Towards powerful experimental and statistical approaches to study intraindividual variability in labile traits

Abstract

There is a long-standing interest in behavioural ecology, exploring the causes and correlates of consistent individual differences in mean behavioural traits (‘personality’) and the response to the environment (‘plasticity’). Recently, it has been observed that individuals also consistently differ in their residual intraindividual variability (rIIV). This variation will probably have broad biological and methodological implications to the study of trait variation in labile traits, such as behaviour and physiology, though we currently need studies to quantify variation in rIIV, using more standardized and powerful methodology. Focusing on activity rates in guppies (Poecilia reticulata), we provide a model example, from sampling design to data analysis, in how to quantify rIIV in labile traits. Building on the doubly hierarchical generalized linear model recently used to quantify individual differences in rIIV, we extend the model to evaluate the covariance between individual mean values and their rIIV. After accounting for time-related change in behaviour, our guppies substantially differed in rIIV, and it was the active individuals that tended to be more consistent (lower rIIV). We provide annotated data analysis code to implement these complex models, and discuss how to further generalize the model to evaluate covariances with other aspects of phenotypic variation.

Metabolic Scope as a Proximate Constraint on Individual Behavioral Variation: Effects on Personality, Plasticity, and Predictability

“…Estimating scope with a single estimate of RMR and MMR per individual, as is often done, will likely lead to highly imprecise estimates of individual scope, given that both are labile traits (Wolak et al 2012). Several recent articles offer a discussion of the nuances and data requirements for estimating trait repeatability and individual means of labile traits with precision (van de Pol 2012; Wolak et al 2012;Biro and Stamps 2015;Cleasby et al 2015;Mitchell et al 2016). With modern multiarena tracking software and multichannel respirometry equipment, it is now feasible to get many repeated measures of individuals for behavior and metabolism over reasonable time intervals to address these sampling considerations head-on.…”

“…Individual variation in plasticity and predictability is an important aspect of behavioral variation and represents what is often assumed to be adaptive behavioral flexibility (Briffa 2013;Westneat et al 2015). The key distinction between plasticity and predictability is that the former is explainable and attributed to some temporal or contextual gradient, whereas the latter is not (Stamps et al 2012;Biro and Adriaenssens 2013;Mitchell et al 2016). Note that these generally accepted terms in the behavioral literature differ from those referred to elsewhere as flexibility and stereotypy, respectively (Wainwright et al 2008).…”

Is behavioural plasticity consistent across different environmental gradients and through time?

“…The model was run in the Bayesian software STAN [38], through the RStan interface [39]. All parameters were given uninformative priors (electronic supplementary material), and followed the methods described in [37] and details specific to this analysis and model code is given in the electronic supplementary material. Normality of random effects and the residual variation were checked visually in plots of predicted random effect values and fitted versus residual values.…”

Roll with the fear: environment and state dependence of pill bug (Armadillidium vulgare) personalities

“…Finally, 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 (Stamps et al 2012;Biro and Adriaenssens 2013;Briffa 2013;Briffa et al 2013). Hence, within-individual behavioural plasticity (hereafter: behavioural plasticity) and within-individual residual variation (hereafter: residual variation) should be considered as potentially independent components of individual behavioural strategy (Dingemanse et al 2010;Kralj-Fišer and Schneider 2012;Briffa 2013;Dingemanse and Wolf 2013;Westneat et al 2013Westneat et al , 2015Mitchell et al 2016). However, background mechanisms affecting emergence of individual variation in behavioural plasticity and residual variation are less understood.…”