Department of Biological Sciences, University of Manitoba, Winnipeg, Manitoba, Canada, R3T 2N2.
J Exp Biol. 2010 Jun 15;213(Pt 12):2165-73. doi: 10.1242/jeb.040188.
Torpor is an adaptation for energy conservation employed by many species of small-bodied endotherms. However, surprisingly little is known regarding proximate factors influencing day-to-day variation in torpor expression in the wild. We used open-flow respirometry to quantify torpor expression in nine little brown bats (Myotis lucifugus, LeConte 1831) at two ambient temperatures (7 degrees C and 17 degrees C) following either sham feeding or consumption of a high-protein meal (50% or 100% of the mass required to reach satiation for each individual). Food consumption significantly increased the time spent normothermic before torpor entry but did not affect either the rate of body cooling or torpid metabolic rate. Bats did not fully exploit potential energy savings by maximising their use of torpor. Instead they varied torpor expression such that total energy expenditure over the course of each 22-h trial was balanced against gross energy intake immediately before the trial, independent of ambient temperature. This was accomplished by adjusting the timing of entry into torpor (thus altering the time spent torpid), rather than by modulating torpid metabolic rate. However, pre-trial body mass was also a significant predictor of torpor expression, which suggests that energy reserves combine with recent foraging success to influence individuals' decisions about depth and duration of their torpor bouts. We also present evidence that little brown bats use the heat generated through digestion (i.e. the heat increment of feeding) to substitute for active thermogenesis at sub-thermoneutral temperatures, thereby reducing the energetic costs of thermoregulation prior to torpor entry.
蛰伏是许多小型内温动物为节约能量而采取的一种适应方式。然而，对于影响野生环境下蛰伏表达的日常变化的近因因素，人们知之甚少。我们使用开放式呼吸测量法，在两种环境温度（7°C 和 17°C）下，分别在假喂食或消耗高蛋白食物（对于每个个体，达到饱食所需质量的 50%或 100%）后，对九只小褐蝙蝠（Myotis lucifugus，LeConte 1831）的蛰伏表达进行了量化。食物消耗显著增加了进入蛰伏前的正常体温时间，但对身体冷却速度或蛰伏代谢率均无影响。蝙蝠并没有通过最大限度地利用蛰伏来充分利用潜在的节能。相反，它们改变了蛰伏表达，使得在每次 22 小时的试验过程中，总能量支出与试验前立即摄入的总能量相平衡，而与环境温度无关。这是通过调整进入蛰伏的时间（从而改变蛰伏时间）来实现的，而不是通过调节蛰伏代谢率。然而，试验前的体重也是蛰伏表达的一个重要预测因素，这表明能量储备与最近的觅食成功相结合，影响个体对蛰伏时间和深度的决策。我们还提供了证据表明，小褐蝙蝠利用消化过程中产生的热量（即摄食的热增量）来替代亚热中性温度下的主动产热，从而降低进入蛰伏前的体温调节的能量成本。
