Genetic differentiation and gene flow of the Amazonian catfish Pseudoplatystoma punctifer across the Madeira River rapids prior to the construction of hydroelectric dams

The large catfish Pseudoplatystoma punctifer plays an important role as a top predator in the Amazonian Basin ecosystem. The Madeira River is the largest tributary of the Amazon River marked by a series of rapids and waterfalls. Between 2011 and 2012 some of the rapids were submerged by two hydroelectric dams. Upstream and downstream of the rapids are two sub-basins Mamore/Guapore and lower Madeira, respectively. Using mitochondrial and microsatellite markers, we estimated genetic diversity, genetic differentiation, and gene flow between sub-basins and tested if the rapids functioned as barriers limiting the gene flow for this species of catfish. We identified three population clusters, one representing the individuals from the Mamore/Guapore sub-basin (upstream) and the other two representing the individuals from the lower Madeira sub-basin (downstream). The rapids restricted but did not block gene flow, which corroborates a clinal pattern of genetic differentiation.