Filogeografia e genética de populações de inia geoffrensis (cetartiodactyla: iniidae) nos rios Negro e Branco e evidência de linhagem evolutiva independente na Bacia do Orinoco

Abstract

The river dolphins of the genus Inia belong to the family Iniidae. This family has three species distributed in different hydrographic regions: Inia boliviensis (Bolivian sub-basin); I. araguaiaensis (Tocantins/Araguaia basin); and I. geoffrensis (Amazon and Orinoco basins). The last one is represented for two subspecies whose the taxonomy is controversy: Inia geoffrensis geoffrensis (Amazon basin) and I. g. humboldtiana (Orinoco basin). These species have adaptations that enable them to explore flooded areas, common in several regions in Central Amazon and Orinoco Llanos. The Amazon and Orinoco basin are connected by the Casiquiare Channel, that connects the upper Orinoco River to the upper Negro River. This channel has been acting as well a corridor as a barrier to aquatic fauna shared by these two basins. The aims of this study were: I) to test if Inia geoffrensis humboldtiana represents an independent evolutionary unit; II) to understand the geographic patterns of the population structure of the Inia geoffrensis from the Negro River basin and the Branco River sub-basin. To reach aim I), we performed Bayesian and Maximum Parsimony analysis on sequencies of Inia individuals from the type localities: 108 individuals for control region, 122 for citochrome b and 129 for 10 loci microsatelitis. The results showed four lineages, corresponding to the Inia species and subspecies. A fifth lineage was observed for the individuals from the upper Orinoco basin. The two lineages of the Orinoco basin has different estimated time of divergence. The estimated divergence of the upper Orinoco lineage from its Inia Central Amazon sister lineage is 0.354 million years ago. This clade is sister to Inia from lower/middle Orinoco with an estimated time of divergence of 1.66 mya. Our evidences suggest that Inia from the lower/middle Orinoco basin is a different species, and we called it Inia humboldtiana stat nov. (Pilleri & Gihr, 1977). Furthermore, the data analysed are not yet enough to evaluate the taxonomic status of the upper Orinoco Inia lineage. To reach aim II), we perform Bayesian and Maximum Likelihood analysis on 131 individuals for the control region, 127 individuals for the citochrome b, and 143 individuals for 10 loci microsatelities. The individuals were sampled from the Orinoco basin, and from the Negro, Branco, Madeira and Solimões rivers. The results for the individuals from the Orinoco basin was the same as that obtained to reach the aim I. To the other individuals, different patterns of genetic differentiation were observed as marker used. For nuclear DNA was observed a low degree of population subdivision (FST = 0.04762, P<0.001) and an high gene flow index; and for mitochondrial DNA was observed an opposite situation (ФST = 0.75490, P<0.001). From these results subpopulations were determined whose the genetic diversity levels were relatively high. The genetic differentiations of the subpopulations seem to correspond to the rivers evolution. Furthermore, we observed female philopatry. The rapids of São Gabriel da Cachoeira (Negro River) and Bem Querer (Branco River) are not barrier for the dolphins, both female as male. Thus, the construction of dams designed for these areas, will fragment that subpopulations, both demographically as genetically.