Abstract：
Glucocorticoid (GC) hormones have traditionally been interpreted as indicators of stress, but the extent to which they provide information on physiological state remains debated. GCs are metabolic hormones that amongst other functions ensure increasing fuel (i.e. glucose) supply on the face of fluctuating energetic demands, a role often overlooked by ecological studies investigating the consequences of GC variation. Furthermore, because energy budget is limited, in natural contexts where multiple stimuli coexist, the organismś ability to respond physiologically may be constrained when multiple triggers of metabolic responses overlap in time. Using free-living spotless starling (Sturnus unicolor) chicks, we experimentally tested whether two stimuli of different nature known to trigger a metabolic or GC response respectively cause a comparable increase in plasma GCs and glucose. We further tested whether response patterns differed when both stimuli occurred consecutively. We found that both experimental treatments caused increases in GCs and glucose of similar magnitude, suggesting that both variables fluctuate along with variation in energy expenditure, independently of the trigger. Exposure to the two stimuli occurring subsequently did not cause a difference in GC or glucose responses compared to exposure to a single stimulus, suggesting a limited capacity to respond to an additional stimulus during an ongoing acute response. Lastly, we found a positive and significant correlation between plasma GCs and glucose after the experimental treatments. Our results add-up to the increasing research on the role of energy expenditure on GC variation, by providing experimental evidence on the association between plasma GCs and energy metabolism.
摘要：
糖皮质激素（GC）激素传统上被解释为压力的指标，但是它们提供生理状态信息的程度仍存在争议。GCs是代谢激素，在其他功能中，确保在能量需求波动的情况下增加燃料（即葡萄糖）供应，研究GC变异后果的生态学研究经常忽略的作用。此外，因为能源预算有限，在多种刺激共存的自然环境中，当代谢反应的多个触发因素在时间上重叠时,生物体的生理反应能力可能受到限制.使用自由生活的一尘不染的八哥（Sturnusunicolor）小鸡，我们通过实验测试了已知的两种不同性质的刺激是否会分别触发代谢或GC反应，从而导致血浆GC和葡萄糖的相当增加。我们进一步测试了两种刺激连续发生时反应模式是否不同。我们发现两种实验处理都导致了GCs和葡萄糖的增加，这表明这两个变量都随着能量消耗的变化而波动，独立于触发器。与暴露于单一刺激相比，暴露于随后发生的两种刺激不会导致GC或葡萄糖反应的差异，表明在持续的急性反应期间对额外刺激的反应能力有限。最后,我们发现实验治疗后血浆GCs和葡萄糖之间呈正相关。我们的结果增加了关于能量消耗对GC变化的作用的研究，通过提供血浆GCs与能量代谢之间关联的实验证据。
