Abstract Cooperative breeding, i.e. individuals helping others to successfully raise offspring, is among the most complex social behavior in animals. It can be explained by helpers
Cooperative breeding, i.e. individuals helping others to successfully raise offspring, is among the most complex social behavior in animals. It can be explained by helpers gaining indirect fitness benefits through increasing the survival of related individuals. However, such indirect benefits cannot explain why unrelated individuals help others to reproduce. Here, direct benefits like increased chances of territory inheritance, reproductive share or predator protection, are of importance. Predation risk in known as a major factor selecting for group living. However, it has been undervalued as a driver of complex sociality, despite the potential to influence direct and indirect benefits of cooperation alike. We investigated the interplay of direct benefits, i.e. predator protection, and indirect benefit, i.e. within-group relatedness, in wild populations of the cooperatively breeding cichlid Neolamprologus pulcher. Breeders of these fish accept up to 25 helpers within their territory. Helpers show size-dependent task specialization, with larger individuals investing more in anti-predator defense. We measured group structure, aggressive interactions and within-group relatedness of eight N. pulcher populations, differing in predation risk. We show that group structure was significantly influenced by risk and related ecological factors. Dominants reduced aggression towards subordinates under increased risk, and aggressive interactions between subordinates similarly decreased. Young helpers were more related to breeders in high risk populations, while this relationship was reversed for larger and older helpers. Finally, the presence of large subordinates was associated with a higher likelihood of a territory containing offspring under high predation risk. These results reveal the complex interplay between predation risk, intra-specific aggression, and relatedness, highlighting the importance of predation risk for the evolution of complex social systems.
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Maria Tello Ramos, Niki Khan, Nick Jones