Abstract
The Paraná-Paraguay basin encompasses central western Brazil, northeastern Paraguay, eastern Bolivia and northern Argentina. The Pantanal is a flooded plain with marked dry and rainy seasons that, due to its soil characteristics and low declivity, has a great water holding capacity supporting abundant fish fauna. Piaractus mesopotamicus, or pacu, endemic of the Paraná-Paraguay basin, is a migratory species economically important in fisheries and ecologically as a potential seed disperser. In this paper we employ eight microsatellite loci to assess the population structure of 120 pacu sampled inside and outside the Pantanal of Mato Grosso. Our main objective was to test the null hypothesis of panmixia and to verify if there was a different structuring pattern between the Pantanal were there were no physical barriers to fish movement and the heavily impounded Paraná and Paranapanema rivers. All loci had moderate to high levels of polymorphism, the number of alleles varied from three to 18. The average observed heterozygosity varied from 0.068 to 0.911. After the Bonferroni correction three loci remained significant for deviations from Hardy-Weinberg, and for those the frequency of null alleles was estimated. F ST and R ST pairwise comparisons detected low divergence among sampling sites, and differentiation was significant only between Paranapanema and Cuiabá and Paranapanema and Taquari. No correlation between genetic distance and the natural logarithm of the geographic distance was detected. Results indicate that for conservation purposes and for restoration programs small genetic differences detected in the Cuiabá and Paranapanema rivers should be taken in consideration.
Highlights
The Paraná-Paraguay basin encompasses central western Brazil, northeastern Paraguay, eastern Bolivia and northern Argentina (Swarts, 2000)
Results indicate that for conservation purposes and for restoration programs small genetic differences detected in the Cuiabá and Paranapanema rivers should be taken in consideration
Heterozygote deficiency when compared to Hardy-Weinberg expectations is common in fish and these deficiencies could arise either by population subdivision (Wahlund effect) or by inbreeding (O’Connell & Wright, 1997)
Summary
The Paraná-Paraguay basin encompasses central western Brazil, northeastern Paraguay, eastern Bolivia and northern Argentina (Swarts, 2000). The rio Paraná, the 10th longest river in the world, runs towards the rio De La Plata in Argentina, and is divided into upper, high, middle and lower sections (Agostinho et al, 1995). The Paraguay can be divided into upper and lower sections. The upper Paraguay comprises two different geological regions, the highlands and the Pantanal. The latter remained isolated from the Paraná until the Holocene (10.000 ya to today) the fish fauna from upper Paraguay is slightly different from the lower Paraguay and Paraná rivers (Lundberg et al, 1998; Britski, 1999)
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