Energetics of stress: linking plasma cortisol levels to metabolic rate in mammals

Abstract

Physiological stress may result in short-term benefits to organismal performance, but also long-term costs to health or longevity. Yet, we lack an understanding of the variation in stress hormone levels (i.e. glucocorticoids) that exist within and across species. Here, we present comparative analyses that link the primary stress hormone in most mammals (i.e. cortisol) to metabolic rate. We show that baseline concentrations of plasma cortisol vary with mass-specific metabolic rate among cortisol-dominant mammals, and both baseline and elevated concentrations scale predictably with body mass. The results quantitatively link a classical measure of physiological stress to whole-organism energetics, providing a point of departure for cross-species comparisons of stress levels among mammals.

Keywords: allometry; metabolism; scaling; stressor.

Figure 1.

Relationships in cortisol-dominant mammals (a) between baseline plasma cortisol concentrations (ng ml⁻¹) and resting mass-specific metabolic rate (mW g⁻¹; N = 49) and (b) between elevated plasma cortisol concentrations and baseline cortisol concentrations (N = 43). Data are natural-log transformed.

Figure 2.

Relationships in cortisol-dominant mammals of (a) baseline (N = 49) and (b) elevated plasma cortisol concentrations (ng ml⁻¹) (N = 78) to body mass (g). Data are natural-log transformed.