PHYSIOLOGY OF THE WHITE CHROMATOPHORES IN THE FIDDLER CRAB, UCA PUGILATOR 1 K. RANGA RAO, MILTON FINGERMAN AND CLELMER K. BARTELL Department of Biology, Tulane University, New Orleans, Louisiana 70118 A survey of the literature on chromatophores (Fingerman, 1965) reveals that much more information is available concerning the control of melanophores in the fiddler crab, Uca pugilator, than about its white chromatophores. Brown and Sandeen (1948) reported that the white chromatophoric pigment of Uca pugilator from the region of Woods Hole, Massachusetts, was more dispersed in animals on a white background than on a black background. The white pigment as well as the melanin of Uca pugilator also exhibited a daily rhythm whereby both pigments were more dispersed during the daytime than at night (Brown and Webb, 1948). Removal of both eyestalks from Uca pugilator results in concentration of the melanin (Carlson, 1935) ; extracts of the sinus glands cause its dispersion (Sandeen, 1950). The white chromatophores respond differently to eyestalk removal; the white pigment becomes maximally dispersed. Furthermore, subsequent injection of extracts of sinus glands did not alter this state in Woods Hole crabs. However, Sandeen did find a high concentration of white pigment-concentrating hormone in the circumesophageal connectives. Because the white chromatophoric pigment of the assay animals used by Sandeen was initially maximally dispersed she could demonstrate only a white pigment-concentrating hormone. She also postulated that an antagonism exists between the melanin-dispersing hormone and the white pigment-concentrating hormone, such that the presence of a large amount of the former decreases the expression of the latter. At that time no evidence was available for the presence of a white pigment-dispersing substance in any crab. Recent studies on Rhithropanopeus Jiarrisi (Pautsch et at., I960), Carcinus maenas (Powell, 1962a), Ocypode platytarsis (Nagabhushanam and Rao, 1964), Ocypode macrocera (Rao, 1967), and Uca annulipes (Nagabhushanam and Rao, 1967) have, however, revealed that the white chromatophores in each of these crabs are con-trolled by two hormones, pigment-concentrating and pigment-dispersing. Therefore, it was decided to reinvestigate the endocrine control of the white chromatophores of Uca pugilator to determine whether evidence for a white pigment-dispersing substance could be obtained with this crab also. To assay for white pigment-dispersing and -concentrating substances it was necessary to obtain two sets of assay animals, one with white pigment in a con-centrated state and the other in a maximally dispersed state. In a preliminary experiment it was found that fiddler crabs obtained from Panacea, Florida, would be suitable assay animals. The responses of the white chromatophores of these crabs to light and background were quite different from those reported for Woods Hole 1 This investigation was supported by Grant GB-5236 from the National Science Foundation. 606
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