Visual and Acoustical Signalling during Courtship by Fiddler Crabs (Genus Uca)

Male fiddler crabs (Genus Uca) employ both visual and acousticalsignals to attract females for mating. In U. pugilator and severalother American species, the males attract females during theday first by waving, then by producing sounds just within theirburrows. At night, the males produce sounds at low rates, butwhen touched by a female, they increase their rate of soundproduction. In the European species, U. tangeri, many elements of courtshipare similar to those in U. pugilator, but two types of soundsare produced. One of these, the short drumwhirl, appears tosubstitute for waving when the male is temporarily obscuredfrom the female during his diurnal courtship activities. Thelong drumwhirl is used under different circumstances. The acoustical responses of a male to a female influence thecourtship behavior of other males in the area. When sounds fromstimulated males are played back to test males during the day,their lates of waving increase. At night, the playbacks elicitincreases in rates of sound production. The influence of tidal oscillations, temperature, and lightcycles on the behavior of males is discussed. Courtship activities of aquatic crabs are compared to thoseof terrestrial Brachyura. In aquatic forms, courtship may beabsent or, if present, does not involve elaborate signallingby the male. Chemical or visual cues at close range are themost important stimuli. In several genera of terrestrial crabs,visual signalling for prolonged periods is common, and soundsare often emitted by males to "call" females from their burrowsto the surface for mating. Some of the factors that may accountfor differences in courtship activities in aquatic and terrestrialspecies are discussed.