Morphometric Differentiation among Experimental Lines of the Housefly in Relation to a Bottleneck

Differentiation in morphometric traits among experimental populations of the housefly subjected to an experimental bottleneck was examined for replicate lines founded with one, four or 16 pairs of flies. Differentiation among lines within a bottleneck size was significantly greater than predicted by drift in relation to the additive genetic variation for these traits within the founding population. Two models of nonadditive genetic variance were investigated to interpret these results, one involving dominance of allelic effects within loci and another incorporating multiplicative epistasis. Both models generated more variation among lines as a direct result of sampling during the bottleneck than predicted by a model with additive gene action. The pattern of differentiation among our experimental lines in relation to these models conformed more to the model incorporating epistasis. Nevertheless, it may be difficult to distinguish differentiation among lines occurring during a bottleneck as a result of nonadditive gene action from that caused by diversifying selection among lines after the bottleneck.     

中华猕猴桃和美味猕猴桃自然居群遗传结构及其种间杂交渐渗

 利用9对SSR引物对中华猕猴桃（Actinidia chinensis）和美味猕猴桃（A. deliciosa）两近缘种的5个同域分布复合体和各自1个非同域分布居群进行了遗传多样性、居群遗传结构的分析以及种间杂交渐渗的探讨。结果表明：1）两物种共有等位基因比例高达81.13%,物种特有等位基因较少（中华猕猴桃：13.27%,美味猕猴桃：5.61%）,但共享等位基因表型频率在两近缘种间存在差异,而且与各同域复合体中两物种样本的交错程度或间距存在关联;2）两种猕猴桃均具有极高遗传多样性,美味猕猴桃的遗传多样性（H_o＝0 .749, PIC＝0.818）都略高于中华猕猴桃（H_o＝0.686,PIC＝0.799）;3）两猕 猴桃物种均具有较低的Nei’s居群遗传分化度,但AMOVA分析结果揭示种内异域居群间（F_ST=0.091 5）和同域复合体种间（F_ST=0.111 5）均存在一定程度的遗传分化;中华猕猴桃居群遗传分化（G_ST=0.086; F_ST=0.212 1）高于美味猕猴桃（G_ST= 0.080;F_ST=0.142 0）;4）同域分布复合体两物种间的遗传分化（G_ST=0.020）低于物种内异域居群间的遗传分化（中华猕猴桃：G_ST=0.086; 美味猕猴桃：G_ST=0.080）,同域复合体物种间的基因流（N_m＝7.89 -29.75）远远高于 同种异域居群间（中华猕猴桃：N_m =2.663; 美味猕猴桃：N_m=2.880）; 5）居群UPGMA聚类揭示在同一地域的居群优先聚类,个体聚类结果显示多数个体聚在各自居群组内,但各地理居群并不按地理距离的远近聚类,这与Mantel相关性检测所揭示的居群间遗传距离与地理距离没有显著性相关的结果一致。进一步分析表明两种猕猴桃的遗传多样性和居群遗传结构不仅受其广域分布、远交、晚期分化等生活史特性的影响,同时还与猕猴桃的染色体基数高 (x=29)、倍性复杂和种间杂交等因素密切相关,其中两种猕猴桃的共享祖先多态性和同域分布种间杂交基因渗透对两猕猴桃的居群遗传结构产生了重要影响。     

EFFECT OF AN EXPERIMENTAL BOTTLENECK ON MORPHOLOGICAL INTEGRATION IN THE HOUSEFLY

Three measures of multivariate integration were derived from both additive genetic covariance and correlation matrices estimated from parent-offspring covariances to investigate the effect of bottlenecks of different sizes on genetic integration of morphological traits in the housefly, Musca domestica L. Bottleneck lines were initiated with one, four, or 16 pairs of flies sampled from a natural outbred (control) population. Bottlenecks of intermediate size significantly increased the average genetic correlation among traits, resulting in nearly isomorphic variation among all traits in these lines. Single-pair bottlenecks significantly disrupted the trait interrelationships, and the suites of traits identified by principal components of the additive genetic correlation and covariance matrices for the control population were no longer evident in these bottleneck lines. The alteration of the genetic relationships among traits as a result of a bottleneck suggests that nonadditive components of genetic variation affecting these traits were present in the control line. We discuss the implications of nonadditive gene action, particularly epistasis, for speciation via bottlenecks.     

GENETIC DIFFERENTIATION AMONG ANCESTRAL AND INTRODUCED POPULATIONS OF THE EURASIAN TREE SPARROW (PASSER MONTANUS)

We compared genetic variation in three introduced North American populations of Passer montanus with an ancestral German population, a native Swedish population, and an introduced Australian population. The North American P. montanus were less variable genetically than the ancestral German birds, presumably a result of the founding event. The genetic structure of all six populations of P. montanus can be explained in terms of interaction among mutation, genetic drift, effective population size, and unknown selective factors. Cluster analyses and an ordination of distance measures derived from electrophoretic data generally showed relationships in phenetic space among populations consistent with the magnitude of their geographic separation. An exception occurred with the Swedish population, which was closer in the ordination to a North American population than to the geographically neighboring German population. This seemingly anomolous juxtaposition was attributed to the relative abundance of alleles present in the Swedish birds. Populations of P. montanus seem to have diverged in a manner similar to that seen in conspecific disjunct populations, i.e., at present showing no trenchant indication of genetic speciation.     

The Effect of an Experimental Bottleneck upon Quantitative Genetic Variation in the Housefly

Effects of a population bottleneck (founder-flush cycle) upon quantitative genetic variation of morphometric traits were examined in replicated experimental lines of the housefly founded with one, four or 16 pairs of flies. Heritability and additive genetic variances for eight morphometric traits generally increased as a result of the bottleneck, but the pattern of increase among bottleneck sizes differed among traits. Principal axes of the additive genetic correlation matrix for the control line yielded two suites of traits, one associated with general body size and another set largely independent of body size. In the former set containing five of the traits, additive genetic variance was greatest in the bottleneck size of four pairs, whereas in the latter set of two traits the largest additive genetic variance occurred in the smallest bottleneck size of one pair. One trait exhibited changes in additive genetic variance intermediate between these two major responses. These results were inconsistent with models of additive effects of alleles within loci or of additive effects among loci. An observed decline in viability measures and body size in the bottleneck lines also indicated that there was nonadditivity of allelic effects for these traits. Several possible nonadditive models were explored that increased additive genetic variance as a result of a bottleneck. These included a model with complete dominance, a model with overdominance and a model incorporating multiplicative epistasis.     

JOINT ALLELIC EFFECTS ON FITNESS AND METRIC TRAITS

Theoretical explanations of empirically observed standing genetic variation, mutation, and selection suggest that many alleles must jointly affect fitness and metric traits. However, there are few direct demonstrations of the nature and extent of these pleiotropic associations. We implemented a mutation accumulation (MA) divergence experimental design in Drosophila serrata to segregate genetic variants for fitness and metric traits. By exploiting naturally occurring MA line extinctions as a measure of line‐level total fitness, manipulating sexual selection, and measuring productivity we were able to demonstrate genetic covariance between fitness and standard metric traits, wing size, and shape. Larger size was associated with lower total fitness and male sexual fitness, but higher productivity. Multivariate wing shape traits, capturing major axes of wing shape variation among MA lines, evolved only in the absence of sexual selection, and to the greatest extent in lines that went extinct, indicating that mutations contributing wing shape variation also typically had deleterious effects on both total fitness and male sexual fitness. This pleiotropic covariance of metric traits with fitness will drive their evolution, and generate the appearance of selection on the metric traits even in the absence of a direct contribution to fitness.     

High genetic diversity and low structure in an endemic long-lived tree,Yucca capensis (Asparagaceae)

• Endemic species distributed in fragmented habitats are highly vulnerable to extinction because they may have low genetic diversity. However, some life-history traits can mitigate the effect of genetic drift on populations. We analysed the level and distribution of genetic variation and ancestral population size of Yucca capensis, a long-lived endemic plant of the Baja California Peninsula, Mexico. Its populations are scattered across a habitat that is suffering accelerated transformation.
• We used six nuclear microsatellites to genotype 224 individuals from 17 locations across the entire species' geographic range. We estimated polymorphisms, heterozygosity and genetic structure. We also evaluated the ancestral and recent effective size and time since the population started to change.
• We found high heterozygosity, high polymorphism and low differentiation among locations, suggesting a panmictic population across the range. We also detected a large ancestral effective population size, which suffered a strong reduction in the Mid-Holocene.
• Despite changes in environmental conditions caused by habitat modification, the high diversity and low differentiation in Y. capensis may result from its large ancestral effective size and life-history traits, such as plant longevity, clonal growth and mating system, which reduce the rate of loss of genetic variation. However, the dependence on a specialist pollinator that displays short flight range can reduce gene flow among the plant populations and could, shortly, lead them into an extinction vortex.

     

RESISTANCE OF GENETIC CORRELATION STRUCTURE TO DIRECTIONAL SELECTION IN DROSOPHILA MELANOGASTER

The genetic covariance and correlation matrices for five morphological traits were estimated from four populations of fruit flies, Drosophila melanogaster, to measure the extent of change in genetic covariances as a result of directional selection. Two of the populations were derived from lines that had undergone selection for large or small thorax length over the preceding 23 generations. A third population was constituted using flies from control lines that were maintained with equivalent population sizes as the selected lines. The fourth population contained flies from the original cage population from which the selected and control lines had been started. Tests of the homogeneity of covariance matrices using maximum likelihood techniques revealed significant changes in covariance structure among the selected lines. Prediction of base population trait means from selected line means under the assumption of constant genetic covariances indicated that genetic covariances for the small population differed more from the base population than did the covariances for the large population. The predicted small population means diverged farther from the expected means because the additive genetic variance associated with several traits increased in value and most of the genetic covariances associated with one trait changed in sign. These results illustrate that genetic covariances may remain nearly constant in some situations while changing markedly in others. Possible developmental reasons for the genetic changes are discussed.     

Molecular Genetic Variation in a Clonal Plant Population of Leymus chinensis (Trin.) Tzvel.

Randomly amplified polymorphic DNA (RAPD) analysis was used to investigate the genetic variation among populations, between populations, and within populations, relationships between genetic distance and geographic distance, and the molecular variation and population size. The effects of geographic and genetic distances, as well as of genetic differentiation and population size, on genetic variations of Leymus chinensis (Trin.) Tzvel. are discussed. The present study showed that there was significant RAPD variation between the Baicheng region population and the Daqing region population, with a molecular variance of 6.35% (P ＜ 0.04), and for differentiation among area populations of the Daqing region, with a molecular variance of 8.78% (P ＜ 0.002). A 21.06% RAPD variation among all 16 populations among two regions was found (P ＜ 0.001), as well as 72.59% variation within populations (P ＜ 0.001). Molecular variation within populations was significantly different among 16 populations.     

Relationships among tetraploid wheat (Triticum turgidum L.) landrace populations revealed by isozyme markers and agronomic traits

Diversity and relationships among ten tetraploid wheat landrace populations, collected from different localities in the central highlands of Ethiopia, were studied using isozyme markers and agronomic traits. This type of analysis in crop species is fundamental for designing optimal germ plasm collection, management practices and for developing an index for parental selection. The populations differed in allelic frequencies. Gene-diversity estimates showed that the populations encompass an appreciable amount of variation. However, differentiation between them was low, as was also confirmed by the presence of gene flow. Much of the diversity (85%), was attributable to the within-population level. The genetic distances were mostly small with the exception of those between a few pairs of populations. Thus, the relationships discerned among the populations were more of a similarity nature which could be ascribed to sharing a common ancestral population and/or adaptation to similar climatic conditions. The pattern of genetic divergence appeared to be independent of geographic distance. Considerable divergence in the agronomic traits was observed for certain populations. Cluster analyses of the isozyme and agronomic data produced different patterns and memberships of groupings. This lack of agreement could be ascribed to the different forces of evolution acting on isozyme markers and agronomic traits since agronomic traits, are the prime target of artificial selection. The clustering based on agronomic traits resulted in grouping together populations with similar agronomic performance. The results of this study suggest that taking more samples within a locality or population would be a better approach to capture the range of variation in the landrace populations of the central highlands of Ethiopia.     

Effects of Population Size and Selection Intensity on Correlated Responses to Selection for Postweaning Gain in Mice

Correlated responses to selection for postweaning gain in mice were studied to determine the influence of population size and selection intensity. Correlated traits measured were three-, six- and eight-week body weights, litter size, twelve-day litter weight, proportion infertile matings and two indexes of reproductive performance. In general, the results agreed with observations made on direct response: correlated responses in the body weight traits and litter size increased as (1) selection intensity increased and (2) effective population size increased. Correlated responses in the body weight traits and litter size were positive in the large population size lines (16 pairs), as expected from the positive genetic correlation between these traits and postweaning gain. However, several negative correlated responses were observed at small population sizes (one and two pairs). Within each level of selection intensity, traits generally associated with fitness tended to decline most in the very small populations (one and two pairs) and in the large populations (16 pairs) for apparently different reasons. The fitness decline at the small effective population sizes was attributable to inbreeding depression. In contrast, it was postulated that the fitness decline at the large effective population size was due to selection moving the population mean for body weight and a trait positively correlated genetically with body weight (i.e., percent body fat) away from an optimum.     

Molecular Genetic Variation in a Clonal Plant Population of Leymus chinensis （Trin.） Tzvel.

Randomly amplified polymorphic DNA （RAPD） analysis was used to investigate the genetic variation among populations, between populations, and within populations, relationships between genetic distance and geographic distance, and the molecular variation and population size. The effects of geographic and genetic distances, as well as of genetic differentiation and population size, on genetic variations of Leymus chinensis （Trin.） Tzvel. are discussed. The present study showed that there was significant RAPD variation between the Baicheng region population and the Daqing region population, with a molecular variance of 6.35% （P 〈 0.04）, and for differentiation among area populations of the Daqing region, with a molecular variance of 8.78% （P 〈 0.002）. A 21.06% RAPD variation among all 16 populations among two regions was found （P 〈 0.001）, as well as 72.59% variation within populations （P 〈 0.001）. Molecular variation within populations was significantly different among 16 populations.     

The changes in genetic and environmental variance with inbreeding in Drosophila melanogaster

We performed a large-scale experiment on the effects of inbreeding and population bottlenecks on the additive genetic and environmental variance for morphological traits in Drosophila melanogaster. Fifty-two inbred lines were created from the progeny of single pairs, and 90 parent-offspring families on average were measured in each of these lines for six wing size and shape traits, as well as 1945 families from the outbred population from which the lines were derived. The amount of additive genetic variance has been observed to increase after such population bottlenecks in other studies; in contrast here the mean change in additive genetic variance was in very good agreement with classical additive theory, decreasing proportionally to the inbreeding coefficient of the lines. The residual, probably environmental, variance increased on average after inbreeding. Both components of variance were highly variable among inbred lines, with increases and decreases recorded for both. The variance among lines in the residual variance provides some evidence for a genetic basis of developmental stability. Changes in the phenotypic variance of these traits are largely due to changes in the genetic variance.     

Effects of hydrographic barriers on population genetic structure of the sea star Coscinasterias muricata (Echinodermata, Asteroidea) in the New Zealand fiords

New Zealand's 14 deep-water fiords possess persistent salinity stratification and mean estuarine circulation that may serve to isolate populations of marine organisms that have a dispersal larval phase. In order to investigate this idea, we analysed the population structure of the sea star Coscinasterias muricata using a mitochondrial DNA marker. Genetic differentiation among populations of C. muricata was analysed using 366 base pairs of mtDNA D-loop. We compared populations from the fiords with several others sampled from around New Zealand. At a macro-geographical scale (> 1000 km), restricted gene flow between the North and South Islands was observed. At a meso-geographical scale (10-200 km), significant population structure was found among fiords and between fiords and open coast. The pattern of population genetic structure among the fiords suggests a secondary contact between a northern population and a southern one, separated by a contact or mixing zone. These populations may have diverged by the effects of random genetic drift and population isolation as a consequence of the influence of estuarine circulation on dispersal. In northern Fiordland, genetic structure approximated an isolation by distance model. However, the pattern in genetic differences suggests that distance alone cannot explain the most divergent populations and that fiord hydrography may increase the effect of genetic drift within populations in the fiords. Finally, our study indicates that populations within the fiords underwent recent rapid expansion, followed most probably by genetic drift due to a lack of gene flow among the fiords.     

The role of propagule pressure in the invasion success of bluegill sunfish, Lepomis macrochirus, in Japan

The bluegill sunfish, Lepomis macrochirus, is a widespread exotic species in Japan that is considered to have originated from 15 fish introduced from Guttenberg, Iowa, in 1960. Here, the genetic and phenotypic traits of Japanese populations were examined, together with 11 native populations of the USA using 10 microsatellite markers and six meristic traits. Phylogenetic analysis reconfirmed a single origin of Japanese populations, among which populations established in the 1960s were genetically close to Guttenberg population, keeping high genetic diversity comparable to the ancestral population. In contrast, genetic diversity of later-established populations significantly declined with genetic divergence from the ancestral population. Among the 1960s established populations, that from Lake Biwa showed a significant isolation-by-distance pattern with surrounding populations in which genetic bottlenecks increased with geographical distance from Lake Biwa. Although phenotypic divergence among populations was recognized in both neutral and adaptive traits, P(ST)-F(ST) comparisons showed that it is independent of neutral genetic divergence. Divergent selection was suggested in some populations from reservoirs with unstable habitats, while stabilizing selection was dominant. Accordingly, many Japanese populations of L. macrochirus appear to have derived from Lake Biwa population, expanding their distribution with population bottlenecks. Despite low propagule pressure, the invasion success of L. macrochirus is probably because of its drastic population growth in Lake Biwa shortly after its introduction, together with artificial transplantations. It not only enabled the avoidance of a loss in genetic diversity but also formed a major gene pool that supported local adaptation with high phenotypic plasticity.     

Patterns of genetic and phenotypic variation in Iris haynei and I. atrofusca (Iris sect. Oncocyclus = the royal irises) along an ecogeographical gradient in Israel and the West Bank

Iris haynei and I. atrofusca are two closely related narrow endemics distributed vicariously along an ecogeographical north-south gradient in Israel and the West Bank. To obtain baseline information of the taxonomic status, conservation and population history of these taxa, we investigated patterns of phenotypic variation and the partitioning of genetic variation within and among populations using dominant random amplified polymorphic DNA (RAPD) markers. Multivariate (principal components analysis) and taxonomic distance analyses based on morphometric traits from eight populations revealed no unambiguous separation into two distinct groups. Results of genetic analyses for nine populations differed only slightly when either allele- or marker-based approaches were employed. Mean within-population diversity was high (0.258 for Nei's expected heterozygosity), but there was no significant relationship between genetic diversity and either population size or latitude. Although the range-wide estimate of GST ( approximately 0.20) revealed relatively high differentiation among populations this value was inflated because of a small, but significant, component of molecular variance among regions viz. taxa ( approximately 5%). Limited long-distance dispersal capabilities in conjunction with a linearized habitat distribution are proposed to contribute to the approximate isolation by distance pattern observed. It also appears that extant populations are currently deviating from equilibrium conditions because of primary divergence of a formerly more widespread ancestral population. Given the absence of deep genetic and phenotypic subdivision among northern (I. haynei) vs. central/southern (I. atrofusca) populations, we argue for a revision of their species status. Nonetheless, we recommend conservation attention to these geographically differentiated segments as separate management units, which can be seen as an instructive example of incipient species formation.     

Quantitative trait and allozyme divergence in the Greenfinch (Carduelis chloris, Aves: Fringillidae)

Quantitative trait divergence and variability among 12 greenfinch populations across continental Europe was examined and compared to divergence in neutral genetic markers (allozymes). The added among locality variance component for 16 skeletal traits was large (mean 28%, range 4–48%) equalling a divergence of up to three SD units. The divergence in quantitative traits (Qst = 0.04-0.48) greatly exceeded that in alloymes (F_ST= 0.01-0.07), indicating the differentiation in quantitative traits to be larger than expected by mutation and drift alone. This conclusion was consistent also with results from the multivariate approach of Rogers & Harpending. However, genetic and morphometric distances between populations were positively correlated, even when controlling for the geographic distance separating pairs of populations. In concordance with Bergmann's rule, most traits were strongly and positively correlated with latitude, indicating latitudinally ordered genetic or/and environmental effects. However, the correlation between lower mandible width and latitude was strongly negative, demonstrating an inverse relationship between beak size and body size across the populations. These results are interpreted to reflect the re-colonization of history of northern Europe (genetic and geographic distances correlated) which has been paralleled by selection acting on quantitative traits (Q_ST>F_ST)- In particular, the counter-gradient variation in beak width, a functionally important trait, is suggestive of an adaptive basis for quantitative trait divergence.     

Effect of habitat fragmentation on the genetic diversity and structure of peripheral populations of beech in Central Italy

Fragmentation can affect the demographic and genetic structure of populations near the boundary of their biogeographic range. Higher genetic differentiation among populations coupled with lower level of within-population variability is expected as a consequence of reduced population size and isolation. The effects of these 2 factors have been rarely disentangled. Given their high gene flow, anemophilous forest trees should be more affected, in terms of loss of genetic diversity, by small population size rather than geographic isolation alone. We studied the impact of distance from the main range (a measure of isolation) and reduced population size on the within-population and among population components of genetic variability. We assayed 11 isozyme loci in a total of 856 individuals in 27 marginal populations of European beech (Fagus sylvatica L.) in Central Italy. Populations were divided into 3 groups with an increasing level of fragmentation. In the most fragmented group, the within-population genetic variability was slightly smaller and the among population differentiation significantly larger than in the other 2 groups. Isolation-by-distance was lost when only pairs of populations involving at least one from the most fragmented group were considered and maintained in the other groups. These results support the role of random genetic drift having a larger impact on the most fragmented group, whereas gene flow seems to balance genetic drift in the 2 less fragmented ones. Given that average distance from the main range is not different between the intermediate and the most fragmented group, but average population size is smaller, we can conclude that gene flow is effective, even at relatively long distances, in balancing the effect of fragmentation if population size is not too small.     

Heterosis is common and inbreeding depression absent in natural populations of Arabidopsis thaliana

The importance of genetic drift in shaping patterns of adaptive genetic variation in nature is poorly known. Genetic drift should drive partially recessive deleterious mutations to high frequency, and inter‐population crosses may therefore exhibit heterosis (increased fitness relative to intra‐population crosses). Low genetic diversity and greater genetic distance between populations should increase the magnitude of heterosis. Moreover, drift and selection should remove strongly deleterious recessive alleles from individual populations, resulting in reduced inbreeding depression. To estimate heterosis, we crossed 90 independent line pairs of Arabidopsis thaliana from 15 pairs of natural populations sampled across Fennoscandia and crossed an additional 41 line pairs from a subset of four of these populations to estimate inbreeding depression. We measured lifetime fitness of crosses relative to parents in a large outdoor common garden (8,448 plants in total) in central Sweden. To examine the effects of genetic diversity and genetic distance on heterosis, we genotyped parental lines for 869 SNPs. Overall, genetic variation within populations was low (median expected heterozygosity = 0.02), and genetic differentiation was high (median F_ST = 0.82). Crosses between 10 of 15 population pairs exhibited significant heterosis, with magnitudes of heterosis as high as 117%. We found no significant inbreeding depression, suggesting that the observed heterosis is due to fixation of mildly deleterious alleles within populations. Widespread and substantial heterosis indicates an important role for drift in shaping genetic variation, but there was no significant relationship between fitness of crosses relative to parents and genetic diversity or genetic distance between populations.     

Divergent selection along climatic gradients in a rare central European endemic species,Saxifraga sponhemica

Background and Aims The effects of habitat fragmentation on quantitative genetic variation in plant populations are still poorly known. Saxifraga sponhemica is a rare endemic of Central Europe with a disjunct distribution, and a stable and specialized habitat of treeless screes and cliffs. This study therefore used S. sponhemica as a model species to compare quantitative and molecular variation in order to explore (1) the relative importance of drift and selection in shaping the distribution of quantitative genetic variation along climatic gradients; (2) the relationship between plant fitness, quantitative genetic variation, molecular genetic variation and population size; and (3) the relationship between the differentiation of a trait among populations and its evolvability.Methods Genetic variation within and among 22 populations from the whole distribution area of S. sponhemica was studied using RAPD (random amplified polymorphic DNA) markers, and climatic variables were obtained for each site. Seeds were collected from each population and germinated, and seedlings were transplanted into a common garden for determination of variation in plant traits.Key Results In contrast to previous results from rare plant species, strong evidence was found for divergent selection. Most population trait means of S. sponhemica were significantly related to climate gradients, indicating adaptation. Quantitative genetic differentiation increased with geographical distance, even when neutral molecular divergence was controlled for, and Q_ST exceeded F_ST for some traits. The evolvability of traits was negatively correlated with the degree of differentiation among populations (Q_ST), i.e. traits under strong selection showed little genetic variation within populations. The evolutionary potential of a population was not related to its size, the performance of the population or its neutral genetic diversity. However, performance in the common garden was lower for plants from populations with reduced molecular genetic variation, suggesting inbreeding depression due to genetic erosion.Conclusions The findings suggest that studies of molecular and quantitative genetic variation may provide complementary insights important for the conservation of rare species. The strong differentiation of quantitative traits among populations shows that selection can be an important force for structuring variation in evolutionarily important traits even for rare endemic species restricted to very specific habitats.