Morphology and reproduction of the cavefish Trichomycterus chaverti and the related epigean Trichomycterus cf. barbouri

Hypogean and epigean populations of Trichomycterus catfishes inhabit streams from different environments (cave, headwater, canyon and valley) in the Torotoro National Park in the Andes, Bolivia. A significant reduction in the diameter of the eyes and in the surface area of the mesencephalon was observed in subterranean populations, along with an increase in the surface area of the telencephalon. Contrary to expectations, the barbel did not appear to be longer in hypogean populations. The observed pattern of modification of the other variables (pigmentation, eye asymmetry, surface area of the cerebellum and rhombencephalon, fecundity and egg diameter) corresponded to a gradient of values from valley to canyon, headwater and subterranean populations. This result argues not for a simple distinction between epigean and hypogean populations but for an adaptation to an environmental gradient of constraints in which caves correspond to an extreme situation. (résumé d'auteur