Genetic structure, ecological versatility, and skull shape differentiation in Arvicola water voles (Rodentia, Cricetidae).

Water voles from the genus Arvicola display an amazing ecological versatility, with
aquatic and fossorial populations. The Southern water vole (Arvicola sapidus) is
largely accepted as a valid species, as well as the newly described Arvicola persicus.
In contrast, the taxonomic status and evolutionary relationships within Arvicola amphibius
sensu lato had caused a long-standing debate. The phylogenetic relationships
among Arvicola were reconstructed using the mitochondrial cytochrome b gene.
Four lineages within A. amphibius 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 distinct species. However, the Western European lineage mostly includes
fossorial forms whereas the Eurasiatic lineage tends to include mostly aquatic forms.
A morphometric analysis of skull shape evidenced a convergence of aquatic forms of
the Eurasiatic lineage toward the typically aquatic shape of A. sapidus. The fossorial
form of the Western European lineage, in contrast, displayed morphological adaptation
to tooth-digging behavior, with expanded zygomatic arches and proodont incisors.
Fossorial Eurasiatic forms displayed intermediate morphologies. This suggests
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 (Arvicola italicus). The three other lineages most probably correspond to phylogeographic
variations of a single species (A. amphibius), encompassing the