COMPARATIVE ASPECTS OF THE CHROMATOPHORIC RESPONSES TO LIGHT AND TEMPERATURE IN FIDDLER CRABS OF THE GENUS UCA

¹ Department of Biological Sciences, Northwestern University, Evanston, Illinois

1. Chromatophoric responses to light and temperature were investigated in two tropical species of fiddler crabs, Uca galapagensis herradurensis and Uca zacae, and a temperate species, Uca pugnax.

2. The black, white, and red chromatophores of U. g. herradurensis showed a response to total illumination (primary response) in which the pigment dispersed with increasing light intensity.

3. In U. g. herradurensis there was a specific background, or albedo, response which resulted in concentration of the black and red pigments on a white background and their dispersion on a black background, while the white pigment showed the opposite response. Tue albedo response of the melanophores was present above 25° C. and increased as the temperature was raised to 40° C.

4. In U. zacae a strong albedo response resulted in darkening of the crab on a black background and blanching on a white background. The albedo response was most pronounced above 30° C.

5. In U. pugnax the black pigment concentrated with increasing temperature but the white pigment on a black background dispersed as the temperature was increased above about 20° C. In this regard the pattern of response to temperature in U. pugnax resembled that which had been published for another temperate species, U. pugilator.

6. Differences in the chromatophoric responses among species were emphasized. It was shown that some of these differences can be related to features of the habitats of individual species, such as type of terrain and temperature.

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