The interplay between winner–loser effects and social rank in cooperatively breeding vertebrates

Winner and loser effects are widespread among animal taxa and are known to influence hierarchy formation, although it is unclear how rank influences such effects in species organized in social hierarchies. We investigated the existence of winner and loser effects and the effect of social rank on such effects in Neolamprologus pulcher, a cooperatively breeding cichlid fish. Social groups of these fish are organized in strict linear, size-based hierarchies. We successively assigned a dominant or subordinate rank to each of 18 focal individuals in balanced order, followed by an assigned winning or losing experience, respectively, resulting in a two-by-two factorial design. For each of the four treatment combinations, we recorded the performance of the focal fish in contests over a resource with similar-sized, naive opponents. Assigned winners won subsequent contests more often than losers, were more likely to escalate the contest and showed more overt aggression during a contest. Moreover, individuals with assigned subordinate rank showed more restrained aggression. However, winner and loser effects were not modulated by rank. This study shows that winner–loser effects exist in a highly social fish with linear social hierarchy. Moreover, fighting experience and rank may play complementary roles in conflict resolution.