Data from: Solar radiation during rewarming from torpor in elephant shrews: supplementation or substitution of endogenous heat production?

Many small mammals bask in the sun during rewarming from heterothermy, but the implications of this behaviour for their energy balance remain little understood. Specifically, it remains unclear whether solar radiation supplements endogenous metabolic thermogenesis (i.e., rewarming occurs through the additive effects of internally-produced and external heat), or whether solar radiation reduces the energy required to rewarm by substituting (i.e, replacing) metabolic heat production. To address this question, we examined patterns of torpor and rewarming rates in eastern rock elephant shrews (Elephantulus myurus) housed in outdoor cages with access to either natural levels of solar radiation or levels that were experimentally reduced by means of shade cloth. We also tested whether acclimation to solar radiation availability was manifested via phenotypic flexibility in basal metabolic rate (BMR), non-shivering thermogenesis (NST) capacity and/or summit metabolism (Msum). Rewarming rates varied significantly among treatments, with elephant shrews experiencing natural solar radiation levels rewarming faster than conspecifics experiencing solar radiation levels equivalent to approximately 20% or 40% of natural levels. BMR differed significantly between individuals experiencing natural levels of solar radiation and conspecifics experiencing approximately 20% of natural levels, but no between-treatment difference was evident for NST capacity or Msum. The positive relationship between solar radiation availability and rewarming rate, together with the absence of acclimation in maximum non-shivering and total heat production capacities, suggests that under the conditions of this study solar radiation supplemented rather than substituted metabolic thermogenesis as a source of heat during rewarming from heterothermy.许多小型哺乳动物在从异温性（heterothermy）状态复温时会晒太阳，但该行为对其能量平衡的影响仍鲜为人知。具体而言，目前仍不清楚太阳辐射是会补充内源性代谢产热（即复温过程通过体内产生与外部热量的叠加效应实现），还是会通过替代代谢产热来降低复温所需的能量消耗。为解答该问题，我们针对东部岩象鼩（Elephantulus myurus）开展了对照实验：将其饲养于室外笼舍中，分别设置两组处理，一组允许动物接触自然水平的太阳辐射，另一组则通过遮阳布实验性降低太阳辐射强度，随后观察其蛰伏（torpor）模式与复温速率。我们同时测试了动物对太阳辐射可获得性的驯化响应，是否可通过基础代谢率（BMR）、非颤抖性产热（NST）能力以及极限代谢产热（Msum）的表型可塑性得以体现。不同处理组的复温速率存在显著差异：接触自然太阳辐射水平的东部岩象鼩，其复温速度显著快于接触约为自然水平20%或40%太阳辐射的同种个体。接触自然太阳辐射水平的个体与接触约20%自然水平太阳辐射的个体，其基础代谢率存在显著差异；但非颤抖性产热能力与极限代谢产热能力在各处理组间均无显著差异。太阳辐射可获得性与复温速率之间的正相关关系，结合最大非颤抖性产热与总产热能力未出现驯化响应的结果，表明在本实验条件下，太阳辐射在动物从异温性状态复温过程中，是补充而非替代代谢产热作为热量来源。