Genetic differentiation in 20 hierarchically sampled populations of wild barley was analyzed with quantitative traits, allozymes and Random Amplified Polymorphic DNAs (RAPDs), and compared for three marker types at two hierarchical levels. Regional subdivision for both molecular markers was much lower than for quantitative traits. For both allozymes and RAPDs, most loci exhibited minor or no regional differentiation, and the relatively high overall estimates of the latter were due to several loci with exceptionally high regional differentiation. The allozymeand RAPD-specific patterns of differentiation were concordant in general with one another, but not with quantitative trait differentiation. Divergent selection on quantitative traits inferred from very high regional Q ST was in full agreement with our previous results obtained from a test of local adaptation and multilevel selection analysis. In contrast, most variation in allozyme and RAPD variation was neutral, although several allozyme loci and RAPD markers were exceptional in their levels of regional differentiation. However, it is not possible to answer the question whether these exceptional loci are directly involved in the response to selection pressure or merely linked to the selected loci. The fact that Q ST and F ST did not differ at the population scale, that is, within regions, but differed at the regional scale, for which local adaptation has been previously shown, implies that comparison of the level of subdivision in quantitative traits, as compared with molecular markers, is indicative of adaptive population differentiation only when sampling is carried out at the appropriate scale. Heredity (2005) 95, 466-475.

We present a study of fine-scale spatial genetic structure (SGS) and assess the impact of seed and pollen dispersal on the pattern of genetic diversity in the predominantly selfing Hordeum spontaneum. The study included (1) direct measurement of dispersal in a controlled environment, and (2) analyses of SGS and estimation of the ratio of pollen to seed flow in three natural populations sampled in linear transects at fixed increasing inter-plant distances. Analysis of SGS with 10 nuclear SSRs showed in all three populations a significant autocorrelation for the distance classes of 1 or 2 m and a negative linear relationship between kinship coefficients, calculated for pairs of individuals, and logarithm of geographical distance between members of the pairs. Major seed dispersal (95%) was found to be within 1.2 m from the mother plant. Pollen flow, estimated from the comparison of nuclear and chloroplast variation, was spatially limited as much as was seed dispersal, and tended to be overestimated when measured at spatial scales exceeding that of SGS. We conclude that combined effects of selfing, occasional outcrossing, localized seed dispersal and high plant density create an equilibrium between drift and gene flow in this species resulting in SGS at a very fine spatial scale.

Populations of predominantly selfing plant species often show spatial genetic structure but little is known whether epistatic gene interactions are spatially structured. To detect a possible epistatic effect and a spatial scale at which it operates, we created artificial crosses between plants spanning a range of fixed distances from 1 to 400 m in three populations of wild barley. The self-pollinated and crossed progeny (F 1 ) and two generations of segregated progeny (F 2 and F 3 ) were tested in experimentally simulated population environments for relative performance (RP). The measured fitness traits included number of seeds, total seed weight and seed germination. For any of these traits, there was no association between RP of F 1 , F 2 and F 3 plants and either pairwise kinship coefficients or crossing distance. In contrast, in all three populations, we found lower seed viability of outcrossed as compared with self-pollinated genotypes in the first generation of segregation. However, in the F 3 generation this outbreeding effect disappeared in the two populations and greatly decreased in the third population. For seed production, heterosis in F 1 and outbreeding depression in F 2 were observed only in the population with unusually high number of heterozygotes. Our findings support the view that in selfing species a spatial mosaic of various locally abundant genotypes represents not randomly fixed combinations of alleles but the co-adapted gene complexes that were sieved by selection, while heterozygotes are characteristic for the transient phase of this process, when segregation and purging of maladaptive genotypes have not yet occurred.

The adaptive potential of a population defines its importance for species survival in changing environmental conditions such as global climate change. Very few empirical studies have examined adaptive potential across species' ranges, namely, of edge vs core populations, and we are unaware of a study that has tested adaptive potential (namely, variation in adaptive traits) and measured performance of such populations in conditions not currently experienced by the species but expected in the future. Here we report the results of a Triticum dicoccoides population study that employed transplant experiments and analysis of quantitative trait variation. Two populations at the opposite edges of the species range (1) were locally adapted; (2) had lower adaptive potential (inferred from the extent of genetic quantitative trait variation) than the two core populations; and (3) were outperformed by the plants from the core population in the novel environment. The fact that plants from the species arid edge performed worse than plants from the more mesic core in extreme drought conditions beyond the present climatic envelope of the species implies that usage of peripheral populations for conservation purposes must be based on intensive sampling of among-population variation. Heredity (2014) 113, 268-276; doi:10.1038/hdy.2014; published online 2 April 2014 INTRODUCTION Plant performance and adaptive potential across species rangeThe 'abundant center' model (Sagarin and Gaines, 2002) predicts a decrease in population size toward the species distributional periphery that implies that evolutionarily stable limits of species geographic distributions are shaped by two genetic parameters, effective population size and the amount of gene flow, and that these two parameters are higher at the range center and lower at range margins. According to this concept, species do not expand beyond range edges and plants fail to adapt to local conditions there because of lower genetic diversity and higher genetic differentiation in geographically peripheral as compared with core populations and therefore limited availability of locally beneficial alleles in these populations (Mayr, 1963;Hoffmann and Blows, 1994; Hoffmann and Parsons, 1997;Lennon et al., 1997; Keitt, 2000, 2005;Blows and Hoffmann, 2005;Alleaume-Benharira et al., 2006).The 'abundant center' model also has implications for a question of how population position within a species range affects its evolutionary potential, namely, its ability to adapt to changing environmental conditions. If peripheral populations have lower genetic variation in potentially adaptive traits than populations at the species core because of strong genetic drift, as predicted by the 'abundant center' model, then their potential for evolutionary adaptation to future changes will be low. On the other hand, if peripheral populations maintain substantial genetic variation in traits conferring adaptation to the specific range conditions, then their evolutionary potential and hence conservation value will be hig...