Phylogeographic patterns in suckermouth catfish <i>Hypostomus ancistroides</i> (Loricariidae): dispersion, vicariance and species complexity across a Neotropical biogeographic region

The upper Paraná River system (UP) is a highly diverse biogeographic province for freshwater fishes, but little is known about processes which shaped that diversity. This study describes the phylogeographic pattern in <i>Hypostomus ancistroides</i>, a suckermouth catfish species that is widespread in the UP and also reported from the adjoining Ribeira do Iguape basin. We used complete mtDNA sequences of ATPase 6/8 of 162 specimens to infer haplotype distribution using phylogenetic and demographic analyses and a Bayesian molecular clock. Results suggest that during the Quaternary <i>H. ancistroides</i> has undergone superimposed phylogeographic histories, alternating between isolation and subsequent merging of different populations. Occurrence of an isolated population on the Ribeira de Iguape is demonstrated to be a Pleistocene headwater capture event. Widely distributed haplotypes indicate deep genetic differences and suggest that populations of <i>H. ancistroides</i> were isolated for considerable time, but did not undergo speciation because of recurrent population mixing.