Evans Alina L, Fuchs Boris, Singh Navinder J, Thiel Alexandra, Giroud Sylvain, Blanc Stephane, Laske Timothy G, Frobert Ole, Friebe Andrea, Swenson Jon E, Arnemo Jon M
Department of Forestry and Wildlife Management, Faculty of Applied Ecology and Agricultural Sciences, Inland Norway University of Applied Sciences, Campus Evenstad, 2418, Elverum, Norway.
Department of Wildlife, Fish and Environmental Studies, Faculty of Forest Sciences, Swedish University of Agricultural Sciences, 901 83, Umeå, Sweden.
Front Zool. 2023 Aug 17;20(1):27. doi: 10.1186/s12983-023-00501-3.
Despite centuries of research, debate remains on the scaling of metabolic rate to mass especially for intraspecific cases. The high variation of body mass within brown bears presents a unique opportunity to study the intraspecific effects of body mass on physiological variables. The amplitude of metabolic rate reduction in hibernators is dependent on body mass of the species. Small hibernators have high metabolic rates when euthermic but experience a drastic decrease in body temperature during torpor, which is necessary to reach a very low metabolic rate. Conversely, large hibernators, such as the brown bear (Ursus arctos), show a moderate decrease in temperature during hibernation, thought to be related to the bear's large size. We studied body mass, abdominal body temperature, heart rate, and accelerometer-derived activity from 63 free-ranging brown bears (1-15 years old, 15-233 kg). We tested for relationships between body mass and body temperature, heart rate, and hibernation duration.
The smallest individuals maintained lower body temperatures during hibernation, hibernated longer, and ended hibernation later than large bears. Unlike body temperature, winter heart rates were not associated with body mass. In summer, the opposite pattern was found, with smaller individuals having higher body temperature and daytime heart rates. Body mass was associated with body temperature in the winter hypometabolic state, even in a large hibernating mammal. Smaller bears, which are known to have higher thermal conductance, reached lower body temperatures during hibernation. During summer, smaller bears had higher body temperatures and daytime heart rates, a phenomenon not previously documented within a single mammalian species.
We conclude that the smallest bears hibernated more deeply and longer than large bears, likely from a combined effect of basic thermodynamics, the higher need for energy savings, and a lower cost of warming up a smaller body.
尽管经过了数百年的研究，但关于代谢率与体重之间的比例关系仍存在争议，尤其是在种内情况下。棕熊体重的高度变异性为研究体重对生理变量的种内影响提供了独特的机会。冬眠动物代谢率降低的幅度取决于物种的体重。小型冬眠动物在正常体温时具有较高的代谢率，但在蛰伏期间体温会急剧下降，这对于达到极低的代谢率是必要的。相反，大型冬眠动物，如棕熊（Ursus arctos），在冬眠期间体温下降幅度适中，这被认为与熊的体型较大有关。我们研究了63只自由放养的棕熊（1至15岁，体重15至233千克）的体重、腹部体温、心率以及加速度计测量的活动情况。我们测试了体重与体温、心率和冬眠持续时间之间的关系。
最小的个体在冬眠期间保持较低的体温，冬眠时间更长，结束冬眠的时间比大型熊更晚。与体温不同，冬季心率与体重无关。在夏季，发现了相反的模式，较小的个体体温和白天心率更高。即使在大型冬眠哺乳动物中，体重在冬季低代谢状态下也与体温有关。已知具有较高热传导率的较小棕熊在冬眠期间体温更低。在夏季，较小的棕熊体温和白天心率更高，这一现象此前在单一哺乳动物物种中尚未有记录。
我们得出结论，最小的棕熊比大型熊冬眠更深、时间更长，这可能是基本热力学、更高的能量节约需求以及较小身体升温成本较低等多种因素共同作用的结果。
