Corticosterone Concentration Varies With Metabolic Rate in Vertebrates.

Characterizing the adaptive or maladaptive effects of physiological stress based on glucocorticoid hormone levels remains a challenge in vertebrates. It remains unclear to what extent these measures capture the multi-dimensional nature of physiological stress, how to compare measures across species, and how to quantify the cumulative effects of stress on health or longevity. To address these issues, we aim to characterize the relationship of glucocorticoid hormone levels to body mass, metabolic rate, and lifespan across species of vertebrates. Specifically, we focus on investigating these relationships for the glucocorticoid hormone corticosterone using data from 160 species of reptiles, birds, and mammals. Results from each vertebrate class show that plasma corticosterone increases with mass-specific metabolic rate and declines with increasing body mass like mass-specific metabolic rate. Moreover, across classes, a strong, positive relationship was observed between elevated and baseline corticosterone values. However, no relationship was observed between corticosterone levels and lifespan after removing the effects of metabolic rate. These results suggest that measures of corticosterone across species largely reflect differences in rates of species' energy use. Understanding to what extent corticosterone is linked to individual energetics represents a step forward in developing a conceptual and quantitative framework for linking stress, energetics, and life-history traits across species.