Differentiation In Life-history Traits Research Articles

Genetic differentiation in life history traits and thermal stress performance across a heterogeneous dune landscape in Arabidopsis lyrata.

Over very short spatial scales, the habitat of a species can differ in multiple abiotic and biotic factors. These factors may impose natural selection on several traits and can cause genetic differentiation within a population. We studied multivariate genetic differentiation in a plant species of a sand dune landscape by linking environmental variation with differences in genotypic trait values and gene expression levels to find traits and candidate genes of microgeographical adaptation. Maternal seed families of Arabidopsis lyrata were collected in Saugatuck Dunes State Park, Michigan, USA, and environmental parameters were recorded at each collection site. Offspring plants were raised in climate chambers and exposed to one of three temperature treatments: regular occurrence of frost, heat, or constant control conditions. Several traits were assessed: plant growth, time to flowering, and frost and heat resistance. The strongest trait-environment association was between a fast switch to sexual reproduction and weaker growth under frost, and growing in the open, away from trees. The second strongest association was between the trait combination of small plant size and early flowering under control conditions combined with large size under frost, and the combination of environmental conditions of growing close to trees, at low vegetation cover, on dune bottoms. Gene expression analysis by RNA-seq revealed candidate genes involved in multivariate trait differentiation. The results support the hypothesis that in natural populations, many environmental factors impose selection, and that they affect multiple traits, with the relative direction of trait change being complex. The results highlight that heterogeneity in the selection environment over small spatial scales is a main driver of the maintenance of adaptive genetic variation within populations.

Maternal investment decreases under stressful environments in 11 plateau brown frog (Rana kukunoris) populations

Environmental pressures vary by geographic location and will lead to differentiation in life history traits according to which maximize fitness. Life history theory predicts that harsh environments are likely to select for larger egg or offspring size, and for a stronger trade-off between offspring size and number. To test this prediction, we compared life history traits among 11 plateau brown frog (Rana kukunoris) populations at different altitudes. We found that females with a concomitant increase in body size produce larger eggs and more offspring in warm environments than females in cold environments do. Moreover, females from two natural populations produced offspring of different sizes between years. The decreasing resource allocation to current offspring size and number may increase survival and future fecundity in harsh environments. Thus, there may be a trade-off between mortality and fecundity in different environments. In addition to body size, we suggest that temperature plays an important role in shaping maternal investment variation in R. kukunoris across geographical gradients.

Differentiation of Life-History Traits among Palmer Amaranth Populations (Amaranthus palmeri) and Its Relation to Cropping Systems and Glyphosate Sensitivity

Palmer amaranth’s ability to evolve resistance to different herbicides has been studied extensively, but there is little information about how this weed species might be evolving other life-history traits that could potentially make it more aggressive and difficult to control. We characterized growth and morphological variation among 10 Palmer amaranth populations collected in Florida and Georgia from fields with different cropping histories, ranging from continuous short-statured crops (vegetables and peanut) to tall crops (corn and cotton) and from intensive herbicide use history to organic production. Palmer amaranth populations differed in multiple traits such as fresh and dry weight, days to flowering, plant height, and leaf and canopy shape. Differences between populations for these traits ranged from 36% up to 87%. Although glyphosate-resistant (GR) populations collected from cropping systems including GR crops exhibited higher values of the aforementioned variables than glyphosate-susceptible (GS) populations, variation in traits was not explained by glyphosate resistance or distance between populations. Cropping system components such as crop rotation and crop canopy structure better explained the differences among populations. The higher growth of GR populations compared with GS populations was likely the result of multiple selection forces present in the cropping systems in which they grow rather than a pleiotropic effect of the glyphosate resistance trait. Results suggest that Palmer amaranth can evolve life-history traits increasing its growth and reproduction potential in cropping systems, which explains its rapid spread throughout the United States. Furthermore, our findings highlight the need to consider the evolutionary consequences of crop rotation structure and the use of more competitive crops, which might promote the selection of more aggressive biotypes in weed species with high genetic variability.

Geographic variation in life-history traits: growth season affects age structure, egg size and clutch size in Andrew's toad (Bufo andrewsi).

BackgroundEnvironmental variation associated with season length is likely to promote differentiation in life-history traits, but has been little studied in natural populations of ectotherms. We investigated patterns of variation in egg size, clutch size, age at sexual maturity, maximum age, mean age, growth rate and adult body size in relation to growth season length among 17 populations of Andrew’s toad (Bufo andrewsi) at different latitudes and altitudes in the Hengduan Mountains, western China.ResultsWe found that egg size, age at sexual maturity, and mean age increased with decreasing length of the growth season, whereas clutch size showed a converse cline. Body size did not increase with decreasing length of the growth season, but was tightly linked to lifetime activity (i.e. the estimated number of active days during lifetime). Males and females differed in their patterns of geographic variation in growth rates, which may be the result of forces shaping the trade-off between growth and reproduction in different environments.ConclusionsOur findings suggest that growth season plays an important role in shaping variation in life-history traits in B. andrewsi across geographical gradients.Electronic supplementary materialThe online version of this article (doi:10.1186/s12983-016-0138-0) contains supplementary material, which is available to authorized users.

Variation in thermal performance of a widespread pathogen, the amphibian chytrid fungus Batrachochytrium dendrobatidis.

Rates of growth and reproduction of the pathogens that cause emerging infectious diseases can be affected by local environmental conditions; these conditions can thus influence the strength and nature of disease outbreaks. An understanding of these relationships is important for understanding disease ecology and developing mitigation strategies. Widespread emergence of the fungal disease chytridiomycosis has had devastating effects on amphibian populations. The causative pathogen, Batrachochytriumdendrobatidis (Bd), is sensitive to temperature, but its thermal tolerances are not well studied. We examined the thermal responses of three Bd isolates collected across a latitudinal gradient in eastern Australia. Temperature affected all aspects of Bd growth and reproduction that we measured, in ways that often differed among Bd isolates. Aspects of growth, reproduction, and their relationships to temperature that differed among isolates included upper thermal maxima for growth (26, 27, or 28°C, depending on the isolate), relationships between zoospore production and temperature, and zoospore activity and temperature. Two isolates decreased zoospore production as temperature increased, whereas the third isolate was less fecund overall, but did not show a strong response to temperature until reaching the upper limit of its thermal tolerance. Our results show differentiation in life-history traits among isolates within Australia, suggesting that the pathogen may exhibit local adaptation. An understanding of how environmental temperatures can limit pathogens by constraining fitness will enhance our ability to assess pathogen dynamics in the field, model pathogen spread, and conduct realistic experiments on host susceptibility and disease transmission.

The ecology of plant populations: their dynamics, interactions and evolution.

What regulates the size and distribution of plant populations? What determines whether a population of plants will increase in size or decline? What allows some species to become aggressive invaders of exotic habitats, and what prevents this from occurring? When do individuals from different species exclude each other from a community by competition, and when do their interactions facilitate coexistence? These are just a few of the questions that arise when one contemplates the ebb and flow of plants across our landscapes, the magnificent diversity one finds in some habitats, or the tendency of one species to exclude all others in habitats that would appear to be very similar. This Special Issue brings together 15 articles presenting recent research bearing on these and other questions that have become, or continue to be, hot topics in the study of plant populations. The topics covered in this issue range from the epigenetic inheritance of characters that influence defence traits to the abiotic factors and biotic interactions that contribute to community assembly and the coexistence of plant species. Several of the studies consider the ecology and evolution of invasive species. Others address questions about the evolutionary ecology of local adaptation and differentiation in lifehistory traits, including differentiation between the sexes of dioecious plants. With this breadth, it is perhaps not sensible to look for themes that unite all the papers ‐ beyond the common concern with plant populations. Nevertheless, one theme does echo hither and thither between the contributions made: that ecological interactions take place between organisms that vary genetically, and that the extent of genetic, indeed phylogenetic, divergence between interacting populations can matter. The integration of a formal phylogenetic perspective into comparative functional ecology represented an important step in the field of plant ecology (Harvey and Pagel, 1991; Silvertown et al., 1997). The point is a simple one: traits may be associated among species either because they are functionally related, or simply because traits are inherited together from common ancestors (or both). It is now accepted that failure to account for the latter possibility is tantamount to pseudoreplication, because species are not independent units, and can lead to spurious conclusions about function. In phylogenetically corrected analyses, trait associations between more closely related species are effectively downplayed in relation to those found between more distantly related species (Felsenstein, 1985; Grafen, 1989; Harvey and Pagel, 1991). But how distant is distant, in an absolute sense? In this Special Issue, two papers incorporate a phylogenetic perspective into their analyses, the second of which considers

Genetic differentiation in life-history traits of introduced and native common ragweed (Ambrosia artemisiifolia) populations

Introduced species represent opportunities to observe evolution over contemporary time scales, and as exotics encounter new environments, adaptive responses can occur, potentially contributing to invasion. Here, we compare 22 native North American populations and 12 introduced European populations of common ragweed (Ambrosia artemisiifolia) in five common gardens (control, herbivory, light stress, nutrient stress and drought). We found evidence for improved growth and reproduction of the introduced populations in most environments, particularly in the light stress. However, under drought conditions, the introduced plants experienced more rapid wilting and mortality than their native counterparts, evidence consistent with a life-history trade-off between rapid growth and drought tolerance. Moreover, we found parallel latitudinal clines in flowering time and correlations between fitness components and the local climate of the source populations in both ranges. Together these data provide evidence for adaptation to local environmental conditions in the native and introduced range of common ragweed.

PHENOTYPIC DIFFERENTIATION AT SOUTHERN LIMIT BORDERS: THE CASE STUDY OF TWO FUCOID MACROALGAL SPECIES WITH DIFFERENT LIFE-HISTORY TRAITS1.

Marginal populations are often geographically isolated, smaller, and more fragmented than central populations and may frequently have to face suboptimal local environmental conditions. Persistence of these populations frequently involves the development of adaptive traits at phenotypic and genetic levels. We compared population structure and demographic variables in two fucoid macroalgal species contrasting in patterns of genetic diversity and phenotypic plasticity at their southern distribution limit with a more central location. Models were Ascophyllum nodosum (L.) Le Jol. (whose extreme longevity and generation overlap may buffer genetic loss by drift) and Fucus serratus L. (with low genetic diversity at southern margins). At edge locations, both species exhibited trends in life-history traits compatible with population persistence but by using different mechanisms. Marginal populations of A. nodosum had higher reproductive output in spite of similar mortality rates at all life stages, making edge populations denser and with smaller individuals. In F. serratus, rather than demographic changes, marginal populations differed in habitat, occurring restricted to a narrower vertical habitat range. We conclude that persistence of both A. nodosum and F. serratus at the southern-edge locations depends on different strategies. Marginal population persistence in A. nodosum relies on a differentiation in life-history traits, whereas F. serratus, putatively poorer in evolvability potential, is restricted to a narrower vertical range at border locations. These results contribute to the general understanding of mechanisms that lead to population persistence at distributional limits and to predict population resilience under a scenario of environmental change.

Selection on life‐history traits and genetic population divergence in rotifers

A combination of founder effects and local adaptation - the Monopolization hypothesis - has been proposed to reconcile the strong population differentiation of zooplankton dwelling in ponds and lakes and their high dispersal abilities. The role genetic drift plays in genetic differentiation of zooplankton is well documented, but the impact of natural selection has received less attention. Here, we compare differentiation in neutral genetic markers (F(ST)) and in quantitative traits (Q(ST)) in six natural populations of the rotifer Brachionus plicatilis to assess the importance of natural selection in explaining genetic differentiation of life-history traits. Five life-history traits were measured in four temperature x salinity combinations in common-garden experiments. Population differentiation for neutral genetic markers - 11 microsatellite loci - was very high (F(ST) = 0.482). Differentiation in life-history traits was higher in traits related to sexual reproduction than in those related to asexual reproduction. Q(ST) values for diapausing egg production (a trait related to sexual reproduction) were higher than their corresponding F(ST) in some pairs of populations. Our results indicate the importance of divergent natural selection in these populations and suggest local adaptation to the unpredictability of B. plicatilis habitats.

Evolutionary Differentiation of Fitness Traits Across Multiple Geographic Scales inAedes albopictus(Diptera: Culicidae)

AbstractAedes albopictus (Skuse) (Diptera: Culicidae) is an invasive, container-inhabiting mosquito that was introduced into North America from Japan in 1985. Although previous studies using neutral biochemical markers have found high levels of population differentiation across both the North American and global distribution of Ae. albopictus, relatively little is known regarding evolutionary differentiation of life history traits underpinning fitness. We performed common-garden and line-cross experiments to examine the genetic differentiation of fitness (r')and underlying performance traits at three spatial scales: 1) local (among populations within Florida), 2) regional (between populations from Florida and New Jersey), and 3) long distance (between populations from Florida and Hawaii, Malaysia, and Japan). We found that North American populations (Florida and New Jersey) had lower fitness (r') than populations from outside North America (Hawaii, Malaysia, and Japan). Bivariate means of female, but not male, pupal mass and developmental time differed among regions (Florida, New Jersey, outside North America). Larval survivorship did not differ among regions nor among populations within regions, whereas size-specific fecundity varied among populations within regions but not among regions. Population crosses resulted in significant heterosis and outbreeding depression Of F1 hybrids but the results of crossing did not depend on the geographic distance separating parental populations in a consistent manner. Together, our results imply a role for local genetic drift affecting the life-history differentiation of Ae. albopictus populations. These conclusions corroborate previous studies of population structure based on neutral biochemical markers.

Local adaptation in moss life histories: population-level variation and a reciprocal transplant experiment

We examine the extent of population-level differentiation in life history traits of Pogonatum aloides, Polytrichum commune and Polytrichum juniperinum (Polytrichaceae) between upland and lowland localities within Britain. Reciprocal transplant studies are used to estimate the relative importance of genetic versus environmental effects on observed differences. We demonstrate significant life history differentiation between moss populations, and show that at least some of these are genetically determined, although environment and phenotypic plasticity are also significant components of the observed variation. The transplant experiments indicate divergence among populations in plasticity of male reproductive effort and of investment in vegetative shoots by females. Two tradeoffs are identified; one between the number and the size of spores, and the second between reproduction by spores versus vegetative reproduction. The patterns of life history variation observed between populations of Polytrichum juniperinum are consistent with selection along these implied tradeoff curves, and we propose that they reflect selective pressures arising from the spatial and demographic distribution of mortality at upland versus lowland sites. The results underscore the need for more studies of intra-specific life history variation in mosses.

Diversity of Daphnia galeata life history traits in a vertically structured environment

We used laboratory experiments to investigate the life history traits of clonal lineages of Daphnia galeata isolated from two vertically segregated subpopulations in a deep dimictic reservoir: one from the epilimnion and the other from the deep hypolimnion. We collected clones twice for the experiments, first at the beginning of thermal stratification in May and then towards the end of the season in September. The results for May showed longer postembryonic development (PED), bigger eggs in the first clutch and slightly higher somatic increments in the hypolimnetic clones. In addition, a remarkable tendency to produce ephippia was recorded in the hypolimnetic clones, but not in the epilimnetic clones. In September, the results were reversed—hypolimnetic clones had shorter PED, lower somatic increments and a slightly higher number of eggs in the first clutch. Our results suggest a differentiation of life history traits in the two D. galeata populations inhabiting contrasting microhabitats of a reservoir as a result of (i) different depth preferences of certain clones in the beginning of thermal stratification in spring and (ii) divergent selection processes due to segregation in different environmental conditions. The ability of Daphnia to live in diverse environments, causing divergent selection processes, enhances the overall phenotypic and genotypic diversity of the whole reservoir population.

Adaptive genetic differentiation in life-history traits between populations of Mimulus guttatus 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.

Fine-scale genetically based differentiation of life-history traits in the perennial shrub Lupinus arboreus.

Across large spatial scales, plants often exhibit genetically based differentiation in traits that allow adaptation to local sites. At smaller spatial scales, sharp boundaries between edaphic conditions also can create strong gradients in selection that counteract gene flow and result in local adaptation. Few studies, however, have examined the degree to which continuous populations of perennial plants exhibit genetically based differentiation in life-history traits over small spatial scales. We quantified the degree of genetically based differentiation in adaptive traits among bush lupine (Lupinus arboreus) from nearby dune and grassland sites (sites separated by < 0.75 km) that formed part of a larger continuous population of L. arboreus. We also investigated the spatial genetic structure of bush lupine by examining how genetic structure differed between seeds and juvenile plants that were less than two years old. We calculated F-statistics from gel electrophoresis of 10 polymorphic loci. We then used these values to infer levels of gene flow. To examine differentiation in adaptive traits, we created full-sibling/half-sibling families of lupine within each area and established reciprocal common gardens at each site. Across two years, we measured canopy volume, flowering time, seed set, and mortality of progeny planted in each garden. Spatial genetic structure among seeds was virtually nonexistent (F(ST) = 0.002), suggesting that gene flow between the three areas could be quite high. However, genetic structure increased 20-fold among juvenile plants (F(ST) = 0.041). We found strong evidence for fine-scale genetically based differentiation and local adaptation in adaptive traits such as plant size, flowering phenology, fecundity, and mortality. Thus, it is likely that strong but differing selection regimes within each area drive spatial differentiation in lupine life-history traits.

FINE-SCALE GENETICALLY BASED DIFFERENTIATION OF LIFE-HISTORY TRAITS IN THE PERENNIAL SHRUB LUPINUS ARBOREUS

Across large spatial scales, plants often exhibit genetically based differentiation in traits that allow adaptation to local sites. At smaller spatial scales, sharp boundaries between edaphic conditions also can create strong gradients in selection that counteract gene flow and result in local adaptation. Few studies, however, have examined the degree to which continuous populations of perennial plants exhibit genetically based differentiation in life-history traits over small spatial scales. We quantified the degree of genetically based differentiation in adaptive traits among bush lupine (Lupinus arboreus) from nearby dune and grassland sites (sites separated by <0.75 km) that formed part of a larger continuous population of L. arboreus. We also investigated the spatial genetic structure of bush lupine by examining how genetic structure differed between seeds and juvenile plants that were less than two years old. We calculated F-statistics from gel electrophoresis of 10 polymorphic loci. We then used these values to infer levels of gene flow. To examine differentiation in adaptive traits, we created full-sibling/half-sibling families of lupine within each area and established reciprocal common gardens at each site. Across two years, we measured canopy volume, flowering time, seed set, and mortality of progeny planted in each garden. Spatial genetic structure among seeds was virtually nonexistent (FST = 0.002), suggesting that gene flow between the three areas could be quite high. However, genetic structure increased 20-fold among juvenile plants (FST = 0.041). We found strong evidence for fine-scale genetically based differentiation and local adaptation in adaptive traits such as plant size, flowering phenology, fecundity, and mortality. Thus, it is likely that strong but differing selection regimes within each area drive spatial differentiation in lupine life-history traits.Corresponding Editor: S. Tonsor

Sex ratio variation and spatial distribution of Siparuna grandiflora, a tropical dioecious shrub.

Populations of dioecious plant species often exhibit biased sex ratios. Such biases may arise as a result of sex-based differences in life history traits, or as a result of spatial segregation of the sexes. Of these, sex-based differentiation in life history traits is likely to be the most common cause of bias. In dioecious species, selection can act upon the sexes in a somewhat independent way, leading to differentiation and evolution toward sex-specific ecological optima. I examined sex ratio variation and spatial distribution of the tropical dioecious shrub Siparuna grandiflora to determine whether populations exhibited a biased sex ratio, and if so, whether the bias could be explained in terms of non-random spatial distribution or sex-based differentiation in life history traits. Sex ratio bias was tested using contingency tables, a logistic regression approach was utilized to examine variation in life history traits, and spatial distributions were analyzed using Ripley's K, a second-order neighborhood analysis. I found that although populations of S. grandiflora have a male-biased sex ratio within and among years, there was no evidence of spatial segregation of the sexes. Rather, the sex ratio bias was shown to result primarily from sex-based differentiation in life history traits; males reproduce at a smaller size and more frequently than females. The sexes also differ in the relationship between plant size and reproductive frequency. Light availability was shown to affect reproductive activity in both sexes, though among infrequently flowering plants, females require higher light levels than males to flower. The results of this study demonstrate that ecologically significant sex-based differentiation has evolved in S. grandiflora.

Adaptive inter-population differences in blue tit life-history traits on Corsica

Few studies of natural populations have investigated how phenotypic variation across populations relates to key factors in the environment and landscape structure. In the blue tits of southern France, inter-population differences in reproductive life-history traits (e.g. laying date and clutch size) are small, whatever the timing of maximum caterpillar availability, a key factor for offspring survival in tits. These small differences are attributed to gene flow between local populations occupying different habitat types. In contrast, in blue tits on the island of Corsica, we noted large differences in reproductive life-history traits between two populations, where each population is synchronized with the peak-date of caterpillar abundance. These occur over a short geographical distance (25 km). Considering our study within a framework of long-term population studies in tits, our results support the hypothesis that different blue tit populations on Corsica show adaptive differences in life-history traits, and suggest that landscape structure at a small spatial scale can have profound effects on adaptive between-pop illation differentiation in life-history traits that are closely linked with fitness.

Environmental and population-specific contributions to growth rate variation in the marine amphipod Jassa marmorata Holmes

Local selective regimes and limited dispersal may contribute to genetic differentiation of life history traits among local populations of the marine amphipod Jassa marmorata Holmes. Reciprocal transplant experiments were used to explore growth rate variation and to determine the effects of environment versus source population (genotype) on the observed variation. Gravid females were collected at two sites in Narragansett Bay, Rhode Island. Hatchlings were measured and reared in field enclosures following a split brood design. Measurements of total body size (length in mm) were made initially and at two additional time intervals. Experiments were conducted in spring and summer of 1994 and again in the spring of 1995. Growth curve analysis was used to test the effects of two independent variables, source population and environment, on growth rate. Results of the spring 1994 experiment revealed both source population (genetic) and environmental effects on growth rate. Individuals collected from and grown at Point Judith attained the highest body size. In the summer of 1994, there were no significant effects of environment or source population on growth rates. In the spring of 1995 only environmental effects were detected; animals grew faster at Point Judith. These results suggest that divergence between populations may occur with respect to growth rate but this divergence is not consistent interannually. An alternative mechanism, phenotypic plasticity, may also be employed by these amphipods to cope with environmental heterogeneity.

Genetic variation and ecotypic differentiation in the wild rice species Oryza rufipogon. I. Population differentiation in life-history traits and isozymic loci.

To examine the genetic differentiation between two ecotypes (annuals and perennials) in the wild rice species O. rufipogon, seeds and juveniles were collected from eight populations in Thailand, and compared regarding both life-history traits and enzyme loci. While no appreciable differentiation was found at the enzyme level, the two ecotypes showed a clear differentiation in life-history traits. This suggests either that gene flow occurs between the two ecotypes and ecotypic differentiation is maintained by selection, or that the annual-perennial differentiation is recent compared to the geographic differentiation between wild rice strains, and the evolution of life-history traits occurred rapidly.