Stable isotope analysis: modelling lipid normalization for muscle and eggs from arctic mammals and birds

Abstract

2Chaire de recherche du Canada en conservation des e´cosyste`mes Nordiques et Centre d'e´tudes nordiques, Universite´du Que´bec aR imouski, Rimouski, QC G5L 3A1, Canada Summary 1. Lipids are more depleted in 13 C than proteins. Variable lipid contents in tissues affect therefore the measurements of stable carbon isotope ratios. Model based (also called mathematical) normalization has been suggested to correct d 13C values using the ratio of carbon to nitrogen (C ⁄ N) as a proxy for lipid content. This approach has not been thoroughly validated for terrestrial animals and it is not clear to what extent it is generally applicable or species ⁄ tissue specific. 2. Ratios of stable carbon isotopes (d 13 C) were obtained for muscle samples of 22 mainly terrestrial arctic mammal and bird species and for egg samples of 32 bird species from nine sites in the circumpolar Arctic. We used linear and nonlinear equations to model the difference in d 13C between samples from which lipids had been extracted chemically and bulk tissue samples. Models were compared on the basis of a model selection criterion (AIC) and of prediction error as estimated by cross-validation. 3. For muscle samples, a linear and a nonlinear equation performed equally well. The observed values were also well predicted by a previously published general equation for aquatic organisms. For egg samples, a nonlinear equation fitted separately to waterfowl and non waterfowl bird species fitted the data best. Prediction errors were, however, larger than for muscle samples. 4. The generality of the inferred normalization equations was assessed by applying them to a second data set from a similar ecosystem, but produced in the frame of another study. The predicted lean d

Nutritional stress and body condition in the Great Gray Owl (Strix nebulosa) during winter irruptive migrations

“…This suggests that lipid reserves in muscle of emaciated individuals were greatly reduced or exhausted. Overall, our results suggest that C/N of muscle may serve as a general indicator of nutritional condition in owls, with higher C/N indicative of greater lipid reserves (Okumura et al 2002;Post et al 2007;Ehrich et al 2010). This assay is more convenient and less invasive than other methods for quantifying nutritional condition, such as the measurement of bone marrow (Thouzeau et al 1997) or whole body homogenization followed by lipid extraction (Baduini et al 2001).…”

Monitoring Least Weasels after a Winter Peak of Lemmings in Taimyr: Body Condition, Diet and Habitat Use

“…In addition, samples of main prey were analyzed: muscle of Siberian and collared lemmings; egg content of passerines, waders, and geese; muscle samples of birds accidentally killed in snap traps or of dead chicks; and samples of fish (see Appendix 1 for species list and sample numbers). Preparation of muscle and egg samples was carried out as described by Ehrich et al (2010). Fur samples were washed in 2:1 chloroform-methanol to remove hair surface fat, dried, clipped to very small pieces with scissors, and weighed as for the muscle samples.…”

“…Isotope ratios were determined by combustion in a mass spectrometer at the Stable Isotopes in Nature Laboratory (SINLAB, Canadian Rivers Institute, Biology Department, University of New Brunswick, Fredericton, New Brunswick). Because the presence of lipids in samples can introduce a bias in δ 13 C, lipids were extracted chemically from some egg samples, and the rest of the samples were corrected for lipid content arithmetically, using the equations from Ehrich et al (2010).…”

Comparison of the stable carbon and nitrogen isotopic values of gill and white muscle tissue of fish

“…The lipid content of a tissue is influenced by several factors besides just the food source (e.g. species, tissue type, reproductive stage, gender, nutritional state), and a high or highly variable lipid content can therefore mask the dietary δ 13 C signal, thereby making inter-or intra species comparisons and diet reconstructions difficult (Ehrich et al, 2011;Hoffman and Sutton, 2010;Post et al, 2007). Indeed, it has been reported that the lipid content in gills may vary substantially between species and with growth conditions (Serrano et al, 2007;Vollaire et al, 2007).…”