engleski

Evolution of Albinism in Caves

The regression of melanin pigmentation (albinism) has evolved in all animal phyla that have successfully invaded cave habitats. The mechanisms of albinism are only known in <i>Astyanax</i> cavefish. In this system, oca2, a gene that acts at the first step of melanin synthesis pathway, is subject to different loss-of-function mutations in independently evolved cavefish lineages. Likewise, a block in the first step of melanin synthesis has been discovered in a diverse group of albino cave animals, including mollusks, annelids, arthropods, and vertebrates. In these animals, exogenously applied L-DOPA can restore melanin pigmentation patterns resembling those of pigmented surface relatives. Therefore, albinism has evolved via convergent evolution by interfering with the first step of melanin biosynthesis pathway in a diverse assemblage of cave animals. What are the evolutionary processes that result in a block at the same step of the pathway in different animals? Studies with <i>Astyanax</i> cavefish suggest an explanation: blockage at the first step maybe be advantageous because it results in shunting excess L-tyrosine from the melanin pathway to a branch pathway leading to catecholamine synthesis. Several adaptive traits such as changes in feeding, foraging and sleep behaviors that evolved in cavefish are under the control of catecholaminergic systems. Furthermore, our results show that a number of cave invertebrates (bivalve, polychaete, leech, diplopod and insect) have significantly increased catecholamine levels when compared to their closest surface relatives. It seems that the loss of melanin may have a beneficial effect on survival of cave animals in inhospitable underground habitats.

cave adapted animals, albinism, Astyanax, catecholamines, melanin

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