PHYLOGEOGRAPHIC STRUCTURE OF WHITE OAKS THROUGHOUT THE EUROPEAN CONTINENT

Patterns of chloroplast DNA (cpDNA) variation were studied in eight wh ite oak species by sampling 345 populations throughout Europe. The det ection of polymorphisms by restriction analysis of PCR-amplified cpDNA fragments allowed the identification of 23 haplotypes that were phylo genetically ordered. A systematic hybridization and introgression betw een the eight species studied is evident. The levels of subdivision fo r unordered (G(ST)) and ordered (N-ST) alleles are very high and close (0.83 and 0.85). A new statistical approach to the quantitative study of phylogeography is presented, which relies on the coefficients of d ifferentiation G(ST) and N-ST and the Mantel's test. Based on pairwise comparisons between populations, the significance of the difference b etween both coefficients is evaluated at a global and a local scale. T he mapped distribution of the haplotypes indicates the probable routes of postglacial recolonization followed by oak populations that had pe rsisted in southern refugia, especially in the Iberian peninsula, Ital y and the Balkans. Most cpDNA polymorphisms appear to be anterior to t he beginning of the last recolonization. A subset of the preexisting h aplotypes have merely expanded north, while others were left behind in the south.