Interspecific differentiation and gene exchange among the Slovak Quercus sect. Quercus populations

European white oak species (Quercus sect. Quercus) are known to share a substantial part of their nuclear and cytoplasmic genomes as a result of extensive interspecific hybridization and introgression. We studied natural populations of three species distributed in Slovakia, namely Q. robur, Q. petraea and Q. pubescens, which are largely sympatric but have contrasting ecological requirements, using a combination of leaf morphometry, neutral nuclear microsatellite markers (nSSR) and potentially adaptive amplified fragment length polymorphisms (AFLP). Bayesian analysis of population structure relying on nSSR revealed that the degree of admixture was relatively low in Q. robur but higher in Q. petraea and Q. pubescens. The inferred Q. robur ancestry closely correlated with morphometric scores of the canonical discriminant analysis based on 13 leaf traits, while for the other two species the correlation was much weaker. We identified two AFLP fragments associated with climatic variables, mainly with air vapour pressure and characteristics of temperature regime at the sites of origin. These associations indicate that climatic adaptation is the mechanism driving interspecific divergence and maintaining integrity of white oak species.