Abstract
We studied the natural populations of a flagship fish species of the Amazon, Colossoma macropomum which in recent years has been suffering from severe exploitation. Our aim was to investigate the existence or not of genetic differentiation across the wide area of its distribution and to investigate changes in its effective population size throughout its evolutionary history. We sampled individuals from 21 locations distributed throughout the Amazon basin. We analyzed 539 individuals for mitochondrial genes (control region and ATPase gene 6/8), generating 1,561 base pairs, and genotyped 604 individuals for 13 microsatellite loci obtaining, on average, 21.4 alleles per locus. Mean HE was 0.78 suggesting moderate levels of genetic variability. AMOVA and other tests used to detect the population structure based on both markers indicate that C. macropomum comprises a single and large panmitic population in the main channel of the Solimões-Amazonas River basin, on the other hand localities in the headwaters of the tributaries Juruá, Purus, Madeira, Tapajós, and localities of black water, showed genetic structure. The greatest genetic differentiation was observed between the Brazilian Amazon basin and the Bolivian sub-basin with restricted genetic flow between the two basins. Demographic analyzes of mitochondrial genes indicated population expansion in the Brazilian and Bolivian Amazon basins during the Pleistocene, and microsatellite data indicated a population reduction during the Holocene. This shows that the historical demography of C. macropomum is highly dynamic. Conservation and management strategies should be designed to respect the existing population structure and minimize the effects of overfishing by limiting fisheries C. macropomum populations.
Highlights
The Amazon basin holds the largest diversity of fishes in the world
Eight hundred and thirty-nine base pairs from the control region and 732 base pairs from the ATPase6/8 gene were obtained from 539 individuals
Results based in MSVar analyses show that historically C. macropomum has undergone a pronounced population decline in both the Amazon and Bolivian basins (Figure 7)
Summary
The Amazon basin holds the largest diversity of fishes in the world. It is estimated that approximately 2,411 fish species occur there (Reis et al, 2016), with 1,089 species being endemic. Amazonian rivers drain three principal geological formations, the Andes and the Guyana and Brazilian Shields, with consequences for the physicochemical properties of the waters draining these geological formations Some of these rivers present physical barriers which limit geneflow between different sections of the river, further acting as agents of divergence (Hoorn et al, 2010). All of these forces interact, producing an amazingly diverse ichthyofauna Part of this ichthyofauna is exploited as a fisheries resource that represent the production base of an economic sector that contributes more than US$ 200 million per year to the economy of the Brazilian Amazon basin (Barthem and Fabré, 2003). The average size of the fish landed and sold in the main markets in the Amazon suggests that many individuals are captured before reaching sexual maturation, which occurs in females between 50 and 55 cm in length, at an estimated mean age of 3 years (Goulding and Carvalho, 1982; Isaac et al, 1996) based on the length/age relationship estimated from Bertalanffy’s model by Isaac and Ruffino (1996)
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