Responses of the Chromatophores of the Fiddler Crab, Uca, to Light and Temperature

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Abstract
The condition of the black and white chromatophores of U. pugilator is detd. by several factors operating simultaneously as follows (1) There is an endogenous rhythm of chromatophorotropin secretion, which operates to disperse the black and white pigments in the day phase of the cycle and to concentrate the black and white pigments in the night phase of the cycle. (2) There is a specific background, or albedo, response which operates to concentrate black pigment and disperse white pigment upon a white background and to disperse black pigment and concentrate white pigment upon a black background. (3) There is a response to total illumination which results in an increased dispersion of both black and white pigments as the intensity of illumination increases. (4) There is a response to temp., with the black pigment tending to concentrate as the temp. is increased above, or decreased below, about 15 C. The white pigment, on the other hand, tends to disperse as the temp. is increased above, or decreased be-low, about 20 C. A possible adaptive significance of these chromatophore responses in Uca is discussed.