Energetics, Homeostasis, and Life History in an Arctic Hibernator

[9819540]本项目评估小型冬眠哺乳动物在北极环境越冬的成本和后果。它调查了阿拉斯加北部北极地松鼠自然种群的体温变化模式和冬眠物候，并测试了关于饮食和洞穴选择对个体生存和繁殖的影响的假设。该项目将与c·l·弗兰克（C. L. Frank）博士合作，围绕植物源性必需脂肪酸在限制冬眠生理学中的作用，对饮食假设进行测试。将进行以实验室为基础的实验，量化在北极温度条件下冬眠的代谢成本，并调查限制哺乳动物在冬眠期间保持低温和低代谢多长时间的基本基础。实地考察继续了对北极哺乳动物种群的长期生理监测计划。该项目将重点关注以下具体目标：（1a）使用自动传感，描述北极地松鼠进入冬眠和从冬眠中出现的时间，冬眠期间过冷的自然限制，周期性觉醒的模式和持续时间，以及性别，生殖和年龄群体在冬眠模式和物候方面的差异。（1b）测量每个个体冬眠地的年土壤温度曲线。试点数据表明，冬眠最低温度在-7℃至- 25℃之间的变化决定了这种变化的来源（地表和土壤的物理和气候特征）以及空间（洞间）和时间（年间）变化的程度。通过改变雪流来操纵诸如植被和洞穴上的积雪等物理因素，并确定冬眠地及其居住者的热后果。(2)越冬存活率的变化或生存个体身体状况的变化与其冬眠的热特征相关。因为它们消耗更多的能量来维持身体和土壤之间更大的热梯度，所以在冬眠期间，占据较冷洞穴的地松鼠应该比占据较温暖洞穴的动物有更多的死亡率或损失更多的身体储备。这些实验研究了冬季物理环境及其时空变化对北极哺乳动物肥瘦损失和存活率的影响，并且由于春季繁殖力受越冬体重损失的影响，因此研究了生殖适宜性。(3)测试饲料脂肪和脂肪组织多不饱和水平对个体冬眠模式、深度和越冬存活率的影响。在北极地松鼠的育肥过程中，从北极植物中获得的必需脂肪酸的浓度将通过植入数据记录仪时对储存脂肪进行活组织检查来确定，并对圈养动物的膳食脂质进行控制。(4)在动物进入冬眠和从冬眠中出来的连续几年的采样结果将增加我们关于北极地松鼠种群的生理生态学、年代学、内分泌学和生活史特征的长期数据集。在Toolik野外站进行的其他长期生态和生理研究的背景下，这些实验可以将一种关键的食草哺乳动物的作用整合到北极群落研究的系统方法中。下面的实验室实验量化了在北极条件下冬眠的能量成本，并调查了哺乳动物冬眠时间限制的本质。(5)确定北极地松鼠在-20 ~ + 200℃环境温度下冬眠的稳态代谢率、代谢燃料使用和产热来源。(6)测量冬眠动物在-20 ~ + 200℃条件下的最大冬眠时间（TBL），监测体、脑温度。最大TBL应反作用于冬眠期间未知过程偏离稳态水平的速率。由于北极地松鼠在这个温度范围内冬眠时，体温和代谢率是不耦合的，我们可以研究这一过程的本质，这可能是哺乳动物在低体温和低代谢期间持续体内平衡的基本限制。＊＊＊

9819540BarnesThis project assesses the costs and consequences for small hibernating mammals overwintering in an arctic environment. It investigates patterns of body temperature change and the phenology of hibernation in a natural population of arctic ground squirrels in Northern Alaska and tests hypotheses about the effect of diet and burrow choice for individual survivorship and reproduction. This project will test the diet hypotheses, in collaboration with Dr. C. L. Frank, which revolves around the role of plant-derived essential fatty acids in constraining hibernation physiology. Laboratory-based experiments will be conducted that quantify the metabolic costs of hibernating under arctic temperature conditions and investigate the fundamental basis for what limits how long mammals can stay hypothermic and hypometabolic during hibernation. The fieldwork continues a long-term physiological monitoring program of this arctic mammal population. The project will focus on the following specific goals: (1a) Using automated sensing, describe the timing of immergence into and emergence from hibernation, natural limits to supercooling during torpor, pattern and duration of periodic arousals, and how sex, reproductive, and age cohorts of arctic ground squirrels differ in hibernation patterns and phenology. (1b) Measure annual soil temperature profiles at each individual's hibernaculum. Pilot data show that minimum hibernacula temperatures vary from -7 to - 25 0C determine the sources of this variation (surface and soil physical and climatological features) and the extent of spatial (among-burrow) and temporal (among-year) variation. Manipulate physical factors such as vegetation and snow cover over burrows by altering snowdrift and determine the thermal consequences for the hibernaculum and its occupant. (2) Correlate variation in overwinter survivorship or change in body condition in surviving individuals with thermal features of their hibernacula. Because they expend more energy maintaining larger thermal gradients between body and soil, ground squirrels occupying colder burrows should suffer more mortality or lose more body stores during hibernation than do animals occupying warmer burrows. These experiments investigate the effect of the winter physical environment and its spatial and temporal variation on fat and lean loss and survivorship and, since spring fecundity is affected by overwinter body mass loss, reproductive fitness of a key arctic mammalian species. (3) Test the effect of dietary lipids and polyunsaturated level of adipose tissue on the pattern and depth of hibernation and overwinter survivorship of individuals. The concentration of essential fatty acids obtained from arctic plants during fattening in arctic ground squirrels will be determined from a biopsy of depot fat taken when data loggers are implanted, and dietary lipids will be manipulated in captive animals. (4) Results from samplinganimals as they enter and emerge from hibernation in successive years will add to our long-term data set on the physiological ecology, chronology, endocrinology, and life-history characteristics of this arctic population of ground squirrels. Set in the context of the other long-term ecological and physiological research done at the Toolik Field Station, these experiments can integrate the role of a key mammalian herbivore into the systems approach of study of this arctic community. The following laboratory experiments quantify the energetic costs of hibernation in arctic conditions and investigate the nature of limits to how long a mammal can stay in hibernation. (5) Determine steady-state metabolic rate, metabolic fuel use, and sources of thermogenesis in arctic ground squirrels hibernating at ambient temperatures of -20 to +20 0C. (6) Measure maximum torpor bout length (TBL) of animals hibernating in conditions of -20 to +20 0C and monitored for body and brain temperature. Maximum TBL should inversely reflect the rate by which an unknown process(es) deviates from homeostatic levels during hibernation. Since body temperature and metabolic rate become uncoupled in arctic ground squirrels hibernating over this temperature range, we can investigate the nature of this process, which may represent a fundamental constraint to continued homeostasis during hypothermia and hypometabolism in mammals. ***