Resolution of agonistic conflicts in dyads of acquainted green swordtails ( Xiphophorus helleri): a game with perfect information

Abstract

Conflict resolution of acquainted opponents was compared to that of unacquainted ones in Xiphophorus helleri males. Under the Familiar condition, the 2 males which met had settled contest against each other in a previously staged encounter in another aquarium. Thus one opponent was previously the dominant pair member, the other its subordinate. Under the Unfamiliar condition, 2 males met which were not acquainted with each other but had independently undergone previous experience of victory or defeat. We tested the hypothesis that familiar pairs would conform to some behavioural predictions of an asymmetrical game with perfect information. As for unfamiliar pairs, being imperfectly informed of asymmetries at contest onset, they would have to acquire information on these during the course of interaction ( asymmetrical game with assessment) or alternatively would have to persist for a certain time or cost ( war of attrition). All expectations derived from an asymmetrical game with perfect information applied to familiar pairs but not to unfamiliar ones. In familiar pairs, all previous roles were reinstated without any escalation. Though previous winners predominantly defeated previous losers under both conditions of cognizance, this difference was more extreme in familiar dyads than in unfamiliar ones. This suggests that the respective roles were less clearly identified in the latter. The costs of conflicts, both in terms of aggressive behaviours used and in time, were also higher in unfamiliar pairs than in familiar ones. Unacquainted individuals required a longer period to assess each other. In addition, they had to rely on more pugnacious behaviour to settle disputes in comparison to acquainted pairs. As expected also, familiar pairs being already cognizant of initial respective roles were more characterized in terms of the behavioural patterns typical of each of these roles. Differences between ultimate winners and losers were clearer in acquainted pairs and appeared earlier during conflict. It was also possible earlier during contest to discriminate and predict ultimate winners from losers of acquainted pairs using behavioural interactions. In unacquainted pairs, ultimate winners could be forecasted using multivariate discriminant analyses, mainly by their offering resistance to future losers. A `war of attrition' did not fit to unacquainted pairs.