Lipid normalization and stable isotope discrimination in Pacific walrus tissues

Nicole Misarti,Casey T Clark,Lara Horstmann

doi:10.1038/s41598-019-42095-z

Nicole Misarti, Casey T Clark + Show 1 more

Open Access

https://doi.org/10.1038/s41598-019-42095-z

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Journal: Scientific Reports	Publication Date: Apr 10, 2019
Citations: 13	License type: open-access

Affiliation: University of Alaska Fairbanks

Abstract

Analysis of stable carbon and nitrogen isotope values (δ13C and δ15N) of animal tissues can provide important information about diet, physiology, and movements. Interpretation of δ13C and δ15N values, however, is influenced by factors such as sample lipid content, tissue-specific isotope discrimination, and tissue turnover rates, which are typically species- and tissue-specific. In this study, we generated lipid normalization models for δ13C and investigated the effects of chemical lipid extractions on δ13C and δ15N in Pacific walrus (Odobenus rosmarus divergens) muscle, liver, and skin. We also evaluated tissue-specific isotope discrimination in walrus muscle, liver, skin, and bone collagen. Mean δ13Clipid-free of skin and bone collagen were similar, as were mean δ15N of muscle and liver. All other tissues differed significantly for both isotopes. Differences in δ13Clipid-free and δ15N among tissues agreed with published estimates of marine mammal tissue-specific isotope discrimination factors, with the exception of skin. The results of this work will allow researchers to gain a clearer understanding of walrus diet and the structure of Arctic food webs, while also making it possible to directly compare the results of contemporary walrus isotope research with those of historic and paleoecological studies.

Highlights

Analysis of stable carbon and nitrogen isotope values (δ13C and δ15N) of animal tissues can provide important information about diet, physiology, and movements
Paired t-tests indicated that chemical lipid extraction significantly increased the δ13C values of walrus liver and skin, but walrus muscle δ13C was unchanged
Lipid-normalization models were parameterized for walrus muscle, liver, and skin, but not for bone collagen, which is a purified protein

Summary

Introduction

Analysis of stable carbon and nitrogen isotope values (δ13C and δ15N) of animal tissues can provide important information about diet, physiology, and movements. Carbon and nitrogen stable isotope values (δ13C and δ15N) are useful when evaluating animal diet and trophic position[3]. Chemical lipid extraction is one way to account for differences in sample lipid content In this process, lipids are typically removed using polar organic solvents (often a mixture of chloroform and methanol13,14) and stable isotope values of the lipid-free sample are measured. Lipids are typically removed using polar organic solvents (often a mixture of chloroform and methanol13,14) and stable isotope values of the lipid-free sample are measured This process allows for direct instrumental measurement of the lipid-free sample (δ13Clipid-free), but requires more time and effort. (δ15Nbulk) and the δ13Clipid-free can be interpreted together; this approach increases the time and effort required for sample preparation and doubles the analytical cost

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