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., Δ15NT-S) reflect trophic position in a food web. However, even minor variation in δ15Nsource AA values may influence the magnitude of offset that represents a trophic step, known as the trophic discrimination factor (i.e., TDFT-S). Diet digestibility and protein content can influence the δ15N values of bulk animal tissue, but the effects on AA Δ15NT-S and TDFT-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, Δ15NConsumer-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 NT-S and on TDFT-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 NConsumer-Diet values. However, the similar responses of Δ15 NT-S and of TDFT-S to diet variation suggest that if diet samples are available, Δ15 NT-S accurately tracks trophic position. If diet samples are not available, the patterns presented here provide a basis to interpret Δ15 NT-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).

Comments

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

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