Going with the flow: evidence for phenotypic variation in cooperative plasticity during predator inspection in Trinidadian guppies (Poecilia reticulata)

Abstract

Assortative interactions can be key for the evolution and maintenance of cooperation. Assortment by cooperative phenotype arises from behavioural plasticity, genetic polymorphism, or a combination of both. For example, individuals can cooperate conditional on social partner behaviour, and tolerance of unfavourable behaviour may correlate with an individual’s cooperative phenotype, but this has yet to be investigated outside of humans. Here, we used the Trinidadian guppy (Poecilia reticulata) to explore whether individuals that differed in their cooperativeness also differed in the plasticity of their response to changing cooperativeness in a simulated social partner. To identify when selection may favour high or low plasticity as a function of cooperativeness, we also developed an evolutionary simulation model, where individuals’ probability of cooperating was modelled alongside their plasticity. Our empirical results suggest that guppies that have been bred to make high cooperative investments in the context of predator inspection exhibit higher plasticity when partners switch from defection to cooperation, compared to guppies bred to make lower cooperative investments. Our agent-based model found that more cooperative individuals will show greater plasticity in their propensity to cooperate, compared to less cooperative individuals, except when there are no consequences of nobody cooperating. Combined, our findings show that more cooperative individuals might benefit from a greater capacity to adjust behaviour than less cooperative individuals do. We suggest that this could facilitate assortment by cooperative phenotype, contributing to the evolution of this risky cooperative behaviour.