Methods in Ecology and Evolution
1. Lipid-rich animal tissues have low δ13C values, which can lead to inaccurate ecological inferences. Chemical lipid extraction (LE) or correction models account for this depletion, but the need for LE or correction is tissue- and species-specific. Also, LE can alter δ15N values, increasing labour and costs because bulk samples must be analysed for δ15N values separately. 2. We studied the effects of LE on δ13C and δ15N values in liver, muscle and skin of common bottlenose dolphins Tursiops truncatus and West Indian manatees Trichechus manatus, two ecologically important species that occupy different trophic levels. We fit lipid-correction models to each species. We also performed a meta-analysis to more broadly determine the effects of LE across taxa, tissues and trophic groups (carnivores, omnivores and herbivores) and to fit lipid-correction models to different taxonomic and trophic groups. 3. Lipid extraction increased the δ13C values in dolphin tissues but had little effect on manatee tissues and no effect on the δ15N values in either species. A mass balance lipid-correction model best fit the data from all dolphin tissues, and a linear model best fit data for manatee liver while null models best fit data from manatee muscle and skin. Across 128 terrestrial and aquatic species, the effects of LE varied among tissues and were lower for herbivores compared to carnivores. The best-fitting lipid-correction models varied among tissue, taxa and trophic groups. Finally, the δ15N values from muscle and liver were affected by LE. 4. Our results strengthen the growing body of evidence that the need for LE is tissue- and species-specific, without a reliable C:N ratio predictive threshold. The prediction errors of lipid-correction models generally decreased with taxonomic and trophic specificity. The smaller effects of LE in herbivores may be due to differences in diet composition or the physiology of lipid synthesis in members of this trophic group. These results suggest that researchers should use the most species-, tissue- and trophic group-specific information on LE available and, if not available, perform LE on a subset of samples prior to analysis to determine effects.
Cloyed, Carl S.; DaCosta, Kayla P.; Hodanbosi, Matthew R.; and Carmichael, Ruth H., "Effects of Lipid Extraction on δ13C and δ15N Values and Use of Lipid-Correction Models Across Tissues, Taxa and Trophic Groups" (2020). School of Marine and Environmental Sciences Faculty and Staff Publications and Presentations. 13.