Metabolic rates, and not hormone levels, are a likely mediator of between‐individual differences in behaviour: a meta‐analysis

Abstract

Summary Consistent individual differences in hormone levels and metabolic rates have been proposed to be potential state variables underlying consistent individual differences in behaviour (i.e. animal personality). However, it remains unclear whether either one alone or both of these potential state variables could be an underlying driver of animal personality. We address this question using meta‐analyses of published data from bird species. We hypothesized that state variables that mediate individual differences in behaviour would display similar or higher repeatability estimates than behavioural traits. To test this hypothesis, we quantified repeatability estimates of hormone levels, metabolic rates and behavioural traits. We found moderate to high mean repeatability estimates for both metabolic rates and behavioural traits, but low repeatability estimates for hormone levels. These findings indicate that metabolic rates likely represent an important mechanism for generating adaptive personality differences in behaviour. We also show that: (i) for hormones and behaviour, repeatability decreased with increasing interval time between two measurements; (ii) males and females differed in repeatability for behavioural traits; (iii) stress‐induced hormone levels were more repeatable than baseline levels. Future studies are now required to determine the direction of the association between metabolic rates and behavioural traits. At the same time, these studies should try to investigate which of the proposed mechanisms is responsible for the relationship between state variable and state‐dependent behaviour. In addition, we encourage researchers to report the coefficient of variation for between‐individual variance (CVB) along with repeatability estimates because these two indices carry different information. We discuss how CVB may better facilitate future comparative studies, including meta‐analyses. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.12779/suppinfo is available for this article.

Reduction in baseline corticosterone secretion correlates with climate warming and drying across wild lizard populations

“…We cannot exclude that individuals with higher corticosterone levels at the beginning of the summer were selected against through lower survival rate during the heatwave period, which could have been determined with a repeating sampling all over the exposure to the heatwaves. However, this hypothesis would involve a strong selection and a high repeatability of corticosterone levels over time, which is very unlikely according to current estimates of interindividual repeatability of GC levels (Holtmann, Lagisz, & Nakagawa, ). Our results thus alternatively suggest that individual downregulated corticosterone secretion and decreased their resting metabolism and behavioural activity to limit the costs associated with warm and dry environments (see above).…”

Individual variation in age‐dependent reproduction: Fast explorers live fast but senesce young?

“…The hypothesized integration of risky behaviour and age‐dependent reproduction posits that within‐individual age‐related plasticity varies among behavioural types, requiring approaches that disentangle within‐ from among‐individual age effects (van de Pol & Verhulst, ). Similarly, risky behaviours differ among individuals (Bell, Hankison, & Laskowski, ; Holtmann, Lagisz, & Nakagawa, ) but simultaneously exhibit within‐individual age‐dependent plasticity (Araya‐Ajoy & Dingemanse, ; Brommer & Class, ; Class & Brommer, ; Fisher, David, Tregenza, & Rodriguez‐Munoz, ; Patrick, Charmantier, & Weimerskirch, ). Repeated measures are thus required to estimate relationships between individual‐level behaviour and reproductive senescence while avoiding bias due to within‐individual plasticity (Niemelä & Dingemanse, , ).…”

TheEGA+GNMframework: An integrative approach to modelling behavioural syndromes

“…Research in a variety of taxa has shown that behavioural traits exhibiting personality often correlate across contexts, forming larger clusters termed behavioural syndromes (Sih, Bell, Johnson, & Ziemba, ). Understanding the structure of behavioural syndromes is crucial for quantifying their influence on evolutionary and ecological processes (Dochtermann & Dingemanse, ; Wolf & Weissing, ) and establishing the proximate mechanisms of personality upon which natural selection acts (Araya‐Ajoy & Dingemanse, ; Holtmann, Lagisz, & Nakagawa, ; Van Oers & Mueller, ).…”