A TIDAL RHYTHM IN BEHAVIOR OF MELANOPHORES IN AUTOTOMIZED LEGS OF UCA PUGNAX

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Abstract
Autot-omy of legs of the fiddler crab, U. pugnax, was induced by pressure on a distal segment of the legs. The autotomized legs were placed in sea water, and the behavior of the melanophores of the legs was observed. It was determined that the stage of melanin dispersion observed 30 minutes following autotomy is an accurate measure of the direction and total amount of change in the pigment, as well as of the relative rate of change. A population undergoing the diurnal color change characteristic of these animals was studied by determining the 30-minute value of 5 animals at half-hour intervals during the daytime for a period of 23 days. The melanin tended to concentrate following autotomy, such that a diurnal rhythm was apparent in the behavior following autotomy. This diurnal rhythm was modified by a tidal rhythm of behavior. During the day phase, when the melanin of the intact animals was dispersed, relatively little concentration occurred following autotomy near the time of low tide. An increased degree of concentration was observed when legs were isolated near the time of a high tide occurring during the day phase. This tidally rhythmic behavior was observed for both a population with normally varying degrees of melanin dispersion, and for one with maximally dispersed melanin. The variations in rate of concentration which were observed can not be explained as due solely to the inactivation of the melanin-dispersing hormone. It is necessary to assume that both the state of the melanophores of the intact animals and the character of the response following autotomy are determined by the relative concentrations in the blood of a melanin-dispersing hormone and a melanin-concentrating hormone.