Laboratory experiments to determine if crayfish can communicate chemically in a flow-through system

The importance of chemical cues for transmitting information concerning sexual identity, agonistic state, and stress-related condition in the crayfishProcambarus clarkii (Girard) was examined in a flow-through system. Experiments tested the effects of "conditioned water" from stimulus tanks on the behavior of solitary male or female crayfish. Twenty males and 20 females were subjected to a random sequence of five treatments: unconditioned water (control), conditioned water flowing through tanks containing a solitary male or female, and conditioned water from tanks holding either two males or two females. Durations of the following behaviors were recorded: chelae up, chela(e) in baffle hole, chela waving, climbing, digging, grooming, gross body movement, and meral spread. Results indicated that crayfish chemically detected another animal within 0.25 m without additional visual or tactile stimuli; however, crayfish apparently did not "communicate" information on sexual identity, agonistic state, or stress condition, nor does this detection necessarily imply discrimination between stimuli from crayfish and other taxa (e.g., fish). Our conclusions are contrasted with the two previous reports on chemical communication in crayfish in which experimental animals were tested in static systems. We suggest that a temporal separation of molting and copulation and a long reproductive receptivity period for females (which would allow abundant intersexual encounters) could account for a lack of selective pressure to evolve long-distance sex pheromones.