Physiol Biochem Zool. 2022 Sep-Oct;95(5):438-463. doi: 10.1086/721186.
Allometry predicts that the 12-17-g American water shrew ()-the world's smallest mammalian diver-will have the highest diving metabolic rate coupled with the lowest total body oxygen storage capacity, skeletal muscle buffering capacity, and glycolytic potential of any endothermic diver. Consistent with expectations, and potentially owing to their low thermal inertia, water shrews had a significantly higher diving metabolic rate in 10°C water (8.77 mL O g h) compared with 30°C water (6.57 mL O g h). Unlike larger-bodied divers, muscle myoglobin contributed minimally (7.7%-12.4%) to total onboard O stores of juvenile and adult water shrews, respectively, but was offset by high blood O carrying capacities (26.4%-26.9% v/v). Diving was predominantly aerobic, as only 1.2%-2.3% of dives in 10°C and 30°C water, respectively, exceeded the calculated aerobic dive limits at these temperatures (10.8-14.4 s). The mean voluntary dive time of water shrews during 20-min trials in 3°C-30°C water was s (, ), with a mean maximum dive time of s. However, the average dive duration ( s, ) of radio-telemetered shrews exclusively foraging in a simulated riparian environment (3°C water) for 12-28 h suggests that mean (but not maximum) dive times of water shrews in the wild may be longer. Mean dive duration, duration of the longest dive, and total time in water all decreased significantly as water temperature declined, suggesting that shrews employed behavioral thermoregulation to defend against immersion hypothermia. Additionally, free-diving shrews in the 24-h trials consistently elevated core body temperature by ∼1°C immediately before initiating aquatic foraging bouts and ended these bouts when body temperature was still at or above normal resting levels (∼37.8°C). We suggest that this observed predive hyperthermia aids to heighten the impressive somatosensory physiology, and hence foraging efficiency, of this diminutive predator while submerged.
比较生理学预测，体型最小的哺乳动物——美洲水貂（）——世界上最小的哺乳动物潜水员，其代谢率最高，总身体储氧量、骨骼肌缓冲能力和糖酵解能力最低。与预期一致的是，由于它们的热惯性低，水貂在 10°C 水中（8.77 毫升 O/g/h）的潜水代谢率明显高于 30°C 水中（6.57 毫升 O/g/h）。与体型较大的潜水者不同，肌肉肌红蛋白对幼年和成年水貂总氧储存的贡献极小（分别为 7.7%-12.4%），但被高血液氧携带能力（26.4%-26.9%v/v）所抵消。潜水主要是有氧的，因为在 10°C 和 30°C 水中，只有 1.2%-2.3%的潜水分别超过了这些温度下计算出的有氧潜水极限（10.8-14.4 秒）。水貂在 3°C-30°C 水中进行 20 分钟试验的平均自愿潜水时间为 s（，），最大潜水时间为 s。然而，在 3°C-30°C 水中，经过无线电遥测的水貂在模拟河岸环境中觅食 12-28 小时的平均潜水持续时间为 s（，），表明野生水貂的平均（但不是最大）潜水时间可能更长。平均潜水持续时间、最长潜水持续时间和水中总时间随着水温的降低而显著下降，这表明水貂采用行为体温调节来抵御浸泡性低体温。此外，在 24 小时试验中，自由潜水的水貂在开始水下觅食前，体温会持续升高约 1°C，并在体温仍处于或高于正常静息水平（约 37.8°C）时结束觅食。我们认为，这种观察到的潜水前体温升高有助于提高这种微小捕食者在水下的惊人感觉生理学和觅食效率。
