Systematics of the southern Patagonian-Fueguian endemic Abrothrix lanosus (Rodentia: Sigmodontinae): Phylogenetic position, karyotypic and morphological data

Abrothrix lanosus (Thomas, 1897) is morphologically redescribed on the basis of new specimens collected in Tierra del Fuego (Argentina). Cranial, mandibular, skeletal, penile, and chromosomal characteristics are described and compared with other species of Abrothrix, especially those of the Patagonian-Fueguian region. Its phylogenetic position within Abrotrichini is explored using DNA sequences of the mitochondrial cytochrome b (cyt b) and the nuclear Interphotoreceptor Retinoid Binding Protein (IRBP) genes. Phylogenetically, cyt b places A. lanosus as sister of A. jelskii, whereas IRBP groups A. lanosus and A. longipilis. The latter topology is most consistent with morphological data and taxonomic history. Several cranial and mandibular characters distinguish A. lanosus from the other species of the genus, including A. longipilis, which is its most similar species. A. lanosus shares with other congeners a 2n=52 karyotype and differs from other species of Abrothrix by at least 10% (p-distances) sequence divergence in cyt b. In conclusion, A. lanosus is a valid species, readily distinguishable from other Abrothrix in the southern Patagonian-Fueguian region. Although many data, including penile and skull morphology, suggest that A. longipilis is its closest living relative, A. jelskii is retained as a viable alternative until additional data are obtained.