Morphological and genetic variation within and among four Quercus petraea and Q. robur natural populations

Abstract

Numeric-taxonomical and molecular techniques [nuclear simple sequence repeats (nSSRs), expressed sequence tag (EST) SSRs, and chloroplast SSRs] were used to estimate morphological and genetic differentiation within and among 4 Quercus petraea and Q. robur natural populations in Turkey. Canonical discriminant analysis (CDA) and principal component analysis (PCA) showed that 3 out of 15 studied leaf morphological characters (clustered hairs, number of intercalary veins, petiole length) mainly accounted for the discrimination between species. In accordance with earlier observations, the mean genetic differentiation between Q. petraea and Q. robur at 8 microsatellite loci (F-ST = 0.030) and at chloroplast microsatellites (G(ST) = 0.22) was low, potentially as the result of interspecific gene flow or shared ancestral polymorphisms. Chloroplast microsatellite analyses showed unique chloroplast haplotypes in Turkey, suggesting a glacial refuge in this region. Nuclear microsatellite ssrQrZAG96, described in other studies as being potentially under directional selection (outlier locus) due to high interspecific differentiation, showed considerably lower differentiation between species in the present study (F-ST = 0.028). These different patterns of genetic variation suggest different local adaptations of the species in this putative glacial refugial area in Turkey. It may also be that this marker is not directly associated with morphological or adaptive species differences. Interestingly, the analysed Q. petraea and Q. robur populations appear to have ecological requirements with regard to water availability that are different than those described for European populations. The analysis of additional populations within the species distribution range in Turkey is necessary to confirm this pattern.