Physiological Color Changes in Reptiles

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Abstract
SYNOPSIS. The physiological regulation of color changes in reptiles as studied in the lizard, Anolis carolinensis, is discussed. In Anolis, the ability to adapt to a background is dependent upon the level of circulating MSH, therelease of which is dependent on information received through the eyes. Blinded (or intact) lizards are brown under conditions of strong illumination and green under conditions of lower light intensities, and, again, these color changes are regulated by MSH. According to Kleinholz, color changes in the blinded lizard are regulated by dermal photoreceptors. High or low temperatures directly affect the color of Anolis skins and alter the rate at which skins respond to hormones. Aggregationof melanin granules within Anolis melanophores in response to sympathomimetic stimulation is regulated through alpha adrenergic receptors whereas dispersion of melanin granules in response to such stimulation is controlled through beta adrenergicreceptors possessed by the melanophores. Most Anolis melanophores possess both alpha and beta adrenergic receptors, but some melanophores possess only beta adrenergic receptors. In the normal physiology of the lizard, under conditions of stress, stimulation of alpha adrenergic receptors by catecholamines leads to an “excitement—pallor“followed by an “excitement—darkening“ resulting from stimulation of beta adrenergic receptors which causes dispersion of melanin granules within localized populations of melanophores. Thus, in Anolis, dispersion of melanin granules within melanophores is regulated by both MSH and by catecholamines. Evidence is presented that the intracellular level of cyclic 3', 5'-AMP within melanophores may be responsible for the regulation of movement of melanin granules.

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