Restoring sight in blind cavefish

Twenty-nine populations of the blind cavefish, Astyanax mexicanus, are known from different caves in North-Eastern Mexico (Figure 1). They evolved from eyed, surface-dwelling forms which only reached the area in the mid-Pleistocene [1]. Quantitative genetic analyses have shown that the evolutionary impairment of eye development - as well as the loss of pigmentation and other cave-related changes - results from mutations at multiple gene sites ('eye loci') [2,3]. Eye loss has evolved independently at least three times [4,5] and at least some of the eye loci involved differ between the different cave populations [3]. Hybrids between blind cavefish from different caves have larger and better developed eye rudiments than their parents (Figure 2) [6], reflecting these independent origins and complementation [3,7,8]. Given the large number of mutations at different loci that have accumulated in these populations, we reasoned that hybridization among independently evolved populations might restore visual function. Here we demonstrate restoration of vision in cavefish whose immediate ancestors were blind and whose separate lineages may not have been exposed to light for the last one million years.