Energetics, Homeostasis, and Life History in an Arctic Hibernator

9819540巴恩斯该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。它调查模式的体温变化和冬眠的物候在自然种群的北极地松鼠在北方阿拉斯加和测试假说的影响，饮食和洞穴的选择对个人的生存和繁殖。这个项目将与C。L.弗兰克，围绕植物来源的必需脂肪酸在限制冬眠生理学中的作用。将进行以实验为基础的实验，量化在北极温度条件下冬眠的代谢成本，并研究限制哺乳动物在冬眠期间保持低温和低代谢状态的基本依据。野外工作继续对这种北极哺乳动物种群进行长期的生理监测。该项目将侧重于以下具体目标：（1a）使用自动传感，描述时间浸入和出现从冬眠，自然限制过冷在休眠期间，模式和周期性觉醒的持续时间，以及如何性别，生殖和年龄队列的北极地松鼠不同的冬眠模式和物候。(1b)在每个个体的冬眠处测量每年的土壤温度剖面。试验数据表明，最低冬眠温度从-7到-25 ℃不等，决定了这种变化的来源（表面和土壤物理和气候特征）以及空间（洞穴）和时间（年）变化的程度。通过改变雪堆来操纵物理因素，如洞穴上的植被和积雪，并确定冬眠室及其居住者的热后果。(2)将越冬存活率的变化或存活个体的身体状况变化与其冬眠囊的热特征相关联。因为它们花费更多的能量来维持身体和土壤之间的较大的温度梯度，所以占据较冷洞穴的地松鼠在冬眠期间应该比占据较温暖洞穴的动物遭受更多的死亡率或损失更多的身体储备。这些实验调查的影响，冬季的物理环境及其空间和时间变化的脂肪和瘦肉损失和生存，因为春天的繁殖力是受越冬体重损失，繁殖适合度的一个关键的北极哺乳动物物种。(3)测试食物脂质和脂肪组织多不饱和水平对个体冬眠方式、冬眠深度和越冬存活率的影响。在北极地松鼠育肥期间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器时采集的储存脂肪的活组织检查来确定，并将在圈养动物中操纵膳食脂质。(4)连续几年对进入冬眠和冬眠后的动物进行取样，其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。在图里克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研究这个北极社区的系统方法中。下面的实验室实验量化了在北极条件下冬眠的能量消耗，并调查了哺乳动物可以在冬眠中停留多久的限制的性质。 (5)确定在-20至+20摄氏度环境温度下冬眠的北极地松鼠的稳态代谢率、代谢燃料使用和产热源。(6)测量动物在-20至+20 ℃条件下冬眠的最大冬眠时间（TBL），并监测体温和脑温。最大TBL应该反向反映了一个未知的过程（ES）在冬眠期间偏离稳态水平的速率。 由于体温和代谢率在北极地松鼠在这个温度范围内冬眠时变得不耦合，我们可以研究这个过程的性质，这可能是哺乳动物在低温和低代谢期间持续体内平衡的基本约束。***

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. ***