Phylogeographic patterns of genetic diversity in the common spadefoot toad, Pelobates fuscus (Anura: Pelobatidae), reveals evolutionary history, postglacial range expansion and secondary contact

Based on allozyme variation of 410 newly collected individuals from 52 localities, we reconstructed range-wide phylogeography of the widespread Western Palearctic anuran, Pelobates fuscus. To study genetic diversity, evolutionary history, postglacial range expansion and secondary contact zones, we used a multidisciplinary approach combining information from various genetic analyses and ecological niche modeling. We confirmed the presence of two main groups in P. fuscus, initially revealed by genome size variation. Pelobates f. vespertinus presents a monomorphic group, but two main groups can be identified in P. f. fuscus: an East European and a West European group. We suggest the existence of at least four different Last Glacial refugia for P. fuscus: (1) the area between the Caspian and Azov Seas as the origin for the expansion of P. f. vespertinus; (2) the northwestern part of the Black Sea area for the East European P. f. fuscus; (3) the southwestern part of the Pannonian Plain and (4) the Po Plain for the West European P. f. fuscus. The routes of postglacial range expansions from the refugia are discussed. We newly identified a hybrid zone between P. f. fuscus and P. f. vespertinus. The width of this zone is about 12.5 km. In light of these findings, the two subspecies of P. fuscus constitute distinct evolutionary lineages and merit recognition as separate species. Our data do not provide support for the validity of P.f. insubricus. We therefore propose to synonymize this subspecies with P. f. fuscus.