Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, IA 50011, USA.
Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, IA 50011, USA; Department of Zoology, Ohio Wesleyan University, Delaware, OH 43015, USA.
Gen Comp Endocrinol. 2021 Jun 1;307:113758. doi: 10.1016/j.ygcen.2021.113758. Epub 2021 Mar 24.
Characterizing the physiological response to prolonged cold exposure is essential for understanding the maintenance of long-term energy balance. As part of their natural life cycle, temperate ectotherms are often exposed to seasonal variation in temperatures, including extended periods of cold well below their activity range. Relatively little is known about variation in physiological responses as vertebrate ectotherms enter and exit brumation in response to sustained cold temperatures. We tested the influence of temperature on physiology before, during, and after a simulated brumation in the checkered garter snake (Thamnophis marcianus), a widespread ectothermic vertebrate. We tested for the relative effect of immediate temperature and physiological context (entering or exiting brumation) on hormones regulating energy balance, indicators of energy availability, and resting metabolic rate (V̇). Plasma corticosterone, glucose, and insulin, as well as immune cell heterophil: lymphocyte ratios responded to temperature, though they did so with different thermal response curves. Thermal sensitivity varied both among and within physiological measures depending on whether animals were going into or coming out of brumation. Additionally, V̇ was regulated beyond simple temperature-dependence, whereby post-brumation measures were depressed relative to pre-brumation measures at the same temperature. This pattern was characterized by a change in the temperature coefficient (Q), with a larger pre-brumation Q suggesting reduced thermal sensitivity of metabolic rate following a period of extended cold exposure. The integrated physiological response presented here demonstrates not only temperature dependence across physiological axes, but seasonal variation in thermal responsiveness. Our results suggest that energy allocation decisions and hormonal regulation of underlying processes promote differing levels of thermal sensitivity when entering or exiting brumation.
描述对长时间寒冷暴露的生理反应对于理解长期能量平衡的维持至关重要。作为其自然生命周期的一部分，温带变温动物经常面临温度的季节性变化，包括长时间的寒冷，远低于其活动范围。相对而言，人们对脊椎动物变温动物在进入和退出冬眠以应对持续低温时生理反应的变化知之甚少。我们在模拟 checkerered garter snake（Thamnophis marcianus）的冬眠前后测试了温度对生理学的影响，checkered garter snake 是一种广泛分布的变温脊椎动物。我们测试了立即温度和生理环境（进入或退出冬眠）对调节能量平衡的激素、能量可用性指标和静息代谢率（V̇）的相对影响。血浆皮质酮、葡萄糖和胰岛素以及免疫细胞嗜中性粒细胞：淋巴细胞比率对温度有反应，但它们的热反应曲线不同。热敏感性在生理测量之间和之内都存在差异，具体取决于动物是进入还是退出冬眠。此外，V̇的调节超出了简单的温度依赖性，即冬眠后的测量值在相同温度下低于冬眠前的测量值。这种模式的特征是温度系数（Q）的变化，冬眠后的 Q 值较大表明在长时间的寒冷暴露后，代谢率的热敏感性降低。这里呈现的综合生理反应不仅表明了生理轴之间的温度依赖性，还表明了季节性的热反应变化。我们的结果表明，进入或退出冬眠时，能量分配决策和激素对潜在过程的调节会促进不同水平的热敏感性。
