Czenze Zenon J, Jonasson Kristin A, Willis Craig K R
Physiol Biochem Zool. 2017 Jul/Aug;90(4):502-511. doi: 10.1086/692623.
Mammalian hibernation consists of energy-saving torpor bouts (periods of controlled reduction in body temperature [T]) interspersed with brief arousals to normothermic T. Frequency and duration of torpor bouts and arousals can affect winter survival and are thought to be influenced by an optimization balancing the energetic benefits of prolonged torpor against the physiological and ecological costs (e.g., accumulation of metabolic wastes). Female little brown bats (Myotis lucifugus) spend their fat reserves more slowly than males during winter, presumably so they can emerge from hibernation in good condition to initiate pregnancy. We used temperature telemetry over three winters to test a prediction of the optimization hypothesis that female M. lucifugus would use longer torpor bouts and/or shorter arousals than males. Females did conserve energy relative to males by adjusting the magnitude and duration of arousals but not the duration of torpor bouts. Although torpor bout duration did not vary by sex for adults, it did vary by age. Adults initially used longer torpor bouts than young-of-the-year, but this difference declined as cave temperature warmed in spring. Males and females in better condition spent more energy during hibernation, again via increased arousal duration rather than decreased torpor bout duration. Longer arousals by males could increase reproductive fitness if males mate with torpid females throughout winter. Our results highlight demographic differences in winter behavior for small hibernators facing extreme energy limitation in cold climates and illustrate the influence that reproductive costs have on hibernation energetics.
哺乳动物的冬眠由节能的蛰伏期（体温 [T] 受控降低的时期）组成，其间穿插着短暂的觉醒至正常体温 T。蛰伏期和觉醒的频率及持续时间会影响冬季的生存，并且被认为受到一种优化机制的影响，这种优化在延长蛰伏的能量益处与生理和生态成本（例如代谢废物的积累）之间取得平衡。雌性小棕蝠（北美鼠耳蝠）在冬季消耗脂肪储备的速度比雄性慢，大概是为了能以良好的状态从冬眠中苏醒以开始怀孕。我们在三个冬天使用温度遥测技术来检验优化假说的一个预测，即雌性北美鼠耳蝠会比雄性使用更长的蛰伏期和/或更短的觉醒时间。雌性确实通过调整觉醒的幅度和持续时间而非蛰伏期的持续时间相对于雄性节省了能量。虽然成年个体的蛰伏期持续时间不因性别而异，但因年龄而异。成年个体最初使用的蛰伏期比当年幼体更长，但随着春季洞穴温度升高这种差异减小。状况较好的雄性和雌性在冬眠期间消耗更多能量，同样是通过增加觉醒持续时间而非缩短蛰伏期持续时间。如果雄性在整个冬季与处于蛰伏状态的雌性交配，那么雄性更长的觉醒时间可能会提高繁殖适应性。我们的结果突出了在寒冷气候下面临极端能量限制的小型冬眠动物冬季行为的种群统计学差异，并说明了繁殖成本对冬眠能量学的影响。
