Análise populacional de Brycon amazonicus (SPIX & AGASSIZ, 1829) na bacia do rio Madeira utilizando marcadores moleculares mitocondriais e microssatélites

Abstract

The Amazon Basin is the largest hydrographic system on the planet, covering approximately seven million km². Among its main rivers, the Madeira River stands out as one of the largest tributaries of the Amazon, originating in the Bolivian Andes and flowing for more than 3,000 km before reaching its confluence with the Amazon River. The Madeira River basin harbors high fish diversity, including several species of commercial importance, and six major fish landing ports are recognized in the region. Fisheries production is based primarily on migratory species, among which the fishes popularly known as matrinxã are particularly important. The present study aimed to characterize the genetic diversity of natural populations of Brycon amazonicus along the Madeira River basin using microsatellite and mitochondrial markers. A total of 131 samples were collected along the main channel of the river. The results revealed heterogeneous levels of genetic variability among sampling sites. Neutrality tests (Tajima’s D and Fu’s Fs) were not significant, indicating genetic equilibrium and no evidence of deviation from neutrality for the mitochondrial marker. The 131 sequences of the ATPase gene (subunits 6 and 8) were grouped into seven haplotypes, whose frequencies varied among localities. For 10 microsatellite loci, genetic diversity parameters also showed spatial variation. The mean number of alleles (NA) ranged from 4.50 (Reservoir) to 9.71 (Manicoré). Observed heterozygosity (HO) ranged from 0.49 (Aripuanã River) to 0.73 (Humaitá), while expected heterozygosity (HE) ranged from 0.59 (Aripuanã River) to 0.83 (Nova Olinda). Analysis of Molecular Variance (AMOVA) revealed that 94.63% of the total genetic variation was distributed within populations and 5.37% among populations (FST = 0.05369; P = 0.01). Pairwise genetic differentiation (ΦST) was generally low or negative among most localities, indicating a lack of significant genetic structuring along the Madeira River for the mitochondrial marker (P < 0.05), except for comparisons involving the Montante locality. Bayesian population structure analysis identified the Aripuanã River population as genetically structured relative to the other localities. STRUCTURE results indicated a complex pattern, suggesting the existence of three coexisting and comigrating population stocks within the Madeira River basin. Overall, both markers revealed differentiation of the Aripuanã population and suggest that the waterfalls of the