Validating a novel capability of assessing pathways of animal water gain and loss

Understanding variations in the routes by which wild animals gain and lose
water is challenging, and common methods require longitudinal sampling,
which can be prohibitive. However, a new approach uses Δ′17OBW (Δ′17O of
animal body water), calculated from measurements of δ′17O and δ′18O in a
single sample, as a natural tracer of water flux. Δ′17OBW is promising but
its relationship to organismal variables has not been validated. Here, we
continuously measured oxygen influxes and effluxes of captive deer mice
(Peromyscus maniculatus) and manipulated their water intake and metabolic
rate. We used these oxygen flux data to predict Δ′17OBW for the mice and
compared these model predictions to Δ′17OBW measured in blood plasma
samples. As expected, Δ′17OBW positively correlated with drinking water
intake and negatively correlated with metabolic rate. All predicted
Δ′17OBW (based on measured oxygen fluxes) values differed from measured
Δ′17OBW values by < 30 per meg (mean absolute difference: 11 ± 9
per meg), suggesting high accuracy for this modeling approach because
studies currently report a range of 300 per meg for Δ′17OBW among mammals,
birds, and fish.

厘清野生动物水分获取与流失途径的差异颇具挑战，而主流方法需开展纵向采样，此类要求往往成本高昂、难以实施。不过，一种新兴分析方法可通过单一样本中δ′17O与δ′18O的测定值，计算得到Δ′17O_BW（动物体水的Δ′17O值），以此作为水分通量的天然示踪剂。Δ′17O_BW虽颇具应用前景，但目前尚未验证其与生物体生理变量间的关联关系。本研究针对圈养鹿鼠（Peromyscus maniculatus）持续测定其氧气摄入与排出量，并对其饮水量与代谢速率进行调控。我们利用上述氧气通量数据预测受试鹿鼠的Δ′17O_BW，并将模型预测值与血浆样本中实测的Δ′17O_BW进行对比。实验结果符合预期：Δ′17O_BW与饮水量呈正相关，与代谢速率呈负相关。所有基于实测氧气通量得到的Δ′17O_BW预测值，与实测Δ′17O_BW值的差值均小于30 per meg（平均绝对差值为11±9 per meg），这表明该建模方法精度较高——当前已有研究报道，哺乳类、鸟类与鱼类的Δ′17O_BW差值范围可达300 per meg。