Behavioural profiles in a wild population of a cooperatively breeding cichlid

In cooperatively breeding species, subordinates can obtain group membership through social interactions with other group members or by providing services such as helping with territory defence. Large subordinate individuals, which can reproduce, are expected to adjust their behaviour as a function of the demand of help and group size because if the environmental conditions allow, they may either leave the group to start breeding or queue for the breeding position in their natal group. The number of helpers in a group is expected to affect the need of help by dominants and consequently also the level of subordination shown by helpers. In a series of field experiments, we manipulated the need of help and the opportunities for subordinates to show submissive behaviour in a wild population of the cooperatively breeding species Neolamprologus pulcher. We assessed if group size determines the social behavioural strategy of large subordinate individuals. When experimentally eliciting submissive behaviour, large subordinates from small groups showed a lower frequency of submissive behaviour compared to large groups; moreover, they tended to show a higher frequency of sand digging than in large groups. In contrast, neither territory defence in the presence of a heterospecific egg and larvae predator nor dispersal propensity, measured as prospecting frequency in neighbouring territories, was affected by group size. A principal component analysis revealed that prospecting is uncorrelated with submissive behaviour and helping behaviour. Our results suggest that group size may be involved in shaping behavioural phenotypes of juvenile subordinates.