A Persistent, Light-Preference Rhythm in the Fiddler Crab, Uca pugnax and Its Possible Adaptive Significance

Abstract

A method was devised to measure[long dash]continuously and automatically [long dash] the orientational response of fiddler crabs to a constant, directional light source. In crabs maintained in constant conditions, the response was found to be rhythmic light being preferred during the early morning hours and darkness becoming attractive at night. The possible ecological significance of such a rhythm is discussed.