Dietary Protein Content and Digestibility Influences Discrimination of Amino Acid Nitrogen Isotope Values in a Terrestrial Omnivorous Mammal

Authors

John P. Whiteman, Old Dominion UniversityFollow
Mauriel Rodriguez Curras
Kelli L. Feeser
Seth D. Newsome

Document Type

Article

Publication Date

2021

DOI

10.1002/rcm.9073

Publication Title

Rapid Communications in Mass Spectrometry

Volume

35

Issue

11

Pages

1-25

Abstract

RATIONALE: Ecologists increasingly determine the δ¹⁵N values of amino acids (AA) in animal tissue; "source" AA typically exhibit minor variation between diet and consumer, while "trophic" AA have increased δ¹⁵N values in consumers. Thus, trophic-source δ¹⁵N offsets (i.e., Δ¹⁵N_T-S) reflect trophic position in a food web. However, even minor variation in δ¹⁵N_{source AA} values may influence the magnitude of offset that represents a trophic step, known as the trophic discrimination factor (i.e., TDF_T-S). Diet digestibility and protein content can influence the δ¹⁵N values of bulk animal tissue, but the effects on AA Δ¹⁵N_T-S and TDF_T-S in mammals are unknown.

METHODS: We fed captive mice (Mus musculus) either (A) a low-fat, high-fiber diet with low, intermediate, or high protein; or (B) a high-fat, low-fiber diet with low or intermediate protein. Mouse muscle and dietary protein were analyzed for bulk tissue δ¹⁵N using elemental analyzer-isotope ratio mass spectrometry (EA-IRMS), and were also hydrolyzed into free AA that were analyzed for δ¹⁵N using EA-IRMS.

RESULTS: As dietary protein increased, Δ¹⁵N_{Consumer-Diet} slightly declined for bulk muscle tissue in both experiments, increased for AA in the low-fat, high-fiber diet (A), and remained the same or decreased for AA in the high-fat, low-fiber diet (B). The effects of dietary protein on Δ¹⁵ N_T-S and on TDF_T-S varied by AA but were consistent between variables.

CONCLUSIONS: Diets were less digestible and included more protein in Experiment A than in Experiment B. As a result, the mice in Experiment A probably oxidized more AA, resulting in greater Δ¹⁵ N_{Consumer-Diet} values. However, the similar responses of Δ¹⁵ N_T-S and of TDF_T-S to diet variation suggest that if diet samples are available, Δ¹⁵ N_T-S accurately tracks trophic position. If diet samples are not available, the patterns presented here provide a basis to interpret Δ¹⁵ N_T-S values The trophic-source offset of Pro-Lys did not vary across diets, and therefore may be more reliable for omnivores than other offsets (e.g., Glu-Phe).

Rights

Copyright © 2021 John Wiley & Sons, Inc.

This is the peer reviewed version of the following article:

Whiteman, J. P., Rodriguez Curras, M., Feeser, K. L., & Newsome, S. D. (2021). Dietary protein content and digestibility influences discrimination of amino acid nitrogen isotope values in a terrestrial omnivorous mammal. Rapid Communications in Mass Spectrometry, 1-25, Article e9073. https://doi.org/10.1002/rcm.9073

The final published version is here https://doi.org/10.1002/rcm.9073. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.

Original Publication Citation

Whiteman, J. P., Rodriguez Curras, M., Feeser, K. L., & Newsome, S. D. (2021). Dietary protein content and digestibility influences discrimination of amino acid nitrogen isotope values in a terrestrial omnivorous mammal. Rapid Communications in Mass Spectrometry, 1-25, Article e9073. https://doi.org/10.1002/rcm.9073

Repository Citation

Whiteman, John P.; Curras, Mauriel Rodriguez; Feeser, Kelli L.; and Newsome, Seth D., "Dietary Protein Content and Digestibility Influences Discrimination of Amino Acid Nitrogen Isotope Values in a Terrestrial Omnivorous Mammal" (2021). Biological Sciences Faculty Publications. 442.
https://digitalcommons.odu.edu/biology_fac_pubs/442