Pay-to-stay drives the evolution of helping independent of kin selection in anemonefish societies

Abstract The evolutionary drivers of helping behavior continue to be widely debated, particularly due to challenges in disentangling the effects of different mechanisms. The pay-to-stay hypothesis proposes that helping aims to appease dominant breeders to avoid eviction. We tested pay-to-stay as an independent driver of helping by exploring its dynamics in anemonefishes (Amphiprion spp.) which lack prerequisites for other mechanisms, including kin selection. We experimentally prevented helping (anemone maintenance, territory defence) in A. percula, A. perideraion, and A. clarkii., and assessed 2 pay-to-stay predictions: (i) helpers would be punished and/or (ii) would compensate with increased cooperative effort (pre-emptive appeasement). We show that anemonefish nonbreeders do pay-to-stay: punishment and/or appeasement occurred in all species, with differences reflecting variation in ecological and social constraints. We also highlight a novel trade-off between size and cooperative effort in pay-to-stay dynamics. Overall, this study enhances our understanding of helping evolution, demonstrating that pay-to-stay can drive helping independently of kin selection.