Systematic Studies of the Genus A<Emphasis Type="Italic">egialomys</Emphasis> Weksler et al., 2006 (Rodentia: Cricetidae: Sigmodontinae): Geographic Variation,Species Delimitation,and Biogeography

Aegialomys occurs in open habitats west of the Ecuadorean and Peruvian Andes, including the Galapagos Archipelago. This genus currently includes two species, A. galapagoensis and A. xanthaeolus. We studied patterns of geographic variation to characterize the morphologic and morphometric variation and recognize diagnosable clusters of samples. Employing this evidence, within a phylogenetic framework employing morphological, molecular, and concatenated matrices, we diagnose monophyletic lineages and assign the appropriate names to species–group taxa. Qualitatively, we noted geographic variation in some characters, and quantitatively there is a pronounced increase in cranial dimensions along the north–south distribution axis, revealing the existence of four distinct clusters: North, South, Extreme South, and Galapagos. These results, along with the phylogenetic relationships, allowed us to hypothesize that Aegialomys exhibits four monophyletic species that we call: Aegialomys galapagoensis, restricted to the Galapagos Archipelago; Aegialomys xanthaeolus, distributed from Ecuador to northern Peru; Aegialomys baroni, ocurring in Central Perú; and Aegialomys ica, distributed in southern Peru. Our distributional data suggest that species discontinuities are associated with some well-known barriers in the western portion of South America. Through the Andes and trans–Andean area, there are some geographic features or areas, the Huancabamba Depression, that historically played a key role as barriers to plant and animal dispersion or as a boundaries to species distribution.