Kin recognition by phenotype matching is family- rather than self-referential in juvenile cichlid fish

The ability to differentiate between kin and nonkin is of importance in nepotistic as well as in mate choice contexts. Phenotype matching is a significant kin recognition mechanism, which is widespread in animals. However, the underlying proximate mechanisms are still poorly understood. Phenotype matching can be based on either self-reference or familial imprinting. We investigated phenotype matching in juvenile Pelvicachromis taeniatus based on chemical cues. Pelvicachromis taeniatus is a socially monogamous cichlid fish with biparental brood care. Previous studies indicate that the adults use phenotype matching to recognize kin. Juvenile fish were reared under three different conditions to manipulate recognition templates: (1) reared with kin, (2) reared in isolation or (3) reared with foster siblings. Pelvicachromis pulcher families served as foster families. In the experiments, test fish had to choose between olfactory cues obtained from two stimulus shoals differing in relatedness to the test fish. Test fish reared with kin discriminated unfamiliar kin from unfamiliar nonkin indicating that juvenile P. taeniatus also use phenotype matching to recognize kin. Focal fish reared in isolation or with foster siblings did not significantly discriminate unfamiliar kin from unfamiliar nonkin suggesting that juveniles did not imprint on their own phenotypic traits. However, individuals reared with foster siblings preferred unfamiliar olfactory stimuli of the foster species over those of their own indicating they used rearing partners as reference. Thus, phenotype matching is probably based on familial imprinting rather than self-reference in juvenile P. taeniatus.