Group composition, relatedness, and dispersal in the cooperatively breeding cichlid Neolamprologus obscurus
Cooperative breeding has been studied intensively in many species of birds and mammals but remain less well studied in fish. We report a remarkable new example of a cooperatively breeding cichlid from Lake Tanganyika, Neolamprologus obscurus. Using field observations and microsatellite DNA analyses, we studied group structure, helping behavior, relatedness, and dispersal of this species. We present four major observations. First, large territorial breeding males mated with one to eight breeding females, each of which was territorial and unrelated to another. Second, one to ten smaller fish (“subordinates”) of both sexes were allowed to stay inside the breeding females’ territories. Subordinates were often highly related to both the respective breeding male and female and performed territory defense and shelter maintenance, which is regarded as helping behaviors. Third, one to three subordinate males, similar in size to breeding females, were allowed to stay inside a breeding male’s territory but were not tolerated in the breeding females’ territories. Pairwise relatedness suggests these individuals are usually sons of the respective breeding male. Fourth, pairwise relatedness estimates suggest that juveniles delay dispersal and assist their mothers in raising offspring. As female subordinates grow up, they leave the father’s territory and disperse into other groups. In contrast, male subordinates leave their mother’s territory but remain within the territory of their father. The described social system makes N. obscurus a promising new model species to study the evolution of cooperative breeding.