Phylogeography and taxonomy of grass snakes (Natrix helvetica, N. natrix) in Italy and Corsica: little nuclear genomic differentiation conflicts with extreme mitochondrial differentiation. Phylogeography of grass snakes in Italy

We examined the distribution and phylogeography of grass snakes on the Apennine Peninsula, including the adjacent islands Sicily, Sardinia and Corsica, using two mitochondrial markers and a set of 13 microsatellite loci. While previously only barred grass snakes (Natrix helvetica) of this study area had been analysed using molecular biological methods, this study for the first time genetically confirms the occurrence of N. natrix in northeasternmost Italy. Our cline analysis of the previously unstudied contact zone of the two grass snake species in the region of Veneto revealed a clear genetic distinction between both taxa, with only minor gene flow in this narrow hybrid zone. Furthermore, we analysed the mitochondrial and nuclear genomic structuring within N. helvetica, resulting in partially unexpected findings in nuclear clustering, especially regarding Corso-Sardinian grass snakes and those from Sicily and Calabria, indicating towards a need for taxonomic revision. We cannot support the distinction between the subspecies N. h. cetti and N. helvetica corsa, nor between N. h. lanzai and N. h. sicula, and therefore tentatively propose the recognition of only three N. helvetica subspecies. These are: the nominotypical subspecies N. h. helvetica (Lacepède, 1789), occurring in Western Europe and northwesternmost Italy, N. h. cetti Gené, 1839 on both Sardinia and Corsica, and N. h. sicula (Cuvier, 1829), inhabiting the whole Apennine peninsula, including Sicily, except for northeasternmost Italy, where N. natrix occurs.