Diversidade e estrutura genética de Arapaima gigas (Osteoglossiformes, arapaimidae) na bacia Araguaia-Tocantins

Abstract

Arapaima gigas (pirarucu) is one of the few fish species listed in the Convention on International Trade in Endangered Species of Wild Fauna and Flora Endangered, and has presented various levels of population structure in studies at the Amazon region. However, there is no knowledge about the levels of genetic diversity and population structure for this species at the Araguaia-Tocantins basin. Therefore, this study aimed to verify that the specimens shown were from the same species, using the partial sequence of the COI mitochondrial gene, evaluate the genetic diversity of “pirarucus” coming from marginal lakes of middle Araguaia River until a middle Tocantins River stretch in the municipality Itupiranga, Pará State. The data obtained for COI showed an average genetic distance (K2P) less than 2%, indicating that all the specimens studied belong to Arapaima gigas. A total of 149 individuals from four locations, was performed using five primers for amplification of the ISSR sequences which produce multiple bands, generating a pattern of "fingerprint", while 286 samples from five sites were analyzed with seven SSR makers. 168 loci were obtained with ISSR, with variation 67 of the 86 polymorphic loci. With SSR markers were identified 25 alleles with frequency from 2 to 7 alleles per locus. The expected heterozygosity ranges from 0.080 to 0.190 with ISSR, 0.026 and 0.679 with SSR to different populations. The AMOVA showed 52.63% of interpopulational variation and 47.37% of intrapopulational variation for ISSR marker, while for SSR variation within populations was higher than among populations. The FST indices peer-to-peer ranging from 0.286 to 0.726 for ISSR marker, and 0.06 to 0.66 for SSR. The Mantel test showed that observed structure is not explained only by geographical distance, both ISSR and for microsatellites makers. The results obtained with both ISSR, as with the SSR, indicate that populations of Araguaia-Tocantins basin are structured, it means that there is limited gene flow between them, and they have low genetic diversity. This low variability level can be explained both by overfishing that these populations have suffered over years, but can also be a natural characteristic of these populations. Regardless the causes of low genetic diversity detected, it is important to emphasize the genetic fragility of these populations, since any environmental changes (natural or otherwise) can further reduce these values, endangering your existence. Thus, the data obtained are important for establishment of actions for management and conservation of natural pirarucus stocks in the Araguaia-Tocantins system.