Repeated evolution of cooperative breeding and life history traits in Tanganyikan cichlid fishes

Cooperative breeding is a complex social system in the animal kingdom where offspring receive care not only from their parents but also from other group members. However, the life history traits related to the evolutionary transition toward this complex system are still poorly understood. This study investigated the evolutionary transition from non-cooperativeto cooperative breeding in lamprologine cichlid fishes endemic to Lake Tanganyika using phylogenetic comparative methods. Ancestral state reconstruction revealed that the evolutionary transition from non-cooperative to cooperative breeding occurred at least seven times independently. Comparative analyses using life history data obtained from field observations and sampling and literature review showed an evolutionary link between cooperative breeding and clutch size or body size but not egg size; both clutch and body sizes were smaller in cooperative breeders. These findings suggested the evolutionary scenario that cooperative breeding first evolved in smaller species, most likely because of ecological constraints, such as an increased predation risk, followed by a reduction in clutch size. These results highlight the impact of predation risk on life history traits and how it mediates the transition toward a complex social organization.