Origins and relationship of cave populations of the blind Mexican tetra, Astyanax fasciatus, in the Sierra de El Abra

The blind morph of Astyanax fasciatus (Pisces: Characidae) has been more th oroughly studied than any other cave inhabiting organism. Most studies of A . fasciatus have used individuals from different caves of the Sierra de El Abra, Mexico, and have assumed that each population independently evolved t o live in the cave environment. We analyzed the relationships among several cave populations that delineate the Sierra de El Abra using RAPD markers. The results indicate that all cave populations are more closely related to one another than they are to the surface populations. This suggests that pr esent day cave populations derived from a common ancestral stock, most like ly due to a single colonization event, or alternatively, that strong gene f low among cave populations has occurred, raising precaution against conside ring each cave population as independent.