Do turismo à genética: qual a estrutura populacional do boto-vermelho Inia geoffrensis nas bacias Amazônica, Orinoco e Araguaia-Tocantins?

Abstract

Food-provisioning among wild botos at Negro river have been forming aggregations in tourism floating houses for over two decades. The level of genetic differentiation between aggregations and how these animals relate to other natural populations distributed by different river systems are little described. Recognizing the genetic structure can be crucial for several ecological issues, especially cetaceans who set a mosaic of populations differentiated by heterogeneous and dynamic environments: the real scenario of the botos. Therefore, this study aimed to investigate the genetic structure of the tourist aggregations of Inia geoffrensis in the lower Rio Negro, Amazonas, in addition to patterns of genetic connectivity between different populations of the Amazon, Orinoco and Araguaia-Tocantins basins. In total, 75 individuals were sampled on seven tourism floats and added 73 mitochondrial DNA sequences available in GenBank. Molecular analyzes addressing the regional (macro-scale) and local (micro-scale) scales were performed using the mitochondrial D-loop gene (387 base pairs) and sexual nuclear markers. The results of the Bayesian cluster analysis showed that the populations of the Araguaia (Inia araguaiaensis) and Bolivian Amazon (Inia boliviensis) form highly structured clusters. The botos of the Orinoco basin (Inia geoffrensis humboldtiana), although differentiated, have genetic connectivity with populations in the Amazon basin. The central-western Amazon region is structured due to the greater proportion of certain clusters. The lower Negro river has four distinct clusters; one being exclusive, one predominant (including Balbina reservoir), and two clusters found more frequently in other regions (Colombian and Peruvian Amazon, Solimões, Madeira and Marajó Island). No genetic differentiation was detected between tourist aggregations by hierarchical analysis of molecular variance (ФST = 0.108, p = .01), with high migration rates being estimated. Despite the unrestricted gene flow, the aggregation of Novo Airão had the lowest number of migrants, in addition to low levels of genetic diversity (Hd = 0.222; π = 0.001), the opposite being observed for other tourist aggregations (global value Hd = 0.774 ; π = 0.010). Haplotype sharing in the lower Negro river did not show geographic distribution patterns. Only male individuals form the tourist aggregations. The social organization of the botos and the hydrographic location of the aggregations can be decisive for the absence of females. A genetic-geographic pattern was detected in accordance with the hydrographic basins and the river systems evaluated, both distant and adjacent to the region of the lower Negro river, findings that agree with previous studies. In the macro-scale analyzes, the lower Negro river is the most heterogeneous region for composing, only in this spatial portion, about half of the proposed clusters. Furthermore, the lack of structure regarding the distribution of genetic variation among aggregations seems to correspond to the variable environment that this portion of the Negro river represents.