Estrutura genética das populações de irapuca (podocnemis erythrocephala, podocnemididae) da Amazônia brasileira: implicações para a conservação

Abstract

The chelonians of the genus Podocnemis are endemics of the Orinoco, Amazon and Araguaia basins, and historically form an important part of the cultural habitats of the local human populations who utilize meat, fat and eggs as sources of food. Podocnemis erythrocephala, also known as irapuca, has a restricted distribution, and occupies only black and clear waters. This species is classified by IUCN (International Union for the Conservation of Nature) as vulnerable. This classification is due to hunting of adult individuals and egg collection by the riberinhos (riverine inhabitants), a common activity practiced in practically the whole Rio Negro basin. The objective of this study was to determine the genetic structure of P. erythrocephala using maternal lineage markers (the mitochondrial control region) so that the results of this study could be used for future management and conservation of this species. Samples of blood were collected from each individual by puncturing the femoral vein without the need to sacrifice the animal. Sampled localities included the Viruá National Park, Roraima state, São Gabriel da Cachoeira, Santa Isabel do Rio Negro, Barcelos, Jaú National Park, Barreirinha and Nhamundá, Amazonas state, and Oriximiná and Terra Santa, Pará state. By analyzing 550 base pairs in 246 individuals it was possible to encounter 49 haplotypes of which 36 were unique and only one haplotype was present in all localities. Gene diversity (H) and nucleotide diversity ( ) showed considerable values, 0.608 and 0.0021, respectively. An analysis of molecular variance revealed high levels of population subdivision ( ST = 0.27931, P < 0.001). The results showed that 27.93% of total variance was observed between populations, although majority of the genetic variance was attributable to variance within populations (72.07%). Values of fixation indexes ST were significant for the localities of Jaú National Park, São Gabriel da Cachoeira and Barreirinha, that also showed limited gene flow (Nm) in comparison with other localities. This demonstrates that these populations are distinct from each other, that is, they are genetically differentiated. However, isolation by distance does not explain this pattern, because there is no association between geographic and genetic distance using the Mantel test. In this case, the genetic differentiation is explained by the presence of water falls and rapids that separate the Jaú National Park and São Gabriel da Cachoeira localities from other areas. In the case of Barreirinha, genetic differentiation gives credence to the hypothesis that the Amazon River is a barrier. These geomorphological structures (water falls and/or rapids in the Negro River and the Amazon River) appear to be physical barriers that efficiently limit gene flow of individuals of P. erythocephala between these and remaining localities. Comparisons between other localities showed low nonsignificant ST values and contrasted with high Nm values. These results indicate lack of genetic structure between these localities, and the number of migrants reveals elevated gene flow between the localities. These localities represent one large panmictic population and form part of a large stock that occurs in the Brazilian Amazon. However, among populations of irapuca analyzed in the Amazonian region exist demographically distinct subpopulations (Jaú National Park, São Gabriel da Cachoeira and Barreirinha), and these should be treated as separate management units in the sense of monitoring of these populations and the implementation of conservation measures that maintain the viability of these populations and of the species.