Phylogeography and freshwater basins in central Mexico: recent history as revealed by the fish parasite Rhabdochona lichtenfelsi (Nematoda)

Aim The phylogeography of Rhabdochona lichtenfelsi, a nematode parasite specific to endemic goodeids in Mexico, is used to infer the biogeographical history of fragmentation and recent evolution of the Mesa Central drainages. Geological history of the west‐central region of Mexico suggests that extant freshwater basins are the result of different vicariant events that fragmented ancient watercourses and lakes within the Mesa Central. Location Major freshwater river basins of the Mesa Central, Mexico: Ameca, Cotija, Lerma, Rio Verde, Panuco, and lakes Cuitzeo and Zacapu. Methods Haplotype diversity and phylogeographical structure of 10 populations of R. lichtenfelsi, sampled from the complete range of this species, were analysed with partial sequences of cytochrome c oxidase subunit I (456 bp). Analyses performed included phylogenetic tree estimation methods (neighbour‐joining, maximum parsimony and maximum likelihood), genetic diversity, distance and structure estimates, and nested clade analysis. Results High overall haplotype diversity, unique haplotypes, and strongly structured populations were found in the basins sampled. Three phylogenetically and demographically identifiable clades were recovered. These clades fit an isolation‐by‐distance model. Significant population expansion was observed for two clades and for the entire population. Time of divergence was estimated as 1.0 and 0.84 Ma for the different clades. Main conclusions The distribution of R. lichtenfelsi haplotypes does not correspond to the present distribution of the basins of Mesa Central, but instead reflects the distribution of those basins during a recent geological period (Pleistocene). While our current knowledge of the evolution and geographical relationships of the Mesa Central basins comes from studies of freshwater fish encompassing a more ancient history, our results suggest that, during the past million years, old basins and connections existed where today isolated freshwater bodies stand, thus unravelling a novel biogeographical history for the Mesa Central of Mexico.