engleski

The mechanisms and causes of pigmentation loss in cave adapted animals

The loss of pigmentation is one of specialized traits which evolved as an adaptation to subterranean habitats. It appeared in almost all groups with cave-adapted species, but not much is known about the molecular and evolutionary mechanisms of its appearance. The exception is the teleost model system Astyanax mexicanus, in which a deletion in the oca2 gene underlies albinism in several independently evolved cavefish populations. We have investigated albinism in diverse cave species and discovered that 1. pigment cells are invariably present and 2. there is a lesion in the first step of melanin synthesis pathway. The preservation of pigment cells is suggestive of their function in processes other than pigmentation. Further examination confirmed the role of melanocytes in vertebrate immunity and maintenance of melanin synthesis capacity as a part of the innate immune response in albino cave arthropods. The non-random inactivation of melanin synthesis suggests that there must be an adaptive benefit. The cessation of pigment production could be selected for as a result of minimizing energy expenditure for production of unnecessary substances, or as an indirect effect since many pleiotropic phenotypes are intertwined with pigmentation. We found evidence for both of these hypotheses implicating that natural selection may be involved in the evolution of albinism, contrary to traditional views of pigmentation being a trait that is simply discarded in the absence of light.

albinism ; pigmnetation ; cave-adapted animals ; pleiotrophy

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