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

Chemical signals are an important aspect of ecological interactions in crustacean systems. Repellent chemical signals can be classified into three context-specific categories: chemicals released directly from a repellent stimulus (avoidance chemicals), chemicals released from damaged conspecifics (alarm chemicals) and chemicals released from stressed but undamaged conspecifics (stress chemicals). Our study examines the existence and putative source of the stress signals in crayfish. We hypothesize that Procambarus clarkii can recognize stressed individuals through chemical signals and also that 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 water from stressed and non-stressed animals, and chemicals from damaged conspecifics. Chemical cues were introduced into a test arena while several behavior patterns of P. clarkii were recorded. Stressed crayfish produce significantly more urine than non-stressed crayfish, and this urine caused crayfish to walk significantly faster and farther and away from the source of the signal. These results demonstrate that predator-stressed crayfish release urine that causes other crayfish to move away from the source of the signal. Responses to stress chemical signals may allow receiving organisms to avoid the fate of the signal sender.