Effects of Lipid Extraction on δ13C and δ15N Values in Seabird Muscle, Liver and Feathers (original) (raw)

We determined whether lipid extraction of seabird muscle, liver and feathers is required for δ 13 C and δ 15 N analysis, based on a study of Barau's Petrels (Pterodroma baraui) and Whitetailed Tropicbirds (Phaethon lepturus). Samples were analyzed for stable isotopes before and after lipid removal. Lipid-free muscle and liver were significantly enriched in 13 C compared to those containing lipids (0.52 ‰ and 0.61 ‰ mean differences in δ 13 C respectively) implying that lipids should be extracted from these tissues to avoid effects of uncontrolled differential lipid content. However lipid extraction also slightly increased muscle δ 15 N values in tropicbirds. Researchers should thus run samples separately for δ 13 C and δ 15 N analysis, extracting lipids only in aliquots in which δ 13 C is measured, or apply arithmetic δ 13 C normalization methods on non lipid-extracted samples. Predictive models developed from our data, inferring δ 13 C values of lipid-extracted material from δ 13 C values and C:N ratios of non lipid-extracted material are presented and compared to five normalization methods taken from literature. Our models showed the best prediction efficiencies followed by that developed by McConnaughey and McRoy (1979). In feathers, no difference in stable isotopic measurements were noted between aliquots treated with sodium hydroxide or 2:1 chloroform:methanol. Both protocols seem suitable for preparing feather samples for isotopic analysis.