Energetics, Homeostasis, and Life History in an Arctic Hibernator

这个项目评估了小型冬眠哺乳动物在北极环境中越冬的成本和后果。它调查了阿拉斯加北部一个自然种群的北极地松鼠的体温变化模式和冬眠物候，并测试了关于食物和洞穴选择对个体生存和繁殖的影响的假设。这个项目将与C.L.Frank博士合作，测试饮食假说，该假说围绕植物来源的必需脂肪酸在限制冬眠生理方面的作用展开。将进行基于实验室的实验，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时间的基本依据。田野工作继续着对这种北极哺乳动物种群的长期生理监测计划。该项目将集中于以下具体目标：(1)利用自动传感，描述进入冬眠和从冬眠中苏醒的时间、昏迷期间过冷的自然限度、周期性觉醒的模式和持续时间，以及北极地松鼠的性别、生殖和年龄在冬眠模式和物候上的差异。(1B)在每个人的冬眠期测量年度土壤温度分布。试验数据表明，冬眠最低温度从-7℃到-250℃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(年际)变化的程度。通过改变雪堆来操纵物理因素，如植被和雪覆盖洞穴，并确定冬眠带及其居住者的热后果。(2)越冬存活率的变化或存活个体身体状况的变化与其冬眠的温度特征相关。因为它们花费更多的能量来维持身体和土壤之间更大的温度梯度，所以占据较冷洞穴的地松鼠在冬眠期间应该比居住在温暖洞穴的动物遭受更多的死亡率或失去更多的身体储备。这些实验研究了冬季物理环境及其时空变化对脂肪和瘦肉损失和存活率的影响，以及由于春季繁殖力受到越冬体重损失的影响，因此，一种关键的北极哺乳动物物种的生殖适合性受到影响。(3)测定饲料脂肪和脂肪组织多不饱和水平对个体冬眠和越冬存活方式和深度的影响。在北极地松鼠育肥过程中，从北极植物中获得的必需脂肪酸浓度将通过植入数据记录器时采集的仓库脂肪的活检来确定，并将在圈养动物中操纵饮食脂质。(4)连续几年对冬眠动物进行采样的结果将增加我们关于这种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哺乳动物食草动物的作用整合到对这个北极群落的系统研究方法中。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性质。(5)测定在-20到+200℃环境温度下冬眠的北极地松鼠的稳态代谢率、代谢燃料的使用和产热来源。(6)测量在-20℃至+20℃条件下冬眠的动物的最大僵尸长度(TBL)，并监测体温和脑温。最大总潜伏期应相反地反映一个未知过程在冬眠期间偏离稳态水平的速率。由于在这个温度范围内冬眠的北极地松鼠的体温和代谢率变得不耦合，我们可以研究这一过程的性质，这可能代表着哺乳动物在低温和低代谢过程中持续稳态的根本制约。***

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. ***