The systematics of Aconaemys (Rodentia, Octodontidae) and the distribution of A. sagei in Chile

The systematic relationships among populations of fossorial Aconaemys species (Rodentia, Octodontidae) were assessed using chromosome variation patterns. Cytogenetic data was used since classical taxonomic studies have yielded contradictory results due to the environmentally induced morphological variation observed in these fossorial rodents. The interpopulational karyotypic stability and lack of intrapopulational polymorphism observed in Aconaemys make chromosome data a good predictor of specific differentiation. A distinct karyotype differing in diploid and number of chromosomal arms (FN) was found at each type locality. This kind and degree of karyotypic differentiation together with molecular data indicate that three species of Aconaemys can be recognized: A. sagei (2 n = 54, FN = 104), A. fuscus (2 n = 56, FN = 108), and A. porteri (2 n = 58, FN = 112). Five populations on the western slope of the Andes (Chile: Nahuelbuta, Tolhuaca, Río Colorado, Pedregoso, Reigolil, and Huerquehue), formerly ascribed as A. fuscus shared the same karyotype of A. sagei from the type locality on the eastern slope of the Andes (Argentina: Pampa Hui-Hui). Thus, karyotypic data let us ascribe these disjunct populations to A. sagei. The classical morphospecies in Aconaemys, altered into the biological species based on chromosomal and molecular differentiation, indicates that all three species occur in Chile. After this survey, the range of A. sagei is extended to the northwestern slope of the Andes by more than 300 km.