Effects of Lipid Extraction and Lipid Normalization on Stable Carbon and Nitrogen Isotope Ratios in Double-Crested Cormorants: Implications for Food Web Studies

Toothed whales in the northwestern Mediterranean: Insight into their feeding ecology using chemical tracers

“…Therefore, we applied a lipid normalization equation (McConnaughey and McRoy, 1979), adapted by Post et al (2007) for aquatic animals: Post et al (2007) recommend the use of a lipid normalization equation when C:N > 3.5, which corresponds to a lipid content >5% in samples. However, other authors also warn that such an equation could lead to bias if the lipid content is too high, for example, C:N > 6.5 in cormorants (Doucette et al, 2010), C:N > 7 in zooplankton (Smyntek et al, 2007) or C:N > 8 in deep-sea fish (Hoffman and Sutton, 2010). The majority of our samples contain C:N between 3.4 and 4.4.…”

Accounting for the effects of lipids in stable isotope (δ13C and δ15N values) analysis of skin and blubber of balaenopterid whales

“…We advocate caution against retrospective correction for the effects of lipids on δ 13 C values in any tissues, before both species‐ and tissue‐specific normalization models have been tested. Furthermore, caution must be taken in comparing lipid‐normalization models where the lipid‐extraction techniques may differ between studies . Thus, duplicate measurement of lipid‐extracted and bulk δ 13 C and δ 15 N values, respectively, is recommended for the stable isotope analysis of skin and blubber in balaeonopterid whales.…”

“…There are several commonly used lipid‐extraction techniques using various solvents with a range of polarities. These techniques have the potential to solubilize amino acids to differing degrees, and the lipid‐extraction technique employed may thus have an effect on δ 15 N values …”

Effects of lipid and urea extraction on stable isotope values (δ13C and δ15N) of two batoids: A call for more species‐specific investigations

“…Polar solvents (e.g., choloform‐methanol) remove lipids from a sample but also remove nonlipid components (Dobush et al ), resulting in increases in δ 15 N values following LE (Sweeting et al ; Newsome et al ; Hussey et al ). Nonpolar solvents (e.g., petroleum ether) remove only structural lipids and fewer nonlipid compounds (Dobush et al ) and generally have a minimal effect on δ 15 N values (Doucette et al ; Kaufman et al ). Kim and Koch (), however, found that petroleum ether may also increase δ 15 N values, highlighting the need to understand how chemical treatments affect both δ 13 C and δ 15 N values for the specific tissue and taxa of interest.…”

“…Although LE methods are used to correct biases in δ 13 C due to differences in lipid content, δ 15 N may also be affected by LE (Murry et al 2006;Bodin et al 2007;Yurkowski et al 2015). The influence of LE on δ 15 N appears to vary depending on the extraction method (Doucette et al 2010). Polar solvents (e.g., choloform-methanol) remove lipids from a sample but also remove nonlipid components (Dobush et al 1985), resulting in increases in δ 15 N values following LE (Sweeting et al 2006;Newsome et al 2010;Hussey et al 2012b).…”