Effects of Lipid Extraction on δ13C and δ15N Values in Seabird Muscle, Liver and Feathers (original) (raw)
Related papers
Methods in Ecology and Evolution, 2010
1. Lipids are more depleted in 13C 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 δ13C 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 (δ13C) 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 δ13C 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 δ13C values were within 0·5‰ of the observed values for 73% of the muscle samples, but only for 27% of the egg samples.5. Based on our results, we recommend model based normalization of δ13C values as an economic way to deal with varying lipid contents in muscle samples of mammals and birds. For egg samples, on the contrary, model based predictions had large errors. Therefore, we recommend chemical lipid extraction in order to estimate lipid-free δ13C values for egg content.
Lipid extraction effects on stable isotope values (δ13C and δ15N) of elasmobranch muscle tissue
Journal of Experimental Marine Biology and Ecology, 2012
Given the known effect of lipid content on δ 13 C values and the potential effect of urea on δ 15 N values, examining the effects of lipid extraction, which can potentially extract both, is of particular importance for elasmobranch isotope ecology. Through analysing paired δ 13 C, total %C, δ 15 N, total %N and C:N values of non-lipid extracted (BULK) and lipid extracted (LE) muscle samples from twenty-one elasmobranch species, we assessed whether lipid extraction was required: (i) to remove lipids given reported low lipid content and, (ii) to determine if δ 15 N values were affected and whether this relates to the retention of isotopically light urea by elasmobranchs. The mean (±SD) δ 13 C values of eight out of twenty-one species significantly increased following lipid extraction with two species, the Greenland (Somniosus microcephalus) and whale (Rhincodon typus) shark, showing a marked increase (5.0± 0.4‰ and 3.3‰, respectively). The mean (±SD) and maximum increase in δ 13 C values were 0.6 ±1.2‰ and 5.9‰, respectively. For δ 15 N data, thirteen species showed a significant increase following lipid extraction and a concomitant reduction in total percent nitrogen (%N). The C:N ratio for these species also increased from unexpectedly low values of b 3.0 to~3.0, the value expected for pure protein. The mean and maximum observed increase in δ 15 N values were 0.6±0.6‰ and 2.3‰, respectively. There was no effect of increasing animal size on δ 13 C and δ 15 N difference (LE-BULK) for the two species examined. Field sampled animals (sampled immediately upon capture in the marine environment) showed a greater δ 15 N difference than animals sampled in the laboratory (sampled several hours after capture in the marine environment) (1.0± 0.5‰ and 0.4± 0.4‰ respectively), while estuarine sampled animals (sampled immediately) showed the smallest difference (0.1± 0.6‰). The δ 13 C data demonstrate that lipid extraction is required to remove lipids from elasmobranch muscle tissue given both intra-and inter-species variability. In addition, the increase in δ 15 N values, decrease in %N and increase in C:N ratio indicate that lipid extraction is removing soluble urea. Given lower δ 15 N diet-tissue discrimination factors for large marine predators, removal of urea is required to elucidate accurate trophic position estimates and relative food web position of elasmobranchs and for diet reconstruction. It is recommended that investigators undertake lipid extraction trials on elasmobranch muscle tissue to determine effects on δ 13 C and δ 15 N values on a species-by-species basis.
Lipid normalization and stable isotope discrimination in Pacific walrus tissues
Scientific Reports, 2019
Analysis of stable carbon and nitrogen isotope values (δ13C and δ15N) of animal tissues can provide important information about diet, physiology, and movements. Interpretation of δ13C and δ15N values, however, is influenced by factors such as sample lipid content, tissue-specific isotope discrimination, and tissue turnover rates, which are typically species- and tissue-specific. In this study, we generated lipid normalization models for δ13C and investigated the effects of chemical lipid extractions on δ13C and δ15N in Pacific walrus (Odobenus rosmarus divergens) muscle, liver, and skin. We also evaluated tissue-specific isotope discrimination in walrus muscle, liver, skin, and bone collagen. Mean δ13Clipid-free of skin and bone collagen were similar, as were mean δ15N of muscle and liver. All other tissues differed significantly for both isotopes. Differences in δ13Clipid-free and δ15N among tissues agreed with published estimates of marine mammal tissue-specific isotope discrimina...
Rapid communications in mass spectrometry : RCM, 2012
Stable isotope values (d 13 C and d 15 N) of darted skin and blubber biopsies can shed light on habitat use and diet of cetaceans, which are otherwise difficult to study. Non-dietary factors affect isotopic variability, chiefly the depletion of 13 C due to the presence of 12 C-rich lipids. The efficacy of post hoc lipid-correction models (normalization) must be tested. METHODS: For tissues with high natural lipid content (e.g., whale skin and blubber), chemical lipid extraction or normalization is necessary. C:N ratios, d 13 C values and d 15 N values were determined for duplicate control and lipid-extracted skin and blubber of fin (Balaenoptera physalus), humpback (Megaptera novaeangliae) and minke whales (B. acutorostrata) by continuous-flow elemental analysis isotope ratio mass spectrometry (CF-EA-IRMS). Six different normalization models were tested to correct d 13 C values for the presence of lipids. RESULTS: Following lipid extraction, significant increases in d 13 C values were observed for both tissues in the three species. Significant increases were also found for d 15 N values in minke whale skin and fin whale blubber. In fin whale skin, the d 15 N values decreased, with no change observed in humpback whale skin. Non-linear models generally out-performed linear models and the suitability of models varied by species and tissue, indicating the need for high model specificity, even among these closely related taxa. CONCLUSIONS: Given the poor predictive power of the models to estimate lipid-free d 13 C values, and the unpredictable changes in d 15 N values due to lipid-extraction, we recommend against arithmetical normalization in accounting for lipid effects on d 13 C values for balaenopterid skin or blubber samples. Rather, we recommend that duplicate analysis of lipidextracted (d 13 C values) and non-treated tissues (d 15 N values) be used.
Journal of Experimental Marine Biology and Ecology, 2017
Stable isotope analysis (SIA) of carbon and nitrogen is now a common tool to investigate trophic relationships and food-web structure in aquatic ecosystems. However, species-specific and tissue-specific lipid content sometimes hinders the correct interpretation of δ 13 C and δ 15 N values because lipids are 13 C-depleted with respect to proteins, and thus tissue lipid extraction is generally invoked. We assessed the effects of lipid extraction on δ 13 C and δ 15 N compositions and C:N ratios of muscle, liver (or hepatopancreas) and gonads of three common Mediterranean deep-sea species with different locomotory activity, buoyancy mechanisms and feeding modes: the benthic-feeder shrimp Aristeus antennatus, the nektobenthic-feeder shark Galeus melastomus and the pelagicfeeder fish Micromesistius poutassou to evaluate both the effect of lipid extraction on SIA data and the validity of δ 13 C lipid correction models. Results showed that the effect of lipid extraction is not unique but some common patterns can be identified. Lipid extraction resulted in increased δ 15 N values in the liver and the muscle and in decreased δ 15 N values in the gonads, in increased δ 13 C values in all the tissues of the three species, except in the hepatopancreas of A. antennatus, and in decreased C:N ratios. The magnitude of the changes was species-and tissue-specific. We assessed the validity of δ 13 C bulk correction equations for lipid content in muscle and liver tissues available from literature in the species from this study. Such equations provided corrected δ 13 C values equivalent to those obtained through lipid extraction when applied to a species with similar characteristics (i.e., taxon, behavior, etc.) to those for which the equations were designed. Our results for muscle tissue showed that not one of the equations tested was valid for the deep-sea shark G. melastomus, and we propose a species-specific model with a fairly feasible model efficiency. Besides, tissue-specific equations for liver in G. melastomus provided non-significant differences between δ 13 C corrected and δ 13 C lipid free values, but all model efficiencies were fairly low. Thus, lipid extraction trials on elasmobranch muscle and liver tissue to determine effects on δ 13 C and δ 15 N values on a species-by-species basis are recommended. Our research together with a comprehensive literature review on this topic, highlights that there is no accepted or mandated standard of treatment for lipids when using stable isotope analyses.
Rapid Communications in Mass Spectrometry
RationaleThe coupled analysis of δ13C and δ15N stable isotope values of blubber and skin biopsy samples is widely used to study the diet of free‐ranging cetaceans. Differences in the lipid content of these tissues can affect isotopic variability because lipids are depleted in 13C, reducing the bulk tissue 13C/12C. This variability in carbon isotope values can be accounted for either by chemically extracting lipids from the tissue or by using mathematical lipid normalisation models.MethodsThis study examines (a) the effects of chemical lipid extraction on δ13C and δ15N values in blubber and skin of southern hemisphere humpback whales, (b) whether chemical lipid extraction is more favourable than mathematical lipid correction and (c) which of the two tissues is more appropriate for dietary studies. Strategic comparisons were made between chemical lipid extraction and mathematical lipid correction and between blubber and skin tissue δ13C and δ15N values, as well as C:N ratios. Six exis...
2019
Using stable isotope measurements of inert tissues to determine origins and migratory patterns is well established. However, isotopically determining nutritional origins of lipids, the primary fuel of migration, has not been attempted. I explored isotopic links between diet and stored lipids in captive White-throated Sparrows (Zonotrichia albicollis) and true armyworm moths (Mythimna unipuncta) using δ 13 C and δ 2 H measurements. Isotopic discrimination between body lipids and diet was established as linear calibration functions. Isotopic uptake following a diet switch in moths was used to trace lipid accumulation over time. Isotopic correlations between breath metabolic by-products of fed and fasted sparrows were explored as indicators of lipid use. This study established isotopic (δ 13 C, δ 2 H) linkages between diet and stored lipids for migratory insects and passerines and advocates the use stable isotopes in lipids as a tool to evaluate nutrient origins and allocation strategies in a variety of migratory species.
Marine Ecology Progress Series, 2010
Accurately predicting errors related to preservation, lipid extraction, and lipid normalization on chemical tracers would enable the use of archived samples in long-term studies of trophic ecology and habitat use of aquatic species. We determined whether stable carbon and nitrogen isotope ratios and concentrations of 14 trace elements can be accurately predicted from dimethyl sulfoxide (DMSO)-preserved mammal skin, which would provide equivalent estimates to that from unpreserved tissue. We tested 3 lipid-correction approaches for applicability to cetacean skin, a largely unexplored taxon and tissue, and provide a model for evaluating impacts of errors from lipid extraction or normalization on diet composition estimated using isotopic mixing models. DMSO had unpredictable effects on trace element concentrations, rendering DMSO-preserved samples inefficient for retrospective studies. However, lipid extraction and DMSO preservation resulted in predictable and similar, although not identical, effects on isotopic signatures across 4 cetacean species with different skin structure and thickness, making correction for these effects a potentially viable alternative to lipid and DMSO extraction. Generally, lipid-normalization models were reliable when applied to cetacean skin, as errors were similar to those from other species or tissues. Because model fit generally improved with data specificity, developing tissue-and species-specific parameters and equations is probably more important than model choice, although the mass-balance model was considered the most robust across aquatic vertebrates and tissues. The effects of errors associated with the various treatments and lipid normalization on isotopic mixing results increased as the isotopic distance among prey sources decreased, suggesting that empirical corrections as an alternative to δ 13 C determination from lipid-extracted duplicate samples need to be evaluated a priori relative to study objectives and anticipated results.