The extended personality: indirect effects of behavioural syndromes on the behaviour of others in a group-living cichlid

Consistent individual variation in behaviour is widespread across taxa and behavioural categories. Because social behaviour is often a plastic response to the social environment, consistent variation in social behaviours such as aggression and cooperation may generate consistent variation in the behaviour of social partners and others in the group. In this study, we moved individual subordinate males between groups of a cooperatively breeding cichlid, Neolamprologus pulcher. We found that subordinate males varied consistently in their aggressive interactions with neighbouring fish. The effects of individual subordinate males extended beyond their direct interactions; agonistic interactions between dominant males and dominant females varied consistently with subordinate male identity. We suggest that variation in helping behaviour through territorial defence influences the net fitness effects of subordinate males on dominant males and, thus, the potential for conflict between dominant males and dominant females over subordinate male presence. The existence of indirect phenotypic effects of subordinate males on interactions not directly involving the subordinate male suggests that individual personalities extend into the social environment and may be an important selective influence on social behaviour and on variation among social groups.