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（母性投资），无论是行为上的（如保护免受捕食者的侵害）还是物质上的（如乳汁），都必须与未来的繁殖努力相平衡。 了解不同物种的雌性如何平衡当前和未来对后代的投资，可以深入了解替代生殖策略的演变。 在哺乳动物中，量化母体投资可能是困难的。 这是由于以下几个原因：1）很难给母亲的行为赋值; 2）后代可能与母亲呆在一起多年，观察期长得不切实际; 3）通过妊娠和哺乳直接从母亲转移到后代的物质可能很难确定。 北方象海豹（Mirounga angustirostris）提供了一个独特的系统内，研究母亲的投资。 海象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，因此更有可能量化母亲的投资。 此外，雌性海象在哺乳期不吃也不喝。 禁食和哺乳的结合限制了雌性对幼崽的投资能力，因为用于满足自身能量需求的营养素（脂肪和蛋白质）也用于为幼崽生产牛奶。 材料和能源投资在海象幼崽以前已经确定，但其关系的精力充沛的成本的母亲还没有得到表征。 本文提出的研究将调查哺乳期海象如何利用营养储备来支持其新陈代谢，确定和量化保护母乳生产的母体营养素的生理机制，并描述有助于最大限度地投资于幼崽的营养素使用策略。 同位素标记的化合物将用于研究为哺乳期母海豹提供能量的重要生化途径。 具体而言，将估计在泌乳过程中葡萄糖和脂肪作为燃料来源的重要性的变化，并确定甘油（脂肪分解的副产品）对葡萄糖产生（脂肪生成）的贡献。 胰岛素和胰高血糖素是调节身体如何利用糖和脂肪的两种重要激素，将被操纵以确定这些激素是否以该系统特有的方式相互作用。 这些信息将提供有关海象如何在禁食限制下优化对后代的投资的见解，因此，将提供有助于未来生殖努力的最终策略的见解。 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。 一个研究生，谁将从拟议的工作中得出一个论文的研究问题，也将通过该计划的财政支持。 将本科生和研究生融入研究将确保学生体验创新和动态的课程，重点是有机体生物学的综合方法。

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.