Variation in morphological traits and trait asymmetry in field Drosophila serrata from marginal populations

Drosophila serrata occurs along the eastern coast of Australia with a southern range boundary near Sydney. To compare levels of phenotypic variation in marginal and central populations, we examined morphological variation in populations of this species from the southern range boundary and two more northerly populations. The populations differed for wing traits and there was an increase in wing size in the marginal locations which persisted under laboratory culture. The means of wing and bristle traits increased under laboratory culture, whereas wing trait coefficients of variation and variances decreased. Heritability estimates for wing size traits tended to be lower in the field compared with the laboratory, whereas bristle and crossvein length heritabilities were similar across environments. There was evidence for heritable variation in wing and bristle traits in both the marginal and more northern populations, suggesting that genetic variation was not limiting in marginal populations. Fluctuating asymmetry (FA) was also assessed as a measure of genomic and environmental stress. There were no consistent differences among populations for the FA of individual traits, or for a total FA score summed across traits. FA levels in field parents and laboratory‐reared progeny were similar. Overall, the results do not support the conjecture that levels of phenotypic and genetic variability differ between central and marginal D. serrata populations.     

Natural phenological variation in aspen (Populus tremula): the SwAsp collection

The genus Populus is currently the main model system for genetic, genomic, and physiological research in trees. Phenotypic variation in aspen (Populus tremula) populations growing in different environments across Sweden is expected to reflect genetic variation that is important for local adaptation. To analyze such natural phenotypic and genetic variation, the Swedish Aspen (SwAsp) Collection was established. Trees were taken from 12 different populations across Sweden, from 56° to 66° latitude north and planted in two common gardens in Ekebo (55.9°N) and Sävar (63.4°N). Data related to phenological and growth traits were collected during the second year of growth. Some traits like the date of bud set and leaf area duration showed strong clinal variation patterns with latitude in both field trials, but the date of bud flush did not change along a latitudinal cline. The phenological traits showed moderate within-populations heritabilities, although growth traits showed weaker clinal patterns and lower heritabilities than the phenological traits. This research forms the starting point for the development of the SwAsp collection, a resource facilitating analysis of the natural genetic variation in aspen, the elucidation of the structure and dynamics of aspen populations, and the future identification of the genes controlling adaptive traits using association mapping of selected candidate genes.     

Quantitative genetics of larval life-history traits in Rana temporaria in different environmental conditions

The degree to which genetic variation in a given trait varies among different populations of the same species and across different environments has seldom been quantified in wild vertebrate species. We investigated the expression of genetic variability and maternal effects in three larval life-history traits of the amphibian Rana temporaria. In a factorial laboratory experiment, five widely separated populations (max. 1600 km) were subjected to two different environmental treatments. Animal model analyses revealed that all traits were heritable (h(2) approximately 0.20) in all populations and under most treatment combinations. Although the cross-food treatment genetic correlations were close to unity, heritabilities under a restricted food regime tended to be lower than those under an ad libitum food regime. Likewise, maternal effects (m(2) approximately 0.05) were detected in most traits, and they tended to be most pronounced under restricted food conditions. We detected several cross-temperature genetic and maternal effects correlations that were lower than unity, suggesting that genotype-environment interactions and maternal effect-environment interactions are a significant source of phenotypic variation. The results reinforce the perspective that although the expression of genetic and maternal effects may be relatively homogeneous across different populations of the same species, local variation in environmental conditions can lead to significant variation in phenotypic expression of quantitative traits through genotype-environment and maternal effect-environment interactions.     

Plasticity to daylength of <Emphasis Type="Italic">Iris pumila</Emphasis> leaf phenological traits

 Plastic responses to photoperiod of Iris pumila leaf phenological traits were investigated in two populations experiencing contrasting light conditions in the dune system at Deliblato Sands (44°48′ N, 38°58′ E; Serbia, Yugoslavia). The population “Dune” occupied an exposed area at the top and slope of a relatively large dune, and the population “Woods” was situated in the understory of a Pinus nigra stand. Plants developed from rhizome segments of 15 and 12 clonal genotypes sampled individually in an exposed and a shaded site, respectively, were grown under alternating daylength conditions (long day, 16 h; short day, 8 h) in an environmentally controlled growth room, and scored for a number of leaf traits (live and senescent leaf number per ramet, leaf longevity, and phyllochron). The photoperiodic treatments used significantly affected the phenotypic values of all traits analyzed, regardless of the population origin. Leaf longevity decreased, whereas the proportion of senescent to live leaves increased under short as compared to long photoperiod. The amount of plasticity to daylength appeared to be strongly trait specific: senescent leaf number was the most plastic, and live leaf number per ramet the least plastic trait, in both populations. The factorial ANOVAs did not reveal a significant population effect on any of the leaf traits observed, except the phyllochron, indicating the presence of genetic variation between populations only for that particular trait. A statistically significant interaction term obtained in each of the ANOVAs provides the evidence of the existence of genetic variation for plasticity in all the leaf phenological traits studied. Genetic correlations among all trait pairs were close to zero and mostly statistically nonsignificant, indicating that the analyzed I. pumila leaf phenological traits are not genetically constrained to evolve by natural selection toward their optimal reaction norms within each light habitat. Received: September 17, 2002 / Accepted: February 28, 2003     

Variation in and adaptive plasticity of flower size and drought-coping traits

Although phenotypic plasticity of morphological and physiological traits in response to drought could be adaptive, there have been relatively few tests of plasticity variation or of adaptive plasticity in drought-coping traits across populations with different moisture availabilities. We measured floral size, vegetative size, and physiological traits in four field populations of Leptosiphon androsaceus (Polemoniaceae) that were distributed across a rainfall gradient in California, USA. Measurements were made over 5 years that varied in precipitation. We also conducted a growth chamber experiment in which half-sibs from three populations were divided equally among a well-watered and a drought treatment. We tested for selection on traits in each of the watering treatments, and evaluated whether traits exhibited plasticity. In the field, plant traits exhibited substantial variation across populations and years. Flower size, leaf size, and water-use efficiency (WUE) were generally higher for populations that received greater average rainfall. However, in dry years, we observed a decrease in flower and leaf size, but an increase in WUE across the populations. In the growth chamber experiment, leaf and physiological traits exhibited plasticity, with smaller leaves and higher WUE found in the drought, as compared to the well-watered treatment. Only specific leaf area exhibited differentiation in plasticity among populations. Although there was no observed plasticity in floral size, selection favored smaller flowers in the drought treatment and larger flowers in the well-watered treatment. Our results suggest that moisture availability has led to trait variation in L. androsaceus via a combination of selection and phenotypic plasticity.     

Genetic variation in leaf pigment,optical and photosynthetic function among diverse phenotypes of <Emphasis Type="Italic">Metrosideros polymorpha</Emphasis> grown in a common garden

Coordinated variation has been reported for leaf structure, composition and function, across and within species, and theoretically should occur across populations of a species that span an extensive environmental range. We focused on Hawaiian keystone tree species Metrosideros polymorpha, specifically, 13-year old trees grown (2–4 m tall) in a common garden (approximately 1 ha field with 2–3 m between trees) from seeds collected from 14 populations along an altitude–soil age gradient. We determined the genetic component of relationships among specific leaf area (SLA), the concentrations of nitrogen (N) and pigments (chlorophylls, carotenoids, and anthocyanins), and photosynthetic light-use efficiency. These traits showed strong ecotypic variation; SLA declined 35% with increasing source elevation, and area-based concentrations of N, Chl a + b and Car increased by 50, 109 and 96%, respectively. Concentrations expressed on a mass basis were not well related to source elevation. Pigment ratios expressed covariation that suggested an increased capacity for light harvesting at higher source elevation; Chl/N and Car/Chl increased with source elevation, whereas Chl a/b declined; Chl a/b was higher for populations on younger soil, suggesting optimization for low N supply. Parallel trends were found for the photosynthetic reactions; light-saturated quantum yield of photosystem II (Φ _PSII) and electron transport rate (ETR) increased with source elevation. Correlations of the concentrations of photosynthetic pigments, pigment ratios, and photosynthetic function across the ecotypes indicated a stoichiometric coordination of the components of the light-harvesting antennae and reaction centers. The constellation of coordinated morphological, biochemical and physiological properties was expressed in the leaf reflectance and transmittance properties in the visible and near-infrared wavelength region (400–950 nm), providing an integrated metric of leaf status among and between plant phenotypes.     

Leaf physiological aspects of nitrogen-use efficiency in Brassica campestris L.: quantitative genetic variation across nutrient treatments

Summary Quantitative genetic parameters for leaf physiological and whole-plant aspects of nitrogen-use efficiency in Brassica camprestris L. were estimated in three nutrient treatments in the greenhouse. Narrow-sense heritabilities and genetic correlations varied across treatments for some traits. Sire effects were significant for leaf nitrogen content in near-optimal and super-optimal, but not in suboptimal nutrient treatments. Additive genetic variation for two estimates of leaf physiological nitrogen-use efficiency (nitrogen-based photosynthetic capacity and leaf carbon: nitrogen ratio) was significant only in the suboptimal nutrient treatment. Area-based photosynthetic capacity, on the other hand, exhibited no heritable variation in any nutrient treatment. Heritability estimates of aboveground biomass and flower production were greatest in sub- and super-optimal treatments, respectively. Negative genetic correlations between leaf nitrogen content and both estimates of leaf nitrogen-use efficiency were evident in the super-optimal treatment. Aboveground biomass and leaf nitrogen-use efficiency were positively correlated in the suboptimal treatment, suggesting that growth differences were due in part to the efficiency with which nitrogen was utilized in physiological processes. Although implications for breeding may differ for different sources of germ plasm or different measures of performance or yield, selection for improved whole-plant performance through increased nitrogen-use efficiency should proceed best in suboptimal nutrient treatments.     

Life history responses to irradiance at the early seedling stage of Picea omorika (Pančić) Purkyňe: adaptiveness and evolutionary limits

A multivariate selection analysis has been implemented for testing the adaptiveness of life history plasticity to irradiance during the seedling establishment in Picea omorika plants raised in a growth-room. Siblings of a synthetic population comprising 21 families from six natural populations were exposed to contrasting light levels to explore variation in phenotypic expression of three seedling traits: days from germination to cotyledon opening (DGTOC), days from cotyledon opening to epicotyl appearance (DCTOE), and epicotyl length at 6 weeks (EPL6). Ambient light conditions significantly affected DCTOE and EPL6, but not DGTOC. Phenotypic selection analysis revealed that DGTOC was under negative directional selection in both radiation environments, suggesting that canalization of DGTOC was promoted across different light conditions, as well as that the observed pattern of canalization might be regarded as adaptive. DCTOE was also found to be under negative directional selection in both light treatments, but the plastic responses of this trait were opposite to the values favoured by selection within environments. Since there was evidence for selection against plasticity in DCTOE, the pattern of plastic responses in DCTOE to variation in light conditions could be diagnosed as maladaptive. Multiple regression analysis revealed a cost of canalization in DGTOC regardless of light environment, as well as a cost of plasticity in DCTOE under high light intensity. All genetic correlations across light environments were significantly different from unity, indicating the existence of heritable variation for plasticity in these traits. However, since DGTOC and DCTOE were involved in a genetic trade-off with respect to both trait mean and plasticity, these early life histories would never reach their optimal values across radiation environments.     

Environmentally induced dispersal‐related life‐history syndrome in the tropical butterfly,Bicyclus anynana

Dispersal is a key process for understanding the persistence of populations as well as the capacity of organisms to respond to environmental change. Therefore, understanding factors that may facilitate or constrain the evolution of dispersal is of crucial interest. Assessments of phenotypic variation in various behavioural, physiological and morphological traits related to insect dispersal and flight performance are common, yet very little is known about the genetic associations among these traits. We have used experiments on the butterfly Bicyclus anynana to estimate genetic variation and covariation in seven behavioural, physiological and morphological traits related to flight potential and hence dispersal. Our goal was to characterize the heritabilities and genetic correlations among these traits and thus to understand more about the evolution of dispersal‐related life‐history syndromes in butterflies. Using a version of the animal model, we showed that all of the traits varied between the sexes, and most were either positively or negatively (phenotypically and/or genetically) correlated with body size. Heritable variation was present in most traits, with the highest heritabilities estimated for body mass and thorax ratio. The variance in flight activity among multiple measurements for the same individual was high even after controlling for the prevailing environmental conditions, indicating the importance of behavioural switching and/or inherent randomness associated with this type of movement. A number of dispersal‐related traits showed phenotypic correlations among one another, but only a few of these were associated with significant genetic correlations indicating that covariances between these traits in Bicyclus anynana are mainly environmentally induced.     

THE ASSOCIATION BETWEEN FLUCTUATING ASYMMETRY,TRAIT VARIABILITY,TRAIT HERITABILITY,AND STRESS: A MULTIPLY REPLICATED EXPERIMENT ON COMBINED STRESSES IN DROSOPHILA MELANOGASTER

A number of hypotheses have been proposed about the association between developmental stability phenotypic variability, heritability, and environmental stress. Stress is often considered to increase both the asymmetry and phenotypic variability of bilateral traits, although this may depend on trait heritability. Empirical studies of such associations often yield inconsistent results. This may reflect the diversity of traits and conditions used or a low repeatability of any associations. To test for repeatable associations between these variables, multiply replicated experiments were undertaken on Drosophila melanogaster using a combination stress at the egg, larval and adult stages of reduced protein, ethanol in the medium, and a cold shock. Both metric and meristic traits were measured and levels of heritable variation for each trait estimated by maximum likelihood and parent-offspring regression over three generations. Trait means were reduced by stress, whereas among-individual variation increased Fluctuating asymmetry (FA) was increased by stress in some cases, but few comparisons were significant. Only one trait orbital bristle, showed consistent increases in FA. Changes in trait means, trait phenotypic variability, and developmental stability as a result of stress were not correlated. Extreme phenotypes tended to have higher levels of FA but only the results for orbital bristles were significant. All traits had low to intermediate heritabilities except orbital bristle, which showed no heritable variation. Only traits with low heritability and high levels of phenotypic variability may show consistent increases in FA under stress. Overall, the independence of phenotypic variability, plasticity, and the developmental stability of traits extend to changes in these measures under stressful conditions.     

Opportunities and challenges of next‐generation sequencing applications in ecological epigenetics

Evolutionary theory posits that adaptation can result when populations harbour heritable phenotypic variation for traits that increase tolerance to local conditions. However, the actual mechanisms that underlie heritable phenotypic variation are not completely understood (Keller 2014 ). Recently, the potential role of epigenetic mechanisms in the process of adaptive evolution has been the subject of much debate (Pigliucci & Finkelman 2014 ). Studies of variation in DNA methylation in particular have shown that natural populations harbour high amounts of epigenetic variation, which can be inherited across generations and can cause heritable trait variation independently of genetic variation (Kilvitis et al. 2014 ). While we have made some progress addressing the importance of epigenetics in ecology and evolution using methylation‐sensitive AFLP (MS‐AFLP), this approach provides relatively few anonymous and dominant markers per individual. MS‐AFLP are difficult to link to functional genomic elements or phenotype and are difficult to compare directly to genetic variation, which has limited the insights drawn from studies of epigenetic variation in natural nonmodel populations (Schrey et al. 2013 ). In this issue, Platt et al. provide an example of a promising approach to address this problem by applying a reduced representation bisulphite sequencing (RRBS) approach based on next‐generation sequencing methods in an ecological context.     

Evolutionary potential in the Alpine: trait heritabilities and performance variation of the dwarf willow Salix herbacea from different elevations and microhabitats

Alpine ecosystems are seriously threatened by climate change. One of the key mechanisms by which plants can adapt to changing environmental conditions is through evolutionary change. However, we still know little about the evolutionary potential in wild populations of long‐lived alpine plants. Here, we investigated heritabilities of phenological traits, leaf size, and performance traits in natural populations of the long‐lived alpine dwarf shrub Salix herbacea using relatedness estimates inferred from SSR (Simple Sequence Repeat) markers. Salix herbacea occurs in early‐ and late‐snowmelt microhabitats (ridges and snowbeds), and we assessed how performance consequences of phenological traits and leaf size differ between these microhabitats in order to infer potential for evolutionary responses. Salix herbacea showed low, but significant, heritabilities of leaf size, clonal and sexual reproduction, and moderate heritabilities of phenological traits. In both microhabitats, we found that larger leaves, longer intervals between snowmelt and leaf expansion, and longer GDD (growing‐degree days) until leaf expansion resulted in a stronger increase in the number of stems (clonal reproduction). In snowbeds, clonal reproduction increased with a shorter GDD until flowering, while the opposite was found on ridges. Furthermore, the proportion of flowering stems increased with GDD until flowering in both microhabitats. Our results suggest that the presence of significant heritable variation in morphology and phenology might help S. herbacea to adapt to changing environmental conditions. However, it remains to be seen if the rate of such an evolutionary response can keep pace with the rapid rate of climate change.     

Among‐individual heterogeneity in maternal behaviour and physiology affects reproductive allocation and offspring life‐history traits in the garter snake Thamnophis elegans

Accumulating evidence suggests that within‐individual plasticity of behavioural and physiological traits is limited, resulting in stable among‐individual differences in these aspects of the phenotype. Furthermore, these traits often covary within individuals, resulting in a continuum of correlated phenotypic variation among individuals within populations and species. This heterogeneity, in turn, affects individual fitness and can have cross‐generational effects. Patterns of trait covariation, among‐individual differences, and subsequent fitness consequences have long been recognized in reptiles. Here, we provide a test of patterns of among‐individual heterogeneity in behaviour and physiology and subsequent effects on reproduction and offspring fitness in the garter snake Thamnophis elegans. We find that measures of activity levels vary among individuals and are consistent within individuals in reproductive female snakes, indicating stable behavioural phenotypes. Blood hormone and glucose concentrations are not as stable within individuals, indicating that these traits do not describe consistent physiological phenotypes. Nonetheless, the major axes of variation in maternal traits describe behavioural and physiological phenotypes that interact to predict offspring body condition and mass at birth. This differential allocation of energy to offspring, in turn, strongly influences subsequent offspring growth and survival. This pattern suggests the potential for strong selection on phenotypes defined by behaviour–physiology interactions.     

苦豆子表型性状多样性分析及综合评价

该研究以自然分布的内蒙、宁夏、甘肃、新疆、陕西等23个不同地理来源(种源)的野生苦豆子种子及其播种于内蒙古鄂托克前旗同质园内的当年生植株为材料,采用方差分析、主成分分析、聚类分析等方法对种子长、宽、千粒重以及植株的叶长、叶宽、叶面积、叶形指数、苗高、地径及生物量等10个表型性状的多样性进行了研究。结果表明:各个表型性状种源间均呈极显著差异,其中种子表型性状的变异系数为5.24%,植株表型性状的变异系数为18.34%,表明种子性状的稳定性高于植株性状。同时,10个性状的表型分化系数均高于70%,说明苦豆子表型多样性主要来源于种源间的表型变异;各种源苦豆子种子性状的表型分化系数均值高达97.55%,且种长、千粒重分别与采集地经度、纬度和海拔等环境因子呈极显著相关性,说明种子表型性状受环境因素的影响较大;相关性分析显示,苦豆子植株性状叶长(LL)、叶面积(LA)分别与种子性状千粒重(TW)、种长(SL)和种宽(SW)有显著相关性,暗示表型性状中的可遗传变异影响;利用主成分和聚类分析对23个种源苦豆子进行综合评价,筛选出生物量较大、苗高较高、千粒重较重、叶面积较大等综合表现较好的6个种源,共分为两类,分别是DK、JY、WY、WH、ETK和YN,这为苦豆子种质资源定向开发以及选育和栽培提供了一定的理论支撑和基础材料。     

Testing the adaptive plasticity of Iris pumila leaf traits to natural light conditions using phenotypic selection analysis

A multivariate selection analysis has been used to test the adaptiveness of several Iris pumila leaf traits that display plasticity to natural light conditions. Siblings of a synthetic population comprising 31 families of two populations from contrasting light habitats were grown at an open dune site and in the understory of a Pinus nigra stand in order to score variation in phenotypic expression of six leaf traits: number of senescent leaves, number of live leaves, leaf length, leaf width, leaf angle, and specific leaf area. The ambient light conditions affected the values of all traits studied except for specific leaf area. In accordance to ecophysiological expectations for an adaptive response to light, both leaf length and width were significantly greater while the angle between sequential leaves was significantly smaller in the woodland understory than at the exposed dune site. The relationship between leaf traits and vegetative fitness (total leaf area) differed across light habitats as predicted by functional hypotheses. The standardized linear selection gradient (β′) for leaf length and width were positive in sign in both environments, but their magnitude for leaf length was higher in the shade than under full sunlight. Since plasticity of leaf length in the woodland shade has been recognized as adaptive, fitness cost of producing plastic change in leaf length was assessed. In both of the available methods used, the two-step and the multivariate regression procedures, a rather high negative association between the fitness value and the plasticity of leaf length was obtained, indicating a cost of plasticity. The selection gradient for leaf angle was weak and significant only in the woodland understory. Genetic correlations between trait expressions in contrasting light environments were negative in sign and low in magnitude, implying a significant genetic variation for plasticity in these leaf traits. Furthermore, leaf length and leaf width were found to be genetically positively coupled, which indicates that there is a potential for these two traits to evolve toward their optimal phenotypic values even faster than would be expected if they were genetically independent.     

Genetic basis of variation in morphological and life-history traits of a wild population of pink salmon

Understanding the genetic basis of phenotypic variation is essential for predicting the direction and rate of phenotypic evolution. We estimated heritabilities and genetic correlations of morphological (fork length, pectoral and pelvic fin ray counts, and gill arch raker counts) and life-history (egg number and individual egg weight) traits of pink salmon (Oncorhynchus gorbuscha) from Likes Creek, Alaska, in order to characterize the genetic basis of phenotypic variation in this species. Families were created from wild-caught adults, raised to the fry stage in the lab, released into the wild, and caught as returning adults and assigned to families using microsatellite loci and a growth hormone locus. Morphological traits were all moderately to highly heritable, but egg number and egg weight were not heritable, suggesting that past selection has eliminated additive genetic variation in egg number and egg weight or that there is high environmental variance in these traits. Genetic correlations were similar for nonadjacent morphological traits and adjacent traits. Genetic correlations predicted phenotypic correlations fairly accurately, but some pairs of traits with low genetic correlations had high phenotypic correlations, and vice versa, emphasizing the need to use caution when using phenotypic correlations as indices of genetic correlations. This is one of only a handful of studies to estimate heritabilities and genetic correlations for a wild population.     

A general model of the relation between phenotypic selection and genetic response

The phenotypic view of selection assumes that genetic responses can be predicted from selective forces and heritability — or in the classical quantitative genetic equation: R = h²S. However, data on selection in bird populations show that often no selection responses is found, despite consistent selective forces on phenotypes and significant heritable variation. Such discrepancies may arise due to the assumption that selection only acts on observed phenotypes. We derive a general selection equation that takes into account the possibility that some relevant (internal or external) traits are not measured. This equation shows that the classic equation applies if selection directly acts on the measured, phenotypic traits. This is not the case when, for instance, there are unknown internal genetic trade-offs, or unknown common environmental factors affecting both trait and fitness. In such cases, any relationship between phenotypic selection and genetic response is possible. Fortunately, the classical model can be tested by comparing phenotypic and genetic covariances between traits and fitness; an indication that important internal or external traits are missing can thus be obtained. Such an analysis was indeed found in the literature; for selection on fledging weight in Great Tits it yielded valuable extra information.     

Genetic and phenotypic correlations among size-related traits, and heritability variation between body parts in Drosophila buzzatii

Recent studies have shown that body size is a heritable trait phenotypically correlated with several fitness components in wild populations of the cactophilic fly Drosophila buzzatii. To obtain further information on size-related variation, heritabilities as well as genetic and phenotypic correlations among size-related traits of several body parts (head, thorax and wings) were estimated. The study was carried out on an Argentinean natural population in which size-related selection was previously detected. The genetic parameters were estimated using offspring-parent regressions (105 families) in the laboratory G₂ generation of a sample of wild flies. The traits were also scored in Wild-Caught Flies (WCF). Laboratory-Reared Flies (LRF) were larger and less variable than WCF. Although heritability estimates were significant for all traits, heritabilities were higher for thorax-wing traits than for head traits. Phenotypic and genetic correlations were all positive. The highest genetic correlations were found between traits which are both functionally and developmentally related. Genetic and phenotypic correlations estimated in the lab show similar correlation patterns (r = 0.49; TP = 0.02, Mantel's test). However, phenotypic correlations were found to be typically larger in WCF than in LRF. The genetic correlation matrix estimated in the relatively homogeneous lab environment is not simply a constant multiplicative factor of the phenotypic correlation matrix estimated in WCF. This revised version was published online in July 2006 with corrections to the Cover Date.     

Developmental and genetic effects on behavioral and life‐history traits in a field cricket

A fundamental goal of evolutionary ecology is to identify the sources underlying trait variation on which selection can act. Phenotypic variation will be determined by both genetic and environmental factors, and adaptive phenotypic plasticity is expected when organisms can adjust their phenotypes to match environmental cues. Much recent research interest has focused on the relative importance of environmental and genetic factors on the expression of behavioral traits, in particular, and how they compare with morphological and life‐history traits. Little research to date examines the effect of development on the expression of heritable variation in behavioral traits, such as boldness and activity. We tested for genotype, environment, and genotype‐by‐environment differences in body mass, development time, boldness, and activity, using developmental density treatments combined with a quantitative genetic design in the sand field cricket (Gryllus firmus). Similar to results from previous work, animals reared at high densities were generally smaller and took longer to mature, and body mass and development time were moderately heritable. In contrast, neither boldness nor activity responded to density treatments, and they were not heritable. The only trait that showed significant genotype‐by‐environment differences was development time. It is possible that adaptive behavioral plasticity is not evident in this species because of the highly variable social environments it naturally experiences. Our results illustrate the importance of validating the assumption that behavioral phenotype reflects genetic patterns and suggest questions about the role of environmental instability in trait variation and heritability.