Nonlethal sampling for stable isotope analysis of juvenile Chinese sturgeon (Acipenser sinensis): Comparing δ13C and δ15N signatures in muscle and fin tissues

We compared δ¹³C and δ¹⁵N values of muscle with fin from juvenile Chinese sturgeon (Acipenser sinensis), to evaluate the feasibility of using nonlethal (fin) as an alternative to lethal (muscle) sampling. Size and lipid effect on the relationship between fin and muscle were also investigated. Dorsal muscle (DM) and fin clip (FC) were collected from A. sinensis with different body length (120–373 mm) in the Yangtze Estuary for isotope analysis. The result showed that (1) muscle isotope values could estimated by the values of fin, from either use the regression model (δ¹³C_DM = 0.939 × FC ? 2.577; δ¹⁵N_DM = 0.737 × FC + 4.638) or constants factors (δ¹³C_DM = δ¹³C_FC ? 1.27; δ¹⁵N_DM = δ¹⁵N_FC + 0.59); (2) no size‐based relationships with δ¹³C and δ¹⁵N from either fin or muscle; (3) lipid extraction significantly improving the fin and muscle regression model fit for both δ¹³C and δ¹⁵N values. Therefore, this study support the use of nonlethal fin tissues for isotope analysis of juvenile A. sinensis, and will allow trophic studies to avoid the effect of lipid accumulation from muscle.     

Factors controlling the stable isotope composition and C:N ratio of seston and periphyton in shallow lake mesocosms with contrasting nutrient loadings and temperatures

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Environmental and species‐specific controls on δ13C and δ15N in dominant woody plants from central‐western Argentinian drylands

Spatial variation in mean annual precipitation is the principal driver of plant water and nitrogen status in drylands. The natural abundance of carbon stable isotopes (δ¹³C) in photosynthetic tissues of C3 plants is an indicator of time‐integrated behaviour of stomatal conductance; while that of nitrogen stable isotopes (δ¹⁵N) is an indicator of the main source of plant N (soil N vs. atmospheric N₂). Previous studies in drylands have documented that plant δ¹³C and δ¹⁵N values increase with decreasing mean annual precipitation due to reductions in stomatal conductance, and soil enriched in ¹⁵N, respectively. However, evidence for this comes from studies focused on stable isotopes measurements integrated at the plant community level or on dominant plants at the site level, but little effort has been made to study C and N isotope variations within a species growing along rainfall gradients. We analysed plant δ¹³C, δ¹⁵N and C/N values of three woody species having different phenological leaf traits (deciduous, perennial and aphyllous) along a regional mean annual precipitation gradient from the central‐western Argentinian drylands. Noticeably, plant δ¹³C and δ¹⁵N values in the three woody species did not increase towards sites with low precipitation or at the start of the growing season (drier period), as we expected. These results suggest that environmental factors other than mean annual precipitation may be affecting plant δ¹³C and δ¹⁵N. The short‐term environmental conditions may interact with species‐specific plant traits related to water and nitrogen use strategies and override the predictive influence of the mean annual precipitation on plant δ¹³C and δ¹⁵N widely reported in drylands.     

Use of stable isotopes to understand food webs in Macao wetlands

In this study, components of the food-web in Macao wetlands were quantified using stable isotope ratio techniques based on carbon and nitrogen values. The δ¹³C and δ¹⁵N values of particulate organic matter (δ¹³C_POM and δ¹⁵N_POM, respectively) ranged from ?30.64 ± 1.0 to ?28.1 ± 0.7 ‰, and from ?1.11 ± 0.8 to 3.98 ± 0.7 ‰, respectively. The δ¹³C values of consumer species ranged from ?33.94 to ?16.92 ‰, showing a wide range from lower values in a freshwater lake and inner bay to higher values in a mangrove forest. The distinct dietary habits of consumer species and the location-specific food source composition were the main factors affecting the δ¹³C values. The consumer ¹⁵N-isotope enrichment values suggested that there were three trophic levels; primary, secondary, and tertiary. The primary consumer trophic level was represented by freshwater herbivorous gastropods, filter-feeding bivalves, and plankton-feeding fish, with a mean δ¹⁵N value of 5.052 ‰. The secondary consumer level included four deposit-feeding fish species distributed in Fai Chi Kei Bay and deposit-feeding gastropods in the Lotus Flower Bridge flat, with a mean δ¹⁵N value of 6.794 ‰. The tertiary consumers group consisted of four crab species, one shrimp species, and four fish species in the Lotus Flower Bridge Flat, with a mean δ¹⁵N value of 13.473 ‰. Their diet mainly comprised organic debris, bottom fauna, and rotten animal tissues. This study confirms the applicability of the isotopic approach in food web studies.     

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.     

Factors influencing stable nitrogen isotope ratios in wing membranes of insectivorous bat species: A field study

Nitrogen stable isotope analysis studies have become a useful tool in dietary studies to quantify differences in diet composition among species or individuals. However, laboratory studies have revealed several factors that influence the nitrogen isotope ratios (δ¹⁵N) in animal tissues (e.g. habitat, amount of ingested food, and metabolic rate). The influence of these factors has not been validated for free-ranging bat species, which is important for interpreting nitrogen isotope data in field studies. In this study, we measured δ¹⁵N from wing membranes (δ¹⁵N_w) and habitat samples (δ¹⁵N_h; soil and leaf, or sediment) to test for effects of diet, age, and individual energy demand in three free-living bat species (Myotis daubentonii, Nyctalus noctula and Nyctalus leisleri). We hypothesised that based on differences in diet composition δ¹⁵N_w values should increase in the sequence M. daubentonii, N. leisleri, and highest N. noctula. Furthermore, juveniles should have significantly lower δ¹⁵N_w compared to their mothers. Thirdly, the δ¹⁵N_w values of reproductively active individuals should be significantly higher than those of non-reproductive individuals. Values of δ¹⁵N_w were significantly influenced by differences in feeding ecology among species and individual reproductive status, but not by animal age. Our results show that species feeding on primary consumers have lower δ¹⁵N_w values than species feeding on secondary and tertiary consumers. Further, independent young did not differ in their δ¹⁵N_w values from adults suggesting that their tissues already reflect the insect diet. The effect of reproductive status varied among species which might reflect intra-specific differences in foraging behaviour of generalist vs. specialist species. In this study, we demonstrated that δ¹⁵N can provide information on the dietary range of bats, but researchers should account for variation owing to reproductive status, habitat, and species.     

The relationship between carbon and nitrogen stable isotopes of zooplankton and select environmental variables in low-latitude reservoirs

Cyclopoids were collected from 18 reservoirs in southern China during August (a wet month) and December (a dry month) of 2010 for the analysis of carbon and nitrogen stable isotopes (δ¹³C_Zoo and δ¹⁵N_Zoo). The objectives of this study were to examine whether δ¹³C_Zoo and δ¹⁵N_Zoo can be better indicators of primary productivity and trophic state than the stable isotope composition of suspended particulate organic matter (POM), and to evaluate the relationship between δ¹³C_Zoo and δ¹⁵N_Zoo and select environmental variables. The δ¹³C_Zoo in these reservoirs was enriched in August and depleted in December, and varied significantly along the continuum of trophic levels. By contrast, δ¹⁵N_Zoo was depleted in August and enriched in December, and did not increase significantly with an increase in trophic state. Both δ¹³C_Zoo and δ¹⁵N_Zoo were more strongly correlated with environmental factors than δ¹³C_POM and δ¹⁵N_POM were. In addition, more environmental factors were significantly correlated with δ¹³C_Zoo and the δ¹⁵N_Zoo than with δ¹³C_POM and δ¹⁵N_POM. When data from two seasons were pooled, δ¹³C_Zoo was strongly correlated with dissolved inorganic nitrogen (DIN), soluble reactive phosphorus (SRP) and the DIN:SRP ratio, while δ¹⁵N_Zoo was weakly correlated with nutrient concentrations. This study indicates that, compared to the stable isotope composition of POM, δ¹³C_Zoo is a better indicator of primary productivity and trophic state, while δ¹⁵N_Zoo may be used as a proxy for nitrogen sources in aquatic ecosystems.     

Niche overlap and diet composition of three sympatric coastal dolphin species in the southwest Atlantic Ocean

Sympatric species are expected to differ in ecological requirements to minimize niche overlap and avoid competition. Here we assess the trophic interactions among three coexisting dolphin species from southern Brazil: the franciscana dolphin (Pontoporia blainvillei), the Guiana dolphin (Sotalia guianensis), and the Lahille's bottlenose dolphin (Tursiops truncatus gephyreus). We evaluated temporal variation in carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope values of bone collagen to examine potential dietary shifts resulting from increased fishing activity over the past three decades. We estimated the degree of niche overlap among these species and the contribution of potential prey sources to their diet. δ¹⁵N values were consistent among species and across years, while δ¹³C values increased for Guiana dolphins and decreased for bottlenose dolphins, suggesting changes in diet and/or foraging habitats through time. The similar δ¹³C and δ¹⁵N values and the high niche overlap between Guiana and bottlenose dolphins indicate that these species are primarily feeding on demersal prey. The franciscana diet is primarily composed of pelagic prey, resulting in a lower niche overlap in comparison with the other dolphin species. Our study provides further information about the foraging ecology of this unique dolphin community in southern Brazil with implications for its management and conservation.     

Diet,society, and economy in late medieval Spain: Stable isotope evidence from Muslims and Christians from Gandía,Valencia

This article investigates the diets of neighboring Christians and Muslims in late medieval Spain (here 13th–16th centuries) through the analysis of the stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N) in adult human and animal bone collagen. Twenty‐four Christians and 20 Muslims are sampled from two adjacent and contemporaneous settlements in the township of Gandía on the Mediterranean coast, together with the remains of 24 animals. Statistical differences in both δ¹³C and δ¹⁵N reveal that the diets of the two faith communities differed, despite living side‐by‐side. These differences may relate to inequalities in their access to foodstuffs, particularly to C₃/C₄ grain and/or possibly terrestrial meat sources, though cultural preferences are also highlighted. Isotopic values for animals were also found to vary widely, both between and within species, and this provides a window into the local livestock economy. Am J Phys Anthropol 156:263–273, 2015. © 2014 The Authors. American Journal of physical Anthropology published by Wiley Periodicals,Inc.     

IMPACT OF TAXONOMY,GEOGRAPHY, AND DEPTH ON δ13C AND δ15N VARIATION IN A LARGE COLLECTION OF MACROALGAE1

The natural abundance of carbon stable isotopes (δ¹³C) of marine macrophytes has been measured in previous studies and used to analyze differences in C_i assimilation among the three macroalgal phyla, Chlorophyta, Ochrophyta, and Rhodophyta, and seagrasses, distinguishing diffusive CO₂ entry from the operation of a CO₂‐concentrating mechanisms (CCM). The work reported here further resolves the patterns of δ¹³C variation in aquatic macrophytes related to their taxonomy, geographic location (and consequently climatic conditions), and vertical zonation. Analyses of δ¹³C for 87 species are reported, including eight that have not been previously examined, belonging to taxa in the three macroalgal phyla, plus two species of seagrasses, collected at different latitudes. For one species of each phylum, analyses were also conducted through a vertical depth gradient. Representative species were used in a pH drift experiment, in order to compare the mechanism of C_i acquisition for photosynthesis with the δ¹³C subsequently determined on the same specimen. Our results suggest that the δ¹³C values were mostly determined by taxonomy. Depth effects on C stable isotope composition differed among taxa. The parallel measurements of δ¹⁵N are more difficult to interpret mechanistically; there are no robust phylogenetic and large‐scale biogeographic correlations; local factors of natural (e.g., upwellings) and anthropogenic (e.g., sewage outfall) inputs predominate in determining the macrophyte δ¹⁵N.     

Fatty-Acid and Stable-Isotope Compositions in Shallow-Water Bivalve Mollusks and their Food

We conducted a comparative analysis of the fatty acid (FA) composition and the ratios of stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N) in soft tissues of ten species of bivalve mollusks collected simultaneously on adjacent biotopes in shallow Vostok Bay (the Sea of Japan). Comparison of the FA composition of the lipids of digestive gland and all soft tissues showed that the percentages of C₁₆ and C₁₈ marker FAs were greater in the digestive gland and the levels of marker C₂₀ and C₂₂ FAs were, in most cases, higher in soft tissues. According to the results of cluster analysis and principal component analysis, four groups of samples were identified with a similarity of the FA composition of more than 80% within groups. The carbon stableisotope ratios varied within very wide limits in the studied species of bivalves; the range of δ¹³C variations was 8.1‰. The range of δ15N variations was much smaller, 2.5‰. Two pairs of species of mollusks (Saxidomus purpurata–Protothaca euglypta and P. jedoensis–Diplodonta semiasperoides) did not differ in the values of both δ¹⁵N and δ¹³C, the remaining species differed in at least one of these parameters. The greatest similarity of the FA composition and stable-isotope ratios was found in species that inhabit similar substrates, except Macoma irus and D. semiasperoides. Particularly marked differences in the FA composition and stable-isotope ratios were found between a filter-/surface deposit-feeder M. irus and filter-feeders Arca boucardi and Mytilus coruscus that live next to this species.     

Environmental niches and metabolic diversity in Neoarchean lakes

The diversification of macro‐organisms over the last 500 million years often coincided with the development of new environmental niches. Microbial diversification over the last 4 billion years likely followed similar patterns. However, linkages between environmental settings and microbial ecology have so far not been described from the ancient rock record. In this study, we investigated carbon, nitrogen, and molybdenum isotopes, and iron speciation in five non‐marine stratigraphic units of the Neoarchean Fortescue Group, Western Australia, that are similar in age (2.78–2.72 Ga) but differ in their hydro‐geologic setting. Our data suggest that the felsic‐dominated and hydrologically open lakes of the Bellary and Hardey formations were probably dominated by methanogenesis (δ¹³C_org = ?38.7 ± 4.2‰) and biologic N₂ fixation (δ¹⁵N_bulk =?0.6 ± 1.0‰), whereas the Mt. Roe, Tumbiana and Kylena Formations, with more mafic siliciclastic sediments, preserve evidence of methanotrophy (δ¹³C_org as low as ?57.4‰, δ¹³C_carb as low as ?9.2‰) and NH₃ loss under alkaline conditions. Evidence of oxygenic photosynthesis is recorded only in the closed evaporitic Tumbiana lakes marked by abundant stromatolites, limited evidence of Fe and S cycling, fractionated Mo isotopes (δ^98/95Mo = +0.4 ± 0.4‰), and the widest range in δ¹³C_org (?57‰ to ?15‰), suggesting oxidative processes and multiple carbon fixation pathways. Methanotrophy in the three mafic settings was probably coupled to a combination of oxidants, including O₂ and SO₄^2‐. Overall, our results may indicate that early microbial evolution on the Precambrian Earth was in part influenced by geological parameters. We speculate that expanding habitats, such as those linked to continental growth, may have been an important factor in the evolution of life.     

Trophic level delineation and resource partitioning in a South African afromontane forest bird community using carbon and nitrogen stable isotopes

Southern African forests are naturally fragmented yet hold a disproportionately high number of bird species. Carbon and nitrogen stable isotopes were measured in feathers from birds captured at Woodbush (n = 27 species), a large afromontane forest in the eastern escarpment of Limpopo province, South Africa. The δ¹³C signatures of a range of forest plants were measured to categorise the food base. Most plants sampled, including two of five grass species, had δ¹³C signatures typical of a C₃ photosynthetic pathway (?29.5 ± 1.9‰). Three grass species had a C₄ signature (?12.0 ± 0.6‰). Most bird species had δ¹³C values representing a predominantly C₃‐based diet (?24.8‰ to ?20.7‰). δ¹⁵N values were as expected, with higher levels of enrichment associated with a greater proportion of dietary animal matter. The cohesive isotopic niche defining most species (n = 22), where the ranges for δ¹³C and δ¹⁵N were 2.4‰ and 3.4‰, respectively, highlight the difficulties in understanding diets of birds in a predominantly C₃‐based ecosystem using carbon and nitrogen stable isotopes. However, variation in isotopic values between and within species provides insight into possible niche width and the use of resources by different birds within a forest environment.     

Variations in bone collagen δC and δN values of fauna from Northwest Europe over the last 40?000 years

We report here a signal in the temporal variation of stable isotopes in protein from surviving animal bone in Northwest Europe over the past glacial cycle. There is a change in the average δ¹³C values of fauna in the Holocene, and there is also a significant reduction in δ¹⁵N values of herbivore bone collagen towards the end of the last glaciation, with a subsequent recovery soon after the start of the Holocene. This change is observed for several species and is restricted to those regions most affected by the glacial advance. Comparison with ice core data shows that there is a strong correlation between the average δ¹³C values of three herbivore species and ice core CO₂ concentration. The data presented here show how readily available faunal bone collagen δ¹³C and δ¹⁵N measurements provide a record of past climate and environmental change on a regional to continental scale.     

An elemental and stable isotope assessment of water strider feeding ecology and lipid dynamics: synthesis of laboratory and field studies

1. Despite the ubiquity and abundance of water striders (Hemiptera: Gerridae) in temperate streams and rivers and their potential usefulness as sentinels in contaminant studies, little is known about their feeding ecology and lipid dynamics. 2. In this study we used stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N) and elemental carbon to nitrogen ratios (C/N) to assess dietary habits and lipid content, respectively, for water striders. 3. To determine diet‐tissue fractionation factors, nymphs of the most common species in New Brunswick, Canada, Aquarius remigis were reared in the laboratory for 73 days and exhibited rapid isotopic turnover in response to a switch in diet (C half‐life = 1.5 days, N half‐life = 7.8 days). Their lipid content increased towards the end of the growing season and resulted in lower δ¹³C values. Diet‐tissue fractionation factors were established after correction of δ¹³C data for the confounding effect of de novo lipid synthesis (strider δ¹³C_adj– diet δ¹³C_adj = 0.1‰, strider δ¹⁵N – diet δ¹⁵N = 2.7‰). 4. Water striders from the majority of 45 stream sites (83%) in New Brunswick had less than 50% contribution of aquatic carbon to their diets but showed a gradual increase in the contribution of this carbon source to their diet with increasing stream size. 5. These data indicate that striders exhibit a strong connection to terrestrial carbon sources, making them important users of energy subsidies to streams from the surrounding catchment. However, this dependence on terrestrial organic matter may limit their utility as indicators of contamination of aquatic systems by heavy metals and other pollutants.     

Modern macaque dietary heterogeneity assessed using stable isotope analysis of hair and bone

Dietary variability might have been a major factor in the dispersal and subsequent persistence of the genus Macaca in both tropical and temperate areas. Macaques are found from northern Africa to Japan, yet there have been few systematic attempts to compare diets between different modern populations. Here we have taken a direct approach and sampled museum-curated tissues (hair and bone) of Macaca mulatta (rhesus macaques) for carbon and nitrogen stable isotope dietary analyses. Samples from India, Vietnam, and Burma (Myanmar) were taken, representing both tropical and temperate populations. The δ¹³C values obtained from hair show that the temperate macaques, particularly those from Uttar Pradesh, have a δ¹³C signature that indicates at least some use of C₄ resources, while the tropical individuals have a C₃-based diet. However, δ¹³C values from bone bioapatite indicate a C₃-based diet for all specimens and they do not show the C₄ usage seen in the hair of some animals, possibly because bone represents a much longer turnover period than that of hair. The results of δ¹⁵N analyses grouped animals by geographic region of origin, which may be related to local soil nitrogen values. The greatest variation in δ¹⁵N values was seen in the specimens from Burma, which may be partly due to seasonality, as specimens were collected at different times of year. We also investigated the relationship between the hair, bone collagen, and bone bioapatite δ¹³C results, and found that they are highly correlated, and that one tissue can be used to extrapolate results for another. However, our results also suggest that hair may pick up discrete feeding traces (such as seasonal usage), which are lost when only bone collagen and bioapatite are examined. This has important implications for dietary reconstructions of archaeological and paleontological populations.     

Stable carbon isotope composition of bone hydroxylapatite: significance in paleodietary analysis

The stable carbon isotope composition of the structural carbonate derived from animal bone hydroxylapatite (δ¹³C_B-HA) could record an animal’s diet. These records provide critical evidence for different paleontological disciplines, e.g., paleodiet analyses, and paleoclimate reconstructions. Compared to those of other body tissues, such as bone collagen or teeth enamel hydroxylapatite, δ¹³C_B-HA values record information on the whole diet of an animal in its last years. δ¹³C_B-HA can be applied to fossil animals of various body sizes. The δ¹³C analytical instruments available only require that prepared bone samples be approximately 2–5 mg for precise measurement, allowing δ¹³C_B-HA analysis to be feasible on most vertebrate fossils without destructive sampling, especially on small mammals or birds whose teeth are not large enough for sampling or are lost. Moreover, δ¹³C_B-HA can be used from different times or under less than ideal burial environments. For fossils dating back to Devonian or buried in hot and humid regions, dietary information has been completely lost in bone collagen during post-depositional processes but still remained in the δ¹³C_B-HA values because hydroxylapatite is less influenced by diagenetic effects after deposition. In addition, systematic methods such as X-ray diffraction and Fourier transform infrared spectroscopy have been developed to qualitatively or semiquantitatively assess the influence of diagenesis on bone hydroxylapatite to ensure the credibility of the δ¹³C_B-HA values. With the above merits, δ¹³C_B-HA analysis is therefore becoming an increasingly important method in paleodiet-related research. Currently, applications of the δ¹³C_B-HA method on fossil animals are primarily focused on two aspects, namely, paleodietary reconstruction of fossil animals with uncertain diets and paleoenvironmental reconstruction based on the δ¹³C_B-HA values of fossil herbivores. The published researches, combined with our new results from early birds, demonstrate the considerable significance of the δ¹³C_B-HA method in paleontological and paleoenvironmental research. Notably, the δ¹³C_B-HA-based paleodietary analysis of early vertebrates, especially the large number of small birds or mammals discovered in the past decades would be an important work in the near future.     

Species-specific differences in temporal and spatial variation in δ13C of plant carbon pools and dark-respired CO2 under changing environmental conditions

Stable carbon isotope signatures are often used as tracers for environmentally driven changes in photosynthetic δ¹³C discrimination. However, carbon isotope signatures downstream from carboxylation by Rubisco are altered within metabolic pathways, transport and respiratory processes, leading to differences in δ¹³C between carbon pools along the plant axis and in respired CO₂. Little is known about the within-plant variation in δ¹³C under different environmental conditions or between species. We analyzed spatial, diurnal, and environmental variations in δ¹³C of water soluble organic matter (δ¹³C_WSOM) of leaves, phloem and roots, as well as dark-respired δ¹³CO₂ (δ¹³C_res) in leaves and roots. We selected distinct light environments (forest understory and an open area), seasons (Mediterranean spring and summer drought) and three functionally distinct understory species (two native shrubs—Halimium halimifolium and Rosmarinus officinalis—and a woody invader—Acacia longifolia). Spatial patterns in δ¹³C_WSOM along the plant vertical axis and between respired δ¹³CO₂ and its putative substrate were clearly species specific and the most δ¹³C-enriched and depleted values were found in δ¹³C of leaf dark-respired CO₂ and phloem sugars, ~?15 and ~?33 ‰, respectively. Comparisons between study sites and seasons revealed that spatial and diurnal patterns were influenced by environmental conditions. Within a species, phloem δ¹³C_WSOM and δ¹³C_res varied by up to 4 ‰ between seasons and sites. Thus, careful characterization of the magnitude and environmental dependence of apparent post-carboxylation fractionation is needed when using δ¹³C signatures to trace changes in photosynthetic discrimination.     

Using stable isotopes and C:N ratios to examine the life‐history strategies and nutritional sources of larval lampreys

Natural abundance stable‐isotope analysis (δ¹³C and δ¹⁵N) and C:N ratios were used to study the ammocoete phase of two common non‐parasitic lamprey species (least brook lamprey Lampetra aepyptera and American brook lamprey Lethenteron appendix) in two tributaries of the Ohio River (U.S.A.). The C:N ratios suggest that each species employs different lipid accumulation strategies to support its metamorphosis and recruitment into an adult animal. Ammocoete δ¹³C values generally increased with increasing C:N values. In contrast to δ¹³C, ammocoete δ¹⁵N values were weakly related to the total length (L_T) in L. aepyptera, but positively correlated to both L_T and C:N ratios in L. appendix. In L. appendix, C:N also correlated positively with L_T, and presumably age. A Bayesian mixing model using δ¹³C and δ¹⁵N was used to estimate nutritional subsidies of different potential food resources to ammocoetes at each site. The models suggested that although nutritional subsidies to ammocoetes varied as a function of site, ammocoetes were generally reliant on large contributions (42–62% at three sites) from aquatic plants. Contributions from aquatic sediment organic matter were also important at all sites (32–63%) for ammocoetes, with terrestrially derived plant materials contributing smaller amounts (4‐33%). These findings provide important insights into the feeding ecology and nutrition of two species of lampreys. They also suggest that similar and other quantitative approaches are required to (1) fully understand how the observed stable‐isotopes ratios are established in ammocoetes and (2) better assess ammocoete nutritional subsidies in different natal streams.     

Tracing prey origins,proportions and feeding periods for predatory beetles from agricultural systems using carbon and nitrogen stable isotope analyses

Predatory beetles are an important component of the natural enemy complex that preys on insect pests such as aphids within agroecosystems. Tracing diet origins and movement of natural enemies aids understanding their role in the food web and informs strategies for their effective conservation. Field sampling and laboratory experiments were carried out to examine the changes of carbon and nitrogen stable isotope ratios (δ¹³C and δ¹⁵N) among crops (cotton and maize), pests (cotton and maize aphids), and between wing and abdomen of predatory beetles, Propylea japonica, and to test the hypothesis that prey origins, proportions and feeding periods of the predatory beetles can be deduced by this stable isotope analysis. Results showed that the δ¹³C values both in wing and abdomen of adult P. japonica were changing from a C₃- to a C₄-based diet of aphids reared on maize or cotton, respectively; the isotope ratio of their new C₄ substrates were detectable within 7 days and the δ¹⁵N values began to reflect their new C₄ substrates within 3 days. The relationship between δ¹³C and δ¹⁵N values of P. japonica adults in wing or abdomen and diets of aphids from a C₃-based resource transitioning to a C₄-based resource were described best in linear or quadratic equations. Results suggest that integrative analysis of δ¹³C and δ¹⁵N values can be regarded as a useful method for quantifying to trace prey origins, proportions of diets and feeding periods of natural enemies. The results can provide quantifying techniques for habitat management of natural enemies.