Data from: Biomarker of burden: feather corticosterone reflects energetic expenditure and allostatic overload in captive waterfowl

1.Allostatic load describes the interplay between energetic demand and availability and is highly context dependent, varying between seasons and life history stages. When energy demands exceed physiological set points modulated by glucocorticoid hormones, individuals may experience allostatic overload and transition between stages in sub-optimal physiological states. 2.Corticosterone, the major glucocorticoid hormone regulating energy expenditure in birds, is incorporated into growing feathers (CORTf), and it has been suggested that CORTf reflects long-term records of allostatic load during feather growth. However, relationships between allostatic load and CORTf have not been adequately evaluated. If such relationships exist, the use of CORTf to investigate cross-seasonal effects could provide novel insights into impacts of past allostatic load and/or overload events. 3.We tested whether experimental increases in daily workload during two adjacent life history stages would be reflected in CORTf levels, and examined if CORTf levels reflected either current energetic demand or allostatic load prior to feather growth. 4.Daily workloads in female mallard (Anas platyrhynchos) ducklings were increased over a 6-week period using physical obstacles and/or carrying back-mounted weights. We measured daily energy expenditure, growth, body mass, and CORTf in growing ducklings. Then, we induced feather moult and reapplied combinations of workload treatments for an additional 6 weeks to investigate whether effects of past energetic demands would be detected in future CORTf levels. 5.Ducklings confronted with higher workloads during development had reduced body mass, growth rates, and consequently higher daily energy expenditure and CORTf values compared to controls. When ducklings were fully developed, CORTf patterns in birds re-exposed to workload treatments reflected only current, rather than past, energetic demands. However, under allostatic overload conditions, past levels of CORTf were associated with CORTf in the subsequent moult. 6.Our study confirms the previously untested assumption that CORTf reflects energetic demand during the period of feather growth in a precocial bird. We show that allostatic overload conditions early in life, which temporarily supress growth, can be detected using CORTf; an event potentially missed in studies which rely solely on measures of body condition alone. 7.We suggest that CORTf can provide a valuable biomarker of allostatic load and overload conditions during the period of feather growth, but highlight how context should be considered for studies using CORTf to investigate influences of carry-over effects. Our study contributes to building a physiological foundation to inform interpretations of ecological patterns using CORTf.1. 稳态负荷（allostatic load）指能量需求与能量供给之间的动态平衡关系，其高度依赖具体情境，会随季节和生活史阶段的不同而发生变化。当能量需求超出糖皮质激素（glucocorticoid hormones）调控的生理设定阈值时，个体可能出现稳态过载（allostatic overload），并在亚最优生理状态下完成不同生活史阶段的过渡。 2. 皮质酮（corticosterone）是调控鸟类能量消耗的主要糖皮质激素，会掺入正在生长的羽毛中，即羽毛皮质酮水平（CORTf）。已有研究推测，CORTf能够反映羽毛生长期间稳态负荷的长期变化情况。然而，学界尚未对稳态负荷与CORTf之间的关联进行充分评估。若二者确实存在关联，利用CORTf探究跨季节效应，将有助于深入理解过往稳态负荷或稳态过载事件所带来的影响。 3. 本研究旨在验证：两个相邻生活史阶段内实验性提升每日工作量的操作，是否会体现在CORTf水平的变化中；同时检验CORTf水平究竟是反映当前的能量需求，还是羽毛生长前的稳态负荷水平。 4. 研究对象为雌性绿头鸭（Anas platyrhynchos）雏鸭，我们通过设置物理障碍和/或背负负重的方式，在6周的周期内提升其每日工作量。我们测定了生长阶段雏鸭的每日能量消耗、生长速率、体质量以及CORTf水平。随后，我们诱导雏鸭换羽，并再次施加不同的工作量组合处理，持续6周，以探究过往能量需求带来的效应能否在后续的CORTf水平中被检测到。 5. 与对照组相比，发育阶段承受更高工作量的雏鸭体质量更低、生长速率更慢，因此每日能量消耗和CORTf水平也更高。当雏鸭完全发育后，再次接受工作量处理的个体其CORTf模式仅反映当前的能量需求，而非过往的能量需求。但在稳态过载条件下，过往的CORTf水平与后续换羽阶段的CORTf水平存在关联。 6. 本研究验证了一项此前未被检验的假设：在早成鸟中，CORTf能够反映羽毛生长阶段的能量需求。本研究证实，早期生命阶段的稳态过载条件会暂时抑制生长，且能够通过CORTf被检测到——这类事件在仅依赖体况指标的研究中可能会被忽略。 7. 我们认为，CORTf可作为羽毛生长阶段稳态负荷与稳态过载情况的有效生物标志物，但同时强调，在利用CORTf探究遗留效应（carry-over effects）的研究中，应当考虑具体的情境因素。本研究为利用CORTf解读生态模式的相关研究构建了生理学基础。