Olfactory Recognition of Urine Signals in Dominance Fights Between Male Lobster, Homarus Americanus

The maintenance of dominance hierarchies in the American lobster (Homarus americanus) is based on recognition of the dominant animal by the loser of a recent fight. It is hypothesized that chemical signals are the basis of this recognition. Adult male lobsters were paired for initial boxing matches between unfamiliar animals. The same pairs were re-matched for 3 more consecutive fights. In the first experiment, treatment animals had their primary olfactory receptor cells of the lateral and medial antennules lesioned before fights 2-4 and control animals received sham lesions. The durations of fights 2-4 for control pairs were significantly shorter than the durations of fights between lesioned animals. In the second experiment, male pairs were again allowed to establish a dominance relationship in a first fight. During second fights, urine release by both animals was prevented by the use of catheters in treatment animals while control pairs wore sham catheters. Again, durations of the second fights of control animals were significantly shorter than those of treatment animals. Together, these experiments indicate that urine-carried chemical signals, perceived by the antennules, reduce the duration and aggression of male dominance fights on subsequent days because the loser of the first fight backs off almost immediately when he smells the urine of the known dominant.