Intraspecific variation in audience effects during outgroup conflict in a cooperatively breeding fish

Abstract

Conspecific audiences have frequently been shown to affect behaviour during competitive interactions. However, research on audience effects has focused almost exclusively on how individual observers influence dyadic contests. Few studies have investigated more complex social scenarios, such as when groups defending a collective territory against outsiders can be monitored by neighbours. We used groups of the cooperatively breeding cichlid fish Neolamprologus pulcher to test experimentally how the presence of neighbours influences group and individual level defence behaviour towards a female intruder, as well as associated within-group interactions. In the presence of neighbours, groups performed more defensive acts and spent more time defending their territory, but the nature of the response to neighbour presence differed between group members. Dominant females attacked intruders more, while subordinate females produced aggressive displays of longer mean duration; dominant males also tended to increase mean display duration. Despite the significant audience effects on defence behaviour, neighbour presence did not lead to any discernible changes in within-group aggression, affiliation or submission during the intrusions. Our study expands the small current literature on audience effects in group-living species and thus contributes to a fuller understanding of within- and between-group social dynamics. • We assessed audience effects on collective defence and within-group interactions. • Groups increased their defensive efforts in the presence of neighbours. • The type of defensive behaviour that increased differed between group members. • Within-group behaviour during the intrusion was not affected by neighbour presence.