Stable Isotope Turnover Research Articles

Isotopic turnover of carbon δ13C and nitrogen δ15N in the muscle tissue of tambaqui Colossoma macropomum juveniles fed diets containing different levels of digestible protein

The technique that uses natural stable isotopes rises as a safe alternative to evaluate the deposition of potential food constituents’ elements. Diets with distinct isotopic signatures can be used to measure turnover rates in all animal tissues, improving knowledge of metabolic processes in fish nutrition. The aim of the study was to evaluate the growth and turnover of stable isotopes of carbon and nitrogen in the muscle tissue of tambaqui juveniles fed diets containing different levels of digestible protein. A total of 1750 tambaquis were used (weight 6.53 ± 0.43 g and length 7.58 ± 0.18 cm) and distributed in 35 tanks (450 L), with a density of 50 fish per tank. Seven isoenergetic (3378.4 cal g−1) experimental diets were formulated with digestible protein (DP) levels of 14%, 17%, 20%, 23%, 26%, 29% and 32%. During 120 days of experiment, the animals grew over time in all treatments (P < 0.05); and in the evaluated periods, the protein levels of 29% and 32% stood out from the first biometric evaluations, at 30 days, with similar weight averages (P > 0.05) and higher than the averages in the other treatments (P < 0.05). The speed of isotopic changes in muscle tissue was influenced by the characteristics of the diets, and the rates of carbon and nitrogen turnover were more accelerated the higher the protein level. The trial period of 120 days was sufficient for the fish to reflect the isotopic composition of the diets in all treatments (P < 0.05). However, the isotopic contribution of the diet to the tissue as a function of time was different, with indices that reached about 96–97% in 49–63 days of feeding for the diets of 29% and 32% DP and indices of 81–82% for diets of 14% and 17% DP in the same period. The isotopic data analyzed by exponential equations and exploratory analysis showed the formation of three groups with homogeneous characteristics in response to the effects of protein levels: a grouping of diets with 14%, 17% and 20% DP (P > 0.05); another with intermediate levels (23% and 26%); and a third with the highest levels (29% and 32%). Thus, the diet containing 29% of digestible protein proved to be the most attractive for the productive performance of tambaqui juveniles in the growth phase studied.

Toxicity and Starvation Induce Major Trophic Isotope Variation in Daphnia Individuals: A Diet Switch Experiment Using Eight Phytoplankton Species of Differing Nutritional Quality.

Stable isotope values can express resource usage by organisms, but their precise interpretation is predicated using a controlled experiment-based validation process. Here, we develop a stable isotope tracking approach towards exploring resource shifts in a key primary consumer species Daphnia magna. We used a diet switch experiment and model fitting to quantify the stable carbon (δ13C) and nitrogen (δ15N) isotope turnover rates and discrimination factors for eight dietary sources of the plankton species that differ in their cellular organization (unicellular or filamentous), pigment and nutrient compositions (sterols and polyunsaturated fatty acids), and secondary metabolite production rates. We also conduct a starvation experiment. We evaluate nine tissue turnover models using Akaike's information criterion and estimate the repetitive trophic discrimination factors. Using the parameter estimates, we calculate the hourly stable isotope turnover rates. We report an exceedingly faster turnover value following dietary switching (72 to 96 h) and a measurable variation in trophic discrimination factors. The results show that toxic stress and the dietary quantity and quality induce trophic isotope variation in Daphnia individuals. This study provides insight into the physiological processes that underpin stable isotope patterns. We explicitly test multiple alternative dietary sources and fasting and discuss the parameters that are fundamental for field- and laboratory-based stable isotope studies.

Stable isotope differences of polar bears in the Southern Beaufort Sea and Chukchi Sea

AbstractThe life‐history, genetic, and habitat use differences between the 2 polar bear (Ursus maritimus) subpopulations in Alaska, USA, have been used to determine the geographic border separating them, but it has sparked a debate of the correct placement of the border for several years. Recently, the Southern Beaufort Sea (SBS) polar bear subpopulation has declined because of sea ice loss, while the Chukchi Sea (CS) subpopulation appears stable. To provide additional information about potential differences between the SBS and CS subpopulations, such as differences in prey sources, we used stable isotope analysis of carbon and nitrogen from bone collagen of polar bears in these 2 neighboring subpopulations. We analyzed polar bear bones from 112 individuals collected from 1954–2019. Our purpose was to determine if the SBS and CS subpopulations could be distinguished based on the stable isotope signatures of bone collagen. A difference &gt;1‰ in stable carbon isotope (δ13C) values suggests a change in carbon sources, such as nearshore to offshore, while a 3‰ change in stable nitrogen isotope (δ15N) values equates to a change of about 1 trophic level. Our study indicated a difference in δ13C values (P ≤ 0.001) but not δ15N values (P = 0.654) between the CS (−13.0 ± 0.3‰ and 22.0 ± 0.9‰, respectively) and SBS bears (−14.7 ± 1.3‰ and 22.2 ± 1.0‰, respectively). Our findings indicate that the 2 subpopulations are consuming similar high trophic level prey, while feeding in ecosystems with different δ13C baselines. We performed a logistic regression analysis using δ13C and δ15N values of the polar bears to predict their placement into these 2 subpopulations. Using Icy Cape, Alaska as the geographical boundary, the analysis correctly placed polar bears in their respective subpopulations 82% of the time. Overall accuracy of placement changed to 84% when using the current geographical boundary at Utqiaġvik, Alaska. We predicted samples collected from the Wainwright, Alaska region as 58% CS and 42% SBS polar bears. This suggests that the area between Wainwright and Icy Cape is a polar bear mixing zone that includes bears from both subpopulations. Bone collagen has a long‐term, potentially life‐long, stable isotope turnover rate, and our results could be used to determine the association of harvested polar bears to Alaska subpopulations, thus aiding in transboundary harvest quota management.

Stable isotope turnover rates and fractionation in captive California yellowtail (Seriola dorsalis): insights for application to field studies

Stable isotope analysis (SIA) measurements from long-term captivity studies provide required parameters for interpretation of consumer SIA data. We raised young-of-the-year (14–19 cm) California yellowtail (Seriola dorsalis) on a low δ15N and δ13C diet (pellet aquaculture feed) for 525 days, then switched to a high δ15N and δ13C diet (mackerel and squid) for 753 days. Yellowtail muscle was sequentially sampled from each individual after the diet switch (0 to 753 days) and analyzed for δ15N and δ13C, allowing for calculation of diet-tissue discrimination factors (DTDFs) from two isotopically different diets (low δ15N and δ13C: pellets; high δ15N and δ13C: fish/squid) and turnover rates of 15N and 13C. DTDFs were diet dependent: Δ15N = 5.1‰, Δ13C = 3.6‰ for pellets and Δ15N = 2.6‰, Δ13C = 1.3‰ for fish/squid. Half-life estimates from 15N and 13C turnover rates for pooled yellowtail were 181 days and 341 days, respectively, but varied considerably by individual (15N: 99–239 d; 13C: 158–899 d). Quantifying DTDFs supports isotopic approaches to field data that assume isotopic steady-state conditions (e.g., mixing models for diet reconstruction). Characterizing and quantifying turnover rates allow for estimates of diet/habitat shifts and “isotopic clock” approaches, and observed inter-individual variability suggests the need for large datasets in field studies. We provide diet-dependent DTDFs and growth effects on turnover rates, and associated error around these parameters, for application to field-collected SIA data from other large teleosts.

Nitrogen stable isotope turnover and discrimination in lizards.

Nitrogen stable isotope ratio (δ15 N) processes are not well described in reptiles, which limits reliable inference of trophic and nutrient dynamics. In this study we detailed δ15 N turnover and discrimination (Δ15 N) in diverse tissues of two lizard species, and compared these results with previously published carbon data (δ13 C) to inform estimates of reptilian foraging ecology and nutrient physiology. We quantified 15 N incorporation and discrimination dynamics over 360 days in blood fractions, skin, muscle, and liver of Sceloporus undulatus and Crotaphytus collaris that differed in body mass. Tissue samples were analyzed on a continuous flow isotope ratio mass spectrometer. Δ15 N for plasma and red blood cells (RBCs) ranged between +2.7 and +3.5‰; however, skin, muscle, and liver did not equilibrate, hindering estimates for these somatic tissues. 15 N turnover in plasma and RBCs ranged from 20.7 ± 4 to 303 ± 166 days among both species. Comparison with previously published δ13 C results for these same samples showed that 15 N and 13 C incorporation patterns were uncoupled, especially during winter when hibernation physiology could have played a role. Our results provide estimates of 15 N turnover rates and discrimination values that are essential to using and interpreting isotopes in studies of diet reconstruction, nutrient allocation, and trophic characterization in reptiles. These results also suggest that somatic tissues can be unreliable, while life history shifts in nutrient routing and metabolism potentially cause 15 N and 13 C dynamics to be decoupled.

Individual variability in stable isotope turnover rates of epidermal mucus according to body size in an omnivorous fish

Epidermal mucus (‘mucus’) is increasingly applied to fish ecological studies based on stable isotope analysis (SIA) due to its non-invasive collection. However, knowledge on mucus SI turnover rates of individual fish remains limited, including uncertainty over how they are influenced by fish body sizes. Here, a diet switch experiment predicted mucus SI turnover rates (δ13C and δ15N) as a function of time using samples taken over 200 days from 10 individually tagged common carp Cyprinus carpio covering two size groups. Non-linear mixed effects models revealed rapid turnover of both δ13C and δ15N (T50: 2–5 days; T95: 9–22 days); δ15N turnover rates were slower for the larger cohort, while δ13C turnover rates were independent of body size. Within size groups, turnover rates were not expected to vary between individuals. These experimental results suggest that due to these fast turnover rates, epidermal mucus can provide insights into the diets of fish over very short timeframes, although for δ15N the body size of the fish needs consideration.

The Importance of Isotopic Turnover for Understanding Key Aspects of Animal Ecology and Nutrition

Stable isotope-based methods have proved to be immensely valuable for ecological studies ranging in focus from animal movements to species interactions and community structure. Nevertheless, the use of these methods is dependent on assumptions about the incorporation and turnover of isotopes within animal tissues, which are oftentimes not explicitly acknowledged and vetted. Thus, the purpose of this review is to provide an overview of the estimation of stable isotope turnover rates in animals, and to highlight the importance of these estimates for ecological studies in terrestrial, freshwater, and marine systems that may use a wide range of stable isotopes. Specifically, we discuss 1) the factors that contribute to variation in turnover among individuals and across species, which influences the use of stable isotopes for diet reconstructions, 2) the differences in turnover among tissues that underlie so-called ‘isotopic clocks’, which are used to estimate the timing of dietary shifts, and 3) the use of turnover rates to estimate nutritional requirements and reconstruct histories of nutritional stress from tissue isotope signatures. As we discuss these topics, we highlight recent works that have effectively used estimates of turnover to design and execute informative ecological studies. Our concluding remarks suggest several steps that will improve our understanding of isotopic turnover and support its integration into a wider range of ecological studies.

Estimating stable isotope turnover rates of epidermal mucus and dorsal muscle for an omnivorous fish using a diet-switch experiment

Stable isotope (SI) analysis studies rely on knowledge of isotopic turnover rates and trophic-step discrimination factors. Epidermal mucus (‘mucus’) potentially provides an alternative SI ‘tissue’ to dorsal muscle that can be collected non-invasively and non-destructively. Here, a diet-switch experiment using the omnivorous fish Cyprinus carpio and plant- and fish-based formulated feeds compared SI data between mucus and muscle, including their isotopic discrimination factors and turnover rates (as functions of time T and mass G, at isotopic half-life (50) and equilibrium (95)). Mucus isotope data differed significantly and predictively from muscle data. The fastest δ13C turnover rate was for mucus in fish on the plant-based diet (T_{50}: 17 days, T_{95}: 74 days; G_{50}: 1.08(BM), G_{95}: 1.40(BM)). Muscle turnover rates were longer for the same fish (T_{50}: 44 days, T_{95}: 190 days; G_{50}: 1.13(BM), G_{95}: 1.68(BM)). Longer half-lives resulted in both tissues from the fish-based diet. δ13C discrimination factors varied by diet and tissue (plant-based: 3.11–3.28‰; fishmeal: 1.28–2.13‰). Mucus SI data did not differ between live and frozen fish. These results suggest that mucus SI half-lives provide comparable data to muscle, and can be used as a non-destructive alternative tissue in fish-based SI studies.

Traveling There and Back Again: A Fingernail's Tale

This study focuses on the examination of stable isotope biomarkers in human fingernails of travelers who ventured away from Salt Lake City, UT and subsequently returned. Here, we describe three case studies examining: individual travelers (n = 4), paired travelers (n = 2), and a traveler (n = 1) who repeatedly left and returned. Our case studies examined the influences of dietary and drinking water inputs on fingernail stable isotope profiles for reconstructing travel histories. Stable isotope data were compared with theoretical and predictive models that laid the groundwork for anthropological and forensic geospatial reconstruction of travel histories. Drinking water inputs strongly influenced stable isotope profiles and the patterns observed were consistent with reported travel histories. Finally, observed fingernail stable isotope ratio data were consistent with modeled rates of stable isotope turnover and transition to expected values for the new environment. The results of our study further support the use of fingernail tissues for travel history reconstruction.

Dietary lysine deficiency increases the incorporation rate of nitrogen-free compounds in muscle of pacu (Piaractus mesopotamicus)

Isotopic experiments are conducted to evaluate turnover rates in fish tissue, especially as a function of nutrition. In 2007, Cerling et al. proposed an approach they named the reaction progress variable, which among other functions, allows to correct for growth during the period of data collection and to treat the isotopic incorporation system as a linear function, irrespective of the growth rate model. The objective of present study was to apply “the reaction progress variable” approach to describe stable isotope turnover in muscle tissue of pacu fed a lysine-deficient and a lysine-supplemented diet in order to determine the incorporation rates of nitrogen-free compounds, considering the correction for increases in mass during turnover. Since in muscle tissue carbon compounds are proteins, nucleic acids, lipids and carbohydrates and nitrogen compounds include only proteins and nucleic acids, the incorporation rates of nitrogen-free compounds were calculated by the difference between the incorporation rates of carbon and nitrogen compounds. The δ13C and δ15N values were adjusted for the increase in mass of fish to determine incorporation rate constants through linear fit. High turnover rates were observed when the increase in mass was considered. There was no effect of the diets on the incorporation rates of carbon compounds into muscle tissue of juvenile pacu. Fish fed the lysine-deficient diet exhibited a higher metabolic δ15N turnover rate, probably because of the greater degradation of nitrogen compounds; consequently, the incorporation rate of nitrogen-free compounds was 1.23% day−1. A higher incorporation rate of nitrogen compounds was observed in fish fed the lysine-supplemented diet and the incorporation rate of nitrogen-free compounds was therefore lower in this group (0.05% day−1). The incorporation rate of nitrogen-free compounds (e.g., lipids and glycogen) into muscle tissue was higher in juvenile pacu fed the lysine-deficient diet compared to animals receiving the lysine-supplemented diet. We therefore propose to adopt the reaction progress variable approach as a more useful tool for describing isotopic incorporation datasets.

The Effect of Parasite Infection on Stable Isotope Turnover Rates of δ15N, δ13C and δ34S in Multiple Tissues of Eurasian Perch Perca fluviatilis.

Stable isotope analysis of commercially and ecologically important fish can improve understanding of life-history and trophic ecology. However, accurate interpretation of stable isotope values requires knowledge of tissue-specific isotopic turnover that will help to describe differences in the isotopic composition of tissues and diet. We performed a diet-switch experiment using captive-reared parasite-free Eurasian perch (Perca fluviatilis) and wild caught specimens of the same species, infected with the pike tapeworm Triaenophorus nodulosus living in host liver tissue. We hypothesize that metabolic processes related to infection status play a major role in isotopic turnover and examined the influence of parasite infection on isotopic turn-over rate of carbon (δ13C), nitrogen (δ15N) and sulphur (δ34S) in liver, blood and muscle. The δ15N and δ13C turnovers were fastest in liver tissues, followed by blood and muscle. In infected fish, liver and blood δ15N and δ13C turnover rates were similar. However, in infected fish, liver and blood δ13C turnover was faster than that of δ15N. Moreover, in infected subjects, liver δ15N and δ13C turnover rates were three to five times faster than in livers of uninfected subjects (isotopic half-life of ca.3-4 days compared to 16 and 10 days, respectively). Blood δ34S turnover rate were about twice faster in non-infected individuals implying that parasite infection could retard the turnover rate of δ34S and sulphur containing amino acids. Slower turnover rate of essential amino acid could probably decrease individual immune function. These indicate potential hidden costs of chronic and persistent infections that may have accumulated adverse effects and might eventually impair life-history fitness. For the first time, we were able to shift the isotope values of parasites encapsulated in the liver by changing the dietary source of the host. We also report variability in isotopic turnover rates between tissues, elements and between infected and parasite-free individuals. These results contribute to our understanding of data obtained from field and commercial hatcheries; and strongly improve the applicability of the stable isotope method in understanding life-history and trophic ecology of fish populations.

Impact of food type on respiration, fractionation and turnover of carbon and nitrogen stable isotopes in the marine amphipod Gammarus aequicauda (Martynov, 1931)

This study experimentally determined the impact of food source type on turnover rate and trophic enrichment factors (TEFs or ∆) of δ13C and δ15N, as well as on respiration rate, in captive populations of the marine amphipod Gammarus aequicauda. Gammarus aequicauda (318 individuals) were fed ad libitum with three food sources animal, algae, and dead Posidonia oceanica leaves (also called “litter”), varying in palatability, digestibility, nutritional qualities and isotopic compositions, for between four and six weeks in a controlled feeding experiment. The resulting death rate was lower for the amphipods fed with animal treatment (30.9%) than for individuals fed with algal (65.9%) or litter treatment (64.4%), indicating a better fitness of the individuals fed with the animal food source. Respiration rates also differed highly among the treatments. Animal treatment showed higher respiration rates than algal and litter treatments, potentially due to the toxicity of the algae and the very low nutritional quality of the litter. Amphipods fed with these treatments might have entered in a “low activity state” to cope with these unsuitable food sources, inducing low respiration rates. Due to the very low assimilation and toxicity of the algae source, turnover rate for δ13C was impossible to determine. Turnover rate for δ13C was much faster (half-life=12.55days) for amphipods fed with the animal food source than for amphipods fed with litter (half-life=51.62days), showing the faster assimilation of the most nutritionally optimal food sources by G. aequicauda. Turnover for δ15N was impossible to determine because the amphipods were already at isotopic equilibrium at the beginning of the experiment. Despite the detritus feeder status of Gammarus aequicauda, TEFs for the animal treatments were in accordance with values generally found for carnivorous organisms (∆13C=0.9±0.7‰; ∆15N=2.9±0.6‰). TEFs for the litter treatment were in accordance with values generally corresponding to detritivorous organisms (∆13C=1.2‰; ∆15N=1.0±0.4‰). SIAR mixing model outputs obtained with these new TEF values were more constrained and coherent than outputs obtained with general literature TEFs. This study thus demonstrated the non-negligible impact of the food source on Gammarus aequicauda physiological status, fitness and turnover rates, but also on TEFs—highlighting the importance of TEF experimental calculations for every potential food source of a given organism to ensure more robust isotopic data interpretation.

Stable carbon and nitrogen isotope discrimination and turnover in a small-bodied insectivorous lizard

ABSTRACTLaboratory experiments are useful for estimating the carbon and nitrogen isotope discrimination factors and turnover rates that are critical for drawing field-based inferences on consumer diets using stable isotopes. Although the utility of these discrimination factors is widely recognized, work in terrestrial systems has largely been limited to studies involving mammals and birds. In contrast, scant attention has been paid to the application of isotopic techniques to reptiles, despite their broad diversity in terms of numbers of species as well as their trophic roles. Here we estimate carbon and nitrogen isotope discrimination factors and turnover for the tree lizard (Urosaurus ornatus) using a diet-switch experiment. Lizards were collected from a C4-dominated grassland and then switched to C3-based diet (crickets) in the laboratory. We estimated discrimination by lizard claw tissue as Δ13C = 1.2 ± 0.1 ‰ for carbon and Δ15N = 0.7 ± 0.1 ‰ (mean ± 1 SE) for nitrogen, with 95 % turnover occurring after ∼15.5 days. These estimates should be appropriate for use in trophic studies of U. ornatus, and possibly other related small-bodied insectivorous lizards.

Diet-tissue discrimination factors and turnover of carbon and nitrogen stable isotopes in tissues of an adult predatory coral reef fish, Plectropomus leopardus.

Stable isotope ratios (δ(13)C and δ(15)N values) provide a unique perspective into the ecology of animals because the isotope ratio values of consumers reflect the values in food. Despite the value of stable isotopes in ecological studies, the lack of species-specific experimentally derived diet-tissue discrimination factors (DTDFs) and turnover rates limits their application at a broad scale. Furthermore, most aquatic feeding experiments use temperate, fast-growing fish species and few have considered medium- to large-sized adults with low growth rates from tropical ecosystems. A controlled-diet stable isotope feeding trial was conducted over a 196-day period for the adult predatory reef fish leopard coralgrouper (Plectropomus leopardus). This study calculated δ(13)C and δ(15)N DTDFs and turnover rates in five tissues (liver, plasma, red blood cells (RBC), fin, and muscle) using a continuous flow isotope ratio mass spectrometer equipped with an elemental analyzer. In addition, the effect of chemical lipid extraction (LE) on stable isotope values was examined for each tissue. Turnover was mainly influenced by metabolism (as opposed to growth) with LE δ(15)N half-life values lowest in fin (37 days) and plasma (66 days), and highest in RBC (88 days) and muscle (126 days). The diet-tissue discrimination factors for δ(15)N values in all tissues (Δ(15)N: -0.15 to 1.84‰) were typically lower than commonly reported literature values. Lipid extraction altered both δ(15) N and δ(13)C values compared with untreated samples; however, for the δ(15)N values, the differences were small (mean δ(15)N(LE-Bulk) <0.46‰ in all tissues). This study informs future interpretation of stable isotope data for medium- to large-sized fish and demonstrates that DTDFs developed for temperate fish species, particularly for δ(15)N values, may not apply to tropical species. Sampling of muscle and/or RBC is recommended for a relatively long-term representation of feeding habits, while plasma and/or fin should be used for a more recent indication of diet.

Stable isotope turnover and half-life in animal tissues: a literature synthesis.

Stable isotopes of carbon, nitrogen, and sulfur are used as ecological tracers for a variety of applications, such as studies of animal migrations, energy sources, and food web pathways. Yet uncertainty relating to the time period integrated by isotopic measurement of animal tissues can confound the interpretation of isotopic data. There have been a large number of experimental isotopic diet shift studies aimed at quantifying animal tissue isotopic turnover rate λ (%·day-1, often expressed as isotopic half-life, ln(2)/λ, days). Yet no studies have evaluated or summarized the many individual half-life estimates in an effort to both seek broad-scale patterns and characterize the degree of variability. Here, we collect previously published half-life estimates, examine how half-life is related to body size, and test for tissue- and taxa-varying allometric relationships. Half-life generally increases with animal body mass, and is longer in muscle and blood compared to plasma and internal organs. Half-life was longest in ecotherms, followed by mammals, and finally birds. For ectotherms, different taxa-tissue combinations had similar allometric slopes that generally matched predictions of metabolic theory. Half-life for ectotherms can be approximated as: ln (half-life) = 0.22*ln (body mass) + group-specific intercept; n = 261, p<0.0001, r2 = 0.63. For endothermic groups, relationships with body mass were weak and model slopes and intercepts were heterogeneous. While isotopic half-life can be approximated using simple allometric relationships for some taxa and tissue types, there is also a high degree of unexplained variation in our models. Our study highlights several strong and general patterns, though accurate prediction of isotopic half-life from readily available variables such as animal body mass remains elusive.

Abstract 634: Treatment with Mipomersen Reduces Levels of ApoB-Containing Lipoproteins by Increasing Fractional Removal of VLDL and LDL-apoB Without Reducing VLDL-apob Secretion

Objectives: Mipomersen (MIPO), a second generation antisense oligonucleotide, targets apoB mRNA, thereby inhibiting apolipoprotein B (apoB) synthesis. In humans, MIPO reduces plasma levels of low density lipoprotein-cholesterol (LDL-C), and plasma triglycerides (TG). We hypothesized that these changes are due to reduced assembly and secretion of very low density lipoproteins (VLDL) and lower production of LDL. Methods: Healthy volunteers (HVs) (9M, 8F), mean age 43.5 ± 14.2 yr, completed a single-blind, fixed-sequence, phase I study. They received sc-placebo injections once weekly for 3-wks followed by 200mg sc-MIPO injections once weekly for 7-9 wks. Stable isotope turnover studies were performed after each treatment. Blood samples were collected over 48-hrs to determine fractional catabolic rates (FCRs) and production rates (PRs) of apoB in VLDL, IDL, and LDL, and of TG in VLDL. Rates of de novo lipogenesis (DNL) were also measured. Results: MIPO treatment resulted in significant reductions in plasma LDL-C (45%), TG (29%), and apoB (40%). VLDL, IDL, and LDL apoB levels fell by 29%, 25%, and 42%, respectively. These changes were associated with increases in FCRs of VLDL apoB (42%) and LDL apoB (30%), and by reductions in PRs of IDL apoB (15%) and LDL apoB (27%). The PR of VLDL apoB was unaffected. The FCR of VLDL-TG increased 46% without change in PR. DNL did not change. Conclusion: In summary, 7 wks of MIPO significantly reduced levels of all apoB-lipoproteins in HVs by increasing the FCRs of VLDL and LDL apoB. The absence of a reduction in VLDL apoB secretion is consistent with many studies in isolated hepatocytes demonstrating both intracellular degradation and secretion of newly synthesized apoB. Thus, if MIPO submaximally inhibited apoB synthesis in this study, the liver could have compensated by increasing the efficiency of VLDL assembly and secretion. The basis of increases in VLDL and LDL FCRs requires further investigation.

The effects of sex, tissue type, and dietary components on stable isotope discrimination factors (Δ13C and Δ15N) in mammalian omnivores

We tested the effects of sex, tissue, and diet on stable isotope discrimination factors (Δ13C and Δ15N) for six tissues from rats fed four diets with varied C and N sources, but comparable protein quality and quantity. The Δ13C and Δ15N values ranged from 1.7–4.1 ‰ and 0.4–4.3 ‰, respectively. Females had higher Δ15N values than males because males grew larger, whereas Δ13C values did not differ between sexes. Differences in Δ13C values among tissue types increased with increasing variability in dietary carbon sources. The Δ15N values increased with increasing dietary δ15N values for all tissues except liver and serum, which have fast stable isotope turnover times, and differences in Δ15N values among tissue types decreased with increasing dietary animal protein. Our results demonstrate that variability in dietary sources can affect Δ13C values, protein source affects Δ15N values even when protein quality and quantity are controlled, and the isotope turnover rate of a tissue can influence the degree to which diet affects Δ15N values.

Carbon stable isotope turnover and fractionation in grass carp Ctenopharyngodon idella tissues

AB Aquatic Biology Contact the journal Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AB 19:207-216 (2013) - DOI: https://doi.org/10.3354/ab00528 Carbon stable isotope turnover and fractionation in grass carp Ctenopharyngodon idella tissues Bin Xia, Qin-Feng Gao*, Shuang-Lin Dong, Fang Wang Key Laboratory of Mariculture, Ministry of Education, Ocean University of China, Qingdao, Shandong Province 266003, China *Corresponding author. Email: qfgao@ouc.edu.cn ABSTRACT: Carbon stable isotope signatures can effectively trace food sources, elucidate trophic interactions, and presumably reflect food web structure. The present study conducted a diet-switch experiment using freshwater teleost grass carp Ctenopharyngodon idella cultured for 3 mo with artificial feed that had a distinct carbon stable isotope composition. Turnover and fractionation of carbon stable isotopes were determined based on the proportional contributions of metabolism and growth to the isotopic turnover in different tissues. Carbon isotopic turnover rates showed significant differences among tissues and increased in the sequence of gill < muscle < liver due to the difference in the metabolic activities among the various tissues. Carbon half-lives based on the isotopic turnover models were 22.5 d or 1.13-fold mass increase for liver, 52.7 d or 1.35-fold mass increase for muscle and 101.1 d or 1.73-fold mass increase for gill tissue. Fractionation of carbon stable isotopes differed among the 3 types of tissues due to the differential biochemical constituents of the tissues. Based on the isotopic turnover models, the fractionation of carbon stable isotopes relative to the new diet approximately fitted the traditional carbon fractionation value of 1‰. Metabolism in liver and muscle tissue accounted for approximately 75–85% and 50–60% of tissue turnover, respectively, whereas only 15–25% of tissue turnover might be attributable to metabolism in the gills. KEY WORDS: Carbon stable isotope turnover · Growth · Metabolism · Ctenopharyngodon idella Full text in pdf format PreviousNextCite this article as: Xia B, Gao QF, Dong SL, Wang F (2013) Carbon stable isotope turnover and fractionation in grass carp Ctenopharyngodon idella tissues. Aquat Biol 19:207-216. https://doi.org/10.3354/ab00528 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AB Vol. 19, No. 3. Online publication date: October 24, 2013 Print ISSN: 1864-7782; Online ISSN: 1864-7790 Copyright © 2013 Inter-Research.

Stable isotope turnover in blood and claws: A case study in captive African Penguins

Stable isotope ratios (13C:12C and 15N:14N) increasingly are being used to infer information about the movements and trophic positions of birds. Feathers, blood, muscle, bone and other tissues frequently are sampled, allowing insights at a range of temporal scales, linked to tissue-specific turnover rates. Non-destructive sampling typically is limited to feathers and blood, but some studies have used claws. An experiment was performed manipulating the diet of captive African Penguins (Spheniscus demersus) to test the turnover rates and discrimination factors (δ=δtissue−δdiet) of claws, blood, plasma and erythrocytes. Eight penguins previously fed sardines (Sardinops sagax) were switched to a diet of small hakes (Merluccius paradoxus/capensis) for 49days. The two fish differed in their 15N values but not 13C. Blood and its fractions had half-lives similar to those reported in other studies, with plasma showing a faster turnover rate (7.6±0.7days) than erythrocytes (14.3±1.6days). Claw growth averaged 0.8±0.2mmweek−1, suggesting that the visible portion of penguin nail takes approximately 126days to be replaced. However, no shift in the nitrogen isotope value was detected, despite monitoring nails for 157days after the diet switch. Discrimination factors varied among tissues, with claws having the lowest factor: δ15Nclaw–sardine=+1.5±0.7‰. Although claws can be sampled non-destructively, they need to be used with caution for isotope analyses because they appear to be relatively insensitive to short to medium-term diet shifts.

Isotope incorporation in broad-snouted caimans (crocodilians)

SummaryThe trophic ecology and migration of vertebrate species have been increasingly studied using stable isotope analysis. However, this approach requires knowledge on how dietary isotopic values are reflected in consumers' tissues. To date, this information has only been obtained for a handful of ectotherms; in particular, little is known about crocodilians. In this study, diet-tissue discrimination factors (DTDFs) and carbon and nitrogen stable isotope turnover rates were estimated for plasma, red blood cells (RBCs), and muscle obtained from broad-snouted caimans (Caiman latirostris). Individuals were fed two different control diets for 189 days. DTDFs for δ15N (Δ15N) and δ13C (Δ13C) ranged from −2.24‰ to 0.39‰ and from −0.52‰ to 1.06‰, respectively. Isotope turnover rates in tissues, expressed as half-lives, ranged from 11 to 71 days, with plasma<muscle<RBCs. Δ15N was found to be particularly small, even when compared to values found for other ectotherms, a result that may be linked to the unique excretion physiology of crocodilians. These stable isotope incorporation data should help inform future interpretations of isotopic values obtained in the field for this taxon.