Meeting Abstract
Glucocorticoids are stress hormones that can strongly influence physiology, behavior and an organism’s ability to cope with environmental change. Despite their importance, and the wealth of studies that have sought to understand how and why glucocorticoid concentrations vary within species, we do not have a clear understanding of how glucocorticoids vary across species and with respect to species traits. New research has proposed that much interspecific variation in glucocorticoid concentrations can be explained by variation in metabolism and body mass. Specifically, glucocorticoid concentrations should vary proportionally with mass-specific metabolic rates and, given known scaling relationships between body mass and metabolic rate, should scale to the -0.25 power of body mass. Here, we use HormoneBase, the newly compiled database that includes body mass data and plasma glucocorticoid measures from wild and un-manipulated vertebrate animals, to evaluate this hypothesis. Specifically, we explore the relationship between body mass and baseline cortisol or corticosterone in mammals and body mass and baseline corticosterone in birds. Our phylogenetically-informed models suggest that, while glucocorticoid concentrations do decrease with mass, the scaling exponents were significantly different from the -0.25 power proposed in recent research. Presently, we are exploring whether and how life history stage, sex and sampling method influence the mass-glucocorticoid relationship. Whether inclusion of these covariates reveals a universal-scaling exponent between glucocorticoids and mass or not, our study demonstrates how large-scale comparative methods can be a powerful approach to testing both long-standing and new questions in biology.
