Experimental manipulation of helping in a cooperative breeder: helpers 'pay to stay' by pre-emptive appeasement

The 'pay-to-stay hypothesis' proposes that subordinate group members help dominants in order to be tolerated in the territory. Accordingly, helpers should be punished if they are not helping sufficiently and should increase helping behaviour thereafter. We tested whether helping and social behaviours of group members of the cooperatively breeding cichlid Neolamprologus pulcher change according to these predictions. A focal helper was experimentally prevented from helping to defend the territory against a conspecific intruder by depriving it of the information that an intruder was present. At the same time the other group members witnessed both the intruder and the 'passive' focal helper. When a helper was prevented from providing help, the other group members compensated by increasing defence of the territory, which suggests that the contribution of the passive helper was beneficial. As predicted by the pay-to-stay hypothesis, helpers increased helping behaviour after being prevented from helping. However, we found no indications that dominants punished the focal helper for not having helped before. Punishment may not be measurable, though, because of an appeasement function of helping behaviour. In accordance with this hypothesis, agonistic interactions between focal helpers and dominants were reduced when helpers helped. Apparently, helpers prevent punishment by increasing helping and submissive behaviours. Our data support the pay-to-stay hypothesis and suggest a new mechanism for the regulation of cooperative investment by subordinates: pre-emptive appeasement of dominants through helping and submissive behaviour.