The role of genetic relatedness among social mates in a cooperative breeder

Breeding with relatives can have severe fitness consequences, so avoiding these costs is often evolutionarily favored. There are a number of mechanisms that reduce the likelihood of mating with relatives, including avoiding relatives as mates (through sex-biased dispersal and mate choice) and delayed sexual maturity in the presence of relatives. Here, we examine these mechanisms in Neolamprologus pulcher, a group-living cichlid fish that exhibits male-biased dispersal. Despite sex-biased dispersal in this species, mean relatedness between social mates was not different from that expected if pairs had formed randomly, suggesting individuals neither actively avoid nor prefer pairing with relatives. Furthermore, gonadal investment of subordinates living in social groups was not correlated with their relatedness to the opposite-sex dominant breeder in the group, suggesting that sexual maturation does not depend on the presence or absence of a relative. Highly related social pairs showed higher rates of within-pair aggression and lower rates of nonaggressive social affiliation than less-related social pairs. Breeder investment and indicators of female breeder and group quality were not correlated with relatedness values between social mates. However, scraping rates (a potential quality indicator) were lower in males paired with more closely related females. We consider whether the apparent lack of inbreeding avoidance reflects an evolutionary history of limited breeding opportunities in N. pulcher or a facultative strategy of more-fit individuals and discuss the behavioral results in light of the suggested nonassortative mating with regard to relatedness.