Variation In Adaptive Traits Research Articles

Integrating evolutionary, demographic and ecophysiological processes to predict the adaptive dynamics of forest tree populations under global change

Three types of process-based models (PBMs) are traditionally used to predict the response of forest tree populations to global change (GC): (i) ecophysiological models, which simulate carbon and water fluxes in forest ecosystems by explicitly integrating the effects of climate and CO2; (ii) forest dynamics models which simulate forest successions by explicitly linking mortality, growth and regeneration processes; and (iii) evolutionary dynamics models, which simulate the variation and evolution of adaptive traits by explicitly accounting for selection, mutation, gene flow and inheritance rules. The ongoing context of rapid GC, however, questions the boundaries between these types of models. Here, we review different strategies of model integration: (i) physio-demographic PBMs, integrating physiological and demographic processes; (ii) demo-genetic PBMs, integrating demographic and evolutionary processes; and (iii) physio-demo-genetic PBMs, which attempt to integrate these three types of processes. We show that these integrative models allow a better understanding of how different functional traits influence demographic rates (the phenotype-demography map), how the variation in demographic rates influences fitness (the demography-fitness map) and how individual variations of fitness may in turn influence the genetic composition of a population. Our review highlights that accounting for inter-individual variation in ecological processes is increasingly recognized as crucial for modelling the ecosystem response to environmental change. We argue that the effort of integrating these different processes is valuable, both for a basic understanding of their interactive effects on the responses of forests to GC and for applied horizon scanning to support adaptive strategies.

Ecogenetic plasticity and genetic variation in Populus hybrids under the impact of simulated climate change related stressors


 To meet the needs of carbon sequestration and production of raw materials from renewable natural resources for the timber market of the European Union, it is necessary to expand forest plantation areas. The efficiency of short rotation forestry depends primarily on the selection of hybrids and clones, suitable for the local environmental conditions. We postulate that ecogenetic response, ecogenetic plasticity and genotypic variation of different hybrids of poplars (Populus L.) depend both on the type of stressors (spring frosts, summer drought, increased UV-B radiation, warm winters) and peculiarities of the cross-bred species as well as on their genetic preadaptations to native environmental conditions of their origin. The aim of the study was to estimate the ecogenetic plasticity, genotypic variation of adaptive traits and adaptability of Populus hybrids under simulated conditions of the expected climate change.
 The research was performed with the cultivars and experimental clones of three different intraspecific hybrids of poplars (P. nigra L., P. deltoides Bartr. ex Marsh, and P. trichocarpa Torr. & Gray.) and four interspecific hybrids of poplars (P. deltoides L. × P. nigra, P. deltoides × P. trichocarpa, P. maximowiczii A. Henry × P. trichocarpa, and P. balsamifera L. × P. trichocarpa).
 Simulated spring frosts and summer drought treatments had a substantial impact on growth of trees, but the hybrid and clone effects were also significant and showed that many hybrids and clones in general retain their features/differences under stressful environmental conditions. A strongly expressed hybrid and clone interactions with simulated frost and drought effects (genotype-environment interaction, G × E) showed different ecogenetic response, plasticity and specific ecological preferences of the clones and hybrids. The sensitivity of hybrids to UV-B radiation varied and depended on the origin of their parental trees and this sensitivity partially reflected their susceptibility also to other stressors. Warm winters adversely effected the growth of some hybrids while others - P. nigra × P. nigra and P. trichocarpa × P. trichocarpa, which parents originated from the southern part of their natural distribution range have increased their growth. This treatment also resulted in reduction of the heritability and genotypic variation of growth traits.
 
 Keywords: poplars, clones, genotype-environment interaction, genetic variation, heritability

Desiccation resistance and pigmentation variation reflects bioclimatic differences in the Drosophila americana species complex

BackgroundDisentangling the selective factors shaping adaptive trait variation is an important but challenging task. Many studies—especially in Drosophila—have documented trait variation along latitudinal or altitudinal clines, but frequently lack resolution about specific environmental gradients that could be causal selective agents, and often do not investigate covariation between traits simultaneously. Here we examined variation in multiple macroecological factors across geographic space and their associations with variation in three physiological traits (desiccation resistance, UV resistance, and pigmentation) at both population and species scales, to address the role of abiotic environment in shaping trait variation.ResultsUsing environmental data from collection locations of three North American Drosophila species—D. americana americana, D. americana texana and D. novamexicana—we identified two primary axes of macroecological variation; these differentiated species habitats and were strongly loaded for precipitation and moisture variables. In nine focal populations (three per species) assayed for each trait, we detected significant species-level variation for both desiccation resistance and pigmentation, but not for UV resistance. Species-level trait variation was consistent with differential natural selection imposed by variation in habitat water availability, although patterns of variation differed between desiccation resistance and pigmentation, and we found little evidence for pleiotropy between traits.ConclusionsOur multi-faceted approach enabled us to identify potential agents of natural selection and examine how they might influence the evolution of multiple traits at different evolutionary scales. Our findings highlight that environmental factors influence functional trait variation in ways that can be complex, and point to the importance of studies that examine these relationships at both population- and species-levels.

Adaptive trait variation in the federally endangered Lindera melissifolia (Lauraceae), as it relates to genotype and genotype-environment interaction1

Molecular markers have shown a high level of genetic diversity in most extant populations of the federally endangered Lindera melissifolia (Walt.) Blume in the southeastern United States. However, it is unknown if diversity in adaptive traits exists. We quantified adaptive trait variation in 17 L. melissifolia genotypes by growing genets from two disjunct populations in the Lower Mississippi Alluvial Valley in a common-garden environment. We then examined genotype-environment interaction through introduction of a flooding treatment. Within a common-garden environment, variation in adaptive traits was affected by genotype. Stem height, stem diameter, leaf number, and stem architecture accounted for 56% of variation among genotypes, and an additional 23% of variation was attributed to differences in vegetative fecundity and foliar chlorophyll content. There was no divergence in plant morphology between disjunct populations. Plastic response to a winter flooding regime varied in magnitude and direction among male genotypes, and only in magnitude in female genotypes. A decrease in L. melissifolia population sizes would diminish genetic diversity, as well as adaptive trait variation, and may threaten long-term persistence of extant populations.

Association of the phenylpropanoid pathway with dormancy and adaptive trait variation in apricot (Prunus armeniaca).

Trees use many mechanisms to adapt and respond to stressful conditions. The phenylpropanoid pathway in particular is known to be associated with a diverse suite of plant stress responses. In this study, we explored the relationship between the phenylpropanoid pathway metabolite production, gene expression and adaptive trait variation associated with floral bud reactivation during and following dormancy in Prunus armeniaca L. (apricot). Concentrations of eight phenylpropanoid metabolites were measured during chill accumulation and at developmental stages corresponding to the emergence of sepals and petals in floral buds of varieties that differ phenotypically in bloom date (BD). A significant interaction effect of chill hours and BD phenotype on the concentration of each of the compounds was observed (mixed analysis of variance, P<0.05), with the concentration of most phenylpropanoid metabolites dropping precipitously when sepals and petals emerged. While phenylpropanoid biosynthetic gene expression patterns were more variable in general, expression changed over time and was impacted, although to a lesser degree, by BD phenotype. Furthermore, separation of BD phenotypic groups was most pronounced when early and late BD varieties were at different developmental stages, i.e., 800 chill hours. Taken together, these results suggest that the phenylpropanoid pathway is associated with floral bud reactivation in apricot. Furthermore, we show that the phenylpropanoid pathway is also impacted by phenological trait variation associated with dormancy. A better understanding of how apricot and other perennial tree species respond and adapt to environmental perturbations will be critical for improvement programs aimed at identifying and breeding trees more suitable for rapidly changing environments.

Importance of considering soils in seed transfer zone development: evidence from a study of the native Bromus marginatus.

Seed transfer zones, which define the geographical relationship between adaptive traits and environmental factors, are increasingly used to determine the source populations that can be combined in restoration and revegetation. Climatic variables have been the most commonly used environmental data in transfer zone development, even though soils are also a primary selective force on plants. We assessed the importance of including soils in seed transfer zones using Bromus marginatus, a native grass used for restoration and revegetation in the western United States, as an example. Seeds were collected from 64 populations across Montana and Idaho and grown in a common garden for two years. We assessed among-population variation based on 11 traits related to germination rate, plant size, vigor, inflorescence number, survival, and carbon isotope discrimination (∆13 ), and used this variation to develop seed transfer zone maps using two approaches: (1) a conventional approach, using only climatic variables (climate only) and (2) an expanded approach that included soils and climatic variables (soils+climate). The most influential drivers of trait variation were factors related to soil water availability: soil order, available water content (AWC), and organic carbon levels. Populations from areas with andic soils, which have high soil AWC and soil organic carbon, had low germination, limited first-year survival, low ∆13 , and small seeds. Growing season length and winter temperatures were also predictive of trait variation. In comparison to climate-only models, soils+climate models explained 11% more variance (120% relative increase) for ∆13 and an average of 4.5% more (27% relative increase) for growth traits and survival. The transfer zone map developed using soils+climate differed from the climate-only map in both spatial pattern of ecotypic variation and number of transfer zones; the soils+climate map had more zones and a higher proportion of small (<4km2 ) transfer zone patches, while the climate-only map had more large patches >37km2 . Including soils in transfer zone development may identify adaptive trait variation that is obscured by large-scale differences in climate and could improve plant materials used for ecosystem management.

Genetic drift and uniform selection shape evolution of most traits in Eugenia dysenterica DC. (Myrtaceae)

Knowing how microevolutionary processes, such as genetic drift and natural selection, shape variation in adaptive traits is strategic for conservation measures. One way to estimate local adaptation is to compare divergences in quantitative traits (QST) and neutral loci (FST). Therefore, we have assessed the pattern of phenotypic and molecular genetic divergence among natural subpopulations of the fruit tree Eugenia dysenterica DC. A provenance and progeny test was performed to assess the quantitative traits of the subpopulations collected in a wide distribution area of the species in the Brazilian Cerrado. The sampled environments are in a biodiversity hotspot with heterogeneous soil and climate conditions. By associating quantitative trait variation in initial seedling development with neutral microsatellite marker variation, we tested the local adaptation of the traits by the QST–FST contrast. Genetic drift was prevalent in the phenotypic differentiation among the subpopulations, although the traits seedling emergence time and root green mass, which are relevant for adaptation to the Cerrado climate, showed signs of uniform selection. Our results suggest that E. dysenterica has a spatial genetic structure divided into two large groups, separated by a line that divides the Cerrado biome in a southwestern to northeastern direction. This structure must be taken into account for managing E. dysenterica genetic resources both for conservation and breeding purposes.

Genetic Variation of European Beech Populations and Their Progeny from Northeast Germany to Southwest Switzerland

Climate change can adversely affect the growth of European beech (Fagus sylvatica L.) across its entire distribution range. Therefore, knowledge of the adaptive potential of this species to changing climatic conditions is of foremost importance. Genetic diversity is the basis for adaptation to environmental stress, and the regeneration phase of forests is a key stage affecting genetic diversity. Nevertheless, little is known about the effect of climate change on the genetic diversity of adult trees compared to their progeny. Here, we present genetic diversity data for 24 beech populations ranging from northeast Germany to southwest Switzerland. Potentially adaptive genetic variation was studied using single nucleotide polymorphism (SNP) markers in candidate genes that are possibly involved in adaptive trait variation. In addition, more than 2000 adult trees and 3000 of their seedlings were genotyped with simple sequence repeat (SSR) markers to determine selectively neutral genetic diversity and differentiation among populations. All populations showed high SSR and SNP variation, and no differences in genetic diversity were found between adult trees and their offspring. The genetic differentiation between adults and seedlings within the same stands was also insignificant or very low. Therefore, we can conclude tentatively that the transfer of genetic variation among tree generations, currently, is not much affected by climate change, at least in the studied beech populations.

Development of Target Sequence Capture and Estimation of Genomic Relatedness in a Mixed Oak Stand.

Anticipating the evolutionary responses of long-lived organisms, such as trees, to environmental changes, requires the assessment of genetic variation of adaptive traits in natural populations. To this end, high-density markers are needed to calculate genomic relatedness between individuals allowing to estimate the genetic variance of traits in wild populations. We designed a targeted capture-based, next-generation sequencing assay based on the highly heterozygous pedunculate oak (Quercus robur) reference genome, for the sequencing of 3 Mb of genic and intergenic regions. Using a mixed stand of 293 Q. robur and Q. petraea genotypes we successfully captured over 97% of the target sequences, corresponding to 0.39% of the oak genome, with sufficient depth (97×) for the detection of about 190,000 SNPs evenly spread over the targeted regions. We validated the technique by evaluating its reproducibility, and comparing the genomic relatedness of trees with their known pedigree relationship. We explored the use of the technique on other related species and highlighted the advantages and limitations of this approach. We found that 92.07% of target sequences in Q. suber and 70.36% of sequences in Fagus sylvatica were captured. We used this SNP resource to estimate genetic relatedness in the mixed oak stand. Mean pairwise genetic relatedness was low within each species with a few values exceeding 0.25 (half-sibs) or 0.5 (full-sibs). Finally, we applied the technique to a long-standing issue in population genetics of trees regarding the relationship between inbreeding and components of fitness. We found very weak signals for inbreeding depression for reproductive success and no signal for growth within both species.

Looking at the forest from below: the role of seedling root traits in the adaptation to climate change of two Nothofagus species in Argentina

Global climate change (CC) is an evolutionary challenge for natural tree populations. Scientific experts forecast an increase in temperature and a decrease in precipitation in the Argentine Patagonian Cordillera. Knowledge of the variation of adaptive traits at the seedling stage is crucial to prediction the adaptability of forest tree species. We aim to analyze genetic variation in root and shoot quantitative traits among and within natural populations of two key North Patagonian forest species, in order to evaluate their ability to deal with CC through adaptation. We established two common garden nursery trials: (1) 81 open pollinated families of Nothofagus obliqua from eight natural populations, and (2) 74 families of Nothofagus alpina from seven populations. At the end of the first growing season we measured shoot height, diameter, root length and root and stem dry biomass; we also estimated foliage biomass. In addition the root to stem ratio, specific root length and the root to shoot ratio were calculated. For both species intra-population variation was generally low, and average differentiation was moderate, with high levels of differentiation in some traits related to drought stress, indicating low adaptation capacity but also adaptation to current stressful conditions, which means it may be possible for some populations to survive CC without changing their genetic structures. Further studies are needed, including phenotypic plasticity assays, to complete the picture.

An epigenetic breeding system in soybean for increased yield and stability.

SummaryEpigenetic variation has been associated with a wide range of adaptive phenotypes in plants, but there exist few direct means for exploiting this variation. RNAi suppression of the plant‐specific gene, MutS HOMOLOG1 (MSH1), in multiple plant species produces a range of developmental changes accompanied by modulation of defence, phytohormone and abiotic stress response pathways along with methylome repatterning. This msh1‐conditioned developmental reprogramming is retained independent of transgene segregation, giving rise to transgene‐null ‘memory’ effects. An isogenic memory line crossed to wild type produces progeny families displaying increased variation in adaptive traits that respond to selection. This study investigates amenability of the MSH1 system for inducing agronomically valuable epigenetic variation in soybean. We developed MSH1 epi‐populations by crossing with msh1‐acquired soybean memory lines. Derived soybean epi‐lines showed increase in variance for multiple yield‐related traits including pods per plant, seed weight and maturity time in both glasshouse and field trials. Selected epi‐F2:4 and epi‐F2:5 lines showed an increase in seed yield over wild type. By epi‐F2:6, we observed a return of MSH1‐derived enhanced growth back to wild‐type levels. Epi‐populations also showed evidence of reduced epitype‐by‐environment (e × E) interaction, indicating higher yield stability. Transcript profiling of epi‐lines identified putative signatures of enhanced growth behaviour across generations. Genes related to cell cycle, abscisic acid biosynthesis and auxin response, particularly SMALL AUXIN UP RNAs (SAURs), were differentially expressed in epi‐F2:4 lines that showed increased yield when compared to epi‐F2:6. These data support the potential of MSH1‐derived epigenetic variation in plant breeding for enhanced yield and yield stability.

Adaptive variation in physiological traits of beech provenances in Central Europe

Current climate changes can led to a decline of local beech populations fully adapted to previous climate conditions. In this context, the issue of variation in adaptive traits becomes important. A field experiment with 18-year-old trees of Fagus sylvatica L. was conducted on provenance plot located in Tále (Central Slovakia), where physiological responses of five beech provenances originating from contrasting sites along an altitudinal gradient from 55 to 1100 m a.s.l. across the range of the natural beech distribution were studied. Stomatal characteristics, parameters of chlorophyll a fluorescence and gas exchange parameters were determined. Overall, we observed a significant increase in physiological performance at the leaf level with increasing altitude of origin. Provenances from the higher altitudes showed higher CO2 assimilation rate, stomatal density, potential conductance indices and photochemical efficiency, and lower capability for dissipation of energy by heat. A similar pattern of response was recorded in relation to the precipitation regime of sites of origin. Moreover, in the context of the temperature regime, several negative trends were observed.

Exploiting genetic and physiological variation of the native forage grass Trichloris crinita for revegetation in arid and semi‐arid regions: An integrative review

AbstractIn arid, semi‐arid and dry subhumid regions, which represent ~ 41% of the Earth's land surface, desertification and soil degradation are very frequent, leading to low soil fertility and productivity. In these regions, revegetation with locally adapted native species may aid in ameliorating desertification processes. Trichloris crinita is a C4 perennial grass native to arid and semi‐arid regions of the American continent. Its good forage quality, drought tolerance, resistance to trampling and grazing, and rapid growth and competing aggressiveness among other native species warrant its use as forage and for revegetation purposes. In the last decades, many studies have revealed broad intraspecific genetic variation for ecophysiological, morphological, biomass production, nutritional quality (as forage) and adaptive stress response‐related traits. Also, results from field trials evaluating T. crinita genotypes as forage and for restoration of degraded areas suggest great potential for—and have encouraged—its utilization under different habitats and environmental conditions. In this integrative review, we compiled and discussed the most relevant research data regarding T. crinita, focusing on aspects and traits that influence its utilization both as forage and in rehabilitation of degraded lands. Challenges and prospects towards the improvement of this species in breeding programmes with specific goals are discussed.

Differences in photochemistry and response to heat stress between silver fir (Abies alba Mill.) provenances

The acclimation of silver fir to the conditions of the plantation sites has greater influence on PSII thermostability and performance than does on local adaptation. Forest ecosystems are frequently exposed to heat stress, which adversely affects their growth, performance, and ultimately survival. The knowledge of physiological responses to heat can help mitigate the effects of climate change by facilitating the choosing of suitable reproductive material for future reforestation programs. However, the intraspecific variation of adaptive traits, including the response to heat, has not been well documented. Therefore, we attempted to determine how PSII photochemistry of different silver fir (Abies alba Mill.) provenances varies in responses to heat stress and to reveal if intraspecific variation in PSII performance and thermostability is more affected by the climate of provenance origin or the plantation site. We tested 17 fir provenances sampled at two contrasting international provenance trial sites: Hertnik in Slovakia (390 m a.s.l.) and Kaprun in Austria (1100 m a.s.l.). Short-term heat stress was simulated for seven temperatures ranging from 20 to 51 °C using a water bath. The PSII thermotolerance was assessed via parameters of chlorophyll a fluorescence derived from the OKJIP transient. We observed several climatic variables of the provenances that significantly affected the photochemistry performance and thermostability of PSII, reflecting an additive hereditary basis. Almost all measured parameters varied significantly between trial plots and showed significant trial-by-provenance interactions pointing to acclimation triggered by the different conditions at the trial plots. Overall, the performance of PSII under non-stressing conditions and after heat treatment was better for provenances growing at the warmer trial site at Hertnik.

Local Populations of Arabidopsis thaliana Show Clear Relationship between Photoperiodic Sensitivity of Flowering Time and Altitude.

Adaptation of plants to local conditions that vary substantially within their geographic range is essential for seasonal timing of flowering, a major determinant of plant reproductive success. This study investigates photoperiodic responses in natural populations of Arabidopsis thaliana from high northern latitudes and their significance for local adaptation. Thirty lineages from ten local A. thaliana populations, representing different locations across an altitudinal gradient (2–850 m a.s.l.) in Norway, were grown under uniform controlled conditions, and used to screen for responses to five different photoperiods. We studied relationships between variation in photoperiodic sensitivity of flowering time, altitude, and climatic factors associated with the sites of origin. We found that variation in response to photoperiod is significantly correlated with altitude and climatic variables associated with the sites of origin of the populations. Populations originating from lower altitudes showed stronger photoperiodic sensitivity than populations from higher altitudes. Our results indicate that the altitudinal climatic gradient generates clinal variation in adaptive traits in A. thaliana.

Epistasis × environment interactions among Arabidopsis thaliana glucosinolate genes impact complex traits and fitness in the field.

Despite the growing number of studies showing that genotype × environment and epistatic interactions control fitness, the influences of epistasis × environment interactions on adaptive trait evolution remain largely uncharacterized. Across three field trials, we quantified aliphatic glucosinolate (GSL) defense chemistry, leaf damage, and relative fitness using mutant lines of Arabidopsis thaliana varying at pairs of causal aliphatic GSL defense genes to test the impact of epistatic and epistasis × environment interactions on adaptive trait variation. We found that aliphatic GSL accumulation was primarily influenced by additive and epistatic genetic variation, leaf damage was primarily influenced by environmental variation and relative fitness was primarily influenced by epistasis and epistasis × environment interactions. Epistasis × environment interactions accounted for up to 48% of the relative fitness variation in the field. At a single field site, the impact of epistasis on relative fitness varied significantly over 2yr, showing that epistasis × environment interactions within a location can be temporally dynamic. These results suggest that the environmental dependency of epistasis can profoundly influence the response to selection, shaping the adaptive trajectories of natural populations in complex ways, and deserves further consideration in future evolutionary studies.

Little association of biological trait values with environmental variables in invasive alien round goby (Neogobius melanostomus).

The relative importance of species‐specific biological trait characteristics and environmental factors in invasions of nonindigenous species remains controversial because both have mostly been studied independently. Thus, the main objective of this study was to examine the correlation of biological traits with environmental variation in the globally invasive round goby Neogobius melanostomus from the upper Danube River. Based on a sample of 653 specimens along a continuous 200 km river pathway, links between nine environmental factors (substrate‐type, six water measurements, and the communities of fishes and macroinvertebrates) and seven biological traits (nutritional and energetic status, trade‐offs of parasite resistance and resource allocation, and three growth proxies) were analyzed. Biological trait values of N. melanostomus hardly correlated with the environment, could not explain invasion progress and imply a general low overall importance for invasion success. Instead, alternative individual life‐history trajectories appear to determine invasion success. This is in line with up to 15% of all specimens having outlying biological trait values of potential adaptive value, suggesting a considerable importance of adaptive trait variation among single individuals for the whole invasion progress. This “individual trait utility hypothesis” gives an alternative explanation for success of invasive species by single individuals carrying particular traits, and it should be specifically targeted and analyzed at currently invaded sites.

Variation in Adaptive Traits of an Endemic Meconopsis napaulensis DC. along an Elevation Gradient in Alpine Himalaya, Central Nepal

Understanding the pattern of variation in adaptive traits of rare and endemic species along environmental gradient can suggest important implications for developing optimal strategies for species conservation and sustainable management. In this studywe aimed to study variation in life-history traits of an endemic species M. napaulensis DC. along an elevation gradient in Langtang National Park, Central Nepal covering three populations. Each population was investigated two times (2013 and 2014) covering different seasons. Population sampling was made to read habitat during the peak growing period (during monsoon) except seed output, which was studied during the late growing period (post monsoon). Entire area of each population was extensively surveyed to record all the individuals, including plants in flowering or fruiting and their detailed vegetative characteristics and traits related to population fitness. Analysis of the habitat features showed that M. napaulensis exhibited high habitat specificity. M. napaulensis was restricted to open and rocky habitats of high altitudes. M. napaulensis growing sites had low vegetation cover indicating decreased interspecific competition. M. napaulensis showed high variation in traits due to altitudinal variation, climatic conditions, and disturbances. Specifically, reproductive traits discriminated the populations. M. napaulensis was suffered from human disturbance mainly from livestock grazing, plant harvesting, and garbage pollution as the study area is an important tourist destination and pilgrimage site. Conservation of rare and endemic species such as M. napaulensis requires strong provisions restricting human activities and minimizing the impact of harvesting and grazing; and implementing habitat restoration and population augmentation programs.

Demographic history of the trace metal hyperaccumulator Noccaea caerulescens (J. Presl and C. Presl) F. K. Mey. in Western Europe.

Noccaea caerulescens (Brassicaceae) is a major pseudometallophyte model for the investigation of the genetics and evolution of metal hyperaccumulation in plants. We studied the population genetics and demographic history of this species to advance the understanding of among-population differences in metal hyperaccumulation and tolerance abilities. Sampling of seven to 30 plants was carried out in 62 sites in Western Europe. Genotyping was carried out using a combination of new chloroplast and nuclear neutral markers. A strong genetic structure was detected, allowing the definition of three genetic subunits. Subunits showed a good geographic coherence. Accordingly, distant metallicolous populations generally belonged to distinct subunits. Approximate Bayesian computation analysis of demographic scenarios among subunits further supported a primary isolation of populations from the southern Massif Central prior to last glacial maximum, whereas northern populations may have derived during postglacial recolonization events. Estimated divergence times among subunits were rather recent in comparison with the species history, but certainly before the establishment of anthropogenic metalliferous sites. Our results suggest that the large-scale genetic structure of N.caerulescens populations pre-existed to the local adaptation to metalliferous sites. The population structure of quantitative variation for metal-related adaptive traits must have established independently in isolated gene pools. However, features of the most divergent genetic unit (e.g. extreme levels of Cd accumulation observed in previous studies) question the putative relationships between adaptive evolution of metal-related traits and subunits isolation. Finally, admixture signals among distant metallicolous populations suggest a putative role of human activities in facilitating long-distance genetic exchanges.

Genetic and adaptive trait variation in seedlings of European beech provenances from Northern Germany

AbstractEuropean beech (Fagus sylvaticaL.) will most likely be threatened by climate change. Therefore, more knowledge of its adaptation potential to changing environmental conditions is required. Several studies showed differences in adaptive traits for beech populations from across Europe, but there is also growing evidence for microevolutionary processes occurring within short geographic distances in this species, or even a lack of local adaptation. Hence, a more regional perspective for adaptation research in beech might be appropriate. Here, we investigated the performance (height, height increment and mortality) and genetic structure based on microsatellite markers of 2400 beech seedlings from provenances growing along a temperature and precipitation gradient in Northern Germany in a common garden experiment. Differences for all traits were found among provenances. Provenances from lower precipitation areas did not perform better than provenances from higher precipitation areas at the common garden site, which was located near the lower precipitation limit of beech. Further, neighboring provenances growing on either sandy or loamy soils showed more different adaptive trait variation than distant provenances. We detected minor genetic structure among provenances and a high genetic diversity within them. Thus, small-scale adaptive trait variation in beech can occur, despite low but significant genetic population structure among provenances.