Andrés E. Quiñones, G. Sander van Doorn, Ido Pen, Franz J. Weissing, Michael Taborsky

Cooperation in social groups is easily undermined by selfish behaviour, unless mechanisms are in place to mitigate conflicts of interest between group members. One such mechanism is to preferentially cooperate with relatives, who have aligned fitness interests by virtue of their shared genes. Alternatively, conflicts can be resolved by means of conditional strategies that enforce the reciprocal trading of services or commodities, enabling (unrelated) partners to negotiate a mutually beneficial outcome. How these two processes – kin selection and negotiation – interact in the evolution of cooperation and sociality remains unclear. Here we study this interplay, both with a concrete model for cooperative breeding in fish and by a general theoretical analysis. We show that negotiation and kin selection do not necessarily act synergistically, and that kin structure can hamper rather than facilitate the evolution of effective cooperation. When the interacting individuals are unrelated, the joint evolution of negotiation strategies leads to an equilibrium where subordinates appease dominants by conditional cooperation, resulting in high levels of help and low levels of aggression. In a kin-structured population, evolution often results in an alternative equilibrium where subordinates help their kin unconditionally. The level of help at this kin-selected equilibrium is considerably lower than helping that is achieved by the interplay of aggression and appeasement strategies. We show that, quite generally, the alignment of payoffs due to relatedness hampers the attainment of negotiation-based cooperation. This explains the puzzling finding that in social animals the level of cooperation is often higher between unrelated individuals than among kin.

Quiñones, A. E., Pen, I., G.S. van Doorn, Weissing, F.J., and Taborsky, M. in
prep. Negotiation and appeasement are more effective drivers of sociality than
kin selection