Abstract
Potential mechanistic mediators of Darwinian fitness, such as stress hormones or sex hormones, have been the focus of many studies. An inverse relationship between fitness and stress or sex hormone concentrations has been widely assumed, although empirical evidence is scarce. Feathers gradually accumulate hormones during their growth and provide a novel way to measure hormone concentrations integrated over time. Using liquid chromatography-tandem mass spectrometry, we measured testosterone, corticosterone and cortisol in the feathers of house sparrows (Passer domesticus) in a wild population which is the subject of a long-term study. Although corticosterone is considered the dominant avian glucocorticoid, we unambiguously identified cortisol in feathers. In addition, we found that feathers grown during the post-nuptial moult in autumn contained testosterone, corticosterone and cortisol levels that were significantly higher in birds that subsequently died over the following winter than in birds that survived. Thus, feather steroids are candidate prospective biomarkers to predict the future survival of individuals in the wild.
Highlights
Steroid hormones function as mediators of essential metabolic and energy-allocation processes
Stress-induced corticosterone levels are associated with survival, either positively [6] or, more often, negatively [7,8,9]
We measured steroids using state-of-the-art LC-MS/MS, which permits the measurement of multiple steroids at one time and offers unmatched specificity
Summary
Steroid hormones function as mediators of essential metabolic and energy-allocation processes. (c) Statistical analysis Because many of the feather samples had non-detectable levels of GCs (i.e. below the limit of detection and a zero value in our dataset), we used correlation by randomization to test for associations between steroids. Within the 13 samples with both GCs above the LOQ, cortisol and corticosterone concentrations did not differ (t-test by randomizations: t24 1⁄4 1.8, p 1⁄4 0.11), but the association was not significant (correlation by randomizations: r 1⁄4 0.51, p 1⁄4 0.07), probably owing to the limited power. Non-breeding feather corticosterone levels were significantly lower in birds that survived, relative to those that subsequently died, but only when a year term was included in the model (model 2 in table 1; figure 2). Individuals that survived had significantly lower feather cortisol concentrations in all models tested, regardless of year, sex or. Birds that subsequently died had higher T concentrations that were positively associated with their body size, whereas in the birds that survived T concentrations were lower regardless of their body size
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