Effect of previous fighting on the dynamic of agonistic encounters in zebrafish males

Abstract

Aggression among individuals which compete for resources such as food or territory, or to establish dominance relationships, can cause injuries that may be risky for the contenders. In this way, individuals of many species have strategies to resolve conficts reducing levels of aggression. Thus, if individuals are able to recognize each other and remember previous agonistic experiences and the result of the fght, they will resolve the subsequent encounter with lower levels of aggression. Here, we evaluated the efect of previous fghting experiences (24 h interval) on agonistic behaviors of subsequent encounters in zebrafsh (Danio rerio) males. Specifcally, we examined if any reduction in aggression is because of an individual’s ability to remember other individuals from previous interactions, or if reductions come directly from winning or losing a fght. We found that when a pair of opponents (of the same size) had fought, and 24 h later the same dyad fought again, the number of bites decreases 85% and the duration of aggression decreases 73% in the second encounter, and this efect persisted in a third encounter (a decrease of 90% and 95%, respectively). To evaluate if the efect of previous experience on agonistic behaviors depended on facing the same opponent, in the second fght of a new experiment the opponent was changed. In this case, no decreases in the number of bites or in the duration of aggression was observed. In conclusion, pairs of zebrafsh males resolve a confict with lower levels of aggression when having previously fought with that particular opponent, but not with an unknown opponent. As a whole, these results suggest that zebrafsh males are capable of recognizing the opponent, remembering previous experiences and changing their fghting strategies accordingly, but not only as a consequence of the result of a previous encounter.