Two new species of Thomasomys (Cricetidae: Sigmodontinae) from the western Andes of Ecuador and an updated phylogenetic hypothesis for the genus

Abstract

Abstract The Andean cloud forests of Ecuador are home to numerous unique mammals. Rodents of the tribe Thomasomyini are particularly abundant in many Andean localities, with Thomasomys – the largest genus in the subfamily Sigmodontinae (51 species) – especially species-rich and diverse. Despite recent advances on the systematics of the genus, where seven species have been described in the last five years, there is tantalizing evidence that its true diversity remains completely understood. Over the course of approximately ten years of fieldwork in Ecuador, a significant number of Thomasomys specimens were collected from various localities in both, the eastern and western Andean ranges. Through an extensive genetic study of these specimens, augmented with what is available in public databases, we argue that there exist at least 20 undescribed species in the genus, with no less that twelve potential new species in Ecuador alone. In this paper, we describe two of these species belonging to the group cinereus, one recently collected and the other previously referred to as Thomasomys sp. 1; further, we present an updated cyt b gene tree of the genus. The gene tree includes at least 56 valid and putative species and supports the monophyly of the genus, while at the same time suggest a paraphyletic “aureus” group. Our findings suggest that the genus likely exhibits additional hidden diversity in significant portions of Colombia, Peru, and Bolivia which calls for the need for a comprehensive reassessment of the entire genus. The recognition of these two new species brings the total number of known Thomasomys to 53 species, 19 of which occur in Ecuador, including 17 that are endemic to this country.