Centre for Functional Biodiversity, School of Life Sciences, University of KwaZulu-Natal, Private Bag X54001, Durban, 4000, South Africa.
School of Life Sciences, University of KwaZulu-Natal, Private Bag X54001, Durban, 4000, South Africa.
J Therm Biol. 2022 Dec;110:103341. doi: 10.1016/j.jtherbio.2022.103341. Epub 2022 Sep 28.
Small endotherms commonly use daily torpor to maintain energetic homeostasis. During daily torpor, rewarming rates have a large impact on overall energy savings because they influence heat loss in this energetically costly phase of torpor. These rates are affected by both intrinsic and extrinsic ecological factors; however, data on rewarming rates along temporal and spatial scales between and within species are scant. We investigated how seven insectivorous bat species differing in body size and thermal stability of preferred roosts vary in rewarming rates along an altitude gradient (0-1400 m.a.s.l.) in South Africa, predicting that rewarming rates would increase with altitude. We kept individuals overnight at 15°C and monitored their surface temperature during induced rewarming with infrared thermal imaging to calculate rewarming rates. In contrast to our prediction, we found no significant variation between species or altitudes despite differences in body mass and life history traits. However, we did find evidence that males rewarmed more rapidly than females at low temperatures despite the higher energetic cost of slow rewarming, possibly due to reluctance of females to initiate active rewarming at low ambient temperatures. We found some support for the prediction that cool temperatures at high altitude result in lower initial surface temperatures during cold-exposure, as an adaptation to mitigate heat loss through thermal conductance to the ambient environment. This is particularly important for small insectivorous bats given their high surface area to volume ratios.
小型内温动物通常利用日常蛰眠来维持能量平衡。在日常蛰眠中，复温速率对整体能量节约有很大影响，因为它们影响到蛰眠这一能量消耗大的阶段的热量损失。这些速率受到内在和外在生态因素的影响；然而，关于物种间和种内的时间和空间尺度上的复温速率的数据却很少。我们研究了在南非，七个体型大小和首选栖息地热稳定性不同的食虫蝙蝠物种在海拔梯度（0-1400 米）上的复温速率有何变化，预测复温速率会随着海拔的升高而增加。我们将个体在 15°C 下过夜，并使用红外热成像监测它们在诱导复温过程中的表面温度，以计算复温速率。与我们的预测相反，尽管体重和生活史特征存在差异，但我们没有发现物种或海拔之间存在显著差异。然而，我们确实发现了证据表明，尽管缓慢复温的能量成本更高，但雄性在低温下比雌性复温更快，这可能是由于雌性不愿意在低温下主动复温。我们发现了一些支持高海拔低温导致寒冷暴露时初始表面温度较低的预测的证据，这是一种适应环境，以减轻通过热导向环境散失热量的策略。对于表面积与体积比高的小型食虫蝙蝠来说，这一点尤为重要。
