Variability in troglomorphic adaptations of a Mexican cavefish, Poecilia mexicana, from Tabasco, Mexico

Abstract

The cavefish Poecilia mexicana, earlier known as Poecilia sphenops, is a live-bearing toothcarp or molly found only in Cueva de las Sardinas (also known as Cueva de Villa Luz or El Azufre), in Tabasco, Mexico. The cave ecosystem is based on mixed energy inputs from sulfur springs and chemolithotrophic baceteria, bats, and skylights. The rich food base supports an amazing population density of the cavefish. Earlier studies reported that the fish showed increasing troglomorphic adaptations in physical characteristics and behaviors as you went deeper into the cave. Data presented on eye size reduction show considerable variation and overlap of data by location sampled, and no statistical analyses were done. We sampled from some of the same areas as earlier studies and from the most remote sites in the cave. Our results show considerable variation in troglomorphy of eye reduction from all locations, and no statistical difference with fish from any part of the cave. Evolutionary pressure to develop troglomorphy may be reduced in this cave because of the rich food base, or hybridization with surface forms may not be limited by physical location within the cave.