The Ecological Applications of Δ¹⁷O: Validating a Novel Technique for Assessing Animal Metabolism and Water Intake

Author

Zachary Taylor Steele, Old Dominion UniversityFollow

Date of Award

Summer 2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

Program/Concentration

Ecological Sciences

Committee Director

John P. Whiteman

Committee Member

David T. Gauthier

Committee Member

Margaret R. Mulholland

Committee Member

Ian K. Bartol

Committee Member

Bryan M. Kluever

Abstract

Animals obtain water via different processes such as drinking, consuming food, and through metabolic processes like at the end of the electron transport chain when atmospheric oxygen is combined with hydrogen to form ‘cytochrome oxidase water’. Assessing animal water flux and metabolism has mainly been conducted via stable isotope analysis (SIA) of biological samples using hydrogen (²H) and oxygen isotopes (¹⁶O, ¹⁷O, and ¹⁸O; Δ¹⁷O), typically using enriched isotope tracers. However, natural abundance isotope modeling offers an approach for conducting SIA of biological samples that differs because it relies on the unique, naturally occurring isotope values of different oxygen fluxes. For example, freshwater drinking sources and cytochrome oxidase water have distinct Δ¹⁷O values of 0–40 per meg (0–0.040 ‰) and ~ -441 per meg, respectively. Although promising, this approach: 1) has mainly been limited to solid biological samples (e.g., bone); 2) lacks comparisons of model predictions with measured oxygen fluxes; and 3) lacks ecophysiological adjustments to models that reflect important realistic variation. To address these issues, I refined an approach to distilling blood samples to obtain a body water sample for SIA via cavity ring-down spectroscopy (CRDS). Then, I conducted a validation study by measuring oxygen fluxes of captive deer mice (Peromyscus maniculatus) to predict Δ¹⁷O_BW (Δ¹⁷O of body water) for comparison with measured Δ¹⁷O_BW. Lastly, I conducted a longitudinal study of mule deer (Odocoileus hemionus hemionus) in two regions of Utah, differing in environmental water availability, to demonstrate the potential of this technique to wildlife ecology. My findings indicate that distilled blood samples analyzed via CRDS provide consistent Δ¹⁷O measurements within ± 15 per meg. In captive deer mice, Δ¹⁷O_BW predictions were accurate: 61 % of model predictions were < 15 per meg of measured Δ¹⁷O_BW. Lastly, I found that mule deer had variable reliance on freshwater drinking sources, with some individuals not drinking at all. Importantly, deer Δ¹⁷O_BW predictions were improved by adjusting model parameters based on δ²H and normalized difference vegetation index, reflecting vegetation availability and consumption. Overall, my findings indicate that Δ¹⁷O_BW modeling is a promising technique with applications to wildlife ecology and conservation.

Rights

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DOI

10.25777/xa4r-p516

ISBN

9798384444275

Recommended Citation

Steele, Zachary T.. "The Ecological Applications of Δ¹⁷O: Validating a Novel Technique for Assessing Animal Metabolism and Water Intake" (2024). Doctor of Philosophy (PhD), Dissertation, Biological Sciences, Old Dominion University, DOI: 10.25777/xa4r-p516
https://digitalcommons.odu.edu/biology_etds/398

ORCID

0000-0003-3448-8377