Urine as a source of conspecific disturbance signals in the crayfish Procambarus clarkii

Chemical signals are an important aspect of ecological interactions in crus tacean systems. Repellent chemical signals can be classified into three con text-specific categories: chemicals released directly from a repellent stim ulus (avoidance chemicals), chemicals released from damaged conspecifics (a larm chemicals) and chemicals released from stressed but undamaged conspeci fics (stress chemicals). Our study examines the existence and putative sour ce of the stress signals in crayfish. We hypothesize that Procambarus clark ii can recognize stressed individuals through chemical signals and also tha t the source of the signal that provides P. clarkii with information on the behavioral state of the sender is the urine. We collected urine and gill w ater from stressed and non-stressed animals, and chemicals from damaged con specifics. Chemical cues were introduced into a test arena while several be havior patterns of P. clarkii were recorded. Stressed crayfish produce sign ificantly more urine than non-stressed crayfish, and this urine caused cray fish to walk significantly faster and farther and away from the source of t he signal. These results demonstrate that predator-stressed crayfish releas e urine that causes other crayfish to move away from the source of the sign al, Responses to stress chemical signals may allow receiving organisms to a void the fate of the signal sender.