Meeting Abstract
Life history trade-offs result from individuals allocating a finite amount of resources to multiple life history stages. As such, energetic acquisition and management plays a fundamental role in regulating life history trade-offs, which can be measured through physiological traits. Baseline levels of glucocorticoids mediate energetics in vertebrate species, have been shown to influence foraging behaviour, and have been linked to fat deposition. Although there is a link between variation in baseline corticosterone (CORT; the primary avian glucocorticoid), foraging and fat stores, these links have not been tested experimentally. Working with a captive colony of white-winged scoters (Melanitta fusca) we aim to understand the mechanistic role that CORT plays in mediating body mass gain by manipulating CORT levels within a baseline range. We tested this by treating individuals in a repeated measures design with three different 21-day release pellets in a randomized order including: 1) control (15 mg placebo), 2) low dose of CORT (15 mg CORT pellet) and 3) moderate dose of CORT (35 mg CORT pellet). We tracked the release of the pellets by sampling for baseline plasma CORT once every 3 days, examined HPA axis feedback via ACTH injections and took the body mass of each individual across each of the three trials. Individuals with experimentally elevated CORT had higher body mass (and hence fat deposition rates) compared to control individuals within a wintering life history stage. These results provide insight into how glucocorticoids influence the ability of individuals to acquire fat stores, which will have downstream consequences for life history trade-offs.
