Dominant members of cooperatively-breeding groups adjust their behaviour in response to the sexes of their subordinates

In cooperatively-breeding species, the sexes of subordinate group members may have important consequences for dominant individuals. We varied subordinates’ sexes in aquariumhoused groups of the cooperatively-breeding cichlid fish Neolamprologus pulcher, and compared the behaviours of dominant individuals in groups with sameversus oppositesex subordinates. Dominants tended to be more aggressive towards same-sex subordinates, and dominant males directed more affiliative behaviour towards large female subordinates. These patterns suggest that mixed-sex groups can be viewed as separate male and female dominance hierarchies. Aggressive and affiliative interactions between dominant males and dominant females were more frequent when a large subordinate was female, which indicates that subordinates can be a source of conflict between the members of a breeding pair. Finally, subordinates’ sexes affected dominants’ locations within aquaria and the performance of territory maintenance behaviour by dominant females. In many cases, the effect of one subordinate’s sex depended on a second subordinate’s sex or on group members’ absolute or relative body sizes. Therefore, predicting effects of subordinates’ sexes in larger, more variable groups will be challenging. Our results are the first to experimentally demonstrate the importance of a group’s gender composition for the behaviour of dominant individuals in a cooperatively-breeding species.