The sounds of fighting: contests between violet vinegar crabs, Episesarma versicolor (Tweedie, 1940) (Decapoda: Brachyura: Sesarmidae), are resolved through acoustic communication

Sound plays an important role in animal communication. Sesarmid crabs (family Sesarmidae) are semi-terrestrial crabs found in tropical and temperate regions, and are known to communicate through acoustic signals. The violet vinegar crab Episesarma versicolor (Tweedie, 1940) is a tree-climber known to possess sound-producing structures. The significance of sounds produced by E. versicolor during intraspecific contests, however, remains unknown. We investigated the context in which sound production occurs by staging 27 trials using male crabs. Three main types of acoustic behaviours were documented: rapping, leg stamping, and vibration. With the exception of vibration, these behaviours were also observed in female crabs. The air or the wood substrate was utilised to transmit acoustic signals, with each sound having unique spectral and temporal features serving different purposes. Rapping and leg stamping may be an advertisement of the sender's resource-holding potential for territorial defence and asserting dominance during fights. Vibration is likely a victory display that discourages the contest loser as well as individuals in the vicinity from engaging the victor in another fight. Episesarma versicolor can therefore produce acoustic signals that may contain information about the sender, minimising costs associated with direct conflicts.