Extent of nuclear genome sharing among white oak species (Quercus L. subgen. Lepidobalanus (Endl.) Oerst.) in Slovakia estimated by allozymes
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European white oak species (Quercus subg. Lepidobalanus) are known to share a substantial part of the nuclear and cytoplasmic genome. In spite of this fact, they have preserved their integrity. We analyzed genetic variation at thirteen isozyme loci in nine Quercus robur, ten Q. petraea, two Q. pubescens and two mixed (two-species) populations in Slovakia to assess the extent of allele sharing. Moreover, a detailed morphometric study based on thirteen leaf traits was done in the mixed stands. A Bayesian analysis of population structure in the set of pure populations revealed the existence of three clusters, which coincided with the supposed taxonomical identity of populations. However, the distribution of posterior probabilities of data was bimodal with a second peak at six groups, what indicates a possible substructure in the gene pools of the investigated oak species. Moreover, gene admixture was close to 50% in all investigated populations. Morphometric analysis of the two mixed stands revealed a clear morphological separation of the studied oak species, sharply contrasting with a high degree of gene admixture. Differentiation is not uniformly distributed over the genome. High levels of differentiation (FST > 0.10) were observed at only three out of thirteen loci. The hypotheses explaining extensive allele sharing (shared ancestral polymorphisms vs. high levels of interspecific gene flow) are briefly discussed.
KeywordsQuercus L. subg. Lepidobalanus (Endl.) Oerst. white oaks allele sharing differentiation gene admixture
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