Genomic microsatellite adaptive divergence of wild barley by microclimatic stress in 'Evolution Canyon', Israel

Abstract

We examined diversity levels and patterns of 19 nuclear microsatellites and four chloroplast microsatellites in 275 genotypes of wild barley Hordeum spontaneum, in seven stations at the 'Evolution Canyon' (EC) microsite, Lower Nahal Oren, Mt. Carmel, Israel. EC is sharply subdivided ecologically into a tropical savannoid, 'African', xeric, south-facing slope (SFS) abutting the temperate, dense, liveoak, brushwood, 'European', mesic, north-facing slope (NFS). We found the following. (i) 17 of 19 (89.5%) nuDNA simple sequence repeats (SSRs) were polymorphic across all seven subpopulations and three chDNA SSRs were polymorphic. (ii) A total of 216 nuDNA SSR alleles, with a maximum of 23 alleles in a nuclear locus, and ten chDNA SSRs, with a maximum of four alleles in a locus, were registered. (iii) There were striking and significant inter- and intraslope diversities, based on the 19 nuDNA SSRs, climaxing with a remarkable genetic distance between the mid-slope stations on opposite slopes (DA = 0.481), across a distance of 200 m. This genetic distance is as large as that between the H. spontaneum populations of Jerusalem and Sede Boqer, which are separated by 100 km (x 500 larger in transect length). (iv) Slope-unique alleles (103 = 45.6%) were higher on the 'European' than on the 'African' slope. Slope-specific (predominant) alleles (17) were equal on opposite slopes. (v) nuDNA SSR gene diversity was higher on the 'European' slope and the opposite was found for the chDNA SSR. (vi) nuDNA SSR genic differentiation was very high between opposite slopes, with Gst = 0.187; for chDNA SSR this value was 0.127. Our results are inexplicable by stochastic processes and suggest that: (i) microclimatic diversifying selection is the major evolutionary, fast-acting, interslope force, overriding migration and drift, and (ii) ecological stress can generate local, regional and global adaptive patterns, suggesting that natural selection is a major differentiating force of both coding and noncoding SSRs linking micro- and macroevolutionary processes. © 2005 The Linnean Society of London.