Variabilidade genética do gênero Oecomys Thomas, 1906 (Cricetidae, Sigmodontinae) na região do médio e alto Rio Tapajós, Amazônia, Brasil

Abstract

The genus Oecomys comprises 16 species, 12 of which occur in Brazil. Molecular studies have revealed that the species richness is underestimated in the Amazonia, and apparently, rivers act as barriers for many species in this region. According to the literature, in the region of Tapajós River there are only two species of Oecomys. In this context, this study aimed to reveal the phylogenetic relationships and the genetic variability of Oecomys in the Tapajós River region, and infer whether this river and its tributaries (Teles Pires and Juruena) act as a barrier for the populations of the genus. For that, 78 samples of Oecomys from the right and left banks of the Tapajós and Teles Pires Rivers, and from the left bank of the Juruena River, were analyzed. Two markers were used: a mitochondrial (Cytochrome b) and a nuclear (intron 7 of the β-fibrinogen) for phylogenetic analysis of Maximum Parsimony (MP), Maximum Likelihood (ML), and Bayesian Inference (BI). The mitochondrial marker was also used for constructing network haplotypes and the following analyses: nucleotide and haplotype diversity, population differentiation (FST), molecular analysis of variance (AMOVA), tests of neutrality (Tajima’s D and Fu’s Fs), demographic patterns by Mismatch distribution, sum of squared deviations (SSD), and raggedness index. The phylogenetic relationships revealed the presence of six species in the region, corresponding to five distinct morphotypes, as follows: O. roberti, O. paricola, two undescribed species (Oecomys sp.1 and Oecomys sp. 2), and a fifth morphotype that corresponds to O. bicolor and O. cleberi. These results indicate that a higher species diversity than the one expected for the region. The haplotype network of O. bicolor and O. cleberi revealed unique haplotypes to each species with the occurrence of O. bicolor only in the right bank of the Tapajós River and O. cleberi on the left bank of the Tapajos, Teles Pires and Juruena Rivers. This indicates a separation of these species by the Tapajós River, with largest genetic differentiation (FST and AMOVA) between species than between populations. The haplotype network of O. paricola revealed individuals with the same haplotype on opposite banks of the Teles Pires River, and no significant genetic differentiation (FST) between these populations. For this species, the AMOVA indicated that the greatest variation was within populations and not between them, rejecting the hypothesis of the river acting as an effective barrier. The neutrality test (Tajima’s D) indicated the equilibrium of O. bicolor, O. cleberi, and O. paricola populations. However, the Fu’s Fs test indicated a population expansion of these species. There was no evidence of expansion based on the Mismatch´s distribution, but SSD and raggedness indexes did not discard the expansion, which may be related to the refuges theory in the region.