Genetic Relatedness Promotes Equal Contributions of Males and Females to Brood Care in a Biparental Cichlid Fish.

Kin discrimination, that is, the differential treatment of kin and nonkin has been studied in a wide range of social contexts because kin selection theory predicts that genetic relatedness among interacting individuals can reduce conflicts and promote cooperation. However, the impact of kin discrimination on parental cooperation in biparental systems is neglected so far. Here, we compared the individual contributions of males and females to brood care of kin and nonkin pairs in Pelvicachromis taeniatus, a biparental cichlid fish with a pronounced kin-mating preference. We conducted a cross-fostering experiment to control for offspring effects on parental care and an experiment without brood manipulation. In both experiments, the relative contribution of the sexes differed depending on the degree of relatedness within a pair. In unrelated pairs, females cared more than males, whereas the sexes contributed equally in related pairs. Our results indicate that relatedness affects the resolution of sexual conflict. More equal contribution may suggest higher cooperation between sexes within related pairs. Enhanced parental cooperation may be an important benefit of inbreeding, which might have contributed to the evolution of inbreeding preference in P. taeniatus, but it may also explain inbreeding tolerance found in other biparental systems.