Molecular phylogenetics of oryzomyine rodents: the genus Oligoryzomys

Cytochrome b sequences (401 bp) were used to investigate the phylogenetic relationships of a group of South American rodents. The study focused on the tribe Oryzomyini (Family Muridae, Subfamily Sigmodontinae) and two of its genera, Oryzomys and Oligoryzomys, especially the latter. Genetic distances separating Oryzomys species average 19%, while those separating Oligoryzomys species are much smaller (mean 11%). When analyzed cladistically, cytochrome b sequences provide weak support for the monophyly of Oryzomyini, but strong evidence for paraphyly of Oryzomys. The cladogram supports the monophyly of Oligoryzomys; however, the branching pattern among its species suggests evolutionary relationships that conflict with hypotheses based on morphology and allozymes. In these taxa, sequences of nucleotides making up cytochrome b violate an important assumption of phylogenetic analysis, independence of characters. The implications of this finding are discussed for phylogeny reconstruction and the measurement of support for cladograms.