Modeling changes in energy substrate usage in response to acute stress in birds.

Abstract

Physiological responses to stress, imposed by intrinsic or environmental challenges, result in a rapid mobilization of energy. However, how an organism's current energetic state affects the stress response and the energy substrates used is poorly understood. We measured plasma metabolites (glucose, free glycerol, triglycerides, and the ketone β‐OH‐butyrate) associated with energy storage and mobilization in response to a 30 min long mild stress in five species of free‐ranging birds. We predicted that individuals with greater lipid stores rely more on intrinsic energy stores during stress than individuals with low lipid stores and this difference would be reflected in differential energy substrate utilization. In all species, acute stress was associated with increased total plasma corticosterone and decreased plasma triglycerides. Changes in plasma concentrations of the other metabolites in response to stress reflected differences in phylogeny and/or diet type. Granivorous species (House Sparrows, Abert's and Canyon Towhees) showed a decrease in free glycerol and no change in glucose. By contrast, primarily insectivorous species (Curve‐billed Thrashers and Northern Mockingbirds) showed increased glucose and β‐OH‐butyrate. Metabolic pathways for energy mobilization and usage during stress may, therefore, be related to specific life‐history traits.