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才能生存。水来自各种外部来源(如河流、湖泊、食物)，内部则是食物分解过程中发生的化学反应的副产品。能量是从食物中获得的，其处理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入量的贡献，以及评估动物的能量使用率，对于理解动物功能的各个方面至关重要。然而，测量野生动物的水输入和能量使用是极其困难的。迄今为止的方法需要至少捕获和处理两次不同的动物，或者对给定栖息地的每个潜在水源进行采样。这些任务在现场往往是不可能的，严重限制了对这些重要变量的研究。为了克服这一挑战，该项目将开发使用单一动物体水样本的Δ17O测量(Δ17OBW)，以量化外部和内部来源对动物体内水池的部分贡献。此外，内部水的部分贡献将提供能源使用率的指数，因为内部水是以直接反映能量处理速度的速率产生的。通过这个项目对Δ17OBW的了解将创造新的机会，将动物功能融入到广泛的研究中。Δ17O的价值反映了δ17O和δ18O之间关系的偏差。对于大多数动物来说，有两个来源提供了它们体内80%-99%的水：1)最终来自降水的饮用水/食物水和2)代谢水。这两个输入具有相对恒定且显著不同的Δ17O值：饮用水/食物水Δ17O≈0.030‰和代谢水Δ17O≈-0.450‰。重要的是，这些源的Δ17O值几乎没有变化，因为它们是由与质量无关的分馏过程决定的，不受δ17O和δ18O值变化的影响。本项目将对圈养动物进行研究，以评估外源水分摄入量和代谢率的变化对Δ170BW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Δ170BW值的纵向变化，这将影响它们的水分平衡和新陈代谢。这些Δ170BW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包括有机组织在内的生物样本进行优化，这将降低这种方法的成本和所需的专业知识，并促进生态生理和生态研究团体采用这种方法。对Δ170BW的新理解可以用来研究动物对地球许多地区正在发生的更热、更干燥的气候变化的反应，并评估野外代谢率的质量变化，这是一个关键但众所周知的难以测量的变量。这一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智力优势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.