Genotype x environment interaction for male attractiveness in an acoustic moth: evidence for plasticity and canalization

The lek paradox arises when choosy females deplete the genetic variance for male display traits from a population, yet substantial additive genetic variation (V_A) in male traits persists. Thus, the lek paradox can be more generally stated as one of the most fundamental evolutionary questions: What maintains genetic variation in natural populations? One solution to this problem may be found in the condition‐dependent nature of many sexually selected traits. Genotype × environment (G × E) interactions can maintain V_A under conditions of environmental heterogeneity provided certain restrictions are met, although antagonistic pleiotropy has also been proposed as a mechanism. Here, we provide evidence for G × E interactions and against the role of antagonistic pleiotropy in the maintenance of V_A for sexually selected traits. Using inbred lines of the lesser waxmoth Achroia grisella, we measured V_A for song attractiveness, condition and development rate under different competitive environments and found that genotypes differed in their plasticity. We argue that variation persists in natural populations because G × E interactions prevent any one variant from producing the optimal phenotype across all environments.     

A POPULATION GENETIC THEORY OF CANALIZATION

Canalization is the suppression of phenotypic variation. Depending on the causes of phenotypic variation, one speaks either of genetic or environmental canalization. Genetic canalization describes insensitivity of a character to mutations, and the insensitivity to environmental factors is called environmental canalization. Genetic canalization is of interest because it influences the availability of heritable phenotypic variation to natural selection, and is thus potentially important in determining the pattern of phenotypic evolution. In this paper a number of population genetic models are considered of a quantitative character under stabilizing selection. The main purpose of this study is to define the population genetic conditions and constraints for the evolution of canalization. Environmental canalization is modeled as genotype specific environmental variance. It is shown that stabilizing selection favors genes that decrease environmental variance of quantitative characters. However, the theoretical limit of zero environmental variance has never been observed. Of the many ways to explain this fact, two are addressed by our model. It is shown that a “canalization limit” is reached if canalizing effects of mutations are correlated with direct effects on the same character. This canalization limit is predicted to be independent of the strength of stabilizing selection, which is inconsistent with recent experimental data (Sterns et al. 1995). The second model assumes that the canalizing genes have deleterious pleiotropic effects. If these deleterious effects are of the same magnitude as all the other mutations affecting fitness very strong stabilizing selection is required to allow the evolution of environmental canalization. Genetic canalization is modeled as an influence on the average effect of mutations at a locus of other genes. It is found that the selection for genetic canalization critically depends on the amount of genetic variation present in the population. The more genetic variation, the stronger the selection for canalizing effects. All factors that increase genetic variation favor the evolution of genetic canalization (large population size, high mutation rate, large number of genes). If genetic variation is maintained by mutation-selection balance, strong stabilizing selection can inhibit the evolution of genetic canalization. Strong stabilizing selection eliminates genetic variation to a level where selection for canalization does not work anymore. It is predicted that the most important characters (in terms of fitness) are not necessarily the most canalized ones, if they are under very strong stabilizing selection (k > 0.2V_e). The rate of decrease of mutational variance V_m is found to be less than 10% of the initial V_m. From this result it is concluded that characters with typical mutational variances of about 10^–3 V_e are in a metastable state where further evolution of genetic canalization is too slow to be of importance at a microevolutionary time scale. The implications for the explanation of macroevolutionary patterns are discussed.     

On the relation between genetic and environmental variability in animals

Summary If a phenotypic character is under stabilizing selection, the selective disadvantage of a nonoptimal genotype will decrease exponentially to zero as the proportion of phenotypic variation that is environmental in origin -V _e /V _p - increases. Under the modified mutation-drift hypothesis of genetic polymorphism, the proportion of mutations that are effectively neutral and average heterozygosity should increase with this ratio. Invertebrates, because of their small size, fast development, and low degree of homeostasis (relative to vertebrates), are expected to show a larger environmental component of phenotypic variation than vertebrates. This may help explain why invertebrates are in general more genetically variable than vertebrates and why, when laboratory populations ofDrosophila are maintained in heterogeneous environments, genetic variability is lost less rapidly than when they are kept in constant conditions.     

Heritability and evolvability of fitness and nonfitness traits: Lessons from livestock

Data from natural populations have suggested a disconnection between trait heritability (variance standardized additive genetic variance, V_A) and evolvability (mean standardized V_A) and emphasized the importance of environmental variation as a determinant of trait heritability but not evolvability. However, these inferences are based on heterogeneous and often small datasets across species from different environments. We surveyed the relationship between evolvability and heritability in >100 traits in farmed cattle, taking advantage of large sample sizes and consistent genetic approaches. Heritability and evolvability estimates were positively correlated (r = 0.37/0.54 on untransformed/log scales) reflecting a substantial impact of V_A on both measures. Furthermore, heritabilities and residual variances were uncorrelated. The differences between this and previously described patterns may reflect lower environmental variation experienced in farmed systems, but also low and heterogeneous quality of data from natural populations. Similar to studies on wild populations, heritabilities for life‐history and behavioral traits were lower than for other traits. Traits having extremely low heritabilities and evolvabilities (17% of the studied traits) were almost exclusively life‐history or behavioral traits, suggesting that evolutionary constraints stemming from lack of genetic variability are likely to be most common for classical “fitness” (cf. life‐history) rather than for “nonfitness” (cf. morphological) traits.     

Population size is weakly related to quantitative genetic variation and trait differentiation in a stream fish

How population size influences quantitative genetic variation and differentiation among natural, fragmented populations remains unresolved. Small, isolated populations might occupy poor quality habitats and lose genetic variation more rapidly due to genetic drift than large populations. Genetic drift might furthermore overcome selection as population size decreases. Collectively, this might result in directional changes in additive genetic variation (V_A) and trait differentiation (Q_ST) from small to large population size. Alternatively, small populations might exhibit larger variation in V_A and Q_ST if habitat fragmentation increases variability in habitat types. We explored these alternatives by investigating V_A and Q_ST using nine fragmented populations of brook trout varying 50‐fold in census size N (179–8416) and 10‐fold in effective number of breeders, N_b (18–135). Across 15 traits, no evidence was found for consistent differences in V_A and Q_ST with population size and almost no evidence for increased variability of V_A or Q_ST estimates at small population size. This suggests that (i) small populations of some species may retain adaptive potential according to commonly adopted quantitative genetic measures and (ii) populations of varying sizes experience a variety of environmental conditions in nature, however extremely large studies are likely required before any firm conclusions can be made.     

Selection,structure and the heritability of behaviour

Characters which are closely linked to fitness often have low heritabilities (V_A/V_P). Low heritabilities could be because of low additive genetic variation (V_A), that had been depleted by directional selection. Alternatively, low heritabilities may be caused by large residual variation (V_R=V_P – V_A) compounded at a disproportionately higher rate than V_A across integrated characters. Both hypotheses assume that each component of quantitative variation has an independent effect on heritability. However, V_A and V_R may also covary, in which case differences in heritability cannot be fully explained by the independent effects of elimination‐selection or compounded residual variation. We compared the central tendency of published behavioural heritabilities (mean=0.31, median=0.23) with morphological and life history data collected by 26 ). Average behavioural heritability was not significantly different from average life history heritability, but both were smaller than average morphological heritability. We cross‐classified behavioural traits to test whether variation in heritability was related to selection (dominance, domestic/wild) or variance compounding (integration level). There was a significant three‐way interaction between indices of selection and variance compounding, related to the absence of either effect at the highest integration level. At lower integration levels, high dominance variance indicated effects of selection. It was also indicated by the low CV_A of domestic species. At the same time CV_R increased disproportionately faster than CV_A across integration levels, demonstrating variance compounding. However, neither CV_R nor CV_A had a predominant effect on heritability. The partial regression coefficients of CV_R and CV_A on heritability were similar and a path analysis indicated that their (positive) correlation was also necessary to explain variation in heritability. These results suggest that relationships between additive genetic and residual components of quantitative genetic variation can constrain their independent direct effects on behavioural heritability.     

The effect of trait type and strength of selection on heritability and evolvability in an island bird population

The heritability (h²) of fitness traits is often low. Although this has been attributed to directional selection having eroded genetic variation in direct proportion to the strength of selection, heritability does not necessarily reflect a trait's additive genetic variance and evolutionary potential (“evolvability”). Recent studies suggest that the low h² of fitness traits in wild populations is caused not by a paucity of additive genetic variance (V_A) but by greater environmental or nonadditive genetic variance (V_R). We examined the relationship between h² and variance‐standardized selection intensities (i or β_σ), and between evolvability (I_A:V_A divided by squared phenotypic trait mean) and mean‐standardized selection gradients (β_μ). Using 24 years of data from an island population of Savannah sparrows, we show that, across diverse traits, h² declines with the strength of selection, whereas I_A and I_R (V_R divided by squared trait mean) are independent of the strength of selection. Within trait types (morphological, reproductive, life‐history), h², I_A, and I_R are all independent of the strength of selection. This indicates that certain traits have low heritability because of increased residual variance due to the age at which they are expressed or the multiple factors influencing their expression, rather than their association with fitness.     

Quantifying natural seasonal variation in mutation parameters with mutation accumulation lines

Mutations create novel genetic variants, but their contribution to variation in fitness and other phenotypes may depend on environmental conditions. Furthermore, natural environments may be highly heterogeneous. We assessed phenotypes associated with survival and reproductive success in over 30,000 plants representing 100 mutation accumulation lines of Arabidopsis thaliana across four temporal environments at a single field site. In each of the four assays, environmental variance was substantially larger than mutational variance. For some traits, whether mutational variance was significantly varied between seasons. The founder genotype had mean trait values near the mean of the distribution of the mutation accumulation lines in all field experiments. New mutations also contributed more phenotypic variation than would be predicted, given phenotypic and sequence‐level divergence among natural populations of A. thaliana. The combination of large environmental variance with a mean effect of mutation near zero suggests that mutations could contribute substantially to standing genetic variation.     

Condition dependence and the maintenance of genetic variance in a sexually dimorphic black scavenger fly

The maintenance of genetic variation in traits under strong sexual selection is a longstanding problem in evolutionary biology. The genic capture model proposes that this problem can be explained by the evolution of condition dependence in exaggerated male traits. We tested the predictions that condition dependence should be more pronounced in male sexual traits and that genetic variance in expression of these traits should increase under stress as among‐genotype variation in overall condition is exposed. Genetic variance in female and nonsexual traits should, by contrast, be similar across environments as a result of stabilizing selection on trait expression. The relationship between the degree of sexual dimorphism, condition dependence and additive genetic variance (V_a) was assessed for two morphological traits (body size and relative fore femur width) affecting male mating success in the black scavenger fly Sepsis punctum (Diptera: Sepsidae) and for development time (a nonsexual trait often correlated with body size). We compared trait expression between the sexes for two cross‐continental populations that differ in degree of sexual dimorphism (Ottawa and Zurich). Condition dependence was indeed most pronounced in males of the strongly dimorphic Zurich population (males larger), and V_a was similar for males and females unless the trait was strongly sex specific and condition dependent. Contrary to prediction, however, V_a primarily increased under food limitation in both sexes, and genetic variance in fore femur width was low to nil, perhaps depleted by putatively strong sexual selection. Solely for body size of Zurich males, V_a increased more in males than females at limited food, in accordance with the predictions of the genic capture model. Overall therefore, quantitative genetic evidence in support of the model was inconsistent and weak at best.     

Genetic variance in fitness and its cross-sex covariance predict adaptation during experimental evolution

The additive genetic variation (V_A) of fitness in a population is of particular importance to quantify its adaptive potential and predict its response to rapid environmental change. Recent statistical advances in quantitative genetics and the use of new molecular tools have fostered great interest in estimating fitness V_A in wild populations. However, the value of V_A for fitness in predicting evolutionary changes over several generations remains mostly unknown. In our study, we addressed this question by combining classical quantitative genetics with experimental evolution in the model organism Tribolium castaneum (red flour beetle) in three new environmental conditions (Dry, Hot, Hot-Dry). We tested for potential constraints that might limit adaptation, including environmental and sex genetic antagonisms captured by negative genetic covariance between environments and female and male fitness, respectively. Observed fitness changes after 20 generations mainly matched our predictions. Given that body size is commonly used as a proxy for fitness, we also tested how this trait and its genetic variance (including nonadditive genetic variance) were impacted by environmental stress. In both traits, genetic variances were sex and condition dependent, but they differed in their variance composition, cross-sex and cross-environment genetic covariances, as well as in the environmental impact on V_A.     

EXPRESSION OF GENETIC VARIATION IN BODY SIZE OF THE COLLARED FLYCATCHER UNDER DIFFERENT ENVIRONMENTAL CONDITIONS

Heritability of body size in two experimentally created environments, representing good and poor feeding conditions, respectively, was estimated using cross-fostered collared flycatcher Ficedula albicollis nestlings. Young raised under poor feeding conditions attained smaller body size (tarsus length) than their full-sibs raised under good feeding conditions. Parent-offspring regressions revealed lower heritability (h²) of body size under poor than under good feeding conditions. Hence, as the same set of parents were used in the estimation of h² in both environments, this suggests environment-dependent change in additive genetic component of variance (V_A), or that the genetic correlation between parental and poor offspring environment was less than that between parental and good offspring environment. However, full-sib analyses failed to find evidence for genotype-environment interactions, although the power of these tests might have been low. Full-sib heritabilities in both environments tended to be higher than estimates from parent-offspring regressions, indicating that prehatching or early posthatching common environment/maternal effects might have inflated full-sib estimates of V_A. The effect of sibling competition on estimates of V_A was probably small as the nestling size-hierarchy at day 2 posthatch was not generally correlated with size-hierarchy at fledging. Furthermore, there was no correlation between maternal body condition during the incubation and final size of offspring, indicating that direct maternal effects related to nutritional status were small. A review of earlier quantitative genetic studies of body size variation in birds revealed that in eight of nine cases, heritability of body size was lower in poor than in good environmental conditions. The main implication of this relationship will be a decreased evolutionary response to selection under poor environmental conditions. On the other hand, this will retard the loss of genetic variation by reducing the accuracy of selection and might help explain the moderate to high heritabilities of body-size traits under good environmental conditions.     

Spatio‐temporal variation in fitness responses to contrasting environments in Arabidopsis thaliana

The evolutionary response of organisms to global climate change is expected to be strongly conditioned by preexisting standing genetic variation. In addition, natural selection imposed by global climate change on fitness‐related traits can be heterogeneous over time. We estimated selection of life‐history traits of an entire genetic lineage of the plant Arabidopsis thaliana occurring in north‐western Iberian Peninsula that were transplanted over multiple years into two environmentally contrasting field sites in southern Spain, as southern environments are expected to move progressively northwards with climate change in the Iberian Peninsula. The results indicated that natural selection on flowering time prevailed over that on recruitment. Selection favored early flowering in six of eight experiments and late flowering in the other two. Such heterogeneity of selection for flowering time might be a powerful mechanism for maintaining genetic diversity in the long run. We also found that north‐western A. thaliana accessions from warmer environments exhibited higher fitness and higher phenotypic plasticity for flowering time in southern experimental facilities. Overall, our transplant experiments suggested that north‐western Iberian A. thaliana has the means to cope with increasingly warmer environments in the region as predicted by trends in global climate change models.     

Evolution in heterogeneous environments and the potential of maintenance of genetic variation in traits of adaptive significance

The maintenance of genetic variation in traits of adaptive significance has been a major dilemma of evolutionary biology. Considering the pattern of increased genetic variation associated with environmental clines and heterogeneous environments, selection in heterogeneous environments has been proposed to facilitate the maintenance of genetic variation. Some models examining whether genetic variation can be maintained, in heterogeneous environments are reviewed. Genetic mechanisms that constrain evolution in quantitative genetic traits indicate that genetic variation can be maintained but when is not clear. Furthermore, no comprehensive models have been developed, likely due to the genetic and environmental complexity of this issue. Therefore, I have suggested two empirical approaches to provide insight for future theoretical and empirical research. Traditional path analysis has been a very powerful approach for understanding phenotypic selection. However, it requires substantial information on the biology of the study system to construct a causal model and alternatives. Exploratory path analysis is a data driven approach that uses the statistical relationships in the data to construct a set of models. For example, it can be used for understanding phenotypic selection in different environments, where there is no prior information to develop path models in the different environments. Data from Brassica rapa grown in different nutrients indicated that selection changed in the different environments. Experimental evolutionary studies will provide direct tests as to when genetic variation is maintained.     

NO EFFECT OF ENVIRONMENTAL HETEROGENEITY ON THE MAINTENANCE OF GENETIC VARIATION IN WING SHAPE IN DROSOPHILA MELANOGASTER

Theory suggests that heterogeneous environments should maintain more genetic variation within populations than homogeneous environments, yet experimental evidence for this effect in quantitative traits has been inconsistent. To examine the effect of heterogeneity on quantitative genetic variation, we maintained replicate populations of Drosophila melanogaster under treatments with constant temperatures, temporally variable temperature, or spatially variable temperature with either panmictic or limited migration. Despite observing differences in fitness and divergence in several wing traits between the environments, we did not find any differences in the additive genetic variance for any wing traits among any of the treatments. Although we found an effect of gene flow constraining adaptive divergence between cages in the limited migration treatment, it did not tend to increase within‐population genetic variance relative to any of the other treatments. The lack of any clear and repeatable patterns of response to heterogeneous versus homogeneous environments across several empirical studies suggests that a single general mechanism for the maintenance of standing genetic variation is unlikely; rather, the relative importance of putative mechanisms likely varies considerably from one trait and ecological context to another.     

ECOLOGICAL HISTORY AND EVOLUTION IN A NOVEL ENVIRONMENT: HABITAT HETEROGENEITY AND INSECT ADAPTATION TO A NEW HOST PLANT

Environmental heterogeneity has often been implicated in the maintenance of genetic variation. However, previous research has not considered how environmental heterogeneity might affect the rate of adaptation to a novel environment. In this study, I used an insect-plant system to test the hypothesis that heterogeneous environments maintain more genetic variation in fitness components in a novel environment than do uniform environments. To manipulate recent ecological history, replicate populations of the dipteran leafminer Liriomyza trifolii were maintained for 20 generations in one of three treatments: a heterogeneous environment that contained five species of host plant, and two uniform environments that contained either a susceptible chrysanthemum or tomato. The hypothesis that greater genetic variance for survivorship and developmental time on a new host plant (a leafminer-resistant chrysanthemum) would be maintained in the heterogeneous treatment relative to the uniform environments was then tested with a sib-analysis and a natural selection experiment. Populations from the heterogeneous host plant treatment had no greater genetic variance in either larval survivorship or developmental time on the new host than did populations from either of the other treatments. Moreover, the rate of adaptation to the new host did not differ between the ecological history treatments, although the populations from the uniform chrysanthemum treatment had higher mean survivorship throughout the selection experiment. The estimates of the heritability of larval survivorship from the sib-analysis and selection experiment were quite similar. These results imply that ecologically realistic levels of environmental heterogeneity will not necessarily maintain more genetic variance than uniform environments when traits expressed in a particular novel environment are considered.     

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.     

Reaction norms and the genetic basis of phenotypic plasticity in the wing pattern of the butterfly Bicyclus anynana

The genetic basis of the dry-wet season polyphenism of wing pattern in response to temperature shown by Bicyclus anynana was studied, using a split-family design over four temperatures. Reaction norms crossed, but were only linear in the three highest temperatures, and only when larval development time was used as the environmental axis. Significant full-sib additive variances (V_A) and heritabilities (h²) for plasticity were found using slopes of reaction norms in a bootstrap procedure. Heritabilities were lower in intermediate temperatures, mainly due to differences in the residual variances (V_R). There was no clear trend in V_A across temperatures, contrary to the expectation that V_A would have been depleted by natural selection at the extreme temperatures and not depleted at the intermediate temperatures which occur less frequently in the field. Unpredictability in the onset of the following season at intermediate temperatures might lead to selection for diverse flresponses resulting in relatively high V_Rs. Theoretical models linking reaction norms to genetic parameters in separate environments were difficult to apply in this study, particularly because they are based on the assumption that V_Rs are constant. However the reaction norm approach combined with quantitative genetics provided a valuable insight into the evolution of the observed polyphenism.     

CHARACTERIZING SELECTION ON PHENOTYPIC PLASTICITY IN RESPONSE TO NATURAL ENVIRONMENTAL HETEROGENEITY

Adaptive genetic differentiation and adaptive phenotypic plasticity can increase the fitness of plant lineages in heterogeneous environments. We examine the relative importance of genetic differentiation and plasticity in determining the fitness of the annual plant, Erodium cicutarium, in a serpentine grassland in California. Previous work demonstrated that the serpentine sites within this mosaic display stronger dispersal‐scale heterogeneity than nonserpentine sites. We conducted a reciprocal transplant experiment among six sites to characterize selection on plasticity expressed by 180 full‐sibling families in response to natural environmental heterogeneity across these sites. Multivariate axes of environmental variation were constructed using a principal components analysis of soil chemistry data collected at every experimental block. Simple linear regressions were used to characterize the intercept, and slope (linear and curvilinear) of reaction norms for each full‐sibling family in response to each axis of environmental variation. Multiple linear regression analyses revealed significant selection on trait means and slopes of reaction norms. Multivariate analyses of variance demonstrated genetic differentiation between serpentine and nonserpentine lineages in the expression of plasticity in response to three of the five axes of environmental variation considered. In all but one case, serpentine genotypes expressed a stronger adaptive plastic response than nonserpentine genotypes.     

Estimating the capacity of Chamaecrista fasciculata for adaptation to change in precipitation

Adaptation through natural selection may be the only means by which small and fragmented plant populations will persist through present day environmental change. A population's additive genetic variance for fitness (V_A(W)) represents its immediate capacity to adapt to the environment in which it exists. We evaluated this property for a population of the annual legume Chamaecrista fasciculata through a quantitative genetic experiment in the tallgrass prairie region of the Midwestern United States, where changing climate is predicted to include more variability in rainfall. To reduce incident rainfall, relative to controls receiving ambient rain, we deployed rain exclusion shelters. We found significant V_A(W) in both treatments. We also detected a significant genotype‐by‐treatment interaction for fitness, which suggests that the genetic basis of the response to natural selection will differ depending on precipitation. For the trait‐specific leaf area, we detected maladaptive phenotypic plasticity and an interaction between genotype and environment. Selection for thicker leaves was detected with increased precipitation. These results indicate capacity of this population of C. fasciculata to adapt in situ to environmental change.     

The effects of selection,drift and genetic variation on life‐history trait divergence among insular populations of natterjack toad,Bufo calamita

Although loss of genetic variation is frequently assumed to be associated with loss of adaptive potential, only few studies have examined adaptation in populations with little genetic variation. On the Swedish west coast, the northern fringe populations of the natterjack toad Bufo calamita inhabit an atypical habitat consisting of offshore rock islands. There are strong among‐population differences in the amount of neutral genetic variation, making this system suitable for studies on mechanisms of trait divergence along a gradient of within‐population genetic variation. In this study, we examined the mechanisms of population divergence using Q_ST–F_ST comparisons and correlations between quantitative and neutral genetic variation. Our results suggest drift or weak stabilizing selection across the six populations included in this study, as indicated by low Q_ST–F_ST values, lack of significant population × temperature interactions and lack of significant differences among the islands in breeding pond size. The six populations included in this study differed in both neutral and quantitative genetic variation. Also, the correlations between neutral and quantitative genetic variation tended to be positive, however, the relatively small number of populations prevents any strong conclusions based on these correlations. Contrary to the majority of Q_ST–F_ST comparisons, our results suggest drift or weak stabilizing selection across the examined populations. Furthermore, the low heritability of fitness‐related traits may limit evolutionary responses in some of the populations.