Behavioural phenotype modulates group size effects in a lizard

Abstract

Behaviour is a highly labile trait that can be rapidly modified to mitigate the effects of changing environmental conditions. Among the biotic and abiotic factors acting to prompt plastic responses, the social environment has been proposed as being one of the primary modulating forces on behaviour. Being part of a group has particular influence on the expression of risky behaviour in that added eyes and ears serve to decrease a group member's vulnerability to predation resulting in the mean behavioural expression of behaviours such as activity and/or exploration increasing with group size. A large body of work has documented such group size effects. However, as this process may operate at the individual level it is unclear how the social environment affects the consistent expression of personality. Thus, we examined the interactive effects of behavioural phenotype and social context on the stability of individual behaviour in the delicate skink, Lampropholis delicata . Lizards were exposed to a series of assays measuring activity, exploration and boldness in groups of one, two, four and eight. Repeatability was determined across group size treatments and the combined effects of social context and behavioural type on behavioural plasticity were assessed. We found that the predicted patterns of group size effects were only observed when each lizard's behavioural phenotype was considered. Inactive and shy lizards increased their behaviour with increasing group size whereas active and bold lizards exhibited the opposite pattern. Additionally, the degree to which an individual adjusted its behavioural response was contingent upon its behavioural phenotype, with slow lizards showing higher levels of responsiveness than fast lizards. Despite this plasticity, between-individual differences in the expression of activity, exploration and boldness persisted. Thus, our study provides strong evidence that the effects of an individual's personality are stronger than those of group size. • Predicted group size effects are evident only when behavioural type is considered. • Social context influences the expression of consistent individual behaviour. • Personality dictates degree and direction of responses towards the social context.