Unilocus delimitation methods reveal the underestimated species diversity of Thomasomys (Rodentia, Cricetidae)

Thomasomys is the most diverse genus of the Sigmodontinae subfamily, comprising at least 51 species. Despite recent systematic advances, the monophyly of this genus, the proposed species groups and their content, and the species limits are not yet firmly established. Using a well‐sampled mitochondrial dataset, we aim to test the monophyly of the genus, infer phylogenetic relationships among species and species groups and test the limits between valid species and candidate species. For this, we used a large matrix of 272 partial non‐redundant sequences of the cytochrome b mitochondrial gene from 40 valid and 20 candidate species. Using probabilistic approaches on this dataset, we inferred Thomasomys phylogenetic relationships and explored species boundaries using four unilocus species delimitation methods (ABGD, ASAP, bPTP and GMYC). Thomasomys sensu stricto was recovered monophyletic and well‐supported, excluding a Peruvian lineage misidentified as part of the genus. Analyses consistently recovered 10 well‐supported major clades and several paraphyletic or polyphyletic species. Delimitation methods and genetic divergences estimated that Thomasomys comprises between 81 and 93 putative species, thus potentially doubling the species diversity of Thomasomys. Such a result clearly calls for an urgent taxonomic revision of this genus and the use of further molecular loci within an integrative taxonomic approach to describe its diversity and understand its evolutionary history.