Genetic structure, ecological versatility, and skull shape differentiation in Arvicola water voles. Arvicola genetic and morphological diversity

Water voles from the genus Arvicola display an amazing ecological versality, with aquatic and terrestrial populations. If the Southern water vole (A. sapidus) is largely accepted as a valid species, the taxonomic status and evolutionary relationships within A. terrestris sensu lato had caused a long-standing debate. The phylogenetic relationships among Arvicola were reconstructed using the mitochondrial cytochrome b. Four lineages within A. terrestris s. l. were identified with good support: Western European, Eurasiatic, Italian, and Turkish lineages. Fossorial and aquatic forms were found together in all well-sampled lineages, evidencing that ecotypes do not correspond to a species. However, the Western European lineage mostly includes fossorial forms whereas the Eurasiatic lineage tend to include mostly aquatic forms. A morphometric analysis of skull shape evidenced a convergence of aquatic forms of Eurasiatic lineage towards the typically aquatic shape of A. sapidus. The fossorial forms of the Western European lineages, in contrast, displayed morphological adaptation to tooth-digging behavior, with expanded zygomatic arches. Fossorial Eurasiatic forms displayed intermediate morphologies. This suggest a plastic component of skull shape variation, combined with a genetic component selected by the dominant ecology in each lineage. Integrating genetic distances and other biological data suggest that the Italian lineage may correspond to an incipient species (A. italicus). Other lineages correspond to phylogeographic variations of a single species (A. terrestris).