No evidence for kin selection as an explanation for social group formation in clown anemonefish

Social groups in which some individuals forgo reproduction and others reproduce, are one of the most remarkable products of evolution. To fully understand these social groups, we must understand both why non-breeders tolerate their situation and why breeders tolerate non-breeders. In general, breeders tolerate non-breeders because they help provision the breeders' offspring or the breeders themselves, but in some vertebrate societies the benefits that breeders accrue from non-breeders are surprisingly hard to detect. This raises the question: why do breeders tolerate non-breeders in such societies? Here, we test the hypothesis that breeders of the clown anemonefish (Amphiprion percula) will tolerate non-breeders because they are distant relatives who go on to inherit the territory. We use 40 polymorphic microsatellite loci to assess the pairwise relatedness of 683 individuals from 203 groups. We show that the mean pairwise relatedness among individuals from the same group is effectively zero, and no different from that found among individuals from the same reef or that found among individuals from the population at large. Further, we show that the mean pairwise relatedness found among breeder/breeder dyads is no different from that found among breeder/non-breeder dyads or that found among non-breeder/non-breeder dyads. We conclude that kin selection does not explain why breeders tolerate non-breeders in the clown anemonefish, and suggest that the explanation must lie with other, as yet untested, hypotheses: within-generation bet-hedging or mutualist-mediated benefits.