Effect of social context on behaviour in anemonefish hierarchies

Animal social groups can be organized in hierarchies where individual status determines privileges within the group, and stability is maintained through conflict (aggression–submission) and cooperation. Aggression, submission and cooperation are not homogeneous among group members and are influenced by social context and associated trade-offs. However, studies of rank-specific behaviours are rare which limits our understanding of these patterns. Here, we performed rank ascension experiments using 15 groups of Amphiprion clarkii, a relatively mobile anemonefish, to assess rank-specific behaviour related to social context. We showed that promoted ranks increased cooperation rates compared to nonpromoted ranks to fulfil the tasks associated with their new status within the group. Group size had no effect on cooperation rates, although it did influence rates of submission and neutral interactions, and subordinates did not increase cooperation after group size reduction. Thus, subordinates modulate rates of cooperative behaviour according to their status, irrespective of their body size or group size. We provide evidence that behaviour is plastic and highly influenced by social context, which appears to be the key driver of cooperation and within-group agonistic encounters in this species.