Metabolic Rates Predict Baseline Corticosterone and Reproductive Output in a Free-Living Passerine

• Type of Material: Article
• Authors: Blanca Jimeno, University of Montana; Mackenzie R Prichard, Emory University; Devin Landry, MPG Ranch, Florence; Cole Wolf, University of Montana; Beau Larkin, MPG Ranch, Florence; Zachary Cheviron, University of Montana; Creagh Breuner, University of Montana
• Language: English
• Date: 2020-10-14
• Publisher: Oxford University Press
• Publication Version: Final Published Version
• Copyright Statement: © The Author(s) 2020. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology.
• License: Creative Commons Attribution 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1093/iob/obaa030
• Title of Journal or Parent Work: Integrative Organismal Biology
• Volume: 2
• Issue: 1
• Grant/Funding Information: This work was supported by MPG Ranch and the University of Montana VPRCS.
• Keywords: Metabolic Rates; Reproductive Output
• Research Categories: Psychology, General; Biology, General

Abstract

Organisms continuously face environmental fluctuations, and allocation of metabolic investment to meet changing energetic demands is fundamental to survival and reproductive success. Glucocorticoid (GC) hormones (e.g., corticosterone [CORT]) play an important role in energy acquisition and allocation in the face of environmental challenges, partly through mediation of energy metabolism. Although GCs and metabolic rate are expected to covary, surprisingly few empirical studies have demonstrated such relationships, especially in wild animals. Moreover, studies testing for associations between GCs and fitness generally do not account for among-individual differences in energy expenditure or energy allocation. We measured CORT (baseline and stress-induced) and metabolic traits (resting metabolic rate [RMR], cold-induced VO2max [Msum], and aerobic scope [the difference between Msum and RMR]) in female tree swallows (Tachycineta bicolor) during chick-rearing, and tested for their associations with several variables of reproductive performance. We found a positive relationship between RMR and baseline CORT, but no consistent associations between stress-induced CORT (SI-CORT) and Msum. This suggests that while baseline CORT may be a good indicator of an individual’s baseline metabolic investment, SI-CORT responses are not associated with aerobic scope or the upper limits of aerobic performance. Furthermore, we found that metabolic traits were associated with reproductive performance: females with higher reproductive output showed higher Msum, and also tended to show higher RMR. Overall, these results suggest that metabolic traits are better predictors of reproductive output in tree swallows than CORT concentrations. They further point to the maximal aerobic capacity being higher in females investing more heavily in a current reproductive event, but whether this association reflects trade-offs between current and future reproductive efforts remains to be tested.