“Metabolic scope as a proximate constraint on individual behavioral variation: effects on ‘personality’, plasticity, and predictability”
Peter A. Biro, Theodore Garland Jr., Christa Beckmann, Beata Ujvari, Frederic Thomas, and John R. Post (Aug 2018)
Aerobic metabolic scope can constrain expression of animal personality and behavior plasticity
Why do some individuals of a given species show consistent levels of average behavior over time and across contexts, while others vary in their behavior? And why do some show highly predictable behavior in a given context, while others vary widely about their average behavioral tendency? Peter Biro and his collaborators here present a novel energetic hypothesis for how minimum and maximum metabolic rates can together constrain the expression of behavioral variation at these different levels, limiting what animals can do in terms of finding food and mates, competing, and avoiding predators.
At its core, their hypothesis predicts that individuals with greater aerobic metabolic scope (= maximum − minimum metabolism) have the latitude to express greater variation and plasticity in behavior. The researchers test their hypothesis and show that replicate ‘high-scope’ genotypes of mice are more active on average, more plastic in their behavior, and less predictable than mice with low aerobic scope.
This is the first energetic hypothesis to predict and explain individual behavioral variation at all its hierarchical levels: mean (= personality), plasticity, and predictability, and is also supported by preliminary data on mice.
Behavioral ecologists have hypothesized that among-individual differences in resting metabolic rate (RMR) may predict consistent individual differences in mean values for costly behaviors, or for behaviors that affect energy intake rate. This hypothesis has empirical support and presently attracts considerable attention, but notably it does not provide predictions for individual differences in (a) behavioral plasticity or (b) unexplained variation (residual variation from mean individual behavior, here termed predictability). We outline how consideration of aerobic maximum metabolic rate (MMR) and particularly aerobic scope (= MMR − RMR) can be used to simultaneously make predictions about mean, among- and within-individual variation in behavior. We predict that while RMR should be proportional to an individuals’ mean level of sustained behavioral activity (one aspect of its personality), individuals with greater aerobic scope will also have greater scope to express behavioral plasticity and/or greater unpredictability in behavior (= greater residual variation). As a first step towards testing these predictions, we analyze existing activity data from selectively bred lines of mice that differ in both daily activity and aerobic scope. We find that replicate high-scope mice are more active on average, show greater among-individual variation in activity, greater among-individual variation in plasticity, and greater unpredictability. These data provide some tentative first support for our hypothesis, suggesting that further research on this topic would be valuable.