Phylogeography of Quercus section Quercus Chloroplast DNA variation
Available knowledge on the European white oaks (Quercus, sect. Quercus) plastome still shows large gaps, mostly concerning the lack of a detailed phylogeny and information from southern Europe and adjacent Near East. We investigated DNA sequence polymorphism at two plastid loci on 270 individuals representing 12 white oak species/taxa and retrieved several hundred sequences from GenBank to fill this gap and contribute to a better comprehension of the white oak diversity and evolution. The modern European sect. Quercus species exhibit a little differentiated plastome, despite the current highly diversified taxonomy. In total, 29 haplotypes were identified, including two ancestral variants that are westerly and south easternly partitioned. The high- and low-frequency haplotypes also showed a well-structured geographical distribution consistent with the current phytogeographic framework of the European continent. The climatic and geological events that characterized the end of the Tertiary and Quaternary periods played a crucial role in triggering haplotype mixing, isolation, and in offering niche opportunities for more recent diversification. Euro-Mediterranean southern territories host a high and yet uncovered genetic variation; the role of the Italian peninsula as a crossroad and threshold for haplotype diversity in southern Europe clearly emerged.