Czenze Zenon J, Willis Craig K R
Department of Biology and Centre for Forest-Interdisciplinary Research, University of Winnipeg, Winnipeg, MB, Canada,
J Comp Physiol B. 2015 Jul;185(5):575-86. doi: 10.1007/s00360-015-0900-1. Epub 2015 Mar 26.
Phenology refers to the timing of events in the annual cycle of organisms. For temperate-zone mammals, hibernation is one such event, but little is known about its phenology. Hibernation consists of energy-saving torpor bouts interspersed with energetically expensive arousals to normothermic Tb, and hibernators should benefit from mechanisms which reduce arousal costs and help them time arousals to coincide with foraging opportunities. In a previous study, we showed that, in contrast to hibernating bats from warmer climates, little brown bats (Myotis lucifugus) from central Canada abandon a circadian pattern to arousal in the middle of winter when there is no chance of feeding. Here, we used temperature telemetry to test whether they would re-synchronize arousals with normal foraging time (i.e. sunset) during late winter as the chance of foraging or emergence opportunities improves, and whether they would synchronize arousals with conspecifics, possibly to exploit social thermoregulation. We also used passive transponders to test whether energy reserves and/or sex differences in reproductive timing influence phenology and the sensitivity of emergence timing to environmental cues. In contrast to patterns in mid-winter, after 7 April 2013, bats synchronized arousals with sunset and with conspecifics. Females emerged earlier than males, and females in the best condition emerged first while body condition had no influence on male emergence timing. Both male and female bats appeared to time emergence with falling barometric pressure, a cue that predicts favourable foraging conditions for bats but which, unlike outside temperature, would have been readily detectable by bats inside the hibernaculum. Our results highlight hibernation traits associated with extreme winter energy limitation for insect-eating bats in cold climates and illustrate the influence of reproductive timing and environmental conditions on hibernation energetics and phenology.
物候学是指生物体年度周期中事件发生的时间。对于温带哺乳动物来说，冬眠就是这样一个事件，但人们对其物候学知之甚少。冬眠由节能的蛰伏期和穿插其中的恢复到正常体温的高能量消耗的觉醒期组成，冬眠动物应该会从降低觉醒成本并帮助它们安排觉醒时间以与觅食机会相吻合的机制中受益。在之前的一项研究中，我们发现，与来自温暖气候的冬眠蝙蝠不同，加拿大中部的小棕蝠（Myotis lucifugus）在冬季中期没有觅食机会时会放弃昼夜节律的觉醒模式。在这里，我们使用温度遥测技术来测试，随着觅食或出现机会的增加，它们在冬末是否会将觉醒时间重新同步到正常觅食时间（即日落），以及它们是否会与同种个体同步觉醒时间，可能是为了利用社会体温调节。我们还使用无源应答器来测试能量储备和/或繁殖时间的性别差异是否会影响物候学以及出现时间对环境线索的敏感性。与冬季中期的模式不同，在2013年4月7日之后，蝙蝠将觉醒时间与日落以及同种个体同步。雌性比雄性出现得更早，身体状况最佳的雌性最先出现，而身体状况对雄性出现时间没有影响。雄性和雌性蝙蝠似乎都根据气压下降来安排出现时间，气压下降是一种预测蝙蝠有利觅食条件的线索，但与外界温度不同，蝙蝠在冬眠洞穴内很容易察觉到气压下降。我们的研究结果突出了与寒冷气候中食虫蝙蝠冬季极端能量限制相关的冬眠特征，并说明了繁殖时间和环境条件对冬眠能量学和物候学的影响。
