Phylogeny and evolution of the neotropical rodent genus Calomys: Inferences from mitochondrial DNA sequence data

Field mice of the genus Calomys are small, mostly granivorous rodents commo n to several habitats in South America. To date, phylogenies for the genus have been proposed on the basis of morphological, chromosomal, and biochemi cal data, often with contradictory results due to incomplete species sampli ng or methodological shortcomings. In this paper, we propose relationships among 10 species of Calomys based on the complete cytochrome b gene sequenc e. Our analyses show that Calomys is constituted by two major clades, one m ostly associated with mountain habitats with subsequent invasions to lowlan d habitats and another with species restricted to lowland habitats both nor th and south of the Amazon basin. The evolution of the genus was likely acc ompanied by a reduction of chromosome diploid numbers that occurred indepen dently in each of the two evolutionary lineages. A "clock" calibrated on th e split between Auliscomys and Loxodontomys suggests that the almost nonexi stent fossil record for the genus greatly underestimates divergence times a mong its species. (C) 2001 Academic Press.