Paying to stay or paying to breed? Field evidence for direct benefits of helping behavior in a cooperatively breeding fish

Abstract

Several hypotheses aim to explain the evolution of helping behavior, but conclusive experimental support for evaluating the relative importance of individual hypotheses is still lacking. We report on two field experiments conducted to test the 'territory inheritance' and 'pay-to-stay' hypotheses in the cooperatively breeding cichlid fish Neolamprologus pulcher. The territory inheritance hypothesis was tested by removing one parent, which created breeding vacancies. In 39% of cases, same-sex helpers took over the breeding spot; in 44% of cases helpers continued helping new breeders, and 17% were evicted by new breeders. Helpers that were closely size matched to the removed breeder had a better chance of gaining the breeding spot. Male helpers tended to continue helping after a takeover more often than females. The pay-to-stay hypothesis was tested by temporarily removing helpers. Whereas breeders did not respond aggressively to removals, other group members attacked the removed helpers on their return, and 29% were eventually evicted. The returning helpers assisted more by increasing their rate of territory maintenance and defense and visiting the brood chamber more frequently. Size and sex of removed helpers did not explain the observed aggressive reactions of other group members. Thus, our results support both hypotheses: N. pulcher needs to pay with help to be allowed to remain protected in the family group, and there they may inherit the natal territory. N. pulcher helpers gain direct benefits from helping behavior.