The evolution of cooperation: Interacting phenotypes among social partners

Abstract

Models of cooperation among non-kin suggest that social assortment is important for the evolution of cooperation. Theory predicts interacting phenotypes, whereby an individual’s behaviour depends on the behaviour of its social partners, can drive such social assortment. We measured repeated indirect genetic effects (IGEs) during cooperative predator inspection in eight populations of Trinidadian guppies (Poecilia reticulata) that vary in their evolutionary history of predation. Four broad patterns emerged that were dependent on river, predation history, and sex: i. current partner behaviour had the largest effect on focal behaviour, with fish from low predation habitats responding more to their social partners than fish from high predation habitats, ii. different focal/partner behaviour combinations can generate cooperation, iii. some high predation fish exhibited carryover effects across social partners, and iv. high predation fish were more risk averse. These results provide the first large scale comparison of interacting phenotypes during cooperation across wild animal populations, highlighting the potential importance of IGEs in maintaining cooperation. Intriguingly whilst focal fish responded strongly to current social partners, carryover effects between social partners suggest generalised reciprocity (help anyone if helped by someone) may contribute to the evolution of cooperation in some, but not all, populations of guppies.