Fine-scale phylogeography of Rana temporaria (Anura: Ranidae) in a putative secondary contact zone in the southern Alps

The common frog (Rana temporaria) has been the focus of several broadscale phylogeographic studies, revealing a deep split between eastern and western European populations, most likely induced by the onset of the Pleistocene glaciations. However, the identification of glacial refugia, as well as the understanding of recolonization processes and their genetic legacy remain far from complete. A recent survey on Italian populations revealed a previously unrecognized Pleistocene refuge in the Italian peninsula and suggested the hypothesis of multiple separated microrefugia (‘refugia-within refugia’ model), but fine-scale studies required to confirm this hypothesis are lacking. We examined the phylogeographic structure of 54 common frog populations (540 individuals) by means of COI (cytochrome oxidase I) mitochondrial gene, focusing on a south-eastern Alpine region (Trentino, Italy) with an intensive sampling design. Phylogeographical reconstruction indicated the presence of three different COI lineages, exhibiting different levels of genetic diversity, and a contact zone in the eastern part of the region. Our data supported the scenario of multiple sub-refugia, probably located in the southern slopes of the Alpine chain, where the species survived the ice ages in fragmented populations. The recorded patterns are explained by the biogeographic peculiarity of the study region.