Influence of lipids on stable isotope ratios in mammal hair: highlighting the importance of validation

• Published in: Ecosphere
• Main Authors: Rioux, Ève, Pelletier, Fanie, St‐Laurent, Martin‐Hugues
• Other Authors: Natural Sciences and Engineering Research Council of Canada, Environment Canada
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2019
• Subjects: Canada; Rangifer tarandus
• Online Access: http://dx.doi.org/10.1002/ecs2.2723; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fecs2.2723; https://onlinelibrary.wiley.com/doi/pdf/10.1002/ecs2.2723; https://onlinelibrary.wiley.com/doi/full-xml/10.1002/ecs2.2723; https://esajournals.onlinelibrary.wiley.com/doi/pdf/10.1002/ecs2.2723

Abstract Carbon (δ 13 C) and nitrogen (δ 15 N) stable isotope ratios are increasingly used in ecological studies to evaluate diet composition and trophic relationships. However, lipids may influence stable isotope ratios due to the depletion of 13 C in adipose tissues relative to proteins and carbohydrates. δ 13 C values can be corrected by lipid extraction or normalization models. The aims of our study were to evaluate the effects of lipid extraction on stable isotope ratios in a terrestrial mammal, the caribou ( Rangifer tarandus caribou ), and to propose relevant lipid normalization models that are method‐ and tissue‐specific for δ 13 C values. We also evaluated whether four δ 13 C lipid normalization and correction models proposed in the literature were applicable to our study species. Stable isotope ratios were obtained for hair, plasma, and red blood cell samples of 44 caribou in the Gaspésie National Park (Québec, Canada). The effects of lipid extraction on stable isotope ratios were tested using a paired t ‐test. A simple linear model was used to correct for the effects of lipid extraction and to assess its performance compared to that of published equations. Lipid content significantly influenced δ 13 C values in caribou hair. The four lipid normalization equations commonly used in the literature did not accurately predict δ 13 C lipid‐free values of caribou hair. Based on our results, we recommend controlling systematically for lipids in terrestrial systems and analyzing δ 13 C (lipid‐free) and δ 15 N (bulk) from two separate aliquots to reach a greater precision. We also recommend controlling for lipids in hair tissue. If not possible, we recommend using a lipid normalization model that is tissue‐, method‐, and species‐specific or applying a model that has been previously validated for the tissue and species of interest.