Synchronous waving in an ocypodid crab, Ilyoplax pusilla : analyses of response patterns to video and real crabs

Abstract

In several species of ocypodid crabs, including Ilyoplax pusilla (De Haan), waving displays tend to be synchronized among neighboring individuals. However, no quantitative study has yet been conducted. In this study, responses of I. pusilla males to waving of video and real crabs were examined. Spontaneous, periodic waving was observed even when no stimulus waves were present. When single isolated waves of the video crab were randomly delivered (single pulse perturbation), crabs waved either immediately after the stimuli or after some time had elapsed. Assuming that waves immediately after the stimuli were triggered prior to those stimuli, crabs typically responded after a roughly constant delay from the onset of each stimulus. The delay (response time) was close to, but slightly shorter than, the spontaneous wave period. Dependency of response time upon timing of the stimulus (stimulus time) was at most weak. Responses of crabs to periodic waves of the video crabs and waves of␣the real crabs were basically consistent with the results of single pulse perturbation, although there was a consistent tendency for stimulus time and response time to be negatively correlated near stimulus time = 0 s. Overall, these results demonstrate that males of I. pusilla adjust signal timing relative to a neighbor in a manner of phase delay synchrony. The similar response pattern has also been noted in synchronous flashing of fireflies and the calling of katydids. Moreover, these experiments with I.␣pusilla demonstrate the value of video playback as a research tool in this species.