European common frog (Rana temporaria) recolonised Switzerland from multiple glacial refugia in northern Italy via trans- and circum-Alpine routes

The high mountain ranges of western Europe have had a profound effect on the recolonisation of Europe from glacial refugia. The Alps present a particularly interesting case, because they present an absolute barrier to dispersal to most lineages, obstructing recolonisation from multiple refugia in the Italian Alps. Here we investigate the effect of the European Alps on the the phylogeographic history of Rana temporaria across its range in Switzerland. Based on partial cytochrome b and COX1 sequences we find two mitochondrial lineages that occur roughly north and south of the alpine ridge bisecting Switzerland, with contact zones between them in the east and west. The northern haplogroup falls within the previously identified common western European haplogroup, while the southern haplogroup is unique to Switzerland. We find that the lineages diverged ~110 kya, approximately the onset of the last glacial maximum, indicative of origins in separate refugia. Phylogenetic analyses suggest that the lineages originate from two refugia in northern Italy, and colonised Switzerland via trans- and curcum-alpine routes. Our results show that the European Alps is a semi-permeable barrier to dispersal for R. temporaria, and have contributed to the complex recolonisation history of Switzerland.