Metabolism and foraging strategies of mid‐latitude mesozooplankton during cyanobacterial blooms as revealed by fatty acids,amino acids,and their stable carbon isotopes

Increasing sea surface temperatures (SST) and blooms of lipid‐poor, filamentous cyanobacteria can change mesozooplankton metabolism and foraging strategies in marine systems. Lipid shortage and imbalanced diet may challenge the build‐up of energy pools of lipids and proteins, and access to essential fatty acids (FAs) and amino acids (AAs) by copepods. The impact of cyanobacterial blooms on individual energy pools was assessed for key species temperate Temora longicornis and boreal Pseudo‐/Paracalanus spp. that dominated field mesozooplankton communities isolated by seasonal stratification in the central Baltic Sea during the hot and the cold summer. We looked at (a) total lipid and protein levels, (b) FA trophic markers and AA composition, and (c) compound‐specific stable carbon isotopes (δ¹³C) in bulk mesozooplankton and in a subset of parameters in particulate organic matter. Despite lipid‐poor cyanobacterial blooms, the key species were largely able to cover both energy pools, yet a tendency of lipid reduction was observed in surface animals. Omni‐ and carnivory feeding modes, FA trophic makers, and δ¹³C patterns in essential compounds emphasized that cyanobacterial FAs and AAs have been incorporated into mesozooplankton mainly via feeding on mixo‐ and heterotrophic (dino‐) flagellates and detrital complexes during summer. Foraging for essential highly unsaturated FAs from (dino‐) flagellates may have caused night migration of Pseudo‐/Paracalanus spp. from the deep subhalocline waters into the upper waters. Only in the hot summer (SST>19.0°C) was T. longicornis submerged in the colder subthermocline water (~4°C). Thus, the continuous warming trend and simultaneous feeding can eventually lead to competition on the preferred diet by key copepod species below the thermocline in stratified systems. A comparison of δ¹³C patterns of essential AAs in surface mesozooplankton across sub‐basins of low and high cyanobacterial biomasses revealed the potential of δ¹³C‐AA isoscapes for studies of commercial fish feeding trails across the Baltic Sea food webs.     

Determination of food sources of marine invertebrates from a subtidal sand community using analyses of fatty acids and stable isotopes

The fatty acid compositions and stable isotope ratios of carbon, nitrogen, and sulfur were analyzed in the bivalve mollusks Mactra chinensis, Pandora pulchella, Felaniella usta, and Megangulus zyonoensis, the polychaete Chaetopterus cautus, and the main sources of organic matter in a subtidal sand bottom community in Vostok Bay (Sea of Japan). The fatty acid composition and stable isotope ratios of some bivalves is likely to be indicative of substantial inputs from benthic microalgae and an important role of microbial food chains. Only the filter-feeding polychaete C. cautus showed similarity in these characteristics to suspended particulate organic matter synthesized by phytoplankton. It is suggested that the contribution of benthic microalgae to the diet of a consumer organism, inferred solely from the carbon stable isotope analysis, can be significantly overestimated.     

Fine-fraction carbonate stable isotopes as indicators of seasonal shallow mixed-layer paleohydrography

We have measured stable isotopic compositions of Miocene pelagic fine-fraction (<63 μm) carbonates from oligotrophic deep-sea sites in the Pacific and Atlantic oceans and compared them with those of coexisting foraminifers to test their utility as near sea-surface indicators. Fine-fraction carbonates (primarily polyspecific nannofossils) and surface-dwelling planktic foraminiferal (Globigerinoides) stable isotopes both have been considered to reflect surface-water hydrographic conditions. However, our results indicate that fine-fraction stable isotopes are offset from and do not correlate well with those of Globigerinoides. In contrast, stable isotopic records of the deep-dwelling planktic foraminifer Globoquadrina are in good correspondence with the fine-fraction records in terms of long-term (ca. >1 m.y.) trends and temporal variability. On the basis of a time-series hydrography and flux study site in the oligotrophic subtropical North Atlantic, we interpret the isotopic discrepancies between fine-fraction and Globigerinoides as resulting primarily from season of calcification, as well as possible vital effects. We suggest that fine-fraction stable isotope values from oligotrophic waters reflect late winter–early spring relatively cool, nutrient-rich shallow mixed-layer conditions during the time of deep mixing (i.e., spring bloom), whereas Globigerinoides stable isotope values record conditions that prevailed in the stratified surface waters in the warmer late spring–fall. This implies that paired analyses of fine-fraction and surface-dwelling planktic foraminiferal δ¹⁸O could be applied to reconstruct paleoseasonality of the open oceans. However, because the fine-fraction δ¹³C values are not representative of the annual mean surface-water δ¹³C, we recommend use of near surface-dwelling planktic foraminiferal δ¹³C as a proxy for δ¹³C of stratified surface waters that are more or less in equilibrium with the atmosphere with respect to pCO₂.     

Using stable isotopes to trace long-distance dispersal in birds and other taxa

The study of long‐distance dispersal (LDD) in animals may be advanced by recent applications of stable isotope analyses designed to track migratory organisms and to link populations throughout their annual cycle. This approach depends on there being enough isotopic difference in tissues among potential source populations such that individuals can be unequivocally assigned to their source. The isotopic mapping of such populations will be feasible only for species occurring in relatively few disjunct populations. However, the identification of isotopic outliers within known populations will be an extremely useful first step in the forensic application of stable isotopes to identify dispersal in general, and LDD in particular. The use of deuterium isotope analysis (δD) of tissues that can be assigned to its source (e.g. feather moult or its hair growth location) has provided a recent breakthrough in our ability to associate individuals with geographical origins at continental scales. The combination of this stable isotope with others and the ultimate combination of a variety of techniques, including the measurement of trace elements and molecular genetics markers, will undoubtedly improve resolution. The isotopic cataloguing of known history (i.e. philopatric) individuals within populations will be an important step in applying isotope techniques to evaluating LDD in any species. For aquatic insects, the isotopic marking of large numbers of individuals is possible through isotopic enrichment of local food webs using labelled compounds.     

Differences in feeding behaviour among Chironomus species revealed by measurements of sulphur stable isotopes and cadmium in larvae

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Corticosterone and stable isotopes in feathers predict egg size in Atlantic Puffins Fratercula arctica

Examining factors that operate outside the breeding season may provide new insights into life‐history traits such as egg size, in which individual variation has not been fully explained. We measured corticosterone (CORT) levels and δ¹⁵N values (trophic level) in feathers grown several months before egg‐laying to test the prediction that a female's physiological state and feeding behaviour prior to the breeding season can influence egg mass in Atlantic Puffins Fratercula arctica. As predicted, egg mass increased with both CORT and δ¹⁵N values in feathers, suggesting that the ability of female Puffins to meet the nutritional costs of egg production is related to CORT promoting increased foraging effort during moult and to consumption of a higher trophic‐level diet.     

稳定同位素技术在鲨鱼摄食和洄游行为研究中的应用

随着稳定同位素分析技术的不断成熟,其在生态学领域中的应用也增长迅速,并成为动物摄食生态学的重要研究工具.鲨鱼因其在生物系统进化过程中的独特地位和海洋生态系统中的重要作用已成为海洋食物网研究的重点,然而国内针对鲨鱼摄食习性和洄游行为等方面的研究仍处于起步阶段.本文在总结了国内外鲨鱼稳定同位素分析组织样品选取和样品预处理方法的基础上,系统归纳了稳定同位素技术在鲨鱼摄食生态学,尤其在其摄食和洄游行为研究领域中的应用,着重分析稳定同位素技术在鲨鱼稳定同位素判别值和更新速率、食性分析、营养级评估、洄游路径分析和生态位分布等核心问题上的应用现状和发展前景,以期为国内学者开展鲨鱼类基础生物、生态学研究提供有益参考.     

Disbalance of the natural ratio of cations in water as a factor affecting synthesis of lipids and fatty acids in fish eggs

The effects on the lipid status of developing embryos of a disturbed natural ratio of cations in water as a result of the pollution of water bodies by waste with a high potassium content (130–140 mg/l) were studied in the laboratory. The results obtained confirm the indication of reduced lipid synthesis and altered formation of phospholipids in embryos developing in a medium with a disturbed natural ratio of cations. In addition, the lysophospholipid fraction increased in these embryos, which indicates activation of phospholipid hydrolysis. It was also found that changes in the salt regime lead to a decreased content of cholesterol, the main membrane thickener. It was proposed that the changes discovered lead to disturbed stability and permeability of the membranes of fish eggs, with the subsequent death of embryos.     

Cryptic niche differentiation in West African savannah termites as indicated by stable isotopes

1. Termites consume a wide range of plant material at different stages of decomposition and, accordingly, have been classified into ‘feeding groups’. African savannah ecosystems harbour many termite species, yet most belong to Termitidae. Especially striking is the co‐occurrence of up to eight Macrotermitinae and five Trinervitermes species, each having apparently identical trophic niches, i.e. fungus‐growers and grass‐feeders, respectively. 2. This study examined stable isotope signatures of ¹⁵N and ¹³C of West African savannah termites to test the validity of existing feeding group concepts and whether there is fine‐scaled niche differentiation of species within feeding groups. Despite a phylogenetic signal that species from the same subfamily and congenerics have correlated isotope signatures, evidence of niche differentiation was found. 3. Interestingly, species with similar δ¹⁵N values generally differed in δ¹³C values, and vice versa. The dominant mound‐building fungus‐grower Macrotermes bellicosus had the lowest δ¹⁵N values among all fungus‐growers, indicating that it occupies a different trophic niche. 4. This fine‐scaled differentiation along the trophic niche axis can help to explain the coexistence of so many apparently identical termite species.     

Measuring the trophic ecology of ants using stable isotopes

Ants are prominent components of most terrestrial arthropod food webs, yet due to their highly variable diet, the role ants play in arthropod communities can be difficult to resolve. Stable isotope analysis is a promising method for determining the dietary history of an organism, and has the potential to advance our understanding of the food web ecology of social insects. However, some unique characteristics of eusocial organisms can complicate the application of this technique to the study of their trophic ecology. Using stable isotopes of N and C, we investigated levels of intraspecific variation both within and among colonies. We also examined the effect of a common preservation technique on δ¹⁵N and δ¹³C values. We discuss the implications of our results on experimental design and sampling methods for studies using stable isotopes to investigate the trophic ecology of social insects. Received 4 February 2005; revised 23 June 2005; accepted 4 July 2005.     

Patterns of stable S isotopes in a forested catchment as indicators for biological S turnover

Despite intensive biogeochemical research during the last thirty years, the relative importance of biological S turnover for the overall SO ₄ ^2– budget of forested catchments remains uncertain. The objective of the present study was (i) to gain new insight into the S cycle of theLehstenbach catchment (Northeastern Bavaria, Germany) through the analysis of stable isotopes of S and (ii) to differentiate between sites which are hot spots for SO ₄ ^2– reduction and sites where mineralization and adsorption/desorption processes are more important. The ³⁴S values and SO ₄ ^2– concentrations of soil solutions, throughfall and groundwater at four different sites as well as runoff of the catchment were measured. The relatively low variability of ³⁴S in throughfall and bulk precipitation was in contrast to the high temporal and spatial variability of ³⁴S in the soil solution. Sulfate in the soil solution of upland sites was slightly depleted in³⁴S compared to input values. This was most likely due to S mineralization. Sulfate in the soil solution from wetland soils was clearly enriched in³⁴S, indicating dissimilatory SO ₄ ^2– reduction. The observed spatial and temporal patterns of³⁴S turnover and SO ₄ ^2– concentrations might explain the overall balanced S budget of the catchment. At a time of decreasing anthropogenic deposition SO ₄ ^2– is currently released from upland soils. Furthermore, mineralization of organic S may contribute to SO ₄ ^2– release. Wetland soils in the catchment represent a sink for SO ₄ ^2– due to dissimilatory SO ₄ ^2– reduction.     

水稻土中脂肪酸互营氧化的研究进展

水稻田是温室气体甲烷(CH4)的重要释放源之一,有机质在水稻土中通过厌氧分解途径最终产生CH4和CO2.短链脂肪酸互营氧化是水稻土有机质降解的关键环节,但是由于互营微生物独特的生理生态特性,目前人们对于参与该过程的微生物群落及功能了解甚少.稳定同位素探针(SIP)技术被认为是实现环境中参与物质转化微生物种类与功能相耦合的有力工具.本文首先讨论互营过程的热力学基础和互营微生物的种间相互作用模式,然后简要讨论了互营过程的环境影响因子,最后详细综述稳定同位素探针技术在水稻土短链脂肪酸互营氧化过程中的相关研究.目前的研究表明:参与水稻土脂肪酸互营氧化过程的互营细菌种类丰富、多样性高;除已知互营细菌的作用外,大量未培养、功能未知的细菌类型也可能参与短链脂肪酸的互营氧化;对于互营细菌的伙伴而言,新型产甲烷胞菌属(Methanocella)类型的古菌在不同脂肪酸互营降解过程中均起主要作用,揭示了这类产甲烷古菌在水稻土厌氧产甲烷过程中的重要作用.     

Characterization of riparian species and stream detritus using multiple stable isotopes

Multiple stable isotopes were used to determine the effectiveness of distinguishing among several dominant riparian species and aquatic macrophytes both spatially (three sites) and temporally (three seasons) along an 8-km reach of a blackwater stream. The differences in isotopic composition were used to assess contributions of various organic matter sources to the detrital pool of the stream. Samples of riparian and aquatic macrophyte vegetation and detritus were collected at three times to represent early leaf-out (April), mid-summer (August), and just prior to abscission (October). Each sample was analyzed for stable isotopes of carbon ¹³C, nitrogen ¹⁵N, and sulfur ³⁴S Within a site and sampling date, ¹³C-values were significantly different among certain riparian species and detritus samples. Species differences persisted between seasons. ³⁴S values were the most variable of the three elements examined although they remained fairly constant through time within each species and site. The results suggest that temporal changes in isotopic compositions of riparian species and aquatic macrophytes are site-specific. Discriminant analysis dissimilarity plots (based on all three isotopes) demonstrated that the contribution of species to the detrital pool depended on the site and season. At the upper site, detritus was isotopically most similar to Quercus laurifolia and Sparganium americanum in April, and the aquatic macrophytes (S. americanum and Potamogeton spp.) in August and October. At the middle site, detritus was most similar to Carpinus caroliniana and Q. nigra in April but no single source was similar to detritus in August or October. At the lower site, detritus was most similar to Taxodium distichum for all three seasons.     

Biochemistry of radioiodinated free fatty acids

Summary Radioiodinated free fatty acids have been developed to study myocardial metabolism non-invasively in man. In the present study the distribution of radiolabeled lipids in the myocardium and in arterial and coronary sinus blood was evaluated following injection of three commonly used iodinated fatty acids in fasted (n = 5) and lactate loaded (n = 3) dogs. Five minutes after simultaneous i.v. injection of radioiodinated 17-I-heptadecanoic acid (IHDA),15-(p-I-phenyl) pentadecanoic acid (IPPA) and 15-(p-I-phenyl)-3,3-dimethylpentadecanoic acid (DMIPPA) a biopsy specimen and samples of arterial and coronary sinus blood were taken. After extraction and TLC the relative distribution of radioactivity in the aqueous phase (containing the oxidation products), pellet and organic phase was calculated. The organic phase was further divided into phospholipids, diglycerides, free fatty acids, triglycerides and cholesterolesters. Seventy two percent of IHDA was oxidized, 36% of IPPA and 7% of DMIPPA. The organic phase consisted primarily of triglycerides and phospholipids. The ratios of triglycerides to phospholipids were about the same for IHDA, IPPA and DMIPPA (0.58, 0.65 and 0.50, respectively). Free IHDA in tissue samples was low (4%) and elevated for IPPA and DMIPPA, (17% and 37%). During lactate loading triglycerides were higher for all three fatty acids. For IHDA and IPPA this increase was paralleled by a decrease in the aqueous phase, in case of DMIPPA the aqueous phase remained the same. Five minutes after injection most of the organic phase of both arterial and coronary sinus blood consisted of the injected fatty acids, the aqueous phase contained oxidation products. There were only minor differences during lactate loading. During the evaluation of scintigraphic patterns of the radioiodinated fatty acids under normal conditions (eg at rest) and during elevated lactate levels (eg during exercise) the differences in distribution must therefore be considered.     

Inclusion/exclusion of fatty acids in amylose complexes as a function of the fatty acid chain length

Structural models are proposed for amylose-fatty acid complexes depending on the respective chain lengths of their constituents. The three studied fatty acids induce the Vh amylose crystalline type. However, in contrast to lauric and palmitic acids, caprylic acid is not present in crystals. On the basis of the relative amounts of amylose and fatty acid determined in complexes and previous results of molecular modelling, inclusion of lauric and palmitic acids inside the amylose helices is proposed; the acyl chains are included in crystalline areas and the car☐ylic groups in amorphous areas. The absence of caprylic acid in crystals could be due to the solubility of this compound in the crystallization medium.     

The use of stable isotopes in the study of human pathophysiology

The growing prevalence of metabolic diseases including fatty liver disease and Type 2 diabetes has increased the emphasis on understanding metabolism at the mechanistic level and how it is perturbed in disease. Metabolomics is a continually expanding field that seeks to measure metabolites in biological systems during a physiological stimulus or a genetic alteration. Typically, metabolomics studies provide total pool sizes of metabolites rather than dynamic flux measurements. More recently there has been a resurgence in approaches that use stable isotopes (e.g. ²H and ¹³C) for the unambiguous tracking of individual atoms through compartmentalised metabolic networks in humans to determine underlying mechanisms. This is known as metabolic flux analysis and enables the capture of a dynamic picture of the metabolome and its interactions with the genome and proteome. In this review, we describe current approaches using stable isotope labelling in the field of metabolomics and provide examples of studies that led to an improved understanding of glucose, fatty acid and amino acid metabolism in humans, particularly in relation to metabolic disease. Examples include the use of stable isotopes of glucose to study tumour bioenergetics as well as brain metabolism during traumatic brain injury. Lipid tracers have also been used to measure non-esterified fatty acid production whilst amino acid tracers have been used to study the rate of protein digestion on whole body postprandial protein metabolism. In addition, we illustrate the use of stable isotopes for measuring flux in human physiology by providing examples of breath tests to measure insulin resistance and gastric emptying rates.     

Analysis of cellular fatty acids in Orientia tsutsugamushi as taxonomic markers

Six Orientia strains including 3 prototype strains such as Gilliam, Karp, and Kato, and 3 strains (Boryong, Pajoo, and Yongworl) isolated in Korea, were studied for the profiles of their cellular fatty acids. All tested strains contained octadecenoic acid C (18: 1) omega 9 c(57.3 +/- 3.5%), octadecanoic acid C (18: 0) (15.3 +/- 1.5%), and hexadecanoic acid C (16: 0) (12.7 +/- 1.7%) as major components; however, interestingly, eicosenoic acid C (20: 1) omega 9 c(2.6 +/- 0.6%) was found in all strains except the Yongworl strain. Furthermore none of the strains contained 3-hydroxy fatty acids. The ratios of total saturated fatty acid (SFA) to total unsaturated fatty acid (UFA) were within the range of 0.34 to 0.54. These results showed that the cellular fatty acid profile should provide more reliable information for the identification of these bacteria.