Genetic Variation For Plasticity Research Articles

Patterns of morphological divergence in fruit fly: response to nutritional variations through changes in allometric relationships and trait sizes

AbstractThe morphological structures of organisms may be subject to divergence when exposed to varied nutritive conditions, due to the occurrence of developmental plasticity and its fixation due to the process of genetic accommodation. The allometric relationship of traits with respect to each other and to the whole body defines the shape of an individual. Developmental plasticity in different nutritional regimes affects the absolute value of traits and its relative scaling with respect to body size. We investigated the diversification in wing dimensions and body size in Drosophila ananassae by utilizing isofemale lines of Bilaspur and karyotypically characterized stocks of Varanasi, by rearing flies in nutritional regimes having differences in protein and carbohydrate compositions. The effect of dietary protein variations on plasticity of absolute size of body and wing dimensions was found to be highly genotype‐dependent as compared to sucrose, in both the sexes and in both the populations. This suggests that variation in proteins in natural environment may induce greater selective pressure on traits and may lead to diversification in morphological structures due to the process of genetic accommodation. We found highly significant genetic variation in plasticity for allometric relationship in Bilaspur population for variations in protein as well as carbohydrate in dietary media. However, constraints in plasticity of allometric slopes for wing dimensions in karyotypic stocks of Varanasi were found in response to both the nutritional variations. The analysis of reaction norms also suggested that there is involvement of alpha inversion present in 2L chromosome of Varanasi population, in adapting to different nutritional environmental conditions due to changes in static allometry of different wing dimensions. Overall, this study reveals that the nutritional ecology and evolutionary allometry govern the morphological divergence of traits size and shape in a genotypic‐dependent manner, thereby resulting in morphological evolutions.

Ecotypic variation and stability in growth performance of the thermophilic conifer Pinus halepensis across the Mediterranean basin

The combined effects of local adaptation and phenotypic plasticity influencing plant performance are relevant to understand the capacity for genetic responses to climate change. Pinus halepensis is a native species of low- to mid-elevation Mediterranean forests with a high ecological value in drought-prone areas. Thus, it is of utmost importance to determine its adaptive structure for key traits such as growth or survival. Here, we analyse a highly unbalanced dataset collated from different common-garden networks that cover the distribution range of the species. A total of 82 range-wide populations were evaluated in nine Mediterranean trials located in Israel, Italy and Spain. A climate classification of populations allowed for the definition of six different groups, or ecotypes, which showed contrasting performances for tree height and survival at age 15. The effects of ecotypic differentiation and among-ecotypes genetic variation in plasticity were disentangled by fitting stability models accounting for interaction and heteroscedasticity in genotype-by-environment tables. For growth, a Finlay–Wilkinson model suggested high predictability of ecotypic plastic responses in P. halepensis, as described by different linear reaction norms. However, differences in mean height of ca. 15% among ecotypes dominated intra-specific patterns of tree growth across trials, pointing to preponderance of genotypic adaptation over differential ecotypic plasticity in this species. For survival, ecotypic differences were approximately constant across trials, suggesting lack of genotype-by-environment effects. Sub-humid cool climate populations from the eastern Mediterranean (e.g., Greek populations) showed general adaptation and high sensitivity to improved growing conditions, as opposed to populations from the driest ecological extreme of the species (e.g., south Spain and Maghreb populations), which exhibited specific adaptation to harsh environments. Altogether, our results indicate a general adaptive syndrome by which less reactive ecotypes to ameliorated conditions (e.g., non-water-limited) would be associated with high survival rates and low growth. The reported ecotypic differentiation constitutes the basis for tailoring intra-specific responses to climate and disentangling the relationship between adaptive variation and resilience towards climatic warming for this exemplary Mediterranean pine.

Predation drives local adaptation of phenotypic plasticity.

Phenotypic plasticity is the ability of an individual genotype to alter aspects of its phenotype depending on the current environment. It is central to the persistence, resistance and resilience of populations facing variation in physical or biological factors. Genetic variation in plasticity is pervasive, which suggests its local adaptation is plausible. Existing studies on the adaptation of plasticity typically focus on single traits and a few populations, while theory about interactions among genes (for example, pleiotropy) suggests that a multi-trait, landscape scale (for example, multiple populations) perspective is required. We present data from a landscape scale, replicated, multi-trait experiment using a classic predator-prey system centred on the water flea Daphnia pulex. We find predator regime-driven differences in genetic variation of multivariate plasticity. These differences are associated with strong divergent selection linked to a predation regime. Our findings are evidence for local adaptation of plasticity, suggesting that responses of populations to environmental variation depend on the conditions in which they evolved in the past.

Will phenotypic plasticity affecting flowering phenology keep pace with climate change?

Rising temperatures have begun to shift flowering time, but it is unclear whether phenotypic plasticity can accommodate projected temperature change for this century. Evaluating clines in phenological traits and the extent and variation in plasticity can provide key information on assessing risk of maladaptation and developing strategies to mitigate climate change. In this study, flower phenology was examined in 52 populations of big sagebrush (Artemisia tridentata) growing in three common gardens. Flowering date (anthesis) varied 91days from late July to late November among gardens. Mixed-effects modeling explained 79% of variation in flowering date, of which 46% could be assigned to plasticity and genetic variation in plasticity and 33% to genetics (conditional R2 =0.79, marginal R2 =0.33). Two environmental variables that explained the genetic variation were photoperiod and the onset of spring, the Julian date of accumulating degree-days >5°C reaching 100. The genetic variation was mapped for contemporary and future climates (decades 2060 and 2090), showing flower date change varies considerably across the landscape. Plasticity was estimated to accommodate, on average, a ±13-day change in flowering date. However, the examination of genetic variation in plasticity suggests that the magnitude of plasticity could be affected by variation in the sensitivity to photoperiod and temperature. In a warmer common garden, lower-latitude populations have greater plasticity (+16days) compared to higher-latitude populations (+10days). Mapped climatypes of flowering date for contemporary and future climates illustrate the wide breadth of plasticity and large geographic overlap. Our research highlights the importance of integrating information on genetic variation, phenotypic plasticity and climatic niche modeling to evaluate plant responses and elucidate vulnerabilities to climate change.

Evolutionary divergence of reaction norms in ecological context: a commentary.

Evolutionary divergence of reaction norms in ecological context: a commentary.

Genetic variation in plasticity of life-history traits between Atlantic cod (Gadus morhua) populations exposed to contrasting thermal regimes

We employed common-garden experiments to test for genetic variation in responses of larval life-history traits to temperature between two populations of Atlantic cod (Gadus morhua L., 1758) that naturally experience contrasting thermal environments during early life due to spatial and temporal differences in spawning. Southern Gulf of St. Lawrence cod larvae experienced faster growth in warmer water and low, uniform survival across all experimental temperatures (3, 7, 11 °C), consistent with previous studies on this spring-spawning population. In contrast, larvae from fall-spawning Southwestern Scotian Shelf cod collected near Sambro, Nova Scotia, lacked plasticity for growth but experienced much lower survival at higher temperatures. Phenotypes that are positively associated with fitness were observed at temperatures closest to those experienced in the wild, consistent with the hypothesis that these populations are adapted to local thermal regimes. The lack of growth plasticity observed in Sambro cod might be due to costly maintenance of plasticity in stable environments or energy savings at cold temperatures. However, additional experiments need to be conducted on Sambro cod and other fall-spawning marine fishes to determine to what extent responses to projected changes in climate will differ among populations.

Genetic variation of Fraxinus excelsior half-sib families in response to ash dieback disease following simulated spring frost and summer drought treatments

Abstract: Ten juvenile Fraxinus excelsior half-sib families from two Lithuanian populations have been tested in the controlled environment for their response to ash dieback disease caused by Hymenoscyphus fraxineus, detecting changes of genetic variation and heritability, as well as estimating genotype by environment (G×E) interaction and phenotypic plasticity following artificial spring frost and summer drought treatments. In 2014, a batch of 200 four-year-old ash seedlings was used for each treatment and control (no treatment). Health condition, bud flushing phenology and height were assessed for each seedling, and disease incidence and survival ratios were assessed for each family both before (at the beginning of the vegetation season) and after the treatments (at the end of the vegetation season). Disease incidence ratio increased from 0.77-0.80 up to 0.90-0.95. Tree mortality rates during one vegetation season were significantly lower in the frost treatment (21%) than in the drought treatment (25%) or control (31%). None of the tested F. excelsior families were completely resistant to ash dieback, although significant among-family differences in disease incidence and damage rates suggest an additive mode of gene action and thus a quantitative resistance to the disease. Neither disease incidence rates, nor tree health condition scores differed significantly among the applied treatments (including control) indicating in general a negligible effect of the simulated adverse conditions on health status of the ash seedlings. However, G×E interaction was found to be significant (at P > 0.05) for disease incidence, length of necrotic shoots and tree survival, implying that susceptibility of ash families to the dieback disease unequally depends on environmental conditions, and indicating a presence of genetic variation in plasticity and reaction norms of the tested families across environments (treatments). Substantially increased coefficients of additive genetic variation and heritability in health condition following both frost and drought treatments and compared to control showed that simulated stress conditions may noticeably contribute to expression of differences among the tested F. excelsior families in their resistance traits, thus enabling a better evaluation of performance of different families, an effective family selection for resistance, and achievement of a marked genetic gain.

Genetic variability in reaction norms in fishes

The ability of populations to adapt to environmental change and the spatial scale at which this adaptation occurs are fundamentally important issues in evolutionary biology, and ones that may benefit greatly from the study of genetic variability in reaction norms, which represent the plasticity of phenotypic traits across an environmental gradient. Therefore variable reaction norms can reflect genetic differences in the ability of individuals, families, populations, and species to respond to natural and anthropogenic environmental change. Fishes are ideal organisms in which to study plasticity because of their remarkable intraspecific morphological, physiological, behavioural, and life history variation. Here, we review studies demonstrating genetic variability in reaction norms in fishes. Genetic variability in plasticity among full- and half-sib families suggests potential for some populations to develop an adaptive norm of reaction (recalling that plasticity need not be adaptive). Reaction norm variability among populations suggests that adaptive genetic divergence can occur rapidly when selection pressures are strong and that the spatial scale of adaptation is much smaller than previously believed for some species with high dispersal capabilities. These studies demonstrate the potential of using reaction norms to study the evolution of novel phenotypes and the influence of temporal environmental variability and gene flow on the evolution of phenotypic plasticity, which can then be used to predict how populations will respond to directional environmental change. To promote future research into genetic variability in reaction norms, we propose questions that would benefit from such an approach and discuss some important considerations for designing experiments to investigate questions related to genetic variation in plasticity and phenotypic evolution.

Divergent phenotypic responses to predators and cyanobacteria inDaphnia lumholtzi

Daphnia lumholtzi is an exotic species of zooplankton that was first introduced in Texas, U.S.A., and has since spread across most of the areas in the country. Research has focussed on the importance of the production of morphological defences in response to predator exposure as a key explanation for the spread of this species. Very little is known about the influence of other common environmental stressors on the fitness of this species or the potential role for genetic variation in plasticity in the spread of this species. We assessed the effects of two common environmental stressors, invertebrate predator cues and increasing concentrations of cyanobacteria, on the life-history traits in D. lumholtzi. This study also included clones from three reservoirs in Texas to measure potential genetic variation in plasticity. We found that the expression of life-history traits depended strongly upon the combined effects of predator exposure and food quality. Increasing concentrations of cyanobacteria resulted in delayed maturation, slower growth, a smaller size at maturation, declines in clutch size and slower rate of population growth. Yet, such declines were much smaller in the presence of predator cues. Divergent responses observed were the size of defence traits; Daphnia reared in the absence of predator cues increased the size of spines as the concentrations of cyanobacteria increased, while the opposite pattern was observed in the presence of predator cues. This study also revealed extensive genetic variation in the magnitude and direction of phenotypic responses to predators and cyanobacteria. These latter results illustrate that significant clonal variation in plasticity may help promote the spread of this species.

Quantitative trait loci × environment interactions for plant morphology vary over ontogeny in Brassica rapa.

Growth in plants occurs via the addition of repeating modules, suggesting that the genetic architecture of similar subunits may vary between earlier- and later-developing modules. These complex environment × ontogeny interactions are not well elucidated, as studies examining quantitative trait loci (QTLs) expression over ontogeny have not included multiple environments. Here, we characterized the genetic architecture of vegetative traits and onset of reproduction over ontogeny in recombinant inbred lines of Brassica rapa in the field and glasshouse. The magnitude of genetic variation in plasticity of seedling internodes was greater than in those produced later in ontogeny. We correspondingly detected that QTLs for seedling internode length were environment-specific, whereas later in ontogeny the majority of QTLs affected internode lengths in all treatments. The relationship between internode traits and onset of reproduction varied with environment and ontogenetic stage. This relationship was observed only in the glasshouse environment and was largely attributable to one environment-specific QTL. Our results provide the first evidence of a QTL × environment × ontogeny interaction, and provide QTL resolution for differences between early- and later-stage plasticity for stem elongation. These results also suggest potential constraints on morphological evolution in early vs later modules as a result of associations with reproductive timing.

Phenotypic plasticity in mating-system traits in the annual Collinsia verna

Variation in abiotic factors can influence the selective advantage of selfing and expression of the mating system if mating-system modifier traits are phenotypically plastic. However, relative to biotic factors, the role of abiotic conditions in driving variation in and evolution of plant mating systems is rarely addressed. We use an experimental approach to evaluate the extent to which genetic and environmental variation influence the expression of mating-system traits in the annual Collinsia verna. We subjected families to two environmental treatments in the greenhouse that varied in light and water availability, simulating natural and short flowering-season conditions, and examined the following: autonomous fruit set, flower number, flower size, rate of anther dehiscence, floral longevity, and timing of selfing. Our results demonstrate plasticity in nearly all traits examined. Compared with natural-season conditions, plants under short-season conditions produced fewer, smaller flowers and selfed approximately one day later due to slower anther dehiscence rates. Autonomous fruit set was similar across treatments, but there was genetic variation for plasticity in this important trait. Further, we show genetic variation in autonomous fruit set, timing of selfing, and flower number and size. Given the effects of global climate change on the duration of growing season, our results suggest that plasticity in mating-system traits will affect mating-system variation and, thus, opportunities for selection.

Plasticity in reproduction and growth among 52 range‐wide populations of aMediterranean conifer: adaptive responses to environmental stress

A plastic response towards enhanced reproduction is expected in stressful environments, but it is assumed to trade off against vegetative growth and efficiency in the use of available resources deployed in reproduction [reproductive efficiency (RE)]. Evidence supporting this expectation is scarce for plants, particularly for long-lived species. Forest trees such as Mediterranean pines provide ideal models to study the adaptive value of allocation to reproduction vs. vegetative growth given their among-population differentiation for adaptive traits and their remarkable capacity to cope with dry and low-fertility environments. We studied 52 range-wide Pinus halepensis populations planted into two environmentally contrasting sites during their initial reproductive stage. We investigated the effect of site, population and their interaction on vegetative growth, threshold size for female reproduction, reproductive-vegetative size relationships and RE. We quantified correlations among traits and environmental variables to identify allocation trade-offs and ecotypic trends. Genetic variation for plasticity was high for vegetative growth, whereas it was nonsignificant for reproduction. Size-corrected reproduction was enhanced in the more stressful site supporting the expectation for adverse conditions to elicit plastic responses in reproductive allometry. However, RE was unrelated with early reproductive investment. Our results followed theoretical predictions and support that phenotypic plasticity for reproduction is adaptive under stressful environments. Considering expectations of increased drought in the Mediterranean, we hypothesize that phenotypic plasticity together with natural selection on reproductive traits will play a relevant role in the future adaptation of forest tree species.

Genotype-by-Environment Interactions for Female Mate Choice of Male Cuticular Hydrocarbons in Drosophila simulans

Recent research has highlighted the potential importance of environmental and genotype-by-environment (G×E) variation in sexual selection, but most studies have focussed on the expression of male sexual traits. Consequently, our understanding of genetic variation for plasticity in female mate choice is extremely poor. In this study we examine the genetics of female mate choice in Drosophila simulans using isolines reared across two post-eclosion temperatures. There was evidence for G×Es in female choosiness and preference, which suggests that the evolution of female mate choice behaviour could differ across environments. However, the ranked order of preferred males was consistent across females and environments, so the same males are favoured by mate choice in spite of G×Es. Our study highlights the importance of taking cross-environment perspectives in order to gain a more comprehensive understanding of the operation of sexual selection.

Differences in transcription levels among wild, domesticated, and hybrid Atlantic salmon (Salmo salar) from two environments

Escaped domesticated individuals can introduce disadvantageous traits into wild populations due to both adaptive differences between population ancestors and human-induced changes during domestication. In contrast to their domesticated counterparts, some endangered wild Atlantic salmon populations encounter during their marine stage large amounts of suspended sediments, which may act as a selective agent. We used microarrays to elucidate quantitative transcriptional differences between a domesticated salmon strain, a wild population and their first-generation hybrids during their marine life stage, to describe transcriptional responses to natural suspended sediments, and to test for adaptive genetic variation in plasticity relating to a history of natural exposure or nonexposure to suspended sediments. We identified 67 genes differing in transcription level among salmon groups. Among these genes, processes related to energy metabolism and ion homoeostasis were over-represented, while genes contributing to immunity and actin-/myosin-related processes were also involved in strain differentiation. Domestic-wild hybrids exhibited intermediate transcription patterns relative to their parents for two-thirds of all genes that differed between their parents; however, genes deviating from additivity tended to have similar levels to those expressed by the wild parent. Sediments induced increases in transcription levels of eight genes, some of which are known to contribute to external or intracellular damage mitigation. Although genetic variation in plasticity did not differ significantly between groups after correcting for multiple comparisons, two genes (metallothionein and glutathione reductase) tended to be more plastic in response to suspended sediments in wild and hybrid salmon, and merit further examination as candidate genes under natural selection.

Phenotypic plasticity and climatic adaptation in an Atlantic maritime pine breeding population

Pinus pinaster Ait. is found in the Iberian Peninsula under Mediterranean and Atlantic conditions. Both climates encounter each other in Galicia (NW Spain), where two bioclimatic regions can be differentiated: coastal and inland. A breeding program was launched in the coastal area, with two breeding and deployment areas delimited. We analyse plasticity patterns across regions in a coastal breeding population to assess the suitability of current breeding areas and how genetic material will likely respond to future climate. Total height at ages 3 and 8 years was assessed in 16 trials established along the coast and in inner Galicia. Clustering of environments with similar genotypic performance, family sensitivities to climatic factors and stability analyses were performed. Sizeable genetic variation in plasticity was found among families, and crossover genotype-by-environment interactions were detected within and between regions. It was unfeasible to regionalize Galicia into alternative areas of stable genotypic performance. Only the cold regime was found to noticeably underlie the array of phenotypic responses to changing environmental conditions. Results suggest that previous delimitation in two breeding areas is pointless and indicate reduced effects of a changing climate towards Mediterranean conditions on decreasing population fitness.

Variation in inbreeding depression and plasticity across native and non-native field environments

Since the early 1990s, research on genetic variation of phenotypic plasticity has expanded and empirical research has emphasized the role of the environment on the expression of inbreeding depression. An emerging question is how these two evolutionary ecology mechanisms interact in novel environments. Interest in this area has grown with the need to understand the establishment of populations in response to climate change, and to human-assisted transport to novel environments. We compare performance in the field of outcrossed (O) and inbred lines (S1, S2) from 20 maternal families from each of two native populations of Mimulus guttatus. The experiment was planted in California in each population's home site, in the other populations's home site, in a novel site within the native range of M. guttatus, and in a novel site within the non-native range in North America. The experiment included nearly 6500 individuals. Survival, sexual reproduction and above-ground biomass were examined in order to evaluate inbreeding depression, and stem diameter and plant height were examined in order to evaluate phenotypic plasticity. Across all field sites, approx. 36 % of plants survived to flowering. Inbreeding depression differed among sites and outcrossed offspring generally outperformed selfed offspring. However, in the native-novel site, self-progeny performed better or equally well as outcross progeny. Significant phenotypic plasticity and genetic variation in plasticity was detected in the two architectural traits measured. The absolute value of plasticity showed the most marked difference between home and non-native novel site or non-native-novel site. Evidence was detected for an interaction between inbreeding and plasticity for stem diameter. The results demonstrate that during initial population establishment, both inbreeding depression and phenotypic plasticity vary among field sites, and may be an important response to environments outside a species' currently occupied range. However, the interaction between inbreeding and plasticity may be limited and environment-dependent.

Plasticity and evolution in drought avoidance and escape in the annual plant Brassica rapa

A key question in ecological genetics is to what extent do plants adapt to changes in climatic conditions, such as drought, through plasticity or evolution. To address this question, seeds of 140 maternal families of Brassica rapa were generated from collections made before (1997) and after (2004) a natural drought. These seeds were planted in the glasshouse and grown under low-water and high-water conditions. Post-drought lines flowered earlier than pre-drought lines, showing an evolutionary shift to earlier flowering. There was significant genetic variation and genotype by environment (G × E) interactions in flowering time, indicating genetic variation in plasticity in this trait. Plants that flowered earlier had fewer leaf nodes and lower instantaneous (A/g) and integrated (δ(13)C) water use efficiency than late-flowering plants. These results suggest that B. rapa plants escape drought through early flowering rather than avoid drought through increased water use efficiency. The mechanism of this response appears to be high transpiration and inefficient water use, leading to rapid development. These findings demonstrate a trade-off between drought avoidance and escape, and indicate that, in this system, where drought acts to shorten the growing season, selection for drought escape through earlier flowering is more important than phenotypic plasticity.

Genetic Variance and Genotype-by-Environment Interaction of Immune Response in <I>Aedes aegypti</I> (Diptera: Culicidae)

Immune response can be negatively affected by resource limitation, so it is expected that organisms evolve strategies to minimize the impact of this environmental outcome. Phenotypic plasticity in immune response could represent a genetic response to face such situations. We investigated the effects of high and low quality and quantity of food at the larval stage on two important immune components, phenoloxidase activity (PO) and nitric oxide production (NO) measured in adults of the Dengue vector, Aedes aegypti. We reared families to determine the magnitude and pattern of expression of genetic variance, environmental variance and genotype-by-environment interaction (GEI). In addition, we quantified whether there were differences in plastic immune responses in both sexes. Our results indicated additive variance for PO and NO, but rearing environment did not produce differences among individuals. For NO and PO in males, there were large differences among families in plasticity, as indicated by the different slopes produced by each reaction norm. Therefore, there is additive genetic variation in plasticity for NO production and PO activity. One possible interpretation of these results is that different genotypes may be favored to fight pathogens under the different food quality situations. Males and females showed similar overall GEI strategies but there were differences in PO and NO. Males showed a phenotypic correlation between PO and NO, but we did not find genetic correlations between immune parameters in both sexes.

Genetic Variance and Genotype-by-Environment Interaction of Immune Response inAedes aegypti(Diptera: Culicidae)

Immune response can be negatively affected by resource limitation, so it is expected that organisms evolve strategies to minimize the impact of this environmental outcome. Phenotypic plasticity in immune response could represent a genetic response to face such situations. We investigated the effects of high and low quality and quantity of food at the larval stage on two important immune components, phenoloxidase activity (PO) and nitric oxide production (NO) measured in adults of the Dengue vector, Aedes aegypti. We reared families to determine the magnitude and pattern of expression of genetic variance, environmental variance and genotype-by-environment interaction (GEI). In addition, we quantified whether there were differences in plastic immune responses in both sexes. Our results indicated additive variance for PO and NO, but rearing environment did not produce differences among individuals. For NO and PO in males, there were large differences among families in plasticity, as indicated by the different slopes produced by each reaction norm. Therefore, there is additive genetic variation in plasticity for NO production and PO activity. One possible interpretation of these results is that different genotypes may be favored to fight pathogens under the different food quality situations. Males and females showed similar overall GEI strategies but there were differences in PO and NO. Males showed a phenotypic correlation between PO and NO, but we did not find genetic correlations between immune parameters in both sexes.

Sex-allocation plasticity in hermaphrodites of sexually dimorphic Fragaria virginiana (Rosaceae)

Sex-allocation plasticity is thought to play an important role in the evolution of separate sexes in plants. Accordingly, much attention has been paid to environmentally induced variation in fruit and seed production in sexually dimorphic species, but we know little about whether this variation arises as a direct response to environmental variation or is instead an indirect consequence of changes in plant size. In this study, we characterize sex-allocation plasticity across a resource gradient for several reproductive traits in hermaphrodites of gyno(sub)dioecious Fragaria virginiana Duch. We find significant plasticity, on average, for flower number, proportion fruit set, ovule number, proportion seed set, and runner number in response to resource variation. Plasticity of most traits examined tended to be at least partially independent of variation in plant size, suggesting that it is not simply an indirect consequence of plant allometry. Moreover, we find genetic variation for plasticity of key reproductive traits. Comparisons of relative plasticities among traits reveal that F. virginiana hermaphrodites are more likely to adjust female investment via changes in fruit and seed set than ovule number, and most likely to adjust male investment via flower number rather than anther number or pollen per anther, although there is genotypic variation for plasticity in pollen per anther. Evidence of within-population variation can logically be extended to suggest that variation in hermaphrodite sex-expression seen among natural populations of F. virginiana may be due, at least in part, to sex-allocation plasticity.