The role of alpha-melanocyte stimulating hormone in environmentally induced color change.
AdvisorBagnara, Joseph T.
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PublisherThe University of Arizona.
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AbstractIt is generally accepted that the endocrine basis of integumental color change in vertebrates is due to pituitary secretion of alpha-melanocyte stimulating hormone (α-MSH). However, physiological levels of α-MSH has not been reported for several species that have historically been the models of choice for investigating changes in pigmentation. The goal of this research was to quantitatively report levels of circulating α-MSH in two important genera: leopard frogs (Rana pipiens and R. chiricahuensis) and the green anole (Anolis carolinensis). Histology of the ventral skin of R. chiricahuensis was also examined due to its unusual melanization and ability to change color. Effects of background color and low temperature on α-MSH levels were examined by radioimmunoassay. In the species examined, black background color induced dark skin color and high levels of α-MSH. Rana chiricahuensis exhibited much greater plasma α-MSH than the other species. Anolis and R. chiricahuensis darkened in response to low temperature, but R. pipiens did not. Cold-induced darkening was associated with increased plasma α-MSH, but not to the extent observed during background adaptation. Ventral skin of R. chiricahuensis, in vivo, darkened at low temperatures, and the skin histology revealed numerous large dermal melanophores dispersed among iridophores. These ventral dermal melanophores are active components of R. chiricahuensis physiological color change.