Data from: Baseline glucocorticoids are drivers of body mass gain in a diving seabird

Life-history trade-offs are influenced by variation in individual state, with individuals in better condition often completing life-history stages with greater success. Although resource accrual significantly impacts key life-history decisions such as the timing of reproduction, little is known about the underlying mechanisms driving resource accumulation. Baseline corticosterone (CORT, the primary avian glucocorticoid) mediates daily and seasonal energetics, responds to changes in food availability, and has been linked to foraging behavior, making it a strong potential driver of individual variation in resource accrual and deposition. Working with a captive colony of white-winged scoters (Melanitta fusca deglandi), we aimed to causally determine whether variation in baseline CORT drives individual body mass gains mediated through fattening rate (plasma triglycerides corrected for body mass). We implanted individuals with each of three treatment pellets to elevate CORT within a baseline range in a randomized order: control, low dose of CORT, high dose of CORT, then blood sampled and recorded body mass over a two-week period to track changes in baseline CORT, body mass, and fattening rates. The high CORT treatment significantly elevated levels of plasma hormone for a short period of time within the biologically relevant, baseline range for this species, but importantly did not inhibit the function of the HPA (hypothalamic–pituitary–adrenal) axis. Furthermore, an elevation in baseline CORT resulted in a consistent increase in body mass throughout the trial period compared to controls. This is some of the first empirical evidence demonstrating that elevations of baseline CORT within a biologically relevant range have a causal, direct, and positive influence on changes in body mass.生活史权衡（life-history trade-offs）受个体状态变异的影响，身体状况更优的个体通常能以更高的成功率完成各生活史阶段。尽管资源积累显著影响诸如繁殖时机等关键生活史决策，但目前对驱动资源积累的内在机制仍知之甚少。基础皮质酮（corticosterone, CORT）作为鸟类主要的糖皮质激素，可介导日常与季节性的能量代谢，响应食物可获得性的变化，并与觅食行为存在关联，因此极有可能是驱动个体资源积累与沉积变异的关键因子。本研究以圈养的白翅海番鸭（Melanitta fusca deglandi）种群为研究对象，旨在通过因果实验明确基础皮质酮的变异是否通过增重速率（经体重校正的血浆甘油三酯）介导个体体重的增加。我们以随机顺序为个体植入三种处理颗粒，使皮质酮水平维持在该物种的生理相关基线范围内：对照组、低剂量皮质酮组、高剂量皮质酮组；随后在为期两周的试验周期内采集血液并记录体重，以追踪基础皮质酮、体重及增重速率的动态变化。高剂量皮质酮处理可在该物种生理相关的基线范围内短期内显著提升血浆激素水平，且关键的是并未抑制下丘脑-垂体-肾上腺轴（hypothalamic–pituitary–adrenal, HPA轴）的功能。此外，与对照组相比，基础皮质酮水平的升高可使试验全程的体重持续增加。本研究为首批实证证据之一，表明在生理相关范围内提升基础皮质酮水平，可对体重变化产生因果性、直接且正向的影响。