Comparative phylogeography and population structure of European Betula species, with particular focus on B-pendula and B-pubescens

Aim To compare the population genetic structures of the haplotype-sharing species Betula pendula and B. pubescens and to draw phylogeographic inferences using chloroplast DNA markers. In particular, we tested whether B. pendula and B. pubescens exhibited the same or different phylogeographic structures. Location Western Europe and Russia. Methods In this study we used both chloroplast DNA polymerase chain reaction-restriction fragment length polymorphism and microsatellites to genotype B. pendula, B. pubescens and, to a limited extent, B. nana, in 53 populations across Eurasia. A spatial amova (samova) was used to identify major clusters within each species. Results The low level of phylogeographic structure previously observed in B. pendula was confirmed, and the samova analysis retrieved only two major clusters. In contrast, seven clusters were observed in B. pubescens, although the overall level of population differentiation was similar to that of B. pendula. Main conclusions We detected a difference in the population genetic structure between the two species, despite extensive haplotype sharing. It is difficult to ascribe this finding to a single factor, but divergence in ecology between the two species may provide part of the explanation. For both species, the contribution of southern western populations to the recolonization after the Last Glacial Maximum seems to have been limited, and eastern and western European populations apparently had different histories.