Temperature-Independence of the Frequency of the Endogenous Tidal Rhythm of Uca

Abstract

Utilizing the fact that the degree of dispersion of melanin in the melanophores of isolated legs of the fiddler crab, Uca, exhibits a minimum at the time of high tide in the place in which the crabs were collected, the influence of temperature upon the frequency was determined. Two-4 hours before the time of a high tide, the animals were placed at 3 temperatures between 13[degree] and 30[degree]C. Thereafter, samples were taken of the crabs at each of these temperatures to learn what the effect of increased or decreased temperatures would be on the time at which the melanin passed through the stage of minimum dispersion. It was found that the time of minimum dispersion was approximately synchronous at all the temperatures indicating temperature independence of the series of processes within the organism leading to minimum dispersion at the particular time relative to tide. Unlike with frequency, the amplitude of the tidal rhythm of melanophore change was greater at higher temperatures and less at lower ones. It is pointed out that to be of an adaptive character, any tidal rhythm within the organisms, must be temperature independent within the normal range of temperature variation to which the animals are subjected.