Visual and Acoustical Signalling during Courtship by Fiddler Crabs (GenusUca)

Abstract

Male fiddler crabs (Genus Uca ) employ both visual and acoustical signals to attract females for mating. In U. pugilator and several other American species, the males attract females during the day first by waving, then by producing sounds just within their burrows. At night, the males produce sounds at low rates, but when touched by a female, they increase their rate of sound production. In the European species, U. tangeri , many elements of courtship are similar to those in U. pugilator , but two types of sounds are produced. One of these, the short drumwhirl, appears to substitute for waving when the male is temporarily obscured from the female during his diurnal courtship activities. The long drumwhirl is used under different circumstances. The acoustical responses of a male to a female influence the courtship behavior of other males in the area. When sounds from stimulated males are played back to test males during the day, their lates of waving increase. At night, the playbacks elicit increases in rates of sound production. The influence of tidal oscillations, temperature, and light cycles on the behavior of males is discussed. Courtship activities of aquatic crabs are compared to those of terrestrial Brachyura. In aquatic forms, courtship may be absent or, if present, does not involve elaborate signalling by the male. Chemical or visual cues at close range are the most important stimuli. In several genera of terrestrial crabs, visual signalling for prolonged periods is common, and sounds are often emitted by males to “call” females from their burrows to the surface for mating. Some of the factors that may account for differences in courtship activities in aquatic and terrestrial species are discussed.