Native rodents of the Cape Horn Biosphere Reserve at the southern end of Chile: advances in their knowledge and conservation

The order Rodentia Bowdich, 1821 constitutes the most diverse group of mammals worldwide. Of these, the subfamily Sigmodontinae Wagner, 1843 gathers almost 490 species, mostly Neotropical. In Chile, the number of sigmodontine species greatly exceeds the diversity of other rodent groups, but the number of species decreases markedly toward higher latitudes. The Cape Horn Biosphere Reserve (CHBR), located at the southern end of the American continent, is characterized by the presence of abrotrichines, euneomyines, and oryzomyines. Also, some nominal forms belonging to these tribes, the validity of which has not been explored since their description. Scarce information about the CHBR rodents includes anecdotal information from explorers and naturalists of the 19th and early 20th centuries. The present study is the first approach to characterizing the current assemblage of native rodents present in the CHBR and the genetic variation of the most abundant and widely distributed species in the archipelagoes at the southern end of Chile. Between 2002 and 2023, 10 expeditions have been carried out to the Alberto de Agostini, Cape Horn, and Yendegaia National Parks. During the expeditions carried out in January, February, and April 2023, 106 individuals of Abrothrix lanosa (Thomas, 1897) (n=1), A. olivacea (Waterhouse, 1837) (n= 93) and Oligoryzomys longicaudatus (Bennett, 1832) (n=12) were collected. The olive field mouse (A. olivacea) was not only the most abundant species, but also the only species captured on the southernmost islands of the CHBR. Exploratory analyses of the genetic variation of Abrothrix olivacea reveal the lack of phylogeographic structure with low levels of divergence between specimens from southern continental Chile, Tierra del Fuego, and Cape Horn