Phylogeny and Evolution of the Neotropical Rodent Genus Calomys: Inferences from Mitochondrial DNA Sequence Data

Field mice of the genus Calomysare small, mostly granivorous rodents common to several habitats in South America. To date, phylogenies for the genus have been proposed on the basis of morphological, chromosomal, and biochemical data, often with contradictory results due to incomplete species sampling or methodological shortcomings. In this paper, we propose relationships among 10 species of Calomysbased on the complete cytochrome bgene sequence. Our analyses show that Calomysis constituted by two major clades, one mostly associated with mountain habitats with subsequent invasions to lowland habitats and another with species restricted to lowland habitats both north and south of the Amazon basin. The evolution of the genus was likely accompanied by a reduction of chromosome diploid numbers that occurred independently in each of the two evolutionary lineages. A “clock” calibrated on the split between Auliscomysand Loxodontomyssuggests that the almost nonexistent fossil record for the genus greatly underestimates divergence times among its species.