Spatial and Temporal Variations in Stable Carbon (δ13C) and Nitrogen (δ15N) Isotopic Composition of Symbiotic Scleractinian Corals

Tropical scleractinian corals are considered autotrophic as they rely mainly on photosynthesis-derived nutrients transferred from their photosymbionts. Corals are also able to capture and ingest suspended particulate organic matter, so heterotrophy can be an important supplementary trophic pathway to optimize coral fitness. The aim of this in situ study was to elucidate the trophic status of 10 coral species under contrasted environmental conditions in a French Polynesian lagoon. Carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopic compositions of coral host tissues and photosymbionts were determined at 3 different fringing reefs during wet and dry seasons. Our results highlighted spatial variability in stable isotopic compositions of both coral host tissues and photosymbionts. Samples from the site with higher level of suspended particulate matter were ¹³C-depleted and ¹⁵N-enriched relative to corals and photosymbionts from less turbid sites. However, differences in both δ¹³C and δ¹⁵N between coral host tissues and their photosymbionts (Δ^{host-photosymbionts 13}C and Δ^{host-photosymbionts 15}N) were small (0.27 ± 0.76‰ and 1.40 ± 0.90‰, respectively) and similar at all sites, thus indicating no general increases in the heterotrophic pathway. Depleted δ¹³C and enriched δ¹⁵N values of coral host tissues measured at the most turbid site were explained by changes in isotopic composition of the inorganic nutrients taken up by photosymbionts and also by changes in rate of isotopic fractionation with environmental conditions. Our results also highlighted a lack of significant temporal variations in δ¹³C and δ¹⁵N values of coral host and photosymbiont tissues and in Δ^{host-photosymbionts 13}C and Δ^{host-photosymbionts 15}N values. This temporal stability indicated that corals remained principally autotrophic even during the wet season when photosymbiont densities were lower and the concentrations of phytoplankton were higher. Increased coral heterotrophy with higher food availability thus appears to be species-specific.     

Factors Controlling the Stable Nitrogen Isotopic Composition (δ15N) of Lipids in Marine Animals

Lipid extraction of biomass prior to stable isotope analysis is known to cause variable changes in the stable nitrogen isotopic composition (δ¹⁵N) of residual biomass. However, the underlying factors causing these changes are not yet clear. Here we address this issue by comparing the δ¹⁵N of bulk and residual biomass of several marine animal tissues (fish, crab, cockle, oyster, and polychaete), as well as the δ¹⁵N of the extracted lipids. As observed previously, lipid extraction led to a variable offset in δ¹⁵N of biomass (differences ranging from -2.3 to +1.8 ‰). Importantly, the total lipid extract (TLE) was highly depleted in ¹⁵N compared to bulk biomass, and also highly variable (differences ranging from -14 to +0.7 ‰). The TLE consisted mainly of phosphatidylcholines, a group of lipids with one nitrogen atom in the headgroup. To elucidate the cause for the ¹⁵N-depletion in the TLE, the δ¹⁵N of amino acids was determined, including serine because it is one of the main sources of nitrogen to N-containing lipids. Serine δ¹⁵N values differed by -7 to +2 ‰ from bulk biomass δ¹⁵N, and correlated well with the ¹⁵N depletion in TLEs. On average, serine was less depleted (-3‰) than the TLE (-7 ‰), possibly due to fractionation during biosynthesis of N-containing headgroups, or that other nitrogen-containing compounds, such as urea and choline, or recycled nitrogen contribute to the nitrogen isotopic composition of the TLE. The depletion in ¹⁵N of the TLE relative to biomass increased with the trophic level of the organisms.     

Organic Matter Stable Isotope (δ13C, δ15N) Response to Historical Eutrophication of Lake Taihu, China

We explored the use of carbon and nitrogen isotope ratios (δ¹³C, δ¹⁵N) in sediment organic matter as proxy indicators of historical changes in the trophic state of Lake Taihu, the third largest freshwater lake in China. Stable isotope signatures in four sediment cores spanning the 20th century were compared with instrumental records of lake-water trophic state. The comparative study shows that, between ∼ ∼1950 and 1990 AD, the δ¹³C and δ¹⁵N of sediment organic matter throughout Lake Taihu increased along the trophic gradient from oligotrophy to eutrophy due to biological isotopic fractionation. However, in the 1990s, the trophic state of Lake Taihu diverged into two different trophic systems, a hypereutrophic western Lake Taihu dominated by blue-green algae and a mesoeutrophic eastern Lake Taihu dominated by vascular aquatic plants. During the post-1990 AD shift from mesoeutrophic to hypereutrophic state in western Lake Taihu, organic matter δ¹³C and δ¹⁵N decreased sharply in response to pronounced shifts in the aquatic ecosystem. The results indicate that ¹³C-depleted phytoplankton replaced macrophytes in western Lake Taihu. δ¹⁵N values in western Lake Taihu also decreased because of N₂ fixation by cyanobacteria in this highly productive ecosystem. By contrast, in eastern Lake Taihu, organic matter δ¹³C and δ¹⁵N values show a post-1990 AD trend towards slightly lower values, but they remain higher than the long-term average. This recent ¹³C–enrichment of organic matter indicates that periods of high productivity in the restricted eastern sub-basin of Lake Taihu limited aqueous CO₂ availability, causing a decrease in isotopic discrimination during photosynthesis. After ∼ ∼1990 AD, organic matter δ¹⁵N values for eastern Lake Taihu only dropped slightly, suggesting that the contribution of phytoplankton to the sediment organic matter increased slightly. Taken together, the results indicate that nitrogen-fixing cyanobacteria probably played a much smaller role in primary productivity in this part of eastern Lake Taihu, compared with western Lake Taihu. Despite the complexity of carbon and nitrogen cycles in lakes, the agreement between the stable isotope signatures and instrumental records for Lake Taihu suggests that δ¹³C and δ¹⁵N in sediment organic matter are capable of recording important shifts in the spatial and temporal evolution of lake-water trophic state.     

Long-Term Trends in Tree-Ring Width and Isotope Signatures (δ13C, δ15N) of Fagus sylvatica L. on Soils with Contrasting Water Supply

We investigated long-term responses (since 1850) of Fagus sylvatica (Luxembourg; central Europe) to shifts in temperature, precipitation, and nitrogen deposition by analyzing diameter at breast height (DBH) increment, basal area increment (BAI), and tree-ring stable isotopes (δ¹³C, δ¹⁵N). We compared stands on soils with contrasting water supply (Regosols and Cambisols with an available water capacity of ca. 40 and 170 mm, respectively) and of two different age classes (ca. 60 vs. 200 years). All stands showed a peak in DBH increment in the decade 1978–1987, but a decline in increment growth in subsequent decades. In addition, BAI declined in mature stands in the last two decades. Decreasing increment rates were attributable to an increasing drought limitation of stands, mainly induced by increasing temperatures in the last two decades. Contrary to our expectations, stands on Cambisols showed a similar susceptibility to shifts in temperature and precipitation as stands on Regosols, suggesting a strong adaptation of the respective ecotypes grown at dryer sites. This result was in line with long-term trends for tree-ring δ¹³C signatures, which did not differ significantly between stands on Cambisols and Regosols. Climate impacts on tree-ring δ¹⁵N signatures were low. High spring precipitation and temperatures caused increasing and decreasing δ¹⁵N values, respectively, but only in mature stands on Cambisols. Stands on Regosols tended to have lower δ¹⁵N values than stands on Cambisols. Decreasing δ¹⁵N values in recent decades suggest an increasing impact of allochthonous N loads with isotopically lighter N.     

δ15N and δ13C diet–tissue discrimination factors for large sharks under semi-controlled conditions

Stable isotopes (δ¹⁵N and δ¹³C) are being widely applied in ecological research but there has been a call for ecologists to determine species- and tissue-specific diet discrimination factors (?¹³C and ?¹⁵N) for their study animals. For large sharks stable isotopes may provide an important tool to elucidate aspects of their ecological roles in marine systems, but laboratory based controlled feeding experiments are impractical. By utilizing commercial aquaria, we estimated ?¹⁵N and ?¹³C of muscle, liver, vertebral cartilage and a number of organs of three large sand tiger (Carcharias taurus) and one large lemon shark (Negaprion brevirostris) under a controlled feeding regime. For all sharks mean ± SD for ?¹⁵N and ?¹³C in lipid extracted muscle using lipid extracted prey data were 2.29‰ ± 0.22 and 0.90‰ ± 0.33, respectively. The use of non-lipid extracted muscle and prey resulted in very similar ?¹⁵N and ?¹³C values but mixing of lipid and non-lipid extracted data produced variable estimates. Values of ?¹⁵N and ?¹³C in lipid extracted liver and prey were 1.50‰ ± 0.54 and 0.22‰ ± 1.18, respectively. Non-lipid extracted diet discrimination factors in liver were highly influenced by lipid content and studies that examine stable isotopes in shark liver, and likely any high lipid tissue, should strive to remove lipid effects through standardising C:N ratios, prior to isotope analysis. Mean vertebral cartilage ?¹⁵N and ?¹³C values were 1.45‰ ± 0.61 and 3.75‰ ± 0.44, respectively. Organ ?¹⁵N and ?¹³C values were more variable among individual sharks but heart tissue was consistently enriched by ~ 1–2.5‰. Minimal variability in muscle and liver δ¹⁵N and δ¹³C sampled at different intervals along the length of individual sharks and between liver lobes suggests that stable isotope values are consistent within tissues of individual animals. To our knowledge, these are the first reported diet–tissue discrimination factors for large sharks under semi-controlled conditions, and are lower than those reported for teleost fish.     

不同生境胡杨叶片δ~(13)C和δ~(15)N及其对环境因子的响应

以新疆南北疆8个不同生境林龄群体的胡杨叶片为材料,测定幼树和成熟胡杨叶片的天然稳定碳、氮同位素组成值(δ~(13)C、δ~(15)N)以及碳含量、氮含量和比叶面积,分析叶片δ~(13)C、δ~(15)N值与海拔、经纬度、叶片碳氮含量、比叶面积以及水分利用效率之间的相互关系。结果表明:(1)胡杨幼树和成熟林叶片δ~(13)C平均值分别为-27.863‰(-28.776‰～-26.695‰)和-28.230‰(-29.717‰～-26.033‰),不同生境胡杨叶片间的δ~(13)C值具有显著差异(P0.05),并且幼树林叶片δ~(13)C均大于对应成熟林;幼树和成熟林叶片δ~(15)N平均值分别为3.259‰(-1.842‰～9.082‰)和3.651‰(0.798‰～5.779‰)。(2)胡杨幼树和成熟林叶片碳含量平均值分别为46.225‰(44.573‰～49.056‰)和45.720‰(43.226‰～47.349‰),它们叶片氮含量平均值分别为1.708‰(1.327‰～2.116‰)和1.823‰(1.164‰～2.450‰);成熟林叶片碳含量与其δ~(13)C和δ~(15)N值分别呈极显著负相关和极显著正相关关系(P0.01),而其氮含量与δ~(13)C值呈不显著正相关关系(P0.05),与δ~(15)N值呈显著正相关关系。(3)胡杨幼树林叶片的比叶面积平均值(91.565 cm~2/g)小于成熟林叶片(103.141 cm~2/g)。(4)幼树和成熟林胡杨叶片δ~(13)C、δ~(15)N值均与纬度呈极显著正相关关系,幼树林叶片δ~(13)C、δ~(15)N值与海拔也呈极显著正相关关系,幼树林叶片δ~(15)N值与经度也呈显著正相关关系。(5)幼树和成熟胡杨林水分利用率的平均值分别为77.618μmol/mol(68.070～91.069μmol/mol)和72.463μmol/mol(62.809～97.111μmol/mol),不同林龄的胡杨水分利用率均与其叶片δ~(13)C呈极显著正相关关系(P0.001),各生境中于田县(阿日系马扎)的幼树和成熟林叶片具有较高的δ~(13)C值(-26.695‰和-26.033‰)和水分利用效率(91.069和97.111μmol/mol)。     

Determining the appropriate pretreatment procedures and the utility of liver tissue for bulk stable isotope (δ13C and δ15N) studies in sharks

Stable-isotope analysis (SIA) provides a valuable tool to address complex questions pertaining to elasmobranch ecology. Liver, a metabolically active, high turnover tissue (~166 days for 95% turnover), has the potential to reveal novel insights into recent feeding/movement behaviours of this diverse group. To date, limited work has used this tissue, but ecological application of SIA in liver requires consideration of tissue preparation techniques given the potential for high concentrations of urea and lipid that could bias δ¹³C and δ¹⁵N values (i.e., result in artificially lower δ¹³C and δ¹⁵N values). Here we investigated the effectiveness of (a) deionized water washing (WW) for urea removal from liver tissue and (b) chloroform-methanol for extraction of lipids from this lipid rich tissue. We then (a) established C:N thresholds for deriving ecologically relevant liver isotopic values given complications of removing all lipid and (b) undertook a preliminary comparison of δ¹³C values between tissue pairs (muscle and liver) to test if observed isotopic differences correlated with known movement behaviour. Tests were conducted on four large shark species: the dusky (DUS, Carcharhinus obscurus), sand tiger (RAG, Carcharias taurus), scalloped hammerhead (SCA, Sphyrna lewini) and white shark (GRE, Carcharodon carcharias). There was no significant difference in δ¹⁵N values between lipid-extracted (LE) liver and lipid-extracted/water washed (WW) treatments, however, WW resulted in significant increases in %N, δ¹³C and %C. Following lipid extraction (repeated three times), some samples were still biased by lipids. Our species-specific “C:N thresholds” provide a method to derive ecologically viable isotope data given the complexities of this lipid rich tissue (C:N thresholds of 4.0, 3.6, 4.7 and 3.9 for DUS, RAG, SCA and GRE liver_LEWW tissue, respectively). The preliminary comparison of C:N threshold corrected liver and muscle δ¹³C values corresponded with movement/habitat behaviours for each shark; minor differences in δ¹³C values were observed for known regional movements of DUS and RAG (δ¹³C_Diffs = 0.24 ± 0.99‰ and 0.57 ± 0.38‰, respectively), while SCA and GRE showed greater differences (1.24 ± 0.63‰ and 1.08 ± 0.71‰, respectively) correlated to large-scale movements between temperate/tropical and pelagic/coastal environments. These data provide an approach for the successful application of liver δ¹³C and δ¹⁵N values to examine elasmobranch ecology.     

Within-Site Variation in Feather Stable Hydrogen Isotope (δ2Hf) Values of Boreal Songbirds: Implications for Assignment to Molt Origin

Understanding bird migration and dispersal is important to inform full life-cycle conservation planning. Stable hydrogen isotope ratios from feathers (δ²H_f) can be linked to amount-weighted long-term, growing season precipitation δ²H (δ²H_p) surfaces to create δ²H_f isoscapes for assignment to molt origin. However, transfer functions linking δ²H_p with δ²H_f are influenced by physiological and environmental processes. A better understanding of the causes and consequences of variation in δ²H_f values among individuals and species will improve the predictive ability of geographic assignment tests. We tested for effects of species, land cover, forage substrate, nest substrate, diet composition, body mass, sex, and phylogenetic relatedness on δ²H_f from individuals at least two years old of 21 songbird species captured during the same breeding season at a site in northeastern Alberta, Canada. For four species, we also tested for a year × species interaction effect on δ²H_f. A model including species as single predictor received the most support (AIC weight = 0.74) in explaining variation in δ²H_f. A species-specific variance parameter was part of all best-ranked models, suggesting variation in δ²H_f was not consistent among species. The second best-ranked model included a forage substrate × diet interaction term (AIC weight = 0.16). There was a significant year × species interaction effect on δ²H_f suggesting that interspecific differences in δ²H_f can differ among years. Our results suggest that within- and among-year interspecific variation in δ²H_f is the most important source of variance typically not being explicitly quantified in geographic assignment tests using non-specific transfer functions to convert δ²H_p into δ²H_f. However, this source of variation is consistent with the range of variation from the transfer functions most commonly being propagated in assignment tests of geographic origins for passerines breeding in North America.     

Variation in hair δ13C and δ15N values in long-tailed macaques (Macaca fascicularis) from Singapore

Much of the primatology literature on stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) has focused on African and New World species, with comparatively little research published on Asian primates. Here we present hair δ¹³C and δ¹⁵N isotope values for a sample of 33 long-tailed macaques from Singapore. We evaluate the suggestion by a previous researcher that forest degradation and biodiversity loss in Singapore have led to a decline in macaque trophic level. The results of our analysis indicated significant spatial variability in δ¹³C but not δ¹⁵N. The range of variation in δ¹³C was consistent with a diet based on C₃ resources, with one group exhibiting low values consistent with a closed canopy environment. Relative to other macaque species from Europe and Asia, the macaques from Singapore exhibited a low mean δ¹³C value but mid-range mean δ¹⁵N value. Previous research suggesting a decline in macaque trophic level is not supported by the results of our study.     

Carbon and nitrogen cycling in a lead polluted grassland evaluated using stable isotopes (δ13C and δ15N) and microbial,plant and soil parameters

Plant and Soil - Carbon (C) and nitrogen (N) cycling are key ecosystem functions potentially altered by heavy metal pollution. We used an ecosystem approach to study the long-term effect of lead...     

应用稳定性同位素(δ~(13)C、δ~(15)N)技术研究长江中游干流主要鱼类的营养级

应用稳定性同位素(δ13C、δ15N)技术对2011年3月至2013年12月采自长江中游干流宜昌、荆州、石首、监利、城陵矶、鄂州、九江和湖口江段的44种鱼类及3种水生无脊椎动物进行了营养级研究。长江中游干流鱼类的δ13C值范围﹣33.83‰(鳙Aristichthys nobilis)~﹣17.36‰(南方鲇Silurus meridionalis),δ15N值范围4.83‰(泥鳅Misgurnus anguillicaudatus)~15.13‰(翘嘴鲌Culter alburnus)。以梨形环棱螺(Bellamya purificata)的δ15N均值5.48‰作为营养级基准线(营养级=2),计算出该江段水生动物的营养级处于2.42~4.88,主要集中在2.83~3.61之间,鱼类平均营养级为3.28。营养级大于2.83的鱼类种类数量占了总生物种数的80.85%。大刺鳅(Mastacembelus armatus)和长春鳊(Parabramis pekinensis)营养级最低,分别为2.42±0.49和2.56±0.52,营养层级大于4.0的高级消费者为太湖新银鱼(Neosalanx taihuensis)、短颌鲚(Coilia brachygnathus)、鳙和长蛇(Saurogobio dumerili),分别为4.88±0.01、4.37±0.27、4.32±0.35和4.09±0.78,小黄黝鱼(Micropercops swinhonis)、(Elopichthys bambusa)、鳜(Siniperca chuatsi)、翘嘴鲌、青鱼(Mylopharyngodon piceus)和南方鲇的营养级分别3.99、3.92±0.16、3.89±0.27、3.87±0.62、3.59±0.69和3.59±0.57。本研究旨为长江中游渔业资源评估及其合理利用提供基础科学资料,为进一步研究长江中游干流渔业资源营养结构的动态变化及受人为活动干扰影响等提供科学参考依据。     

Effects of anticoagulants on stable-isotope values (δ13C and δ15N) of shark blood components

The effects of anticoagulant EDTA and sodium heparin (SH) on stable carbon δ¹³C and nitrogen δ¹⁵N isotopic values of red blood cells (RBC) and blood plasma in juvenile blacktip reef sharks Carcharhinus melanopterus were analysed. Plasma preserved with anticoagulants was not isotopically distinct from plasma stored in no-additive control tubes but RBC δ¹⁵N values exhibited small enrichments when preserved with EDTA and SH. Results suggest EDTA and SH are viable anticoagulants for stable isotopic analyses of blood fractions but further studies are advised to validate results.     

Functional diversity in an Amazonian rainforest of French Guyana: a dual isotope approach (δ15N and δ13C)

Functional aspects of biodiversity were investigated in a lowland tropical rainforest in French Guyana (5°2′N, annual precipitation 2200 mm). We assessed leaf δ¹⁵N as a presumptive indicator of symbiotic N₂ fixation, and leaf and wood cellulose δ¹³C as an indicator of leaf intrinsic water-use efficiency (CO₂ assimilation rate/leaf conductance for water vapour) in dominant trees of 21 species selected for their representativeness in the forest cover, their ecological strategy (pioneers or late successional stage species, shade tolerance) or their potential ability for N₂ fixation. Similar measurements were made in trees of native species growing in a nearby plantation after severe perturbation (clear cutting, mechanical soil disturbance). Bulk soil δ¹⁵N was spatially quite uniform in the forest (range 3–5‰), whereas average leaf δ¹⁵N ranged from −0.3‰ to 3.5‰ in the different species. Three species only, Diplotropis purpurea, Recordoxylon speciosum (Fabaceae), and Sclerolobium melinonii (Caesalpiniaceae), had root bacterial nodules, which was also associated with leaf N concentrations higher than 20 mg g⁻¹. Although nodulated trees displayed significantly lower leaf δ¹⁵N values than non-nodulated trees, leaf δ¹⁵N did not prove a straightforward indicator of symbiotic fixation, since there was a clear overlap of δ¹⁵N values for nodulated and non-nodulated species at the lower end of the δ¹⁵N range. Perturbation did not markedly affect the difference δ¹⁵N_soil−δ¹⁵N_leaf, and thus the isotopic data provide no evidence of an alteration in the different N acquisition patterns. Extremely large interspecific differences in sunlit leaf δ¹³C were observed in the forest (average values from −31.4 to −26.7‰), corresponding to intrinsic water-use efficiencies (ratio CO₂ assimilation rate/leaf conductance for water vapour) varying over a threefold range. Wood cellulose δ¹³C was positively related to total leaf δ¹³C, the former values being 2–3‰ higher than the latter ones. Leaf δ¹³C was not related to leaf δ¹⁵N at either intraspecific or interspecific levels. δ¹³C of sunlit leaves was highest in shade hemitolerant emergent species and was lower in heliophilic, but also in shade-tolerant species. For a given species, leaf δ¹³C did not differ between the pristine forest and the disturbed plantation conditions. Our results are not in accord with the concept of existence of functional types of species characterized by common suites of traits underlying niche differentiation; rather, they support the hypothesis that each trait leads to a separate grouping of species. Received: 18 August 1997 / Accepted: 14 April 1998     

模拟增温对高寒草甸植物叶片碳氮及其同位素δ~(13)C和δ~(15)N含量的影响

基于国际冻原计划(ITEX)模拟增温效应对植物影响的研究方法,以高寒矮嵩草草甸4种植物(矮嵩草、垂穗披碱草、棘豆、麻花艽)为实验材料,设置大(OTC1)和小(OTC2)两类增温小室,测定了其叶片碳氮及其稳定性碳同位素(δ~(13)C、δ~(15)N)等指标在增温3年后的变化。结果表明:除矮嵩草在较小增温小室(OTC2)中C/N比值比对照降低了14.1%,其它物种C/N在两个增温处理下都有所增加,但差异均不显著(P0.05)。4种植物叶片δ~(13)C值在-24.12‰~-28.34‰之间,矮嵩草叶片δ~(13)C值随增温而升高,棘豆、麻花艽随增温而降低,且矮嵩草在OTC2的δ~(13)C值变化达到显著水平(P0.05)。矮嵩草和麻花艽的叶片δ~(15)N值在OTC1和OTC2中均比对照增加,且麻花艽增加较显著(P0.05)。垂穗披碱草在OTC1和OTC2的叶片δ~(15)N值比对照分别减少18.7%和26.9%,差异都不显著(P0.05);棘豆叶片δ~(15)N值在OTC2内比对照低11.0%(P0.05),在OTC1的内比对照高2.8%(P0.05)。可见,高寒矮嵩草草甸不同功能群植物物种碳氮含量及稳定性碳氮同位素含量对短期增温有不同的响应模式和规律。     

Backbone and Ile-δ1, Leu, Val Methyl 1H, 13C and 15N NMR chemical shift assignments for human interferon-stimulated gene 15 protein

Human interferon-stimulated gene 15 protein (ISG15), also called ubiquitin cross-reactive protein (UCRP), is the first identified ubiquitin-like protein containing two ubiquitin-like domains fused in tandem. The active form of ISG15 is conjugated to target proteins via the C-terminal glycine residue through an isopeptide bond in a manner similar to ubiquitin. The biological role of ISG15 is strongly associated with the modulation of cell immune function, and there is mounting evidence suggesting that many viral pathogens evade the host innate immune response by interfering with ISG15 conjugation to both host and viral proteins in a variety of ways. Here we report nearly complete backbone ¹H^N, ¹⁵N, ¹³C′, and ¹³C^α, as well as side chain ¹³C^β, methyl (Ile-δ1, Leu, Val), amide (Asn, Gln), and indole N–H (Trp) NMR resonance assignments for the 157-residue human ISG15 protein. These resonance assignments provide the basis for future structural and functional solution NMR studies of the biologically important human ISG15 protein.     

Patterns of δ~(13) C and δ~(15) N in wolverine Gulo gulo tissues from the Brooks Range,Alaska

Knowledge of carnivore diets is essential to understand how carnivore populations respond demographically to variations in prey abundance.Analysis of stable isotopes is a useful complement to traditional methods of analyzing carnivore diets.We used data on δ 13 C and δ 15 N in wolverine tissues to investigate patterns of seasonal and annual diet variation in a wolverine Gulo gulo population in the western Brooks Range,Alaska,USA.The stable isotope ratios in wolverine tissues generally reflected that of terr...     

Stable isotopes (δD and δ13C) are geographic indicators of natal origins of monarch butterflies in eastern North America

Wing membranes of laboratory and field-reared monarch butterflies (Danaus plexippus) were analyzed for their stable-hydrogen (δD) and carbon (δ¹³C) isotope ratios to determine whether this technique could be used to identify their natal origins. We hypothesized that the hydrogen isotopic composition of monarch butterfly wing keratin would reflect the hydrogen isotope patterns of rainfall in areas of natal origin where wings were formed. Monarchs were reared in the laboratory on milkweed plants (Asclepias sp.) grown with water of known deuterium content, and, with the assistance of volunteers, on native milkweeds throughout eastern North America. The results show that the stable hydrogen isotopic composition of monarch butterflies is highly correlated with the isotopic composition of the milkweed host plants, which in turn corresponds closely with the long-term geographic patterns of deuterium in rainfall. Stable-carbon isotope values in milkweed host plants were similarly correlated with those values in monarch butterflies and showed a general pattern of enrichment along a southwest to northeast gradient bisecting the Great Lakes. These findings indicate that natal origins of migratory and wintering monarchs in Mexico can be inferred from the combined δD and δ¹³C isotopic signatures in their wings. This relationship establishes that analysis of hydrogen and carbon isotopes can be used to answer questions concerning the biology of migratory monarch butterflies and provides a new approach to tracking similar migratory movements of other organisms. Received: 1 July 1998 / Accepted: 11 November 1998     

Protein Retention Assessment of Four Levels of Poultry By-Product Substitution of Fishmeal in Rainbow Trout (Oncorhynchus mykiss) Diets Using Stable Isotopes of Nitrogen (δ15N) as Natural Tracers

This is second part from an experiment where the nitrogen retention of poultry by-product meal (PBM) compared to fishmeal (FM) was evaluated using traditional indices. Here a quantitative method using stable isotope ratios of nitrogen (δ¹⁵N values) as natural tracers of nitrogen incorporation into fish biomass is assessed. Juvenile rainbow trout (Oncorhynchus mykiss) were fed for 80 days on isotopically distinct diets in which 0, 33, 66 and 100% of FM as main protein source was replaced by PBM. The diets were isonitrogenous, isolipidic and similar in gross energy content. Fish in all treatments reached isotopic equilibrium by the end of the experiment. Two-source isotope mixing models that incorporated the isotopic composition of FM and PBM as well as that of formulated feeds, empirically derived trophic discrimination factors and the isotopic composition of fish that had reached isotopic equilibrium to the diets were used to obtain a quantitative estimate of the retention of each source of nitrogen. Fish fed the diets with 33 and 66% replacement of FM by PBM retained poultry by-product meal roughly in proportion to its level of inclusion in the diets, whereas no differences were detected in the protein efficiency ratio. Coupled with the similar biomass gain of fishes fed the different diets, our results support the inclusion of PBM as replacement for fishmeal in aquaculture feeds. A re-feeding experiment in which all fish were fed a diet of 100% FM for 28 days indicated isotopic turnover occurred very fast, providing further support for the potential of isotopic ratios as tracers of the retention of specific protein sources into fish tissues. Stable isotope analysis is a useful tool for studies that seek to obtain quantitative estimates of the retention of different protein sources.