Data from: Individual variation in energy-saving heterothermy affects survival and reproductive success

1.Given fundamental energetic trade-offs among growth, maintenance, and reproduction, individual differences in energy-saving should have consequences for survival and reproductive success. Many endotherms use periodic heterothermy to reduce energy and water requirements and individual variation in heterothermy should have fitness consequences. However, attempts to disentangle individual- and population-level variation in heterothermy are scarce.

2.Here, we quantified patterns of heterothermy of 55 free-ranging eastern chipmunks (Tamias striatus), food-hoarding hibernators. Over five hibernation periods, we obtained a total of 7108 daily individual heterothermy indices (median: 118 per individual).

3.Based on an individual reaction norm approach, we found that the use of heterothermy was repeatable and varied among individuals of the same population under similar environmental conditions. This among-individual variation had consequences for winter survival and reproductive success. Individuals using less heterothermy at the beginning of the winter had decreased survival in resource-rich but not in resource-poor years and higher reproductive success in the subsequent breeding season.

4.These results support the hypothesis that fluctuating selection maintains heterothermic diversity and suggest that individualized eco-physiology can contribute to a more thorough understanding of the evolution of energy-saving strategies in endotherms.

1. 鉴于生长、机体维持与繁殖之间存在基础的能量权衡（energetic trade-offs），个体间的节能差异理应会对生存与繁殖成功率产生影响。许多内温动物（endotherms）会借助周期性异温性（periodic heterothermy）降低能量与水分需求，而异温性的个体差异也理应会对适合度（fitness）产生影响。然而，目前鲜有研究能够厘清异温性的个体水平与种群水平变异间的差异。
2. 本研究对55只自由活动的东部花栗鼠（*Tamias striatus*，贮食冬眠类动物）的异温性模式进行了量化分析。在5个冬眠季中，我们共获得7108条每日个体异温性指数数据，单只个体的有效数据中位数为118条。
3. 基于个体反应规范（individual reaction norm）分析方法，我们发现：在相似环境条件下，同一种群内不同个体的异温性使用模式具有可重复性，且个体间存在显著差异。这种个体间变异会对冬季生存与繁殖成功率产生影响。在冬季初期异温性使用程度较低的个体，在资源充裕的年份存活率会下降，但在资源匮乏的年份则无此现象；且该类个体在后续繁殖季的繁殖成功率更高。
4. 本研究结果支持“波动选择维持异温性多样性”这一假说，并表明个体化生态生理学（individualized eco-physiology）能够帮助我们更深入地理解内温动物节能策略的演化机制。