Phylogenetic and phylogeographic patterns in sigmodontine rodents of the genus oligoryzomys.

The sigmodontine South American rodent genus Oligoryzomys was first described as a subgenus of the genus Oryzomys to group together species distinguished by morphological measurements. To describe the dispersion patterns of this genus in South America, in this study, a total of 100 sequences were analyzed and compared with sequences of 9 Oligoryzomys species from GenBank. The sequences comprised 90 mitochondrial cytochrome b genes and 10 nuclear interphotoreceptor retinoid-binding protein genes, from 75 individuals of 7 species from 27 localities. Topologies of different phylogenetic trees revealed Oligoryzomys as a monophyletic genus containing 2 main species groups, one designated as the "Amazon-Cerrado" assemblage and the second as the "Pampa-Andean" clade. The north-to-south geographic pattern observed supports the hypothesis that the genus started from the northern Andes, occupied the Amazon and the Cerrado, and later inhabited the more southern regions of South America.

Geographic patterns of genetic variation and conservation consequences in three South American rodents.

In this study, the geographic patterns of genetic variation of three rodent species belonging to the tribe Oryzomyini were investigated using the mitochondrial cytochrome b and nuclear IRBP genes in biomes that are undergoing degradation processes to a greater or lesser degree. The samples are from 25 collecting localities distributed throughout the Amazon, Cerrado, Atlantic Forest, and Pampa biomes. The results show that the three species have a population and geographic structure, besides being in demographic equilibrium. The phylogenetic analyses performed on Euryoryzomys russatus and Hylaeamys megacephalus showed these specimens grouped in three distinct clades forming geographic gradients (North-South direction in H. megacephalus). Intraspecific genetic divergence was higher in H. megacephalus (4.53%), followed by E. russatus (1.79%), and lowest in Sooretamys angouya (0.88%). The results obtained indicate that, necessarily, the management strategies to preserve genetic diversity should be different for each species, since each of them presented specific population parameters.