The signalling roles of ultraviolet light and chemical cues in stomatopod agonistic encounters (#563)
Animals commonly compete over resources such as food, territories or mates. To avoid unnecessary injury during these conflicts, opponents may engage in signalling behaviours to convey information about their fighting ability or motivational state. In some cases, more than one signal modality is used to either increase information transfer or allow for signal redundancy. Crustaceans engage in competitive behaviour and it is likely that they use multimodal signals in these contests. In particular, stomatopods fight aggressively over refuges and are known to use chemical and postural displays. However, we know little about chromatic communication and the interaction with chemical communication in stomatopod agonistic encounters. Here, we investigate the signalling role of meral spot UV reflectance (a patch displayed during the postural display known as the meral spread) and if there is redundancy with chemical communication. Neogonodactylus oerstedii were collected at the Smithsonian Research Station in Belize and allocated to size matched, same sex pairs. UV reflectance of the resident’s (with refuge) meral spots was removed using a paint mix and the ability of intruders (without refuge) to detect chemical cues was removed by dipping antennae in fresh water. Thus, we modified the presence of UV reflectance and chemical cues available to intruders during agonistic encounters. When UV reflectance was absent we detected a strong trend towards shorter fights (p = 0.067) with a higher rate of offensive behaviours (p = 0.063). In the absence of chemical cues, the speed of approach towards the burrow was faster (p = 0.029). We propose that stomatopods may be using UV reflectance and chemical cues sequentially (rather than simultaneously) to assess an opponent’s fighting ability and/or the presence of an opponent in a burrow. From here, we can further assess the information encoded in these signals to expand our knowledge of crustacean communication systems.