Bystanders to contests between conspecifics are primed for increased aggression in male fighting fish

摘要

We performed two experiments in which we allowed a male fighting fish, Betta splendens, designated a bystander, to observe aggressive contests between pairs of male conspecifics. Another male (naieve male) observed an empty tank or two nonaggressive males, depending on the experiment. Immediately after these observation periods, we allowed the bystander and naieve male to interact in a neutral area. In both experiments, bystander males were dominant over naieve males in a significant number of the encounters. Bystander males performed significantly more aggressive behaviours (displays, chases and bites) than did naieve males. Differences in dominance were not due to chance differences in body size. These findings demonstrate that exposure to aggression between conspecifics increases aggressive motivation in bystander male fighting fish. We discuss briefly the implications of such social experience on the formation of dominance hierarchies.