Steenweg Rolanda J, Hennin Holly L, Bêty Joël, Gilchrist H Grant, Williams Tony D, Crossin Glenn T, Love Oliver P
Department of Biology, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada; Department of Biological Sciences, University of Windsor, Windsor, Ontario N9B 3P4, Canada.
Department of Biological Sciences, University of Windsor, Windsor, Ontario N9B 3P4, Canada.
Gen Comp Endocrinol. 2015 May 15;216:39-45. doi: 10.1016/j.ygcen.2015.04.012. Epub 2015 Apr 23.
Diel variation in baseline glucocorticoid (GC) secretion influences energetics and foraging behaviors. In temperate breeding, diurnal vertebrates, studies have shown that daily patterns of baseline GC secretion are influenced by environmental photoperiod, with baseline GCs peaking prior to sunrise to stimulate waking and foraging behaviors. Measures of physiological energy acquisition are also expected to peak in response to foraging activity, but their relationship to GC levels have not been well studied. In contrast to temperate breeding species, virtually nothing is known about diel GC and energetic metabolite secretion in Arctic breeding species, which experience almost constant photoperiods in spring and summer. Using a ten-year dataset, we examined the daily, 24-h pattern of baseline corticosterone (CORT) and triglyceride (TRIG) secretion in approximately 800 female pre-breeding Arctic-nesting common eiders (Somateria mollissima). We related these traits to environmental photoperiod and to tidal cycle. In contrast to temperate breeding species, we found that that neither time of day nor tidal trend predicted diel variation in CORT or TRIG secretion in Arctic-breeding eiders. Given the narrow window of opportunity for breeding in polar regions, we suggest that eiders must decouple their daily foraging activity from light and tidal cycles if they are to accrue sufficient energy for successful breeding. As CORT is known to influence foraging behavior, the absence of a distinct diel pattern of CORT secretion may therefore be an adaptation to optimize reproductive investment and likelihood for success in some polar-breeding species.
基础糖皮质激素（GC）分泌的昼夜变化会影响能量代谢和觅食行为。在温带繁殖的昼行性脊椎动物中，研究表明基础GC分泌的每日模式受环境光周期影响，基础GC在日出前达到峰值以刺激觉醒和觅食行为。生理能量获取的指标预计也会随着觅食活动而达到峰值，但其与GC水平的关系尚未得到充分研究。与温带繁殖物种不同，对于北极繁殖物种的昼夜GC和能量代谢物分泌情况几乎一无所知，这些物种在春季和夏季经历几乎恒定的光周期。利用一个十年的数据集，我们研究了大约800只处于繁殖前期、在北极筑巢的普通绒鸭（Somateria mollissima）雌性个体基础皮质酮（CORT）和甘油三酯（TRIG）分泌的每日24小时模式。我们将这些特征与环境光周期和潮汐周期联系起来。与温带繁殖物种不同，我们发现一天中的时间和潮汐趋势都无法预测北极繁殖绒鸭CORT或TRIG分泌的昼夜变化。鉴于极地地区繁殖机会的窗口很窄，我们认为，如果绒鸭要积累足够的能量以成功繁殖，就必须使其日常觅食活动与光照和潮汐周期脱钩。由于已知CORT会影响觅食行为，因此CORT分泌缺乏明显的昼夜模式可能是一种适应性特征，以优化某些极地繁殖物种的生殖投资和成功几率。
