Groningen Institute for Evolutionary Life Sciences, University of Groningen, 9747 AG Groningen, The Netherlands
Max Planck Institute for Ornithology, D-82319 Seewiesen, Germany.
J Exp Biol. 2018 Nov 27;221(Pt 23):jeb187880. doi: 10.1242/jeb.187880.
Glucocorticoid (GC) levels vary with environmental conditions, but the functional interpretation of GC variation remains contentious. A primary function is thought to be metabolic, mobilizing body reserves to match energetic demands. This view is supported by temperature-dependent GC levels, although reports of this effect show unexplained heterogeneity. We hypothesized that the temperature effect on GC concentrations will depend on food availability through its effect on the energy spent to gather the food needed for thermoregulation. We tested this hypothesis in zebra finches living in outdoor aviaries with manipulated foraging conditions (i.e. easy versus hard), by relating within-individual differences in baseline GCs between consecutive years to differences in ambient temperature. In agreement with our hypothesis, we found the GC-temperature association to be significantly steeper in the hard foraging environment. This supports the metabolic explanation of GC variation, underlining the importance of accounting for variation in energy expenditure when interpreting GC variation.
糖皮质激素（GC）水平随环境条件而变化，但 GC 变化的功能解释仍存在争议。一种主要功能被认为是代谢功能，即动员身体储备以匹配能量需求。这一观点得到了温度依赖性 GC 水平的支持，尽管关于这种效应的报告显示存在无法解释的异质性。我们假设，GC 浓度对温度的影响将取决于食物的可获得性，因为食物的可获得性会通过影响为体温调节而获取食物所需的能量消耗来起作用。我们通过在户外鸟舍中饲养具有不同觅食条件（即容易觅食与困难觅食）的斑马雀，来检验这一假设，即通过将连续几年个体间的基础 GC 差异与环境温度差异相关联。与我们的假设一致，我们发现困难觅食环境中的 GC-温度相关性明显更陡峭。这支持了 GC 变化的代谢解释，强调了在解释 GC 变化时，需要考虑能量消耗的变化。
