Adaptive genetic differentiation in life-history traits between populations of <Emphasis Type="Italic">Mimulus guttatus</Emphasis> with annual and perennial life-cycles

The optimal allocation to sexual and vegetative reproduction as well as the optimal values of other life-history characteristics such as phenology, growth and mating system are likely to depend on the life-cycle of the organism. I tested whether plants of Mimulus guttatus originating from temporarily wet populations where the species has an enforced annual life-cycle have higher allocation to sexual reproduction, lower allocation to vegetative reproduction, more rapid phenology, faster growth, and floral traits associated with a self-fertilizing mating system than plants from permanently wet populations where the species has a perennial life-cycle. I grew a total of 1377 plants originating from three populations with an annual life-cycle and 11 populations with a perennial life-cycle in a greenhouse under permanently and temporarily wet conditions. Plants of M. guttatus in permanently wet conditions had significantly more vegetative reproduction and tended to have a faster growth than plants in the temporarily wet conditions, indicating plasticity in these life-history traits. Plants from populations with an annual life-cycle invested significantly more in sexual reproduction and significantly less in vegetative reproduction than the ones from populations with a perennial life-cycle. Moreover, this study showed that plants originating from populations with an annual life-cycle have a significantly faster development and floral traits associated with autonomous self-fertilization. In conclusion, this study suggests that there has been adaptive evolution of life history traits of M. guttatus in response to natural watering conditions that determine the life span of the species.     

Reproductive allocation of biomass and nitrogen in annual and perennial Lesquerella crops

* BACKGROUND AND AIMS: The use of perennial crops could contribute to increase agricultural sustainability. However, almost all of the major grain crops are herbaceous annuals and opportunities to replace them with more long-lived perennials have been poorly explored. This follows the presumption that the perennial life cycle is associated with a lower potential yield, due to a reduced allocation of biomass to grains. The hypothesis was tested that allocation to perpetuation organs in the perennial L. mendocina would not be directly related to a lower allocation to seeds. * METHODS: Two field experiments were carried on with the annual Lesquerella fendleri and the iteroparous perennial L. mendocina, two promising oil-seed crops for low-productivity environments, subjected to different water and nitrogen availability. * KEY RESULTS: Seed biomass allocation was similar for both species, and unresponsive to water and nitrogen availability. Greater root and vegetative shoot allocation in the perennial was counterbalanced by a lower allocation to other reproductive structures compared with the annual Lesquerella. Allometric relationships revealed that allocation differences between the annual and the perennial increased linearly with plant size. The general allocation patterns for nitrogen did not differ from those of biomass. However, nitrogen concentrations were higher in the vegetative shoot and root of L. mendocina than of L. fendleri but remained stable in seeds of both species. * CONCLUSIONS: It is concluded that vegetative organs are more hierarchically important sinks in L. mendocina than in the annual L. fendleri, but without disadvantages in seed hierarchy.     

Patterns of intraspecific trait variation along an aridity gradient suggest both drought escape and drought tolerance strategies in an invasive herb

Background and AimsIn water-limited landscapes, some plants build structures that enable them to survive with minimal water (drought resistance). Instead of making structures that allow survival through times of water limitation, annual plants may invoke a drought escape strategy where they complete growth and reproduction when water is available. Drought escape and resistance each require a unique combination of traits and therefore plants are likely to have a suite of trait values that are consistent with a single drought response strategy. In environments where conditions are variable, plants may additionally evolve phenotypically plastic trait responses to water availability. Invasive annual species commonly occur in arid and semi-arid environments and many will be subject to reduced water availability associated with climate change. Assessing intraspecific trait variation across environmental gradients is a valuable tool for understanding how invasive plants establish and persist in arid environments.MethodsIn this study, we used a common garden experiment with two levels of water availability to determine how traits related to carbon assimilation, water use, biomass allocation and flowering phenology vary in California wild radish populations across an aridity gradient.Key ResultsWe found that populations from arid environments have rapid flowering and increased allocation to root biomass, traits associated with both drought escape and tolerance. Early flowering was associated with higher leaf nitrogen concentration and lower leaf mass per area, traits associated with high resource acquisition. While trait values varied across low- and high-water treatments, these shifts were consistent across populations, indicating no differential plasticity across the aridity gradient.ConclusionsWhile previous studies have suggested that drought escape and drought resistance are mutually exclusive drought response strategies, our findings suggest that invasive annuals may employ both strategies to succeed in novel semi-arid environments. As many regions are expected to become more arid in the future, investigations of intraspecific trait variation within low water environments help to inform our understanding of potential evolutionary responses to increased aridity in invasive species.     

Do annual and perennial populations of an insect-pollinated plant species differ in mating system?

Background and AimsTheory predicts that outcrossing should be more prevalent among perennials than annuals, a pattern confirmed by comparative evidence from diverse angiosperm families. However, intraspecific comparisons between annual and perennial populations are few because such variation is uncommon among flowering plants. Here, we test the hypothesis that perennial populations outcross more than annual populations by investigating Incarvillea sinensis, a wide-ranging insect-pollinated herb native to China. The occurrence of both allopatric and sympatric populations allows us to examine the stability of mating system differences between life histories under varying ecological conditions.MethodsWe estimated outcrossing rates and biparental inbreeding in 16 allopatric and five sympatric populations in which both life histories coexisted using 20 microsatellite loci. In each population we measured height, branch number, corolla size, tube length and herkogamy for ~30 individuals. In a sympatric population, we recorded daily flower number, pollinator visitation and the fruit and seed set of annual and perennial plants.Key ResultsAs predicted, outcrossing rates (t) were considerably higher in perennial (mean = 0.76) than annual (mean = 0.09) populations. This difference in mating system was also maintained at sympatric sites where plants grew intermixed. In both allopatric and sympatric populations the degree of herkogamy was consistently larger in outcrossing than selfing plants. Perennials were more branched, with more and larger flowers than in annuals. In a sympatric population, annuals had a significantly higher fruit and seed set than perennials.ConclusionsGenetically based differences in herkogamy between annuals and perennials appear to play a key role in governing outcrossing rates in populations, regardless of variation in local ecological conditions. The maintenance of mating system and life history trait differentiation between perennial and annual populations of I. sinensis probably results from correlated evolution in response to local environmental conditions.     

Complex Genetic Effects on Early Vegetative Development Shape Resource Allocation Differences Between Arabidopsis lyrata Populations

Costs of reproduction due to resource allocation trade-offs have long been recognized as key forces in life history evolution, but little is known about their functional or genetic basis. Arabidopsis lyrata, a perennial relative of the annual model plant A. thaliana with a wide climatic distribution, has populations that are strongly diverged in resource allocation. In this study, we evaluated the genetic and functional basis for variation in resource allocation in a reciprocal transplant experiment, using four A. lyrata populations and F₂ progeny from a cross between North Carolina (NC) and Norway parents, which had the most divergent resource allocation patterns. Local alleles at quantitative trait loci (QTL) at a North Carolina field site increased reproductive output while reducing vegetative growth. These QTL had little overlap with flowering date QTL. Structural equation models incorporating QTL genotypes and traits indicated that resource allocation differences result primarily from QTL effects on early vegetative growth patterns, with cascading effects on later vegetative and reproductive development. At a Norway field site, North Carolina alleles at some of the same QTL regions reduced survival and reproductive output components, but these effects were not associated with resource allocation trade-offs in the Norway environment. Our results indicate that resource allocation in perennial plants may involve important adaptive mechanisms largely independent of flowering time. Moreover, the contributions of resource allocation QTL to local adaptation appear to result from their effects on developmental timing and its interaction with environmental constraints, and not from simple models of reproductive costs.     

Phenology constrains opportunistic growth response in <Emphasis Type="Italic">Bromus tectorum</Emphasis> L.

Seasonal resource availability may act as a constraint on plant phenology and thereby influence the range of growth responses observed among populations of annual species, especially those occupying a wide range of environments. We compared a mesic and a xeric population of the non-native, annual grass, Bromus tectorum, to examine phenology in response to interspecific competition and water availability. Using a target-neighborhood approach, we assessed how phenological patterns of the two populations affected morphological and growth responses to enhanced resource availability represented by late-season soil moisture. The xeric population exhibited a highly constrained phenology and was unable to extend the growing season despite available soil resources. Because of the low phenotypic variation, allocation to reproduction was similar across resource conditions. In contrast, the mesic population flowered later and showed a more opportunistic phenology in response to late-season water availability. The mesic population was not able to maintain consistent reproductive allocation at low resource levels. The responses of the two populations to late-season water availability were not affected by the density of neighboring plants. We suggest that post-introduction selection pressure on B. tectorum in the xeric habitat has resulted in a more fixed phenology which limits opportunistic response to unpredictable, particularly late-season resource availability. Opportunistic and fixed responses represent contrasting strategies for optimizing fitness in temporally varying environments and, while both play important roles for ensuring reproductive success, these results suggest that local adaptation to temporal resource variation may reflect a balance between flexible and inflexible phenology.     

Life-history variation in the short-lived herb Rorippa palustris: The role of carbon storage

Carbon storage is commonly found among perennials, but only rarely in annuals. However, many short-lived species may behave as annuals or short-lived perennials depending on the date of germination, photoperiod or disturbance. Due to the trade-off between investments into current reproduction vs. survival, these life-history modes presumably differ in carbon allocation. In this study, we aimed to evaluate how carbon storage is affected by germination date and disturbance in an outdoor pot experiment with the short-lived Rorippa palustris. Plants from autumnal and summer cohorts were injured in different ontogenetic stages (vegetative, flowering and fruiting) and the starch content in roots was assessed. Plants from the autumnal cohort invested more carbon into growth and reproduction, whereas plants from the summer cohort invested preferentially into reserves. However, injury changed the allocation pattern: in plants from the autumnal cohort, injury prevented allocation to reproduction and thus injured plants had a larger carbon storage at the end of the season than control plants; injury at the flowering and fruiting stage caused depletion of reserves for regrowth in plants from the summer cohort, resulting in lower starch reserves compared to control plants. We suggest that life-history variation in R. palustris can be caused by changes in its carbon economy: when all resources could not be used for flowering due to weak photoinduction or loss of flowering organs due to injury, part of the resources is stored for over wintering and reproduction in the next year.     

Reproductive efficiency and shade avoidance plasticity under simulated competition

Plant strategy and life‐history theories make different predictions about reproductive efficiency under competition. While strategy theory suggests under intense competition iteroparous perennial plants delay reproduction and semelparous annuals reproduce quickly, life‐history theory predicts both annual and perennial plants increase resource allocation to reproduction under intense competition. We tested (1) how simulated competition influences reproductive efficiency and competitive ability (CA) of different plant life histories and growth forms; (2) whether life history or growth form is associated with CA; (3) whether shade avoidance plasticity is connected to reproductive efficiency under simulated competition. We examined plastic responses of 11 herbaceous species representing different life histories and growth forms to simulated competition (spectral shade). We found that both annual and perennial plants invested more to reproduction under simulated competition in accordance with life‐history theory predictions. There was no significant difference between competitive abilities of different life histories, but across growth forms, erect species expressed greater CA (in terms of leaf number) than other growth forms. We also found that shade avoidance plasticity can increase the reproductive efficiency by capitalizing on the early life resource acquisition and conversion of these resources into reproduction. Therefore, we suggest that a reassessment of the interpretation of shade avoidance plasticity is necessary by revealing its role in reproduction, not only in competition of plants.     

Population- and family-level variation of brittlebush (Encelia farinosa, Asteraceae) pubescence: its relation to drought and implications for selection in variable environments

Because leaf pubescence of the desert shrub Encelia farinosa increases in response to drought and influences photosynthesis and transpiration, we hypothesized that differences in water availability across the range of this species may result in genetic differentiation for pubescence and associated productivity traits. We examined maternal family variation of pubescence-moderated light absorption (absorptance) in three populations of E. farinosa. Absorptance was always greatest for plants from the high-rainfall environment and lowest for those from the driest site, but the rate of absorptance change in response to drought was similar among all populations. Similar patterns were found when we compared families within populations-all genotypes had similar initial leaf absorptances, differentiated very early in seasonal growth, then had concordant changes in absorptance thereafter. However, family-level variance was greatest for plants from the driest site, a region with highly heterogeneous precipitation patterns, whereas low variance was found for plants from the wettest, least heterogeneous site. The concordance of leaf absorptance changes, within and among populations, may be due to integration with other drought-related traits; however, the differences in absorptance values within and among populations suggest that variation of leaf pubescence results from selection associated with geographical and local patterns of water availability.     

DROUGHT AND THE EVOLUTION OF FLOWERING TIME IN DESERT ANNUALS

Drought is often thought to stimulate flowering in desert, and sometimes in mesic, annuals. I review experimental studies of the effect of drought on flowering time in both desert and mesic annuals. No convincing experimental evidence presently exists that drought stimulates flowering in any annual plant; some experimental results suggest the opposite. The design and analysis of flowering time studies are also reviewed; most extant studies have serious flaws. Thus, a convincing demonstration of drought-stimulated flowering will require carefully designed and analyzed experiments. In light of these results, I examine several ways in which drought may affect the ecology and evolution of flowering time in desert annuals, and suggest directions for research. Several mechanisms probably contribute to phenotypic variation in flowering time and size, including water and nutrient limitation, competition, and variation in seed size and germination time. Phenotypic effects of seed traits suggest that seed and flowering time traits may not evolve independently of one another. Water stress during reproduction can influence seed traits; such maternal effects can influence the outcome of selection both on seed traits and on flowering time. The multivariate character of flowering time evolution suggests that genetic and phenotypic correlations among these traits may present important constraints on the evolution of flowering time.     

Joint impact of competition,summer precipitation,and maternal effects on survival and reproduction in the perennial <Emphasis Type="Italic">Hieracium umbellatum</Emphasis>

Most studies on consequences of environmental change focus on evolutionary and phenotypic plastic responses, but parental effects represent an additional mechanism by which organisms respond to their local environment. Parental effects can be adaptive if they enhance offsprings ability to cope with environments experienced by their parents, but can also be non-adaptive for instance when offspring from benign environments are just better provisioned and hence perform better than offspring from less benign environments. Parental effects originate from both the abiotic and biotic environmental variation. However, the effects of the parental abiotic and biotic environment are rarely studied together. We make use of an experimental set-up containing plots in a natural heath land, where summer precipitation was manipulated to reflect either ambient or drought conditions. In both plot types, competition from grasses was prevalent. We assessed survival and reproduction of Hieracium umbellatum offspring originating from ambient and drought plots grown in a factorial design with two levels of moisture (control and drought) and two levels of competition (grown with and without a local perennial grass). The maternal environment strongly affected offspring performance. Biomass and reproduction was higher in offspring from ambient plots in agreement with the hypothesis of a better maternal provisioning in the most benign environment. However, adding competition revealed potentially adaptive responses to survival, and altered allocation to reproduction in offspring from maternal drought plots. Under combined competition and drought (mimicking maternal drought plots), survival was only reduced in offspring from ambient plots, and offspring from drought plots survived best. When grown in competition under control watering conditions mimicking maternal ambient plots, offspring from drought plots (growing in an environment different from their maternal one) showed a 25% reduction in reproduction. Potential adaptive responses to the home maternal environment were only revealed when jointly manipulating levels of competition and water availability.     

Habitat quality and among-population differentiation in reproductive effort and flowering phenology in the perennial herb <Emphasis Type="Italic">Primula farinosa</Emphasis>

In heterogeneous environments, selection on life-history traits and flowering time may vary considerably among populations because of differences in the extent to which mortality is related to age or size, and because of differences in the seasonal patterns of resource availability and intensity of biotic interactions. Spatial variation in optimal reproductive effort and flowering time may result in the evolution of genetic differences in life-history traits, but also in the evolution of adaptive phenotypic plasticity. The perennial herb Primula farinosa occurs at sites that differ widely in soil depth and therefore in water-holding capacity, vegetation cover, and frost-induced soil movement in winter. We used data from eight natural populations and a common-garden experiment to test the predictions that reproductive allocation is negatively correlated with soil depth while age at first reproduction and first flowering date among reproductive individuals are positively correlated with soil depth. In the common-garden experiment, maternal families collected in the field were grown from seed and monitored for 5 years. In the field, reproductive effort (number of flowers in relation to rosette area) varied among populations and was negatively related to soil depth. In the common-garden experiment, among-population differences in age at first reproduction, and reproductive effort were statistically significant, but relatively small and not correlated with soil depth at the site of origin. Flowering time varied considerably among populations, but was not related to soil depth at the site of origin. Taken together, the results suggest that among-population variation in reproductive effort observed in the field largely reflects phenotypic plasticity. They further suggest that among-population differentiation in flowering time cannot be attributed to variation in environmental factors correlated with soil depth.     

Reproductive competence from an annual and a perennial perspective

Plants at early stages of development undergo a juvenile phase during which they are not competent to flower in response to environmental stimuli. The length of this phase varies among species and is extended in perennial plants particularly. In annuals, temporal changes in expression of microR156 (miR156), miR172, and their targets are correlated with the transition from the juvenile to the adult phase and flowering. This developmental transition in perennials is probably more complex than in other plants and the molecular mechanisms are less well understood. In addition, once perennials become adult and capable of reproduction they still keep some meristems in the vegetative state that contribute to their polycarpic growth habit. Juvenility and polycarpy, although considered as two different processes in perennials, might be related.     

Modelling the Coexistence of Annual and Perennial Plants in Temporally Varying Environments*

Abstract The long-term growth and coexistence of species with large mixed populations in varying environments were modelled for representative environments and life-history characteristics of annual and perennial plants. The effects of the relationships between the means, variances, and covariances of seed yield, establishment, and survival, were explored by Taylor's expansion. The main findings are: 1. Individual variation in reproductive success within generations has no effect on long-term growth, which is determined only by the mean growth rate of the individuals of the species. 2. In annual species with nonoverlapping generations and without seed banks, the species with the largest mean log of the annual growth rate Y, that is the product of the average seed yield per plant and the establishment probability per seed, will win in competition with other species, independent of the correlations between the growth rates of the different species. In this case there is a negative tradeoff between the mean and the variance. 3. In perennial species with a lottery type of equal access to vacant sites, a high annual survival probability allows stable coexistence between perennial species with independent or negatively correlated variance in their mean annual product of seed production and establishment Y. 4. The coexistence range and the likely number of coexisting perennial species increase as a function of the variance of the common species, and is decreased by the variance of the rare species. The coexistence range is decreased by the covariance between the growth rates of the species, and between the survival of the rare species and its growth rate. 5. If mortality in the community of long-lived perennials is synchronized, the generations become nonoverlapping, and the competitive dynamics become similar to that of annuals. 6. Coexistence between annual and perennial species is promoted if the covariances between the annual survival and the relative yield of perennials, and between the yields of perennials and annuals, decrease and become more negative. 7. Selection for seed yield and establishment in different conditions in annuals favours a generalist strategy with low variance between years which provides a moderate yield and establishment over a wide range of environmental conditions. In perennial plants, long-term growth rate is determined by the lifetime seed yield and establishment. Because of strong competition with annuals in the more common conditions, selection in perennials favours instead a specialist strategy, with a high seed yield and establishment at relatively rare occasions in space and time, in which there is only weak competition with annuals. 8. Coexistence of annual species with a long-lived seed bank in the soil is also made possible by independent variation in different years of the germination, seed yield and establishment of different species, analogous to the situation of perennial plants.     

Interclonal differences, plasticity and trade-offs of life history traits of Cyperus esculentus in relation to water availability

Cyperus esculentus is an exotic clonal (or pseudoannual) weed in Japan, and its range is steadily increasing. To investigate its interclonal variation and phenotypic plasticity in response to water availability, five clones of C. esculentus , collected from different sites in Japan, were grown singly in pots placed outdoors under dry and wet conditions. All the traits examined showed considerable variation among the five clones. However, two clones from Tochigi were similar to each other; thus, they might have originated from the same founder population. The clone from Ibaraki was quite different from the others. Therefore, it is suggested that the Japanese populations of C. esculentus might have resulted from multiple introductions of genotypes from geographically separated and, hence, genetically differentiated, source populations. All the clones also showed considerable plasticity in response to water availability. Clones with a larger ramet number had a greater plasticity, whereas tuber size was invariant across water treatments. Highly plastic traits had generally low interclonal variation in plasticity. All the clones had high productivity and produced more ramets and tubers under wet conditions than under dry conditions. Moreover, water availability could partially regulate the mode of its reproduction; wet conditions favored tuber production (vegetative propagation) while dry conditions favored sexual reproduction. A number of trade-offs occurred between the traits of clonal growth, storage and sexual reproduction, indicating that allocation among the competing functions/organs is mutually exclusive in plants. The results obtained here suggest that C. esculentus is more likely to invade wet habitats than dry habitats.     

新疆郁金香营养生长、个体大小和开花次序对繁殖分配的影响

植物有性繁殖与资源分配的关系研究对于揭示植物生活史特征及繁育系统进化具有重要意义。新疆郁金香(Tulipa sinkiangensis)是新疆天山北坡荒漠带特有的一种多年生早春短命植物。在自然生境中,该物种仅以有性繁殖产生后代,每株能产生1-8朵花,且不同植株上的花数及果实数以及花序不同位置上的花与果实大小明显不同。本文通过对新疆郁金香有性繁殖与营养生长及植株大小的关系以及花序中不同位置花及果实间的资源分配研究,旨在揭示营养生长、个体大小及开花次序对其繁殖分配的影响。结果表明:在开花和果实成熟阶段,新疆郁金香植株分配给营养器官(鳞茎和地上营养器官)与繁殖器官的资源间均存在极显著的负相关关系(P<0.01),说明其植株的营养生长与生殖生长间存在权衡关系。多花是新疆郁金香的一个稳定性状,其植株上花数目、花生物量、果实生物量和种子数量与植株生物量间均呈极显著的正相关关系(P<0.01),说明新疆郁金香植株的繁殖分配存在大小依赖性。在具2-5朵花的新疆郁金香植株中,花序内各花的生物量、花粉数和胚珠数、结实率、果实生物量、结籽数、结籽率及种子百粒重按其开花顺序依次递减,说明花序内各花和果实的资源分配符合资源竞争假说。植株通过减少晚发育的花或果实获得的资源来保障早发育的花或果实获得较多的资源,从而达到繁殖成功。     

Phenotypic Integration and the Plasticity of Integration in an Amphicarpic Annual

In annual plants, including amphicarpic annuals, variation in light availability can evoke phenotypic plasticity in multiple traits. We examined plasticity to light availability of vegetative and reproductive performance traits in Amphicarpaea bracteata (Fabaceae) by developing and evaluating three path-analysis models using data from a greenhouse study. To assess whether light availability altered the phenotypic integration of these performance traits, we examined the models' fit to data collected within a high- or a low-light treatment. We also examined whether a single model or alternate models were required to fit data from the two contrasting light treatments. Using our path-analysis approach, we also made comparisons among three population types: shade- and sun-native populations of the widespread variety A. bracteata var. bracteata and sun-native populations of the variety A. bracteata var. comosa. Although each type of population was somewhat distinctive in patterns of integration and in the plasticity of integration, patterns did not correspond to contrasting ecological affinity, i.e., shade- and sun-native population types or to genetic relatedness of the two varieties. Counter to the prediction that selection regimes involving variation in one or more environmental factor favor intermediate levels of integration, phenotypic integration in A. bracteata was very flexible, with plasticity occurring in a trait-by-trait manner. In particular, there was an inverse relationship between aerial and subterranean reproductive modes in low but not high light. Previous studies of amphicarpic annuals have not observed this type of environment-specific life history trade-off.     

COST OF REPRODUCTION IN POLEMONIUM VISCOSUM: PHENOTYPIC AND GENETIC APPROACHES

I measured the effect of early reproduction on subsequent growth and survival in the alpine perennial wildflower, Polemonium viscosum. Measurements were made over 4 yr on 34 maternal sibships under natural conditions. A significant phenotypic cost of early reproduction characterized the study population. Plants that flowered after only one year's growth had twice as many leaves and 25% more shoots than nonflowering individuals of equal age. However, early flowering decreased leaf number by 18% in the subsequent year and survivorship by 20% after two years relative to changes in leaf number and survival of nonflowering plants. For such trade-offs to shape the further evolution of reproductive schedules, flowering probability and those age-specific components of plant size that represent the energetic currency for reproductive costs must be heritable. Although families showed significant heterogeneity in the probability of early flowering, most (62%) entirely failed to flower. Moreover, phenotypic variation in vegetative size components at ages 1 and 2 had little genetic basis. Only at ages 3 and 4, after vegetative and demographic costs of early reproduction had been incurred, did vegetative size components (leaf length and number, and shoot number) vary significantly among families. Results of this study provide little evidence of a genetically based trade-off between early reproduction and subsequent survival in P. viscosum.     

Variation and covariation among life-history traits in Rumex acetosella from a successional old-field gradient

In this study morphological variation and the potential for competition to affect biomass and seedling selection of the families of five populations of Rumex acetosella L. sampled along a successional old-field gradient have been investigated. Seeds from 25 families were submitted to four competitive regimes: no competition (one plant per pot), medium competition (two plants/ pot taking plants from the same population), high within-population competition (four individuals from the same population in a pot) and high between-population competition (four individuals from two different populations in a pot). Eight traits were analysed after 3 months of growth for variation among families within populations. A significant difference among families within the two older populations was recorded for sexual biomass and related components. High sensitivity of these traits to density was observed in all populations except the youngest, suggesting specialization to particular environmental conditions in late successional populations, and a good adaptive capacity to buffer environmental variation in the pioneer population. Little significant interaction between competitive regimes and families within populations was found, i.e. genotypes within each population showed little variation in their response to environmental variation. Genotypic variance decreased with increasing competitive conditions for the majority of the traits. However, the percentage of variance in sexual reproduction explained by family was stable among treatments. Tradeoffs between vegetative reproduction and sexual reproduction were recorded at the population level along the successional gradient, with increasing competitive conditions. As succession proceeds, we observed a decrease in sexual reproduction and an increase in vegetative reproduction. At the family level, correlation among traits were similar when plants were grown in the absence of competition and at high density, with a significant negative correlation between sexual reproduction and vegetative reproduction. For both sprout number and sexual biomass, the performance of families grown under all the treatments was positively correlated. Together these results indicate allocational constraints on the reproductive biology of R. acetosella that may be favoured by natural selection and have influenced population differentiation along the successional gradient. However, they also revealed that the potential exists for evolutionary specialization through plasticity, in response to variation in environmental conditions.