Os Botos da Bacia do Rio Madeira: Diversidade Genética, Hibridização e Conservação

Abstract

In the Amazon, dolphins of the genus Inia, popularly known as boto, are exclusive to freshwater rivers. Due to the loss and degradation of their habitat, competition for natural resources and fragmentation of populations caused by the construction of dams, they are among the most threatened cetaceans. Within the genus there are still divergences in the number of species and subspecies, and for IUCN the species Inia geoffrensis is classified as endangered. Considering the need to use other molecular markers to complement the data of Gravena and collaborators, the present study uses new generation sequencing methodology to evaluate the patterns and processes that may be acting on the evolutionary changes in the river dolphins populations that occur along the Madeira River basin. As well as, new responses to questions regarding these populations, providing subsidies for conservation. Our results show that Inia boliviensis is genetically distinct from I. geoffrensis. However, bidirectional gene flow was observed and evidences the migration between the two species, as a result, a hybridization becomes a natural event, as well as other documented cases of hybrids between cetaceans. The biological discontinuity between species can be explained by the isolation by distance model, in which contact are only observed in the hybridization zone, allowing species in adjacent areas to maintain their independent evolutionary histories. Due to the construction of HPP Jirau and Santo Antônio, in the Madeira River rapids, these populations were isolated, but although these populations already have different evolutionary histories, isolation between populations can increase the level of inbreeding, especially among individuals that were restricted in the reservoirs formed with the constructions. In addition, we observed a reduction in the effective population size, suggesting that populations experienced previous population bottlenecks, probably because of fragmentation, continuous degradation of habitat and a decrease in natural resources. In view of the threat levels, conservation plans to I. boliviensis and I. geoffrensis, extended to hybrids, considering them as independent entities, must be evaluated by the conservation agencies.