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

This dataset and model can be accessed using the following link: [https://github.com/ZacharyTSteele/RSOS_Datafiles](https://github.com/ZacharyTSteele/RSOS_Datafiles)

We generated a model for estimating δ17OBW, δ18OBW, and Δ′17OBW by modifying and adjusting the model and code developed by Hu et al. (2023). The Hu et al. (2023) model was derived from the δ18OBW model developed by Kohn (1996), modifying this model to enable calculation of Δ′17OBW. For specific details of the differences between our model and the Hu et al. (2023), please see the methods section of the manuscript.

The model is included in the R file 'E17O_Isotope_Model'. This model estimates δ17OBW, δ18OBW, and Δ′17OBW using the following 32 parameters (in order of appearance in R code):

Timeframe of turnover (Days)

Animal body mass (kg)

Fecal H2O content (%)

Oxygen utilization fraction

Z-value (‰)

Animal body temperature (K)

Animal...,