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The model system we use to study the evolution of eye degeneration is Astyanax mexicanus, a neotropical teleost exhibiting eyed surface populations and eyeless cave populations. During the Late Pleistocene (about 10,000 - 100,000 years ago), surface dwelling Astyanax mexicanus diverged into at least 29 distinct cave-dwelling populations, which eventually lost their eyes and pigmentation. Some of the cave populations appear to have evolved independently from a common surface fish ancestor (Dowling and Jeffery, 2000), and show varying degrees of eye and pigment degeneration. The cave populations have retained the capacity to produce fertile offspring with surface fish and are considered to be the same species (Avise and Selander, 1972). Therefore, Astyanax represents a unique system for studying the evolution of developmental mechanisms in which ancestral and derived stocks with distinct developmental differences are extant and available for experimental analysis. We have collected surface fish and cavefish from 6 caves near Ciudad Valles, Mexico, and have established breeding populations in our laboratory. Astyanax mexicanus is the only cave dwelling vertebrate that can be routinely maintained in the laboratory. |
