Systematics of the Microtus savii complex (Rodentia, arvicolidae) via mitochondrial DNA analyses: paraphyly and pattern of sex chromosome evolution

The genus Microtus underwent a rapid evolutionary radiation that resulted in the extant 59 species distributed throughout the Palaearctic and Nearctic regions. Here we analysed sequences of the mtDNA gene for cytochrome-b (cyt-b) in specimens collected throughout the Italian peninsula, including three subspecies of M. savii (M. s. savii, M. s. niethammericus and M. s. nebrodensis) and M. brachycercus. The here presented results of the phylogenetic analyses show that M. savii is a paraphyletic taxon and that the estimated genetic divergence among taxa does not correspond to that of currently recognized species. We also discuss the pattern of sex chromosome evolution, believed to have had a role in the speciation processes in this species complex.