic or non-plastic genotypes under a wide range of scenarios where we modify environmental variation, mutation rate and costs of plasticity. The model shows that adaptive plasticity contributes to the maintenance of genetic variation within populations, reduces bottlenecks when facing rapid environmental changes and confers an overall faster rate of adaptation. In fluctuating environments, plasticity is favoured by selection and maintained in the population. However, if the environment stabilizes and costs of plasticity are high, plasticity is reduced by selection, leading to genetic assimilation, which could result in species diversification. More broadly, our model shows that adaptive plasticity is a common consequence of selection under environmental heterogeneity, and hence a potentially common phenomenon in nature. Thus, taking adaptive plasticity into account substantially extends our view of adaptive evolution.     

Phenotypic plasticity: Eco-Devo and evolution

Phenotypic plasticity refers to the ability of an organism to alter its physiology/morphology/behavior in response to changes in environmental conditions. Although encompassing various phenomena spanning multi-ple levels of organization, most plastic responses seem to take place by altering gene expression and eventually altering ontogenetic trajectory in response to environmental variation. Epigenetic modifications provide a plausi-ble link between the environment and alterations in gene expression, and the alterations in phenotype based on environmentally induced epigenetic modifications can be inherited transgenerationally. Even closely related species and populations with different genotypes may exhibit differences in the patterns and the extents of plastic responses, indicating the wide existence of plasticity genes which are independent of trait means and directly respond to environmental stimuli by triggering phenotypic changes. The ability of plasticity is not only able to affect the adaptive evolution of species significantly, but is also an outcome of evolutionary processes. Therefore, phenotypic plasticity is a potentially important molder of adaptation and evolution.     

Does thermal plasticity align with local adaptation? An interspecific comparison of wing morphology in sepsid flies

Although genetic and plastic responses are sometimes considered as unrelated processes, their phenotypic effects may often align because genetic adaptation is expected to mirror phenotypic plasticity if adaptive, but run counter to it when maladaptive. Because the magnitude and direction of this alignment has further consequences for both the tempo and mode of adaptation, they are relevant for predicting an organisms’ reaction to environmental change. To better understand the interplay between phenotypic plasticity and genetic change in mediating adaptive phenotypic variation to climate variability, we here quantified genetic latitudinal variation and thermal plasticity in wing loading and wing shape in two closely related and widespread sepsid flies. Common garden rearing of 16 geographical populations reared across multiple temperatures revealed that wing loading decreases with latitude in both species. This pattern could be driven by selection for increased dispersal capacity in the cold. However, although allometry, sexual dimorphism, thermal plasticity and latitudinal differentiation in wing shape all show similar patterns in the two species, the relationship between the plastic and genetic responses differed between them. Although latitudinal differentiation (south to north) mirrored thermal plasticity (hot to cold) in Sepsis punctum, there was no relationship in Sepsis fulgens. While this suggests that thermal plasticity may have helped to mediate local adaptation in S. punctum, it also demonstrates that genetic wing shape differentiation and its relation to thermal plasticity may be complex and idiosyncratic, even among ecologically similar and closely related species. Hence, genetic responses can, but do not necessarily, align with phenotypic plasticity induced by changing environmental selection pressures.     

Landscape genomic signatures indicate reduced gene flow and forest‐associated adaptive divergence in an endangered neotropical turtle

Human‐induced transformations of ecosystems usually result in fragmented populations subject to increased extinction risk. Fragmentation is also often associated with novel environmental heterogeneity, which in combination with restricted gene flow may increase the opportunity for local adaptation. To manage at‐risk populations in these landscapes, it is important to understand how gene flow is changing, and how populations respond to habitat loss. We conducted a landscape genomics analysis using Restriction‐site Associated DNA sequencing to investigate the evolutionary response of the critically endangered Dahl's Toad‐headed turtle (Mesoclemmys dahli) to severe habitat modification. The species has lost almost all of its natural habitat in the southwestern part of its range and about 70% in the northeast. Based on least cost path analysis across different resistance surfaces for 3,211 SNPs, we found that the landscape matrix is restricting gene flow, causing the fragmentation of the species into at least six populations. Genome scans and allele‐environment association analyses indicate that the population fragments in the deforested grasslands of the southwest are adaptively different from those in the more forested northeast. Populations in areas with no forest had low levels of adaptive genetic diversity and the fixation of ancestrally‐polymorphic SNPs, consistent with directional selection in this novel environment. Our results suggest that this forest‐stream specialist is adapting to pond‐grassland conditions, but it is also suffering from negative consequences of habitat loss, including genetic erosion, isolation, small effective population sizes, and inbreeding. We recommend gene flow restoration via genetic rescue to counteract these threats, and provide guidance for this strategy.     

Role of phenotypic plasticity and population differentiation in adaptation to novel environmental conditions

Species can adapt to new environmental conditions either through individual phenotypic plasticity, intraspecific genetic differentiation in adaptive traits, or both. Wild emmer wheat, Triticum dicoccoides, an annual grass with major distribution in Eastern Mediterranean region, is predicted to experience in the near future, as a result of global climate change, conditions more arid than in any part of the current species distribution. To understand the role of the above two means of adaptation, and the effect of population range position, we analyzed reaction norms, extent of plasticity, and phenotypic selection across two experimental environments of high and low water availability in two core and two peripheral populations of this species. We studied 12 quantitative traits, but focused primarily on the onset of reproduction and maternal investment, which are traits that are closely related to fitness and presumably involved in local adaptation in the studied species. We hypothesized that the population showing superior performance under novel environmental conditions will either be genetically differentiated in quantitative traits or exhibit higher phenotypic plasticity than the less successful populations. We found the core population K to be the most plastic in all three trait categories (phenology, reproductive traits, and fitness) and most successful among populations studied, in both experimental environments; at the same time, the core K population was clearly genetically differentiated from the two edge populations. Our results suggest that (1) two means of successful adaptation to new environmental conditions, phenotypic plasticity and adaptive genetic differentiation, are not mutually exclusive ways of achieving high adaptive ability; and (2) colonists from some core populations can be more successful in establishing beyond the current species range than colonists from the range extreme periphery with conditions seemingly closest to those in the new environment.     

Comparing the consequences of natural selection,adaptive phenotypic plasticity,and matching habitat choice for phenotype–environment matching,population genetic structure,and reproductive isolation in meta‐populations

Organisms commonly experience significant spatiotemporal variation in their environments. In response to such heterogeneity, different mechanisms may act that enhance ecological performance locally. However, depending on the nature of the mechanism involved, the consequences for populations may differ greatly. Building on a previous model that investigated the conditions under which different adaptive mechanisms (co)evolve, this study compares the ecological and evolutionary population consequences of three very different responses to environmental heterogeneity: matching habitat choice (directed gene flow), adaptive plasticity (associated with random gene flow), and divergent natural selection. Using individual‐based simulations, we show that matching habitat choice can have a greater adaptive potential than plasticity or natural selection: it allows for local adaptation while protecting genetic polymorphism despite global mating or strong environmental changes. Our simulations further reveal that increasing environmental fluctuations and unpredictability generally favor the emergence of specialist genotypes but that matching habitat choice is better at preventing local maladaptation by individuals. This confirms that matching habitat choice can speed up the genetic divergence among populations, cause indirect assortative mating via spatial clustering, and hence even facilitate sympatric speciation. This study highlights the potential importance of directed dispersal in local adaptation and speciation, stresses the difficulty of deriving its operation from nonexperimental observational data alone, and helps define a set of ecological conditions which should favor its emergence and subsequent detection in nature.     

Genetic analysis of differentiation among breeding ponds reveals a candidate gene for local adaptation in Rana arvalis

One of the main questions in evolutionary and conservation biology is how geographical and environmental features of the landscape shape neutral and adaptive genetic variation in natural populations. The identification of genomic polymorphisms that account for adaptive variation can aid in finding candidate loci for local adaptation. Consequently, a comparison of spatial patterns in neutral markers and loci under selection may help disentangle the effects of gene flow, genetic drift and selection at the landscape scale. Many amphibians breed in wetlands, which differ in environmental conditions and in the degree of isolation, enhancing the potential for local adaptation. We used microsatellite markers to measure genetic differentiation among 17 local populations of Rana arvalis breeding in a network of wetlands. We found that locus RC08604 deviated from neutral expectations, suggesting that it is a good candidate for directional selection. We used a genetic network analysis to show that the allele distribution in this locus is correlated with habitat characteristics, whereas this was not the case at neutral markers that displayed a different allele distribution and population network in the study area. The graph approach illustrated the genomic heterogeneity (neutral loci vs. the candidate locus for directional selection) of gene exchange and genetic divergence among populations under directional selection. Limited gene flow between wetlands was only observed at the candidate genomic region under directional selection. RC08604 is partially located inside an up‐regulated thyroid‐hormone receptor (TRβ) gene coordinating the expression of other genes during metamorphosis and appears to be linked with variation in larval life‐history traits found among R. arvalis populations. We suggest that directional selection on genes coding larval life‐history traits is strong enough to maintain the divergence in these genomic regions, reducing the effective recombination of locally adapted alleles but not in other regions of the genome. Integrating this knowledge into conservation plans at the landscape scale will improve the design of management strategies to preserve adaptive genetic diversity in wetland networks.     

The success of assisted colonization and assisted gene flow depends on phenology

Global warming will jeopardize the persistence and genetic diversity of many species. Assisted colonization, or the movement of species beyond their current range boundary, is a conservation strategy proposed for species with limited dispersal abilities or adaptive potential. However, species that rely on photoperiodic and thermal cues for development may experience conflicting signals if transported across latitudes. Relocating multiple, distinct populations may remedy this quandary by expanding genetic variation and promoting evolutionary responses in the receiving habitat – a strategy known as assisted gene flow. To better inform these policies, we planted seeds from latitudinally distinct populations of the annual legume, Chamaecrista fasciculata, in a potential future colonization site north of its current range boundary. Plants were exposed to ambient or elevated temperatures via infrared heating. We monitored several life history traits and estimated patterns of natural selection to determine the adaptive value of plastic responses. To assess the feasibility of assisted gene flow between phenologically distinct populations, we counted flowers each day and estimated the degree of temporal isolation between populations. Increased temperatures advanced each successive phenological trait more than the last, resulting in a compressed life cycle for all but the southern‐most population. Warming altered patterns of selection on flowering onset and vegetative biomass. Population performance was dependent on latitude of origin, with the northern‐most population performing best under ambient conditions and the southern‐most performing most poorly, even under elevated temperatures. Among‐population differences in flowering phenology limited the potential for genetic exchange among the northern‐ and southern‐most populations. All plastic responses to warming were neutral or adaptive; however, photoperiodic constraints will likely necessitate evolutionary responses for long‐term persistence, especially when involving populations from disparate latitudes. With strategic planning, our results suggest that assisted colonization and assisted gene flow may be feasible options for preservation.     

Potential for adaptive evolution at species range margins: contrasting interactions between red coral populations and their environment in a changing ocean

Studying population‐by‐environment interactions (PEIs) at species range margins offers the opportunity to characterize the responses of populations facing an extreme regime of selection, as expected due to global change. Nevertheless, the importance of these marginal populations as putative reservoirs of adaptive genetic variation has scarcely been considered in conservation biology. This is particularly true in marine ecosystems for which the deep refugia hypothesis proposes that disturbed shallow and marginal populations of a given species can be replenished by mesophotic ones. This hypothesis therefore assumes that identical PEIs exist between populations, neglecting the potential for adaptation at species range margins. Here, we combine reciprocal transplant and common garden experiments with population genetics analyses to decipher the PEIs in the red coral, Corallium rubrum. Our analyses reveal partially contrasting PEIs between shallow and mesophotic populations separated by approximately one hundred meters, suggesting that red coral populations may potentially be locally adapted to their environment. Based on the effective population size and connectivity analyses, we posit that genetic drift may be more important than gene flow in the adaptation of the red coral. We further investigate how adaptive divergence could impact population viability in the context of warming and demonstrate differential phenotypic buffering capacities against thermal stress. Our study questions the relevance of the deep refugia hypothesis and highlights the conservation value of marginal populations as a putative reservoir of adaptive genetic polymorphism.     

LOCAL ADAPTATION MAINTAINS CLINAL VARIATION IN MELANIN‐BASED COLORATION OF EUROPEAN BARN OWLS (TYTO ALBA)

Ecological parameters vary in space, and the resulting heterogeneity of selective forces can drive adaptive population divergence. Clinal variation represents a classical model to study the interplay of gene flow and selection in the dynamics of this local adaptation process. Although geographic variation in phenotypic traits in discrete populations could be remainders of past adaptation, maintenance of adaptive clinal variation requires recurrent selection. Clinal variation in genetically determined traits is generally attributed to adaptation of different genotypes to local conditions along an environmental gradient, although it can as well arise from neutral processes. Here, we investigated whether selection accounts for the strong clinal variation observed in a highly heritable pheomelanin‐based color trait in the European barn owl by comparing spatial differentiation of color and of neutral genes among populations. Barn owl's coloration varies continuously from white in southwestern Europe to reddish‐brown in northeastern Europe. A very low differentiation at neutral genetic markers suggests that substantial gene flow occurs among populations. The persistence of pronounced color differentiation despite this strong gene flow is consistent with the hypothesis that selection is the primary force maintaining color variation among European populations. Therefore, the color cline is most likely the result of local adaptation.     

Adaptation in isolated populations: when does it happen and when can we tell?

Isolated populations with novel phenotypes present an exciting opportunity to uncover the genetic basis of ecologically significant adaptation, and genomic scans have often, but not always, led to candidate genes directly related to an adaptive phenotype. However, in many cases these populations were established by a severe bottleneck, which can make identifying targets of selection problematic. Here, we simulate severe bottlenecks and subsequent selection on standing variation, mimicking adaptation after establishment of a new small population, such as an island or an artificial selection experiment. Using simulations of single loci under positive selection and population genetics theory, we examine how population size and age of the population isolate affect the ability of outlier scans for selection to identify adaptive alleles using both single‐site measures and haplotype structure. We find and explain an optimal combination of selection strength, starting frequency, and age of the adaptive allele, which we refer to as a Goldilocks zone, where adaptation is likely to occur and yet the adaptive variants are most likely to derive from a single ancestor (a ‘hard’ selective sweep); in this zone, four commonly used statistics detect selection with high power. Real‐world examples of both island colonization and experimental evolution studies are discussed. Our study provides concrete considerations to be made before embarking on whole‐genome sequencing of differentiated populations.     

Selection for population‐specific adaptation shaped patterns of variation in the photoperiod pathway genes in Arabidopsis lyrata during post‐glacial colonization

Spatially varying selection can lead to population‐specific adaptation, which is often recognized at the phenotypic level; however, the genetic evidence is weaker in many groups of organisms. In plants, environmental shifts that occur due to colonization of a novel environment may require adaptive changes in the timing of growth and flowering, which are often governed by location‐specific environmental cues such as day length. We studied locally varying selection in 19 flowering time loci in nine populations of the perennial herb Arabidopsis lyrata, which has a wide but patchy distribution in temperate and boreal regions of the northern hemisphere. The populations differ in their recent population demographic and colonization histories and current environmental conditions, especially in the growing season length. We searched for population‐specific molecular signatures of directional selection by comparing a set of candidate flowering time loci with a genomic reference set within each population using multiple approaches and contrasted the patterns of different populations. The candidate loci possessed approximately 20% of the diversity of the reference loci. On average the flowering time loci had more rare alleles (a smaller Tajima's D) and an excess of highly differentiated sites relative to the reference, suggesting positive selection. The strongest signal of selection was detected in photoperiodic pathway loci in the colonizing populations of Northwestern Europe, whereas no evidence of positive selection was detected in the Central European populations. These findings emphasized the population‐specific nature of selection and suggested that photoperiodic adaptation was important during postglacial colonization of the species.     

Mate choice in a changing world

Human activities by altering environmental conditions are influencing the mate choice of animals. This is by impacts on: (i) the production and expression of traits evaluated by mate choosers; (ii) the transmission of information about potential mates to choosers; (iii) the reception and processing of the information by choosers; and (iv) the final mate choice. Here, I first discuss how these four stages of the mate‐choice process can be altered by environmental change, and how these alterations, in turn, can influence individuals, populations, and communities. Much evidence exists for human‐induced environmental changes influencing mate choice, but the consequences for the fitness of courters and choosers are less well known, and even less is known about the impact on population dynamics, species interactions and community composition. More evidence exists for altered mate‐choice systems influencing interspecific matings and thereby community composition and biodiversity. I then consider whether plastic adjustments and evolutionary changes can rescue adaptive mate‐choice systems, and reflect on the possibility of non‐adaptive mate‐choice systems becoming less maladaptive under environmental change. Much evidence exists for plastic adjustments of mate‐choice systems, but whether these are adaptive is seldom known, as is the contribution of genetic changes. Finally, I contemplate the possibility of mate‐choice systems rescuing populations from decline in changing environments. I explain how this is context dependent with both positive and negative outcomes possible. In summary, while much evidence exists for human‐induced environmental changes influencing mate‐choice systems, less is known about the consequences for ecological and evolutionary processes. Considering the importance that mate choice plays in determining individual fitness and population viability, the effects of environmental change on mate‐choice systems should be considered in studies on the ecological and evolutionary consequences of human disturbances to habitats.     

Shedding light on the evolution of plasticity in natural populations

Plasticity allows for changes in phenotype in response to environmental cues, often facilitating local adaptation to seasonal environments. Phenotypic plasticity alone, however, may not always be sufficient to ensure adaptation to new localities. In particular, changing cues associated with shifting seasonal regimes may no longer induce appropriate phenotypic responses in new environments ( Nicotra et al. 2010 ). Plastic responses must thus evolve to avoid being maladaptive. To date, the extent to which plastic responses can change and the genetic mechanisms by which this can happen have remained elusive. In this issue of Molecular Ecology, Blackman et al. (2011a) harness natural variation in flowering time among populations of the wild sunflower, Helianthus annuus, to demonstrate that plasticity has indeed evolved in this species. Remarkably, they are able to detect changes in gene expression that are associated with both a loss of plasticity and a reversal of the plastic response. These changes occur in two separate, but integrated, regulatory pathways controlling the transition to flowering, suggesting that complex regulatory networks that incorporate multiple environmental and developmental cues may facilitate the evolution of plastic responses. This study leverages knowledge from plant genetic models to provide a surprising level of insight into the evolution of an adaptive trait in a non‐model species. Through discoveries of the roles of gene duplication and network modularity in the evolution of plastic responses, the study raises questions about the degree to which species‐specific network architectures may act as a constraint to the potential of adaptation.     

Riverscape genomics of a threatened fish across a hydroclimatically heterogeneous river basin

Understanding how natural selection generates and maintains adaptive genetic diversity in heterogeneous environments is key to predicting the evolutionary response of populations to rapid environmental change. Detecting selection in complex spatial environments remains challenging, especially for threatened species where the effects of strong genetic drift may overwhelm signatures of selection. We carried out a basinwide riverscape genomic analysis in the threatened southern pygmy perch (Nannoperca australis), an ecological specialist with low dispersal potential. High‐resolution environmental data and 5162 high‐quality filtered SNPs were used to clarify spatial population structure and to assess footprints of selection associated with a steep hydroclimatic gradient and with human disturbance across the naturally and anthropogenically fragmented Murray–Darling Basin (Australia). Our approach included F_ST outlier tests to define neutral loci, and a combination of spatially explicit genotype–environment association analyses to identify candidate adaptive loci while controlling for the effects of landscape structure and shared population history. We found low levels of genetic diversity and strong neutral population structure consistent with expectations based on spatial stream hierarchy and life history. In contrast, variables related to precipitation and temperature appeared as the most important environmental surrogates for putatively adaptive genetic variation at both regional and local scales. Human disturbance also influenced the variation in candidate loci for adaptation, but only at a local scale. Our study contributes to understanding of adaptive evolution along naturally and anthropogenically fragmented ecosystems. It also offers a tangible example of the potential contributions of landscape genomics for informing in situ and ex situ conservation management of biodiversity.