Consequences of personalities in interacting phenotypes: behavioural variation in the social environment affects aggression in the Field cricket Gryllus campestris (#262)
Aggressiveness is one of the key behaviours addressed in the field of animal personality. However, despite this trait being a product of an interaction between two or more individuals, the effect of social partners on the focal individual’s phenotype has been neglected. In contests, the opponent is a key determinant an individual’s behavioural decisions, because individuals adjust their plastic response to the different phenotypes they confront. The presence of between individual variation (‘personalities’) in the social environment therefore holds important evolutionary consequences because phenotypes of social partners are expression of their genotypes, and thus can evolve.
Here we investigated how within individual variation (plasticity) in aggression is affected by the personalities in the social environment with novel variance partitioning tools available from the field of quantitative genetics. We repeatedly assayed aggressiveness of wild-caught adult male Field crickets gryllus campestris in staged fights, measuring aggressive phenotypes on both partners. Furthermore, by repeatedly measuring other personality traits in non-social contexts such as activity and exploration, we explicitly investigated which repeatable phenotypes of the social partners affect aggression.
We found that individuals were repeatable in their social and non-social behaviours (repeatabilities range from 0.09 to 0.40), and behavioural traits were also correlated across social and non-social contexts in a behavioural syndrome (between-individual correlations range from 0.39 to 0.81). Interestingly, more explorative individuals elicited consistently higher aggression in their social partners (r = 0.45), suggesting that the plastic response in aggression of the social partners depends in part on the exploratory behavioural type of the other interacting individual.
By applying quantitative genetics models to predictions generated in the field of behavioural ecology, we show that individuals respond plastically to the personality traits of their social partners. Our findings highlight that personality differences in the social environment can have consequences for the accurate prediction of the evolution of behavioural phenotypes.