RUI: Physiological Adaptations for Resolving the Conflicting Metabolic Demands of Lactating While Fasting in Northern Elephant Seals

雌性对后代的投资金额(母体投资)，无论是行为上的(如对捕食者的保护)还是物质上的(如牛奶)，都必须与未来繁殖的努力相平衡。了解不同物种的雌性如何平衡当前和未来对后代的投资，有助于洞察替代生殖策略的演变。在哺乳动物中，量化母体投资可能很困难。发生这种情况的原因有几个：1)很难为母亲的行为赋值；2)后代可能会与母亲呆在一起多年，使得观察期长得不切实际；以及，3)通过怀孕和哺乳直接从母亲传递给后代的物质可能很难确定。北象海豹(Mironga Angustirostris)为研究母体投资提供了一个独特的系统。象海豹的投资期仅限于哺乳期。这段时间很短(约25天)，几乎所有的投资都是以牛奶的形式提供的，这使得量化产妇投资变得更加可行。此外，雌性象海豹在哺乳期不吃不喝。禁食和哺乳的结合限制了雌性幼崽对幼崽的投资能力，因为用于满足自身能量需求的营养物质(脂肪和蛋白质)也被用来为幼崽生产牛奶。之前已经确定了对海象幼崽的材料和能量投入，但它与母亲能量成本的关系尚未确定。这里提出的研究将调查哺乳象海豹如何利用营养储备来支持它们的新陈代谢，识别和量化保护母体营养以生产牛奶的生理机制，并描述有助于最大化投资于幼崽的营养利用策略。同位素标记的化合物将用于研究为哺乳期雌性海豹提供能量的重要生化途径。具体地说，将评估葡萄糖和脂肪在哺乳过程中作为燃料来源的重要性的变化，并确定脂肪分解的副产品甘油对葡萄糖生产(糖异生)的贡献。胰岛素和高血糖素是调节身体如何利用糖和脂肪的两种重要荷尔蒙，它们将被操纵，以确定这些荷尔蒙是否以这个系统特有的方式相互作用。这些信息将提供关于象海豹如何在禁食限制下优化对其后代的投资的洞察，因此，将为有助于未来繁殖努力的最终战略提供洞察。作为NSF-RUI计划的一部分，本科生将积极参与实地研究和数据分析。一名研究生，他将从提议的工作中为一篇论文衍生一个研究问题，也将通过这个项目获得经济上的支持。将本科生和研究生整合到研究中，将确保学生体验到创新和动态的课程，强调有机生物学的综合方法。

The amount of investment that females place in their offspring (maternal investment), whether it is behavioral (such as protection from predators) or material (such as milk), must be balanced against future efforts at reproducing. Understanding how females of different species balance current and future investment in offspring provides insight on the evolution of alternative reproductive strategies. In mammals, quantifying maternal investment can be difficult. This occurs for several reasons: 1) it is difficult to assign value to maternal behaviors; 2) offspring may stay with their mothers for many years making observation periods unrealistically long; and, 3) the material directly transferred from mother to offspring through gestation and lactation may be hard to determine. Northern elephant seals (Mirounga angustirostris) provide a unique system within which to study maternal investment. The investment period for elephant seals is limited to the period of lactation. This period is brief (~ 25 days) and almost all investment is given in the form of milk making it more feasible to quantify maternal investment. Furthermore, elephant seal females do not eat or drink during lactation. This combination of fasting and lactation constrains the ability of females to invest in their pups because the nutrients (fat and protein) used to meet their own energy needs are also used to produce milk for the pup. Material and energy investment in elephant seal pups has been previously determined but its relationship to the energetic costs of the mother has not been characterized. The study proposed here will investigate how lactating elephant seals utilize nutrient reserves to support their metabolism, identify and quantify physiological mechanisms that protect maternal nutrients for milk production, and characterize the strategy for nutrient use that contributes to maximizing investment in pups. Isotopically labeled compounds will be used to study biochemical paths important to supplying energy to lactating female seals. Specifically, changes in the importance of glucose and fat as fuel sources over the time course of lactation will be estimated and the contribution of glycerol, a byproduct of fat breakdown, to the production of glucose (gluconeogenesis) will be determined. Insulin and glucagon, two hormones important in regulating how the body uses sugar and fat, will be manipulated to determine whether these hormones interact in a manner unique to this system. This information will provide insight on how elephant seals optimize investment in their offspring under fasting constraints, and thus, will provide insight on ultimate strategies that contribute to future reproductive effort. As part of the NSF-RUI initiative, undergraduates will be actively involved in field research and data analysis. A graduate student, who will derive a research question for a thesis from the proposed work, will also be financially supported through this program. Integration of undergraduate and graduate students into the research will insure that students experience an innovative and dynamic curriculum with an emphasis on integrative approaches to organismal biology.