Abstract
Most studies on animal personality evaluate individual mean behaviour to describe individual behavioural strategy, while often neglecting behavioural variability on the within-individual level. However, within-individual behavioural plasticity (variation induced by environment) and within-individual residual variation (regulatory behavioural precision) are recognized as biologically valid components of individual behaviour, but the evolutionary ecology of these components is still less understood. Here, we tested whether behaviour of common pill bugs (Armadillidium vulgare) differs on the among- and within-individual level and whether it is affected by various individual specific state-related traits (sex, size and Wolbachia infection). To this aim, we assayed risk-taking in familiar vs. unfamiliar environments 30 times along 38 days and applied double modelling statistical technique to handle the complex hierarchical structure for both individual-specific trait means and variances. We found that there are significant among-individual differences not only in mean risk-taking behaviour but also in environment- and time-induced behavioural plasticity and residual variation. Wolbachia-infected individuals took less risk than healthy conspecifics; in addition, individuals became more risk-averse with time. Residual variation decreased with time, and individuals expressed higher residual variation in the unfamiliar environment. Further, sensitization was stronger in females and in larger individuals in general. Our results suggest that among-individual variation, behavioural plasticity and residual variation are all (i) biologically relevant components of an individual’s behavioural strategy and (ii) responsive to changes in environment or labile state variables. We propose pill bugs as promising models for personality research due to the relative ease of getting repeated behavioural measurements.
Highlights
Behaviour is one of the most flexible traits of animals (WestEberhard 2003), yet some level of repeatability in behaviour across time and ecological situations exists (Bell et al 2009; Garamszegi et al 2012)
Our models suggest the directional effect of time across the experiment (β2 = 0.165, 95% credible intervals (CrI) = [0.034, 0.297]): individuals became slightly risk-averse as time progresses (Fig. 1)
Pill bugs substantially differed in environmentally induced behavioural plasticity and time-induced habituation
Summary
Behaviour is one of the most flexible traits of animals (WestEberhard 2003), yet some level of repeatability in behaviour across time and ecological situations (i.e. animal personality) exists (Bell et al 2009; Garamszegi et al 2012). Extended author information available on the last page of the article the presence of non-random among-individual behavioural variation should constrain behavioural plasticity (Niemelä et al 2013). This is true to a certain extent, but individuals still preserve the ability to alter their behaviour in response to changing environment, while their behaviour relative to each other remains different (Biro et al 2010; Dingemanse et al 2010; Briffa et al 2013; Mathot and Dingemanse 2014). Biological validity and importance of withinindividual behavioural variation not induced by environmental change, or in other words, the ‘rigidity’ of an individual’s behaviour type in a certain environment (within-individual residual variation), were recognized recently
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