Evolutionary Aspects of Communication in the Courtship Behavior of Four Species of Anomuran Crabs (Petrolisthes)

Abstract

Communication during courtship was investigated for exchanges of acts between male and female crabs of four species of the genus Petrolisthes (P. cabrilloi, P. cinctipes, P. eriomerus, P. manimaculis). Acts with a communicatory function can be derived from non-communicatory acts such as feeding, locomotion and tactile investigation of the environment. The communicatory acts are repetitive, conspicuous, and oriented toward other crabs. Several aspects of courtship were similar for all four species: the male crabs held a territory during courtship; courted female crabs performed movements of walking and stretching before copulation; and, just before copulation, the male nudged the female with his chelae and maneuvered her into the mating position with his walking legs. The courtship of P. manimaculis and P. eriomerus was similar in two ways : a pair of animals began courtship behavior an hour or two before copulation; the courting male performed maxilliped oscillations in exchange with the female's movements of walking and stretching. Although the males of these two species performed the same acts, the courting P. manimaculis performed many more communicatory acts than did the P. criomerus male. During the 30 min before the molt of the female one exchange of acts differed between the species for the courting pairs. Antennal taps of the P. manimaculis male were inhibitive of female's movements, but the same was not true for P. eriomerus. Acts which initiated and terminated courtship sequences also differed most significantly during this time for both species. If females perform the discriminating role in mate selection, then P. manimaculus and P. eriomerus females may distinguish the overall differences in frequency of the performance of the male's courtship acts, differences in the acts exchanged, and patterning of acts in sequences during courtship. The courtship of P. cinctipes and P. cabrilloi was also similar in two ways : a pair of crabs could begin courtship anytime between a day and a few seconds before copulation; the courting male performed the act of chelae rocking and the female performed movements of walking and stretching. Because of the variable duration of courtship it was impossible to demonstrate the exchange of male and female acts for the latter two species. The non-communicatory acts of feeding and swimming of Petrolisthes are anomuran in nature. However, those communicatory acts of Petrolisthes employing the chelipeds resembled acts performed by brachyurans having non-predatory feeding habits and chelipeds modified for display.