Population genetic patterns revealed by microsatellite data challenge the mitochondrial DNA based taxonomy of Astyanax in Mexico (Characidae, Teleostei).

Astyanax has become an important model system for evolutionary studies of cave animals. We investigated correlations of population genetic patterns revealed by microsatellite data and phylogeographic patterns shown by mitochondrial DNA sequences in Mexican cave and surface fish of the genus Astyanax (Characidae, Teleostei) to improve the understanding of the colonization history of this neotropical fish in Central and North America and to assess a recent taxonomic classification. The distribution of nuclear genotypes is not congruent with that of the mitochondrial clades. Admixture analyses suggest there has been nuclear gene flow between populations defined by different mitochondrial clades. The microsatellite data indicate that there was mitochondrial capture of a cave population from adjacent populations. Furthermore, gene flow also occurred between populations belonging to different nuclear genotypic clusters. This indicates that neither the nuclear genotypic clusters nor the mitochondrial clades represent independent evolutionary units, although the mitochondrial divergences are high and in a range usually characteristic for different fish species. This conclusion is supported by the presence of morphologically intermediate forms. Our analyses show that the Trans-Mexican Volcanic Belt limited gene flow, but has been crossed by Astyanax several times. In Yucatán, where obvious geographic barriers are missing, the incongruence between the distribution of nuclear and mitochondrial markers reflects random colonization events caused by inundations or marine transgressions resulting in random phylogeographic breaks. Thus, conclusions about the phylogeographic history and even more about the delimitation of species should not be based on single genetic markers.