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

David J Mitchell,Peter A Biro,Benjamin G Fanson,Christa Beckmann

doi:10.1098/rsos.160352

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.

Highlights

Ecologists and evolutionary biologists are often interested in studying the variation among individuals within a population and the consistency of these differences, in the study2016 The Authors
To do so requires resampling individuals and assessing the relative proportion of overall 2 variance that can be attributed to individual differences, most often quantified using ‘repeatability’ to estimate the consistency of scores through time [1–4]
Even after accounting for both these hierarchical levels of systematic variation, considerable residual variation remains in labile traits (hereafter termed ‘residual intraindividual variability’; [8]), which can conceal important biological processes [9]

Summary

Introduction

Ecologists and evolutionary biologists are often interested in studying the variation among individuals within a population and the consistency of these differences, in the study. To do so requires resampling individuals and assessing the relative proportion of overall 2 variance that can be attributed to individual differences, most often quantified using ‘repeatability’ to estimate the consistency of scores through time [1–4]. Even after accounting for both these hierarchical levels of systematic variation, considerable residual variation remains in labile traits (hereafter termed ‘residual intraindividual variability (rIIV)’; [8]), which can conceal important biological processes [9]

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Results