Fish genetics and hydroeletrical powerplants in large Neotropical rivers

Background/Question/Methods

The genetic impact of fragmentation of fish populations due to construction of river dams is relatively well known in temperate regions.  Nothing, however, has been done in the tropical portions of the Neotropical realm, despite the importance of hydroeletrical power supply in the area.  The present scenario of fragmentation of river basins will likely worsen in the near future due to aggressive governmental programs that plan to expand the exploitation of many pristine rivers to support industrial development.   Fragments of mitochondrial DNA (DLoop) of 10 species of fish and microsatelitte markers of one species were analyzed in order to evaluate the extent to which the genetic of native populations was influenced by the construction of hydroeletrical powerplants (HPP) in two river basins in Brazil: Tocantins (5 species and 1 HPP) and São Francisco (5 species and 5 HPP) river basins.  Genetic structuring was evaluated by values of Fst and Amova.

Results/Conclusions

Of the 10 species analyzed, only three presented evidence of genetic differentiation between populations above and below the HPP dams.  These cases of case genetic structuring was interpreted as a consequence of river fragmentation that predates the construction of the HPP.  All remaining species show no evidence of genetic impact despite the fact that none of these HPP present mechanisms that allow upstream movement of the fish species.  Although partially isolated by the impoundments, the analyzed fish populations were apparently not subjected to events that could result in the genetic differentiation of the subpopulations (i.e. genetic drift) because some of the HPP are recently young and the resulting riverine fragments (and, consequently, of the resulting subpopulation) are large.   These conclusions are presently being evaluated in smaller river systems subjected to intensive impoundment by small HPP’s.  We expect that the comprehension of the factors involved in the genetic impact of fish populations in fragmented rivers will provide important insights into the genetic conservation of the aquatic resources in the region.