Collaborative Research: Triple oxygen isotopes as a new method to study water inputs and metabolism in wild animals

所有的动物都需要水和能量来维持生命。水可以从各种外部来源获得（例如，河流、湖泊、食物），也可以作为食物分解过程中化学反应的副产品在体内获得。能量是从食物中获得的，能量的加工速度限制了动物的一切活动：觅食和狩猎、分散、与其他个体竞争、繁殖和其他活动。因此，评估不同水源对动物摄取量的贡献，以及评估动物的能量利用率，对于了解动物功能的各个方面都至关重要。然而，测量野生动物的水投入和能源使用是非常困难的。迄今为止的方法需要捕获和处理动物至少两次，或者对给定栖息地的每一个潜在水源进行采样。这些任务在实地往往是不可能完成的，严重限制了对这些重要变量的研究。为了克服这一挑战，本项目将开发利用Δ17O对单个动物水体样本的测量（Δ17OBW）来量化来自外部和内部来源对动物水体池的部分贡献。此外，内部水的部分贡献将提供能源利用率的指标，因为这种内部水的产生速度直接反映了能源处理的速度。从这个项目中对Δ17OBW的理解将为将动物功能纳入广泛的研究创造新的机会。Δ17O的取值反映了Δ17O与δ18O之间关系的偏差。对大多数动物来说，有两个来源提供了80-99%的体内水输入：1)最终来自降水的饮用水/食物水和2)代谢水。这两种输入的Δ17O值相对恒定且差异显著：饮用水/食物水Δ17O≈0.030‰，代谢水Δ17O≈-0.450‰。重要的是，这些源的Δ17O值变化不大，因为它们是由质量无关的分馏过程决定的，不受Δ17O和δ18O值变化的影响。本项目将研究圈养动物，评估外源摄水量和代谢率的变化对Δ17OBW的影响。此外，在温度和降水的自然波动期间，将跟踪野生动物Δ17OBW值的纵向变化，这将影响它们的水平衡和代谢。这些Δ17OBW结果将与涉及δ18O建模和双标记水技术的传统方法进行比较。最后，Δ17O测量的分析方法将针对生物样本（包括有机组织）进行优化，这将降低该方法的成本和所需的专业知识，并促进其被生态生理和生态研究界采用。对Δ17OBW的新理解可用于研究动物对地球许多地区正在发生的向更热、更干燥气候转变的反应，并评估野外代谢率的定性变化，这是一个关键但众所周知难以测量的变量。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

All animals require water and energy to stay alive. Water is obtained from a variety of external sources (e.g., rivers, lakes, food), and internally as a byproduct of the chemical reactions that occur during the breakdown of food. Energy is obtained from food and is processed at a rate that limits everything an animal does: foraging and hunting, dispersing, competing with other individuals, reproducing, and other activities. Thus, assessing the contributions of different water sources to animal intake, and assessing animal rates of energy use, are critically important for understanding all aspects of animal function. However, measuring water inputs and energy use of wild animals is prohibitively difficult. Methods to date require capturing and handling animals at least two different times, or sampling every potential water source in a given habitat. These tasks are frequently impossible in the field, severely limiting the study of these important variables. To overcome this challenge, this project will develop the use of Δ17O measurements from a single sample of animal body water (Δ17OBW) to quantify the fractional contributions from external and internal sources to the body water pool of an animal. In addition, the fractional contribution of internal water will provide an index of the rate of energy use, because this internal water is created at a rate that directly reflects the rate of energy processing. The understanding of Δ17OBW from this project will create new opportunities to incorporate animal function into a broad variety of studies.The value of Δ17O reflects deviations in the relationship between δ17O and δ18O. For most animals, two sources provide 80–99% of the input into their body water: 1) drinking/food water that is ultimately sourced from precipitation and 2) metabolic water. These two inputs have relatively constant and strikingly different Δ17O values: drinking/food water Δ17O ≈ 0.030‰ and metabolic water Δ17O ≈ -0.450‰. Importantly, the Δ17O values of these sources exhibit little variation because they are determined by mass-independent fractionation processes that are not affected by changes in δ17O and δ18O values. This project will study animals in captivity to evaluate the influence of changes in exogenous water intake and metabolic rate on Δ17OBW. In addition, longitudinal changes in the Δ17OBW values of wild animals will be tracked during natural fluctuations in temperature and precipitation that will influence their water balance and metabolism. These Δ17OBW results will be compared to traditional approaches involving δ18O modeling and the doubly-labeled water technique. Finally, the analytical methods of Δ17O measurements will be optimized for biological samples, including organic tissues, which will reduce the costs and required expertise of this approach and promote its adoption by the ecophysiological and ecological research communities. The new understanding of Δ17OBW can be used to study animal responses to the shift towards a hotter, drier climate that is occurring in many regions of the planet, and to assess qualitative variation in field metabolic rate, a critical but notoriously difficult-to-measure variable.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.