Mécanismes Adaptatifs et Evolution, UMR CNRS/MNHN 7179, Brunoy, France.
PLoS One. 2009 Oct 23;4(10):e7587. doi: 10.1371/journal.pone.0007587.
Daily heterothermia is used by small mammals for energy and water savings, and seems to be preferentially exhibited during winter rather than during summer. This feature induces a trade-off between the energy saved during daily heterothermia and the energy cost of arousal, which can impact energy balance and survival under harsh environmental conditions. Especially, aging may significantly affect such trade off during cold-induced energy stress, but direct evidences are still lacking. We hypothesized that aging could alter the energetics of daily heterothermia, and that the effects could differ according to season. In the gray mouse lemur (Microcebus murinus), a non-human primate species which exhibits daily heterothermia, we investigated the effects of exposures to 25 and 12 degrees C on body composition, energy balance, patterns of heterothermia and water turnover in adult (N = 8) and aged animals (N = 7) acclimated to winter-like or summer-like photoperiods. Acclimation to summer prevented animals from deep heterothermia, even during aging. During winter, adult animals at 12 degrees C and aged animals at 25 degrees C exhibited low levels of energy expenditure with minor modulations of heterothermia. The major effects of cold were observed during winter, and were particularly pronounced in aged mouse lemurs which exhibited deep heterothermia phases. Body composition was not significantly affected by age and could not explain the age-related differences in heterothermia patterns. However, aging was associated with increased levels of energy expenditure during cold exposure, in concomitance with impaired energy balance. Interestingly, increased energy expenditure and depth of heterothermia phases were strongly correlated. In conclusion, it appeared that the exhibition of shallow heterothermia allowed energy savings during winter in adult animals only. Aged animals exhibited deep heterothermia and increased levels of energy expenditure, impairing energy balance. Thus, an impaired control of the heterothermic process induced high energy costs in the aging mouse lemur exposed to cold.
每日异温被小型哺乳动物用于节省能量和水分，而且似乎更倾向于在冬季而不是夏季表现出来。这种特征导致了在每日异温期间节省的能量与唤醒的能量成本之间的权衡，这可能会在恶劣的环境条件下影响能量平衡和生存。特别是，衰老可能会在寒冷引起的能量压力下显著影响这种权衡，但直接证据仍然缺乏。我们假设衰老可能会改变每日异温的能量学，并且这种影响可能因季节而异。在灰鼠狐猴（Microcebus murinus）中，一种表现出每日异温的非人类灵长类物种，我们研究了暴露于 25 和 12 摄氏度对成年（N = 8）和衰老动物（N = 7）身体成分、能量平衡、异温模式和水周转率的影响，这些动物适应了冬季或夏季类似的光周期。适应夏季可以防止动物进行深度异温，即使在衰老期间也是如此。在冬季，12 摄氏度下的成年动物和 25 摄氏度下的老年动物表现出低水平的能量消耗，异温变化较小。在冬季观察到了寒冷的主要影响，并且在老年鼠狐猴中表现出深度异温阶段时，这些影响尤其明显。年龄对身体成分没有显著影响，也不能解释异温模式与年龄相关的差异。然而，衰老与寒冷暴露时能量消耗的增加有关，同时伴随着能量平衡受损。有趣的是，能量消耗的增加和异温阶段的深度呈强烈相关。总之，似乎只有成年动物在冬季表现出浅层异温才能节省能量。老年动物表现出深度异温并增加了能量消耗，破坏了能量平衡。因此，在寒冷暴露下，衰老的鼠狐猴对异温过程的控制受损，导致高能量成本。
