engleski

Evolution in the Dark: Convergence of Albinism in Cave Adapted Animals

The regression of melanin pigmentation (albinism) has evolved in all animal phyla that have successfully invaded cave habitats. The cause of albinism is known only in Astyanax mexicanus cavefish. In this species the oca2 gene, which acts during the initial step of melanin biosynthesis, the conversion of L-tyrosine to L-DOPA, is mutated. Since the melanin synthesis pathway is generally conserved among animals, we have used a melanogenic substrate assay to determine the defect in melanin synthesis in albino cave animals belonging to many different phyla. The assay involves supplying exogenous substrates, such as L-tyrosine or L-DOPA, to lightly fixed specimens, and subsequently detecting the presence of melanin as deposits of black pigment. L-DOPA, but not L-tyrosine, produced black pigment in diverse albino cave animals, including a sponge, a planarian, annelids, mollusks, arthropods, and vertebrates, indicating that the initial step of the pathway is also affected in these animals. Therefore, we conclude that albinism has evolved by a convergent defect at the first step of melanin biosynthesis in all cave-adapted invertebrates and vertebrates tested so far. In some cases, pigmentation was restored by L-DOPA treatment in patterns resembling those of closely related surface-dwelling relatives.

albinism; cave animals; convergent evolution

nije evidentirano