Subterranean Fishes of the World

3707

2016

6

Many cave-adapted animals have lost melanin pigmentation but the underlying molecular and evolutionary mechanisms are unknown. Here we report experiments addressing the evolution of albinism in cave animals. First, applying the melanogenic substrate assay to diverse albino cave animals from different phyla, we have shown that melanin synthesis is always blocked at its first step. In several cave populations of teleost Astyanax mexicanus oca2 is the single gene responsible for albinism, and its knockdown in surface fish abolished melanin synthesis and increased L-tyrosine and the catecholamine (CAT) dopamine. In addition, we found that albino cave Astyanax, bivalves, planthoppers, and polychaetes show increased CAT levels compared to their most closely related surface relatives. These results suggest that albinism may be advantageous for increasing the CAT synthesis pathway by providing additional L-tyrosine. Second, we have also tested the possibility that interference with melanin synthesis is beneficial for energy conservation. Using gene silencing techniques and membrane-inlet mass spectrometry, we found that interruption of melanin synthesis in Astyanax surface fish embryos results in lower oxygen consumption, supporting the energy conservation hypothesis. Third, we have performed experiments to address our finding that diverse albino cave animals retain L-DOPA positive melanoblast-like cells. It is known that arthropods use melanin in their innate immune response, and we discovered that several albino cave arthropods retain the ability to synthesize melanin after an immune challenge, suggesting a benefit of conserving undifferentiated melanoblasts. In addition, we have observed that Astyanax melanophores or L-DOPA positive melanoblasts accumulate around a wound site, and treatment with a chemical agent that kills these cells affects wound repair, suggesting that the melanin synthesizing cells cannot be completely lost because they also function in innate immunity. It is concluded that multiple mechanisms may work together to control the evolution of albinism in cave animals.

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2016 International Conference on Subterranean Biology

13 – 17 June 2016

13 – 17 June 2016

13 – 17 June 2016