Evolutionary history of the Aztec shiner Aztecula sallaei (Günther, 1868) (Teleostei: Cyprinidae): An endemic and monotypic species of Mexico

The distribution and diversification processes of freshwater fishes have been influenced by tecto-volcanic and climatic events that have in turn promoted genesis, destruction, and numerous changes in the drainage networks, leaving complex phylogeographic patterns in the ichthyofauna of highly dynamic regions such as central Mexico. In this study, we evaluated the evolutionary history of the Aztec shiner Aztecula sallaei, which is distributed in currently isolated drainages in the highlands of central Mexico, performing phylogenetic, biogeographic, and phylogeographic analyses using three genes: the mitochondrial cytb and two nuclear genes, S7 and ACTB. The studied populations show three genetically divergent and structured lineages: two are exclusive to the Panuco biogeographic region and the third is widely distributed in the Upper Lerma, Middle Lerma, Cuitzeo, and Balsas (Zempoala Lakes) biogeographic regions, as well as one population in Panuco. This widely distributed lineage also presents a genetic structure that is congruent with these biogeographic regions supported by the cytb gene and partially supported by the S7 gene. The divergence time of these lineages was dated to the Pleistocene period (0.56–2.79 Mya) and was associated with temporally or spatially independent events of river capture, which promoted the exchange of fishes between the river headwaters followed by subsequent isolation, explaining the current distribution of this cyprinid in neighboring but currently isolated basins. Our results indicate that, in the highlands of central Mexico, tecto-volcanic activity has shaped the geographic ranges, diversification, and phylogeographic patterns of freshwater fishes.