Astyanax mexicanus RAPD Trees

This page provides links to bootstrap trees based on RAPD data, which show the relationships among different populations of cave and surface forms of the Mexican Tetra, Astyanax mexicanus. Because all the populations are members of the same species and, at least in theory, capable of interbreeding, distance, rather than parsimony analysis was used to determine relationships. Significant clustering of populations does not necessarily imply phylogenetic relationship, in the sense that clustered populations share a common ancestor. Such clusters can arise from gene flow among populations.

Populations of the Sierra de El Abra region. The outgroup for this analysis is Astyanax aeneus from Guerrero. The data show that the cave populations consist of the groups that cluster separately.

Southern caves - Sierra de El Abra: Pachon and Tinaja

Northern caves - Sierra de Guatemala: Molino, Moro and Vasquez

Western caves - Rio Subterraneo (this clusters with all the othe populations, which are epigean).

All three areas are separated geographically and hydrologically, and the divisions among clusters may be phylogenetically meaningful. The western cave fish are considered by Wilkens to be "phylogenetically young" and this may be reflected in their clustering with epigean populations, instead of other cave fish.

Eyed fish of Caballo Moro cave. The accessible cave of Caballo Moro lies under a karst window, and contains a mxed population of eyed and eyeless fish. The analysis shows that the eyed fish of the cave cluster with other cave fish (Molino and Vasquez), rather than the surface fish (Boquillas, Comandante and La Florida). This closeness may reflect flow of RAPD markers from the blind cave fish into the eyeless karst window population, or may indicate that the eyed fish share a common ancestor with other cave fish. The data show that the eyed fish of the karst window are not simply epigean fish recently captured from the surface.