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. The dataset
includes all pairwise relatedness values within our sample population, as
well as distances between 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.