Ecol Evol Physiol. 2024 May-Jun;97(3):180-189. doi: 10.1086/730867. Epub 2024 May 16.
AbstractDuring periods of torpor, hibernators can reduce metabolic rate (MR) and body temperature () substantially. However, to avoid physiological dysfunction at low temperatures, they defend at a critical minimum, often between ~0°C and 10°C via an increase in MR. Because thermoregulation during torpor requires extra energy, individuals with lower 's and thus minimal MR during torpor should be selected in colder climates. Such inter- and intraspecific variations occur in some placental mammals, but for the evolutionary separate marsupials, available information is scarce. Marsupial eastern pygmy possums (; ~22 g body mass), widely distributed along the Australian southeastern coast including subtropical to alpine areas, were used to test the hypothesis that the defended of torpid individuals is related to the climate of their habitat. Possums were captured from five regions, 1,515 km apart, with midwinter (July) minimum environmental temperatures (min 's) ranging from -3.9°C to 6.6°C. Captive possums in deep torpor were slowly cooled with ambient temperature (), while their MR was measured to determine the minimum torpor metabolic rate (TMR), the at which their MR increased for thermoregulation (min ), and the corresponding minimum (min ). Partial least squares regression analysis revealed that and were the strongest explanatory variables for the min . The min and were also correlated with latitude but not elevation of the capture sites. However, the best correlations were observed between the min and the min and for individuals experiencing min ; these individuals thermoconformed to min 's between -0.8°C and 3.7°C, and their min ranged from 0.5°C to 6.0°C and was 0.5°C-2.6°C below the min at the capture site. In contrast, individuals experiencing a min of -3.9°C regulated at or 4.5°C above the . The minimum TMR of all possums did not differ with and thus did not differ among populations and was 2.6% of the basal MR. These data provide new evidence that thermal variables of marsupials are subject to regional intraspecific variation. It suggests that min is a function of the min but only above 0°C, perhaps because the differential for torpid possums in the wild, at a min of -3.9°C, remains small enough to be compensated by a small increase in MR and does not require the physiological capability for a reduction of below 0°C.
在蛰伏期间，冬眠动物可以大大降低代谢率（MR）和体温（）。然而，为了避免低温下的生理功能障碍，它们通过增加 MR 将 维持在临界最小值，通常在0°C 到 10°C 之间。由于蛰伏期间的体温调节需要额外的能量，因此在较冷的气候中，MR 较低且在蛰伏期间 MR 最小的个体应该被选择。这种种间和种内的变化发生在一些胎盘哺乳动物中，但对于进化上独立的有袋动物，可用信息很少。有袋动物东部小袋鼠（；22 克体重）广泛分布于澳大利亚东南沿海，包括亚热带到高山地区，被用来检验这样一个假设，即蛰伏个体的 与它们栖息地的气候有关。从 5 个相距 1515 公里的地区捕获了小袋鼠，它们的冬季（7 月）最低环境温度（min 's）从-3.9°C 到 6.6°C 不等。将处于深度蛰伏状态的小袋鼠在环境温度（）下缓慢冷却，同时测量它们的 MR，以确定最小蛰伏代谢率（TMR）、MR 增加以进行体温调节时的 （min ）以及相应的最小 （min ）。偏最小二乘回归分析表明，和 是 min 的最强解释变量。min 和 也与纬度有关，但与捕获地点的海拔无关。然而，在经历 min 的个体中，min 和 之间以及 min 和 之间观察到了最佳的相关性；这些个体在-0.8°C 到 3.7°C 之间对 min 's 进行体温调节，其 min 范围为 0.5°C 到 6.0°C，比捕获地点的 min 低 0.5°C-2.6°C。相比之下，经历 min 为-3.9°C 的个体将 调节在 或 4.5°C 以上。所有小袋鼠的最小 TMR 都不受 影响，因此种群之间没有差异，并且比基础 MR 低 2.6%。这些数据提供了新的证据，表明有袋动物的热变量受到区域种内变异的影响。这表明 min 是 min 的函数，但仅在 0°C 以上，这可能是因为在野生状态下，min 为-3.9°C 的蛰伏小袋鼠的 差异足够小，可以通过 MR 的微小增加来补偿，并且不需要将 降低到 0°C 以下的生理能力。
