Social cues affect synchronization of male waving displays in a fiddler crab (Crustacea: Ocypodidae)

The influence of social context in animal signals can lead to complex communicational patterns. In particular, the interaction between individuals can lead to intriguing collective dynamics, such as the temporal synchronization of signals. A fascinating example of such temporal synchronization involves the waving displays of fiddler crabs, in which males raise and lower their enlarged claws in species-specific rhythms. The adaptive significance of this phenomenon is still obscure, but possibly involves female preference for leading waving displays. However, waving displays are highly complex social signals that might be involved in a variety of forms of communication other than simply attracting females, but little is known about the influence of social context on wave synchronization. In this study we carried out field experiments to investigate the effect of two social factors, male density and female presence, on the level of waving synchronization in the fiddler crab Uca leptodactyla . Groups of males at varying densities were established in enclosures and recorded either in the presence or absence of a female. Our results indicate that the main factor driving synchronization is the presence of the female, with males not only changing the timing of their waving displays, but also altering their spatial distribution in the arenas. On the other hand, male density had a negligible effect on synchronization (despite significantly increasing waving rate), suggesting that male–male communication plays a minor role in the emergence of waving synchronization in this species.