Estimativa da variabilidade genética da região controle do dna mitocondrial de nannostomus eques (characiformes, lebiasinidae) da bacia do Rio Negro

Abstract

The middle Negro River Basin is the most important area for ornamental fisheries in the state of Amazonas being that the city of Barcelos is the main trading post. Nannostomus eques (Lebiasinidae: Characiformes), commonly known as pencilfish, is one among the many fish species allowed to be exported as ornamental. This paper presents a study on the genetic variability of Nannostomus eques based on analysis of sequences of the control region of mitochondrial DNA of 125 individuals collected in eight tributaries along the upper (Açaituba, Miuá, Jaradi and Arixanã), middle (Demeni) and lower (Jacundá, Maguari and Catalão) Negro River. The phylogenetic inferences from mitochondrial DNA data of N. eques (parsimony, likelihood and genetic distance methods) showed two evolutionary units separated by 60 mutation steps. The rough geographic boundary between the two units seems to be the vicinity of the Branco River, the main tributary of the Negro River. The genetic distance between the two evolutionary units ranged from 5.50% to 8.30%. Both units differ from 8.50% to 11.80% from sister species, N. unifasciatus. The population analysis (DNA polymorphism, AMOVA, Mantel test) resulted in the identification of high haplotype diversity (h > 0.90) in each evolutionary unit, a strong population genetic structure in the Demeni River and a correlation between genetic divergence and geographic distance in only one of these units. Based on molecular data the rapids and waterfalls near São Gabriel da Cachoeira (upper Negro River) are the main barriers to the gene flow among individuals of the evolutionary unit 1. The emergence of Branco River and the Anavilhanas Archipelago apparently were responsible for the disjoint distribution of the two evolutionary units, except at Igarapé Jacundá where the evolutionary units were sympatric. In view of extent differences between the evolutionary units, N. eques can not be treated as a single stock in the Negro River basin. These results may have important implications for the fishery management of this ornamental fish.