Effects of past riverine connectivity on the population structure and species distribution of 'Geophagus' brasiliensis (Cichlidae) complex in a Neotropical hotspot

1. Once fishes and rivers are intrinsically connected, historical events such as river captures and the reconfiguration of palaeodrainages affect population structure and species distribution. However, direct evidence of these events remains limited. 2. We aimed to directly infer putative connections between adjacent river basins to understand genetic and geographical patterns in populations and species of the 'Geophagus' brasiliensis complex. For that, we analysed 174 sequences of the mitochondrial gene cytochrome c oxidase subunit I (COI) from five species along 35 sites within and near a coastal basin in northeastern Brazil. Based on haplotype network, palaeodrainage reconstruction, geological inferences of river captures and analyses of molecular variance (AMOVAs), we tested how the genetic structure could be associated with variable patterns of habitat connectivity through time. 3. In general, high levels of genetic variation were identified, including shared haplotypes among drainages for most species. AMOVA suggested that drainage rearrangements between adjacent basins were the main drivers of genetic diversification in the 'G.' brasiliensis complex. 4. Our study refuted dispersal routes via the continental shelf, whereas eight putative river captures suggested historical connections that enabled gene flow among drainages until recent interruption. These results provide novel insights on the role of riverscape evolution on the biogeography of neotropical ichthyofauna.