Department of Biology, University of Ottawa, Ottawa, ON, Canada, K1N 6N5.
J Exp Biol. 2022 Sep 15;225(18). doi: 10.1242/jeb.244186. Epub 2022 Sep 20.
In many endotherms, a potentially important yet often overlooked mechanism to save energy is the use of the heat generated by active skeletal muscles to replace heat that would have been generated by thermogenesis (i.e. 'activity-thermoregulatory heat substitution'). While substitution has been documented numerous times, the extent of individual variation in substitution has never been quantified. Here, we used a home-cage respirometry system to repeatedly measure substitution through the concomitant monitoring of metabolic rate (MR) and locomotor activity in 46 female white-footed mice (Peromyscus leucopus). A total of 117 measures of substitution were taken by quantifying the difference in the slope of the relationship between MR and locomotor activity speed at two different ambient temperatures. Consistency repeatability (±s.e.) of substitution was 0.313 (±0.131); hence, about a third of the variation in substitution occurs at the among-individual level. Body length and heart mass were positively correlated with substitution whereas surface area was negatively correlated with substitution. These three sub-organismal traits accounted for the majority of the among-individual variation (i.e. individual differences in substitution were not significant after accounting for these traits). Overall, our results imply that the energetic cost of activity below the thermoneutral zone is consistently cheaper from some individuals than others, and that the energy saved from substitution might be available to invest in fitness-enhancing activities.
在许多恒温动物中，一种潜在的重要但经常被忽视的节能机制是利用活跃的骨骼肌产生的热量来替代由产热（即“活动-体温调节热替代”）产生的热量。虽然替代作用已经被多次记录下来，但个体差异的程度从未被量化过。在这里，我们使用家庭笼呼吸计系统通过同时监测代谢率（MR）和 46 只雌性白足鼠（Peromyscus leucopus）的运动活动，多次重复测量替代作用。通过量化在两个不同环境温度下 MR 和运动活动速度之间关系的斜率差异，共获得了 117 次替代作用的测量值。替代作用的一致性重复性（±s.e.）为 0.313（±0.131）；因此，大约三分之一的替代作用变化发生在个体之间的水平上。体长和心脏质量与替代作用呈正相关，而表面积与替代作用呈负相关。这三个亚机体特征解释了大部分个体间的变异（即，在考虑这些特征后，替代作用的个体差异不显著）。总的来说，我们的研究结果表明，在热中性区以下活动的能量成本对于某些个体来说比其他个体更一致地便宜，并且从替代作用中节省的能量可能可用于投资于增强适应性的活动。
