Taxonomic revision of the populations assigned to Octodon degus (Hystricomorpha: Octodontidae): With the designation of a neotype for Sciurus degus G. I. Molina, 1782 and the description of a new subspecies

The caviomorph Octodon degus is likely the most studied Chilean mammal species. Several studies have centered in its natural history, ecology, behavior, and physiology; in addition, the species is used as model organism in biomedicine and neurobiology research. However, basic aspects such as its genetic and morphological variation throughout its distribution have not been adequately assessed. In fact, the last taxonomic study focused on populations of O. degus dates to the first half of the last century. Here we integrate morphologic (137 specimens from 23 localities) and genetic (cytochrome-b gene sequences of 47 individuals from 17 localities) evidence to assess the level and pattern of geographic variation along the whole species distribution. We found that specimens of O. degus present one of two morphotypes that are quali and quatitative differentiable. A gracile morphotype is found towards the north and a robust morphotype towards the south. Skull size variation correlates with precipitation, temperature and primary productivity. In addition, genealogical analysis uncovered two mains clades, one of them formed by haplotypes from specimens from the north and the other formed by haplotypes from specimens from the south of the distribution. We consider these differences warrant recognition at the subspecies level. As such, after assigning a neotype for Sciurus degus (= O. degus) that attaches this name to the southern morph, we described and named a new subspecies for the northern populations of O. degus.