Systematics of <italic>Oligoryzomys</italic> (Rodentia, Cricetidae, Sigmodontinae) from southern Chilean Patagonia, with the description of a new species.

Abstract: A new species of <italic>Oligoryzomys</italic>, a Sigmodontinae rodent of the tribe Oryzomyini, is described from the Patagonian islands of southern Chile. Phylogenetic analyses that included the new form and known species of <italic>Oligoryzomys</italic> were examined using nucleotide sequence data from the mitochondrial cytochrome b gene. Maximum‐likelihood and Bayesian analyses found the new species to be sister to <italic>Oligoryzomys longicaudatus</italic> and closely related to a clade composed of <italic>O. flavescens</italic>,<italic> O. </italic>spB, and <italic>O. andinus</italic>. Additionally, we analyzed 223 sequences of the mtDNA Control Region belonging to specimens representing the complete geographic distribution of <italic>O. longicaudatus</italic>, as well as six sequences of the new form, obtaining signals of budding speciation for the insular specimens. Also, we present analyses of morphometric data and descriptions of external, cranial, and dental morphology, along with the karyotype of the new taxon, allowing us to find a unique combination of characters that support the taxonomic identity of this new form and to disentangle the complex taxonomy for the southern Patagonia <italic>Oligoryzomys</italic>. This new species is relevant to the insular biogeography of the Patagonia given that, for the first time, we propose the glacial cycles of the Pleistocene as generators of a mammal species in southern Patagonia. [ABSTRACT FROM AUTHOR]