Murine aggression induced by a boar chemosignal: a stimulus presentation dependency.

Male mice were used to assess for the presence of aggression-promoting cues in the boar chemosignal, 5 alpha-androst-16-ene-3-one. The findings of Experiment 1 indicated that this steroid has no aggression-promoting properties when mixed in water. When mixed in urine from castrated males, however, the steroid was shown to induce agonistic behavior in aggressors. Thus, the steroid was shown to possess aggression-promoting cues when associated with urine. Experiment 2 was designed to assess the chemosignal properties of the steroid when mixed in urine or juxtaposed either proximally or distally to urine. It was determined that the steroid needed to be either adjacent to or mixed in urine for chemosignal activity to be evidenced. It was concluded that (1) urine may function as an orienting stimulus for the appropriate detection of the steroid or (2) the conjoint presentation of the steroid and urine provided a qualitatively different stimulus complex than either stimulus presented alone. The findings of both experiments question the species specificity of the boar chemosignal and have methodological implications for studies attempting to isolate a chemocommunicative substance. Appropriate stimulus presentation procedures need to be considered for future research projects.