Last year, researchers raised the possibility that Mexican blind cavefish once could see but traded in their vision for bigger jaws and teeth (SN: 8/23/03, p. 126: Available to subscribers at Did cavefish trade eyes for good taste?). Those same scientists now report genetic evidence bolstering their theory.
William Jeffery of the University of Maryland at College Park and his colleagues had previously reported that the gene sonic hedgehog controls eye and mouth formation in the freshwater fish Astyanax mexicanus. This single species has both a sighted form, which swims in surface waters, and a blind form, which lives in cave ponds.
By examining gene expression in embryos of both fish types, Jeffery's team found that the blind fish express sonic hedgehog and a second gene, tiggy-winkle hedgehog, in a larger region of the body than sighted fish do. This expanded expression prevents normal eye development.