Genetic diversity and stress of Ricotia lunaria in "Evolution Canyon," Israel

We examined the genetic diversity and divergence of Ricotia lunaria, a family relative species of Arabidopsis thaliana, sampled from 6 stations on 2 opposing slopes, the south-facing slope ("African" or AS) and north-facing slope ("European" or ES), separated on average by 200 m, at "Evolution Canyon," Lower Nahal Oren, Mount Carmel, Israel, along a transect presenting sharply differing microclimates. The density of R. lunaria populations was slope specific: a higher density and smaller plants were observed on the AS. In addition, the density was positively correlated with annual plant cover. The interslope and intraslope genetic diversities of R. lunaria populations were examined using the amplified fragment length polymorphism (AFLP) technique with 5 primer pairs. Ricotia lunaria populations inhabiting the ES and AS differed, and among the 468 scored loci, 304 (65%) were polymorphic (at P >or= 0.05 level). Polymorphism values obtained for AS and ES populations were similar (52% vs. 56%), but different loci were polymorphic in different populations; 40% of polymorphic loci were identical on both the ES and AS, 16% were polymorphic for the ES only, and 12% were polymorphic only for the AS. The AFLP results grouped the analyzed genotypes into 2 distinct clusters: one cluster included the plants belonging to the AS and the other included ES plants. The unbiased estimate of Nei genetic distances (D) indicated significantly higher interslope (D = 0.124 +/- 0.011) than intraslope (D = 0.076 +/- 0.015) differences (P < 0.001 in t-test). Correspondingly, mean intraslope gene flow was significantly higher than the interslope gene flow (2.9 +/- 0.6 vs. 1.9 +/- 0.2). Natural selection appears to adaptively diverge the plant ecotypes on the opposite slope, both phenotypically and genotypically. This includes significant divergence in flowering time likely to initiate incipient sympatric speciation.