Ontogeny of unpredictability in escape behaviour of a grasshopper species

Abstract

Animal behaviour changes as individuals mature and these changes may affect not only average behaviour, but also behavioural variability within and between individuals. This could apply to escape behaviour, as behavioural variability might be particularly advantageous in predator-prey interactions, and prey individuals can adhere to different escape strategies. It is not yet known, however, if behavioural variability (unpredictability) is marked early in life, if it arises with time and how stable it is throughout ontogeny. We analysed the escape behaviour of the steppe grasshopper, Chorthippus dorsatus, using burst experiments repeated multiple times across four life stages. We quantified three aspects of escape behaviour and analysed the data using a multivariate double-hierarchical generalized linear model. Interindividual differences in average behaviour increased across life stages, resulting in an increase in population level variability. Unpredictability, however, remained relatively stable both within and across individuals. About 1.7–4.6% of the total phenotypic variance was explained by individual differences in unpredictability. Further, 2–6.5% was explained by differences between bursts of observations, such that interindividual differences in unpredictability explained a maximum of 11% of the total variance in escape behaviour at a given time. Our results indicate a stability of the unpredictability level in grasshopper escape behaviour, and that intraindividual variance in unpredictability is low, but that the overall magnitude of individual differences in escape behaviour increases with age.