Postglacial colonization of Northern Europe by reptiles

During the Last Glacial Maximum (LGM; 20-14 Kya ago), Northern Europe was covered by ice and permafrost and the distribution of many organisms contracted into glacial refugia. After the LGM, species started to colonize areas from which ice and permafrost retracted and Northern Europe was recolonized. The LGM affected past and present distributions of many species. Different mechanisms led to the currently observed distributions and phylogeographic patterns. However, little evidence exists for their importance in determining the currently existing phylogeographic structuring. Here, we compare the post-LGM colonization patterns of four terrestrial reptile species: two lizards (Zootoca vivipara, Lacerta agilis) and two snakes (Vipera berus, Zamenis longissimus). All four species exhibit large natural current distributions in Europe and colonized areas covered by ice and/or permafrost during LGM. The results show that the most important parameters promoting fast and large post-LGM colonisations are: (i) adaptations to cooler temperatures (including the evolution of viviparity), (ii) absence of physical or climatic barriers during expansion from the refugia, and (iii) low competition with other species/subspecies during expansion, i.e. a refugium at the edge of a species distribution that allows first colonization of newly available habitat.