EVOLUTIONARY GENETICS OF CAVE‐DWELLING FISHES OF THE GENUS <i>ASTYANAX</i>

Attempts to understand evolutionary processes in cave organisms have been largely limited to speculation on the causes of loss of photoreceptor organs and pigmentation, increase in size and complexity of tactile sensory structures, and certain modifications in physiology (see review in Barr, 1968).Little is known of the population genetics of cave organisms or of the genetic changes accompanying the transformation of epigean (surface-dwelling) forms to troglobites (obligate cavernicoles) .Yet genetic information is essential to the confident development of theories of troglobite evolution.For this reason, we have compared the genic character and degree of variability in troglobitic and epigean populations of the characid fish Astyanax mexicanus in Mexico.Students of cave biology have generally accepted the thesis that the ancestors of many troglobites entered caves as troglophiles (facultative cavernicoles) before the end of the Pleistocene, and became isolated with the local extinction of surface populations as a result of climatic changes associated with glaciation (Barr, 1968).If this is true, many troglobites have been living