Effects of competition, female size, and their distance on the claw-waving rate of male fiddler crabs (Brachyura, Ocypodidae)

The alteration of signals of animals in response to changes in environmental factors is a common phenomenon. In male fiddler crabs, waving major claws towards females is energetically costly; thus, males need to adjust their waving in a way that increases the chance of potential mate attraction while reducing the waving cost. In this study, I examined how Austruca perplexa males adjusted their waving rate based on male-male competition (male numbers in a cluster [Austruca perplexa males make groups and wave synchronously towards females]), female body size, and the distances of the receiver females from the signaller males. Forty clusters were selected randomly; from each cluster, I randomly selected one male, video recorded his waving behaviour and calculated waving rate (waves/min). Body size (carapace width) and distances of receiver females were measured. To analyze the effects of competition, female size, and their distances on male waving rate through binary logistic regression analysis, all variables were divided into two categories (male waving rate: low and high, competition: low and high, female size: small and large, and female distances: short and long) based on a median split method. Afterwards a series of binary logistic regression models were built and the relative supports of various models were assessed based on the corrected Akaike information criterion. Results showed that competition, female body size and their distances affected the male waving rate in an additive manner, but their interactions did not show any effect. Further research can be conducted to investigate how breeding season and predation risk along with competition, female size and female distances affect the claw-waving display of male fiddler crabs.