Abstract
Crustaceans have two sets of pigmentary effectors, chromatophores and retinal pigment cells. Retinal pigments control the amount of light striking the rhabdom, the photosensitive portion of each ommatidium, screening the rhabdom in bright light and uncovering it in darkness or dim light. Migration of the distal pigment in the fiddler crab, Uca pugilalor, is regulated by a light-adapting hormone and a dark-adapting hormone. The black chromatophores of this crab are also controlled by a pair of hormones. Both pigmentary effectors exhibit circadian rhythms. The effects of some organic and inorganic pollutants on the ability of Uca pugilator to change color have been described. Exposure of this crab to naphthalene or cadmium results in decreased ability to disperse the pigment in their black chromatophores, the exposed crabs becoming paler than the unexposed crabs. Norepinephrine triggers release of both the black pigment-dispersing hormone and the light-adapting hormone. In view of the facts that (a) these hormones which regulate the black chromatophores and distal pigment are synthesized in and released from the eyestalk neuroendocrine complex, (b) the black pigment-dispersing hormone and the light-adapting hormone may actually be the same hormone. having two different activities and (c) release of both the black pigment-dispersing hormonemore » and the light-adapting hormone is triggered by norepinephrine, the present investigation was carried out to determine the effect of cadmium on distal pigment migration in Uca pugilator. More specifically, for comparison with the previously reported effect of cadmium on pigment migration in the black chromatophores, we wished to determine whether the distal pigment of fiddler crabs exposed to cadmium chloride is capable of as wide a range of movement as in unexposed crabs, and if not what might be the explanation. This is the first report of the effect of a pollutant on a retinal pigment of any crustacean. 12 refs., 3 tabs.« less
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