Personality drives physiological adjustments and is not related to survival

Allert I Bijleveld,Anne Dekinga,Bernard Spaans,Georgina Massourakis,Jan A Van Gils,Theunis Piersma,Annemarie Van Der Marel

doi:10.1098/rspb.2013.3135

Abstract

The evolutionary function and maintenance of variation in animal personality is still under debate. Variation in the size of metabolic organs has recently been suggested to cause and maintain variation in personality. Here, we examine two main underlying notions: (i) that organ sizes vary consistently between individuals and cause consistent behavioural patterns, and (ii) that a more exploratory personality is associated with reduced survival. Exploratory behaviour of captive red knots (Calidris canutus, a migrant shorebird) was negatively rather than positively correlated with digestive organ (gizzard) mass, as well as with body mass. In an experiment, we reciprocally reduced and increased individual gizzard masses and found that exploration scores were unaffected. Whether or not these birds were resighted locally over the 19 months after release was negatively correlated with their exploration scores. Moreover, a long-term mark–recapture effort on free-living red knots with known gizzard masses at capture confirmed that local resighting probability (an inverse measure of exploratory behaviour) was correlated with gizzard mass without detrimental effects on survival. We conclude that personality drives physiological adjustments, rather than the other way around, and suggest that physiological adjustments mitigate the survival costs of exploratory behaviour. Our results show that we need to reconsider hypotheses explaining personality variation based on organ sizes and differential survival.

Highlights

Animals modify aspects of their phenotype in response to changes in their environment
We examined two critical notions underlying the hypothesis of organ-size-driven personality variation: (i) that variation in digestive organ sizes cause consistent variation in behaviour; and (ii) that large digestive organs and exploratory behaviour are associated with reduced survival
Our first set of experiments revealed that exploratory behaviour was repeatable (R 1⁄4 0.67, 95% CI (0.38; 0.85), p, 0.01; figure 1a), and that it was negatively correlated with gizzard mass at capture (intercept 1⁄4 5.3, 95% CI (3.0; 7.6), slope 1⁄4 20.72, 95% CI (21.06; 20.50), r 1⁄4 20.52, p 1⁄4 0.01; figure 1b)

Summary

Introduction

Animals modify aspects of their phenotype in response to changes in their environment ( phenotypic plasticity [1]). In order to investigate correlations between exploratory behaviour and body mass, we analysed these variables in a bivariate mixed-effects model with individual identity as random factor (equations 7a and 7b in [40]). In order to account for variation in magnitude of gizzard mass change, as well as to decompose the (co)variance into the between- and within-individual components, we analysed exploratory behaviour and gizzard mass in a bivariate mixedeffects model with individual identity as a random effect [40]. Between 1998 and 2003, 402 islandica knots were captured and promptly released in the Dutch Wadden Sea after their gizzard mass had been measured, and they had been tagged with unique colour-coded combinations of rings Resightings of these birds in the Dutch Wadden Sea (n 1⁄4 1068) were analysed over the period from capture up to March 2013 to estimate ‘apparent survival’ and resighting probability. Data analyses were carried out in R v. 2.15.1 [46] with the packages ‘RMark’ for mark–recapture [47], ‘rptR’ for univariate mixed-effects repeatability [41], ‘smatr’ for standardized major axis [48] and ‘MCMCglmm’ for bivariate mixed-effects analyses [49]

Results

Findings

Discussion