Novel Post-Glacial Haplotype Evolution in Birch – A Case for Conserving Local Adaptation

Despite constituting the western-most edge of the population distributions for several native European flora, Ireland has largely been left out of key Europe-wide phylogeographic studies. This is true for birch (Betula pubescens Ehrh. and Betula pendula Roth.), for which the genetic diversity has yet to be mapped for Ireland. Here, we used eight cpDNA (two RFLP and six SSR) markers to map the genetic diversity of B. pubescens, B. pendula and putative hybrid individuals sampled from 19 populations spread cross most of the island of Ireland. Within Ireland, 11 distinct haplotypes were detected, the most common of which (H1) was also detected in England, Scotland, France and Norway. A moderate level of population structuring (GST = 0.282) was found across Ireland and the genetic diversity of its northern populations was twice that of its southern populations. This indicates that, unlike other native Irish trees, such as oak and alder, post-glacial recolonisation by birch did not begin in the south (i.e., from Iberia). Rather, and in agreement with palynological data, birch most likely migrated in from eastern populations in Britain. Finally, we highlight Irish populations with comparatively unique genetic structure which may be included as part of European genetic conservation networks.