Leaf functional trait variation associated with salt tolerance in perennial ryegrass

Salinity is one of major environmental stresses that dramatically threaten plant growth, and variations in genetic structure and functional traits have important effects on the salt tolerance of perennial ryegrass (Lolium perenne L.). The objectives of this study were to: (i) assess the inter‐clonal variation of functional traits of accessions among geographic groups or between wild and commercial groups in response to salt stress; (ii) develop a mathematical model to effectively assess salt tolerance of perennial ryegrass accessions originating from different geographic populations; and (iii) determine the relation between spatial genetic structure and salt tolerance in perennial ryegrass. Wide variations were found among the accessions for seven functional traits. One regression model (F = 0.49 × F₁ + 0.303 × F₂ + 0.207 × F₃) was established to ascertain salt tolerance of each accession. The highest variation of the traits and salt tolerance were obtained for accessions from the European group. Wild accessions exhibited more variation in functional traits and salt tolerance than commercial cultivars. Both molecular marker techniques and functional traits were used to conduct phylogenetic analysis, and the majority of accessions from the same or adjacent regions were clustered into the same group or subgroup. The perennial ryegrass accessions with similar salt tolerance had a close phylogenetic background. The patterns in functional trait variations associated with salt tolerance might allow acceleration of the process for improving salt stress resistance in perennial ryegrass.     

Inter-annual and spatial climatic variability have led to a balance between local fluctuating selection and wide-range directional selection in a perennial grass species

Background and AimsThe persistence of a plant population under a specific local climatic regime requires phenotypic adaptation with underlying particular combinations of alleles at adaptive loci. The level of allele diversity at adaptive loci within a natural plant population conditions its potential to evolve, notably towards adaptation to a change in climate. Investigating the environmental factors that contribute to the maintenance of adaptive diversity in populations is thus worthwhile. Within-population allele diversity at adaptive loci can be partly driven by the mean climate at the population site but also by its temporal variability.MethodsThe effects of climate temporal mean and variability on within-population allele diversity at putatively adaptive quantitative trait loci (QTLs) were evaluated using 385 natural populations of Lolium perenne (perennial ryegrass) collected right across Europe. For seven adaptive traits related to reproductive phenology and vegetative potential growth seasonality, the average within-population allele diversity at major QTLs (HeA) was computed.Key ResultsSignificant relationships were found between HeA of these traits and the temporal mean and variability of the local climate. These relationships were consistent with functional ecology theory.ConclusionsResults indicated that temporal variability of local climate has likely led to fluctuating directional selection, which has contributed to the maintenance of allele diversity at adaptive loci and thus potential for further adaptation.     

An association mapping approach to identify flowering time genes in natural populations of Lolium perenne (L.)

We describe an association mapping approach using natural populations of perennial ryegrass (Lolium perenne L.) to identify molecular markers associated with heading date, an important trait affecting seasonal production, tillering, digestibility and grassland management regimes. Twenty-three natural populations originating from throughout Europe, with heading date phenotypes ranging from very early to very late, as well as three synthetic populations (varieties) were used for molecular marker genotyping using AFLP. In total, 589 polymorphic markers were identified. Hierarchical clustering, principal coordinate and other statistical analyses identified four outlying populations forming a clearly distinct sub-group. Removal of those four populations from the subsequent analysis reduced population sub-structure twofold. However, this made relatively little difference to the result of the association analysis. Linear regression identified three markers whose frequency of occurrence correlated with the heading date phenotype. Moreover, these markers were shown to be closely linked to each other within a major QTL on Chromosome 7, explaining 70% of the total variation in heading date. Pairwise linkage disequilibrium among them was also significant. These results suggest that association mapping approaches may be feasible in L. perenne, and that the use of natural populations could provide a useful source of genetic variation in traits of importance in crop improvement.     

Divergent population structure and climate associations of a chromosomal inversion polymorphism across the Mimulus guttatus species complex

Chromosomal rearrangement polymorphisms are common and increasingly found to be associated with adaptive ecological divergence and speciation. Rearrangements, such as inversions, reduce recombination in heterozygous individuals and thus can protect favourable allelic combinations at linked loci, facilitating their spread in the presence of gene flow. Recently, we identified a chromosomal inversion polymorphism that contributes to ecological adaptation and reproductive isolation between annual and perennial ecotypes of the yellow monkeyflower, Mimulus guttatus. Here we evaluate the population genetic structure of this inverted region in comparison with the collinear regions of the genome across the M. guttatus species complex. We tested whether annual and perennial M. guttatus exhibit different patterns of divergence for loci in the inverted and noninverted regions of the genome. We then evaluated whether there are contrasting climate associations with these genomic regions through redundancy analysis. We found that the inversion exhibits broadly different patterns of divergence among annual and perennial M. guttatus and is associated with environmental variation across population accessions. This study is the first widespread population genetic survey of the diversity of the M. guttatus species complex. Our findings contribute to a greater understanding of morphological, ecological, and genetic evolutionary divergence across this highly diverse group of closely related ecotypes and species. Finally, understanding species relationships among M. guttatus sp. has hitherto been stymied by accumulated evidence of substantial gene flow among populations as well as designated species. Nevertheless, our results shed light on these relationships and provide insight into adaptation in life history traits within the complex.     

Genetic and morphologic diversity of European fan palm (Chamaerops humilis L.) populations from different environments from Sicily

Chamaerops humilis is decreasing in abundance in Mediterranean Europe, which has induced the European community to call for its protection in Special Areas of Conservation. However, information about its genetic and morphological variability, which is crucial to the development of any conservation strategies, is insufficient. The present study aimed to investigate the genetic and morphological variability of C. humilis in Sicily, which was selected as a model because of the high number of dense populations. The relationships between morphological traits and climatic variables were studied to highlight patterns of adaptation to the environment, along with the genetic similarity among the populations. Ten natural populations were sampled, analyzed using 28 specifically designed SSR primers, and evaluated based on 29 morphological traits. The populations were clustered similarly based on genetic and morphological traits. Heterozygosity was high and inbreeding coefficients were low. These results, along with higher intra‐ than inter‐population differentiation, suggest that C. humilis populations in Sicily differentiated from a common ancestor and that inter‐population variation arose from secondary evolution processes induced by ecological adaptation. The correlations between climatic variables and morphological traits suggest that the morphological adaptation to arid environments depends more on summer temperatures than on evapotranspiration or rainfall and that autumn and winter temperatures are determinants of the species establishment at new sites. Considering the response of C. humilis to seasonal temperatures, the present results indicate this species as a candidate for tracking climatic changes in Europe. Further studies are needed to highlight the adaptation of C. humilis to cold environments. Palaeo‐climatological and ‐ecological studies could help clarify its strategies for the colonization of new sites. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 176 , 66–81.     

LOCAL ADAPTATION,PHENOTYPIC DIFFERENTIATION,AND HYBRID FITNESS IN DIVERGED NATURAL POPULATIONS OF ARABIDOPSIS LYRATA

Selection for local adaptation results in genetic differentiation in ecologically important traits. In a perennial, outcrossing model plant Arabidopsis lyrata, several differentiated phenotypic traits contribute to local adaptation, as demonstrated by fitness advantage of the local population at each site in reciprocal transplant experiments. Here we compared fitness components, hierarchical total fitness and differentiation in putatively ecologically important traits of plants from two diverged parental populations from different continents in the native climate conditions of the populations in Norway and in North Carolina (NC, U.S.A.). Survival and number of fruits per inflorescence indicated local advantage at both sites and aster life‐history models provided additional evidence for local adaptation also at the level of hierarchical total fitness. Populations were also differentiated in flowering start date and floral display. We also included reciprocal experimental F₁ and F₂ hybrids to examine the genetic basis of adaptation. Surprisingly, the F₂ hybrids showed heterosis at the study site in Norway, likely because of a combination of beneficial dominance effects from different traits. At the NC site, hybrid fitness was mostly intermediate relative to the parental populations. Local cytoplasmic origin was associated with higher fitness, indicating that cytoplasmic genomes also may contribute to the evolution of local adaptation.     

Linkages among RFLP,RAPD, isozyme,disease-resistance,and morphological markers in narrow and wide crosses of cucumber

An algorithm of automatic classification is proposed and applied to a large collection of perennial ryegrass wild populations from France. This method is based on an ascendant hierarchical clustering using the Euclidian distance from the principal components extracted from the variance-covariance matrix between 28 agronomic traits. A contiguity constraint is imposed: only those pairs of populations which are defined as contiguous are grouped together into a cluster. The definition of contiguity is based on a geostatistical parameter: the range of the variogramme, i.e. the largest distance above which the variance between pairs of population no longer increases. This method yields clusters that are generally more compact than those obtained without constraint. In most cases the contours of these clusters fit well with known ecogeographic regions, namely, for macroclimatic homogeneous conditions. This suggests that selective factors exert a major influence in the genetic differentiation of ryegrass populations for quantitatively inherited adaptive traits. It is proposed that such a method could provide useful genetic and ecogeographic bases for sampling a core collection in widespread wild species such as forage grasses.Institut National de la Recherche Agrononique     

Which Extent is Plasticity to Light Involved in the Ecotypic Differentiation of a Tree Species from Savanna and Forest?

Light intensity and heterogeneity are some of the main environmental factors that differ between forest and savanna habitats, and plant species from these habitats form distinct functional types. In this study, we tested the hypothesis that not only differences in morphological and physiological traits but also phenotypic plasticity in response to light are involved in adaptation to forest and savanna habitats by investigating ecotypic differentiation between populations of Plathymenia reticulata (Leguminosae: Mimosoideae), a tree from the Brazilian Atlantic Forest and the Brazilian Cerrado (savanna). Seeds from four natural populations (one from each biome core area and two from ecotonal regions) were grown in a common garden with four light treatments. Fifteen morphological and physiological characteristics were evaluated until individuals reached 6 mo old. Comparisons among populations showed differences for seven traits in at least one light treatment. These differences pointed to local adaptation to different biomes. Populations showed different levels of phenotypic plasticity in response to light in seven traits. Higher plasticity was found either in the forest core population or ecotonal populations; lower values were found in the cerrado core population. Lower plasticity in the cerrado population emphasizes the stress resistant syndrome, as lower plasticity is probably advantageous in a habitat where a conservative resource use is crucial. Higher plasticity in forest individuals suggests higher ability in exploiting the light heterogeneity in this habitat. Also, higher plasticity in ecotonal populations can be important to ensure the maintenance of P. reticulata in these temporally and spatially dynamic areas. Abstract in Portugese is available at http://www.blackwell‐synergy.com/loi/btp .     

Climate‐related genetic variation in drought‐resistance of Douglas‐fir (Pseudotsuga menziesii)

There is a general assumption that intraspecific populations originating from relatively arid climates will be better adapted to cope with the expected increase in drought from climate change. For ecologically and economically important species, more comprehensive, genecological studies that utilize large distributions of populations and direct measures of traits associated with drought‐resistance are needed to empirically support this assumption because of the implications for the natural or assisted regeneration of species. We conducted a space‐for‐time substitution, common garden experiment with 35 populations of coast Douglas‐fir (Pseudotsuga menziesii var. menziesii) growing at three test sites with distinct summer temperature and precipitation (referred to as ‘cool/moist’, ‘moderate’, or ‘warm/dry’) to test the hypotheses that (i) there is large genetic variation among populations and regions in traits associated with drought‐resistance, (ii) the patterns of genetic variation are related to the native source‐climate of each population, in particular with summer temperature and precipitation, (iii) the differences among populations and relationships with climate are stronger at the warm/dry test site owing to greater expression of drought‐resistance traits (i.e., a genotype × environment interaction). During midsummer 2012, we measured the rate of water loss after stomatal closure (transpiration_min), water deficit (% below turgid saturation), and specific leaf area (SLA, cm² g^?1) on new growth of sapling branches. There was significant genetic variation in all plant traits, with populations originating from warmer and drier climates having greater drought‐resistance (i.e., lower transpiration_min, water deficit and SLA), but these trends were most clearly expressed only at the warm/dry test site. Contrary to expectations, populations from cooler climates also had greater drought‐resistance across all test sites. Multiple regression analysis indicated that Douglas‐fir populations from regions with relatively cool winters and arid summers may be most adapted to cope with drought conditions that are expected in the future.     

Variation on reaction norm in lodgepole pine natural populations

Variations on the norm of reaction among ten natural lodgepole pine populations sampled from three lodgepole pine subspecies (Pinus contorta ssp. contorta, ssp. latifolia and ssp. murrayana) were studied by using 20 year heights measured in 57 provenance test sites across interior British Columbia (B.C.). There were significant population by site interactions. Concurrent joint regression and the AMMI model were used to dissect these population by environmental interactions. Joint regression analysis indicated that three populations (from the northwest) had a negative linear regression coefficient with environmental deviation, three (from central and southeast sites) had a positive regression coefficient and four (from the southwest) had a zero regression coefficient. The AMMI model revealed a similar pattern of reaction norm among the ten populations. But the three significant IPCA axes, which captured twice as much of the G × E sum of squares than joint regression, were more effective in separating the ten populations and associating their performance with the climate of test sites and their origin. The variation patterns of reaction norm in lodgepole pine populations demonstrated that adaptation of lodgepole pine natural populations to the various physical environments, at sub-species as well as at population level, was due largely to a balance between selection for high growth potential in less severe environments and selection for high cold hardiness in severe environments. Received: 4 May 2000 / Accepted: 10 November 2000     

Comparison of the adaptive potential for <Emphasis Type="Italic">Rhizobium leguminosarum</Emphasis> bv. <Emphasis Type="Italic">viceae</Emphasis> nodule bacterial populations isolated in natural ecosystems and agrocenoses

Polymorphism analysis was performed in Rhizobium leguminosarum bv. viceae populations isolated from geographically distant regions of Ukraine and Middle Asia. Examination of cultural, biochemical, and symbiotic traits revealed interpopulation differences, which were attributed to the difference in conditions between natural ecosystems and agrocenoses. Vetch has high species diversity and is not cultivated in Middle Asia, and the corresponding rhizobial population displayed higher genetic diversity and higher polymorphism of adaptive traits ensuring saprophytic development in soil and the rhizosphere, including melanin synthesis (35%) and active exopolysaccharide production (90%). Strains of the Ukrainian population had a lower exopolysaccharide production (10%), did not produce melanin, had higher herbicide resistance, and utilized glucose and succinate (main components of plant root exudation) as carbon sources. Strains capable of efficient symbiosis with Vicia villosa Roth. had a higher frequency in the Middle Asian than in the Ukrainian population, especially among strains isolated from soil (80 and 35%, respectively). In addition, strains of the Middle Asian population better competed for nodulation. It was assumed that the formation of rhizobial populations in vetch cultivation regions (Ukraine) is aimed at adaptation to ectosymbiotic (rhizospheric) interactions with plants and anthropogenic stress factors, while strains of the vetch original center (Middle Asia) are mostly adapted to the endosymbiotic interaction and to natural edaphic stress factors.     

QTL analysis of lodging resistance and related traits in Italian ryegrass (<Emphasis Type="Italic">Lolium multiflorum</Emphasis> Lam.)

Italian ryegrass (Lolium multiflorum Lam.) is the most widely cultivated annual forage grass in Japan. Lodging damage reduces both harvested yield and forage quality. To identify the chromosomal regions controlling lodging resistance in Italian ryegrass, we analyzed seven quantitative characters—heading date, plant height, culm weight, culm diameter, culm strength, tiller number, and culm pushing resistance—and evaluated lodging scores in the field in a two-way pseudo-testcross F₁ population. Significant correlations between most combinations of the traits examined were found. Seventeen QTLs for all traits except culm weight were detected on six of seven linkage groups by simple interval mapping using cross-pollination (CP) algorithm, and 33 independent QTLs were also detected by composite interval mapping from both male and female parental linkage maps. In addition, up to 18 QTLs for lodging scores evaluated at nine different times were detected on all linkage groups. The flanking markers of those QTLs will serve as a useful tool for marker-assisted selection of lodging resistance in Italian ryegrass.     

Inheritance patterns of the response to in vitro doubled haploid induction in perennial ryegrass (<Emphasis Type="Italic">Lolium perenne</Emphasis> L.)

The ability to produce doubled haploid (DH) plants has found broad application in research and breeding. For major crop species such as maize (Zea mays L.) and barley (Hordeum vulgare L.), routine large-scale production of DHs has enabled the acceleration of breeding processes, for example through efficient generation of homozygous lines. However, in forage crops such as perennial ryegrass (Lolium perenne L.), low and genotype-specific responses to in vitro anther culture (AC) still limit wide-spread use of DHs. Here, we report the responses of nine bi-parental populations, segregating for microspore embryogenesis and plant regeneration capacity, to an effective AC protocol. Genotypes of exceptionally high androgenic ability, producing over 200 green plants per 100 anthers cultured, could be selected. Continuous and distinctly shaped distributions for the evaluated traits were indicative of quantitative polygenic control and the presence of different alleles in each population. An insignificant association of embryo production with plant regeneration, as well as a low correlation between green and albino plant yield (ρ?=?0.20), suggested that different genes influence these traits. The populations evaluated here provide a rich source of alleles needed for the introgression of high levels of androgenic capacity into recalcitrant material. Moreover, this germplasm is ideally suited for use in future genotyping and mapping studies so that the genetic control of androgenic capacity in perennial ryegrass can be elucidated. Ultimately, our results will help to realize the potential of DH induction in one of the world’s most important forage crop species.     

An SSR-based genetic linkage map for perennial ryegrass (<Emphasis Type="Italic">Lolium perenne</Emphasis> L.)

A simple sequence repeat (SSR)-based linkage map has been constructed for perennial ryegrass (Lolium perenne L.) using a one-way pseudo-testcross reference population. A total of 309 unique perennial ryegrass SSR (LPSSR) primer pairs showing efficient amplification were evaluated for genetic polymorphism, with 31% detecting segregating alleles. Ninety-three loci have been assigned to positions on seven linkage groups. The majority of the mapped loci are derived from cloned sequences containing (CA)_n-type dinucleotide SSR arrays. A small number (7%) of primer pairs amplified fragments that mapped to more than one locus. The SSR locus data has been integrated with selected data for RFLP, AFLP and other loci mapped in the same population to produce a composite map containing 258 loci. The SSR loci cover 54% of the genetic map and show significant clustering around putative centromeric regions. BLASTN and BLASTX analysis of the sequences flanking mapped SSRs indicated that a majority (84%) are derived from non-genic sequences, with a small proportion corresponding to either known repetitive DNA sequence families or predicted genes. The mapped LPSSR loci provide the basis for linkage group assignment across multiple mapping populations.     

The spatial scale of adaptive population differentiation in a wide‐spread,well‐dispersed plant species

Adaptation to the specific conditions at different sites may contribute strongly to the wide distribution of a plant species. However, little is known about the scale at which such adaptation occurs in common species. We studied population differentiation, plasticity and local adaptation of the short‐lived perennial Hypochoeris radicata, a widespread and common plant whose seeds are well‐dispersed. We reciprocally transplanted seedlings among several populations of different size within and among three European regions (in the northwest Czech Republic, central Germany and the central Netherlands) and studied several fitness‐related traits over two growing seasons. The region in which the reciprocal transplant experiment was carried out had no influence on the performance of seedlings, indicating that there were no differences in overall habitat quality. In contrast, the site within region, and the plot within site strongly influenced mean plant performance. Plants from different populations of origin differed in their performance, indicating genetic variation among populations, but performance strongly depended on the specific combination of population of origin and transplant site. Plants that grew at their home site produced on average almost twice the number of seeds per transplant (a multiplicative fitness measure) than foreign plants originating from other sites. Survival, rosette size and multiplicative fitness all decreased with increasing distance from the home site to the transplant site. The size of the population of origin did not influence overall plant performance or the strength of local adaptation. In conclusion, our results indicate that the common and widespread H. radicata consists of locally adapted genotypes within its European range at a relatively small scale. Thus a large potential for gene flow by seeds and a high density of populations do not appear to be sufficient to prevent population differentiation by selection.     

Local adaptation in the monocarpic perennial Carlina vulgaris at different spatial scales across Europe

Spatial variation in environmental conditions can lead to local adaptation of plant populations, particularly if gene flow among populations is low. Many studies have investigated adaptation to contrasting environmental conditions, but little is known about the spatial scale of adaptive evolution. We studied population differentiation and local adaptation at two spatial scales in the monocarpic grassland perennial Carlina vulgaris. We reciprocally transplanted seedlings among five European regions (northwestern Czech Republic, central Germany, Luxembourg, southern Sweden and northwestern Switzerland) and among populations of different sizes within three of the regions. We recorded survival, growth and reproduction over three growing periods. At the regional scale, several performance traits and the individual fitness of C. vulgaris were highest if the plants were grown in their home region and they decreased with increasing transplant distance. The effects are likely due to climatic differences that increased with the geographical distance between regions. At the local scale, there were significant interactions between the effects of the population of origin and the transplant site, but these were not due to an enhanced performance of plants at their home site and they were not related to the geographical or environmental distance between the site of origin and the transplant site. The size of the population of origin did not influence the strength of local adaptation. The results of our study suggest that C. vulgaris consists of regionally adapted genotypes, and that distance is a good predictor of the extent of adaptive differentiation at large scales ( > 200 km) but not at small scales. We conclude that patterns of local adaptation should be taken into account for the efficient preservation of genetic resources, when assessing the status of a plant species and during conservation planning.Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Role of phenotypic plasticity and population differentiation in adaptation to novel environmental conditions

Species can adapt to new environmental conditions either through individual phenotypic plasticity, intraspecific genetic differentiation in adaptive traits, or both. Wild emmer wheat, Triticum dicoccoides, an annual grass with major distribution in Eastern Mediterranean region, is predicted to experience in the near future, as a result of global climate change, conditions more arid than in any part of the current species distribution. To understand the role of the above two means of adaptation, and the effect of population range position, we analyzed reaction norms, extent of plasticity, and phenotypic selection across two experimental environments of high and low water availability in two core and two peripheral populations of this species. We studied 12 quantitative traits, but focused primarily on the onset of reproduction and maternal investment, which are traits that are closely related to fitness and presumably involved in local adaptation in the studied species. We hypothesized that the population showing superior performance under novel environmental conditions will either be genetically differentiated in quantitative traits or exhibit higher phenotypic plasticity than the less successful populations. We found the core population K to be the most plastic in all three trait categories (phenology, reproductive traits, and fitness) and most successful among populations studied, in both experimental environments; at the same time, the core K population was clearly genetically differentiated from the two edge populations. Our results suggest that (1) two means of successful adaptation to new environmental conditions, phenotypic plasticity and adaptive genetic differentiation, are not mutually exclusive ways of achieving high adaptive ability; and (2) colonists from some core populations can be more successful in establishing beyond the current species range than colonists from the range extreme periphery with conditions seemingly closest to those in the new environment.     

Forests are not immune to plant invasions: phenotypic plasticity and local adaptation allow <Emphasis Type="Italic">Prunella vulgaris</Emphasis> to colonize a temperate evergreen rainforest

In the South American temperate evergreen rainforest (Valdivian forest), invasive plants are mainly restricted to open sites, being rare in the shaded understory. This is consistent with the notion of closed-canopy forests as communities relatively resistant to plant invasions. However, alien plants able to develop shade tolerance could be a threat to this unique forest. Phenotypic plasticity and local adaptation are two mechanisms enhancing invasiveness. Phenotypic plasticity can promote local adaptation by facilitating the establishment and persistence of invasive species in novel environments. We investigated the role of these processes in the recent colonization of Valdivian forest understory by the perennial alien herb Prunella vulgaris from nearby populations in open sites. Using reciprocal transplants, we found local adaptation between populations. Field data showed that the shade environment selected for taller plants and greater specific leaf areas. We found population differentiation and within-population genetic variation in both mean values and reaction norms to light variation of several ecophysiological traits in common gardens from seeds collected in sun and shade populations. The colonization of the forest resulted in a reduction of plastic responses to light variation, which is consistent with the occurrence of genetic assimilation and suggests that P. vulgaris individuals adapted to the shade have reduced probabilities to return to open sites. All results taken together confirm the potential for rapid evolution of shade tolerance in P. vulgaris and suggest that this alien species may pose a threat to the native understory flora of Valdivian forest.     

Local selection modifies phenotypic divergence among Rana temporaria populations in the presence of gene flow

In ectotherms, variation in life history traits among populations is common and suggests local adaptation. However, geographic variation itself is not a proof for local adaptation, as genetic drift and gene flow may also shape patterns of quantitative variation. We studied local and regional variation in means and phenotypic plasticity of larval life history traits in the common frog Rana temporaria using six populations from central Sweden, breeding in either open‐canopy or partially closed‐canopy ponds. To separate local adaptation from genetic drift, we compared differentiation in quantitative genetic traits (Q_ST) obtained from a common garden experiment with differentiation in presumably neutral microsatellite markers (F_ST). We found that R. temporaria populations differ in means and plasticities of life history traits in different temperatures at local, and in F_ST at regional scale. Comparisons of differentiation in quantitative traits and in molecular markers suggested that natural selection was responsible for the divergence in growth and development rates as well as in temperature‐induced plasticity, indicating local adaptation. However, at low temperature, the role of genetic drift could not be separated from selection. Phenotypes were correlated with forest canopy closure, but not with geographical or genetic distance. These results indicate that local adaptation can evolve in the presence of ongoing gene flow among the populations, and that natural selection is strong in this system.     

Genomic and phenotypic differentiation of Arabidopsis thaliana along altitudinal gradients in the North Italian Alps

Altitudinal gradients in mountain regions are short‐range clines of different environmental parameters such as temperature or radiation. We investigated genomic and phenotypic signatures of adaptation to such gradients in five Arabidopsis thaliana populations from the North Italian Alps that originated from 580 to 2350 m altitude by resequencing pools of 19–29 individuals from each population. The sample includes two pairs of low‐ and high‐altitude populations from two different valleys. High‐altitude populations showed a lower nucleotide diversity and negative Tajima's D values and were more closely related to each other than to low‐altitude populations from the same valley. Despite their close geographic proximity, demographic analysis revealed that low‐ and high‐altitude populations split between 260 000 and 15 000 years before present. Single nucleotide polymorphisms whose allele frequencies were highly differentiated between low‐ and high‐altitude populations identified genomic regions of up to 50 kb length where patterns of genetic diversity are consistent with signatures of local selective sweeps. These regions harbour multiple genes involved in stress response. Variation among populations in two putative adaptive phenotypic traits, frost tolerance and response to light/UV stress was not correlated with altitude. Taken together, the spatial distribution of genetic diversity reflects a potentially adaptive differentiation between low‐ and high‐altitude populations, whereas the phenotypic differentiation in the two traits investigated does not. It may resemble an interaction between adaptation to the local microhabitat and demographic history influenced by historical glaciation cycles, recent seed dispersal and genetic drift in local populations.