Going with the flow: evidence that cooperative individuals adjust their cooperative behaviour in response to the social environment in the Trinidadian guppy (Poecilia reticulata)

Assortative interactions can be key for the evolution and maintenance of cooperation. The propensity for cooperative behaviour to be met with equal cooperativeness can arise from partner conditional responses or fixed cooperative traits, but also a combination of both; something that has yet to be investigated outside of humans. We explored whether individuals differing in trait cooperativeness also differed in plasticity of their conditional response to partner cooperativeness. 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 (Poecilia reticulata) bred to make high cooperative investments in the context of predator inspection exhibit greater conditional response plasticity than guppies bred to make lower 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 - this could have implications for assortment by cooperative behaviour.