The effect of heterospecific and conspecific competition on inter-individual differences in tungara frog tadpole (Engystomops pustulosus) behaviour

Repeated social interactions with conspecifics and/or heterospecifics during early development may drive the differentiation of behaviour among individuals. This behavioural differentiation may occur through individuals behaving more different from each other on average and/or individuals behaving more consistently. Competition is a major form of social interaction and its impacts can depend on whether interactions occur between conspecifics or heterospecifics and the directionality of a response could be specific to different behavioural traits. To test this, we reared tungara frog tadpoles (Engystomops pustulosus) either in isolation, with a conspecific tadpole or with an aggressive heterospecific tadpole, the whistling frog tadpole, Leptodactylus fuscus. In each treatment, we measured the body size, activity, exploration and risk taking in the presence of a predator in focal E. pustulosus tadpoles six times during development. We used univariate and multivariate hierarchical mixed effect models to investigate the effect of treatment on mean behaviour and on among individual variance between and within individuals across behavioural traits. There was a strong effect of competition on behaviour, with different population and individual level responses across social treatments. Within their home tank, individuals were more consistent in their movements under conspecific competition but heterospecific competition caused more variance in the average movement among individuals. Behavioural responses were also trait specific as conspecific competition caused greater variability in movements among individuals in a novel environment. The results highlight that the impact of competition on inter-individual differences in behaviour is dependent on competitor species identity and is trait specific.