Use of Stable Isotopes to Investigate Keratin Deposition in the Claw Tips of Ducks

Stable isotopes derived from the claws of birds could be used to determine the migratory origins of birds if the time periods represented in excised sections of claws were known. We investigated new keratin growth in the claws of adult female Lesser Scaup (Aythya affinis) by estimating the equilibration rates of stable isotopes (δ ¹³C, δ ¹⁵N, and δ ²H) from the breeding grounds into 1 mm claw tips. We sampled birds on their breeding ground through time and found that it took approximately 3–3.5 months for isotope values in most claw tips to equilibrate to isotope values that reflected those present in the environment on their breeding grounds. Results from this study suggest that isotopes equilibrate slowly into claw tips of Lesser Scaup, suggesting isotopes could potentially be used to determine the wintering grounds of birds. We suggest using controlled feeding experiments or longitudinal field investigations to understand claw growth and isotopic equilibration in claw tips. Such information would be valuable in ascertaining whether claw tips can be used in future studies to identify the migratory origins of birds.     

干旱、半干旱区土壤蚯蚓稳定性碳同位素组成与轮作模式的关系

对10个不同耕地生境中蚯蚓(Lumbricus terrestris)的稳定性碳同位素进行了分析,研究了豫西洛阳干旱、半干旱地区土地轮作模式和耕作历史。结果表明,耕地表层土壤(0～30cm)中蚯蚓的δ13C介于-18.3‰和-25.6‰之间,变化幅度较大。经稳定性同位素质量平衡模式计算,10个生境中蚯蚓取食C3作物的比例在40.1%和99.4%之间波动,蚯蚓的取食生态受到土地上C3/C4作物轮作模式的影响。C4作物轮作频率与蚯蚓稳定性碳同位素比值之间呈正相关。土壤动物的稳定性碳同位素比值可较客观地反映出耕作制度和轮作模式。     

稳定同位素技术在植物水分利用研究中的应用

近20a稳定同位素技术在植物生态学研究中的应用得到了长足发展,使得对植物与水分关系也有了更深一步的了解。介绍稳定同位素性碳、氢、氧同位素在研究植物水分关系中的应用及进展,以期能为国内植物水分利用研究提供参考。由于植物根系从土壤中吸收水分时并不发生同位素分馏,对木质部水分同位素分析有助于对植物利用水分来源,生态系统中植物对水分的竞争和利用策略的研究,更好地了解生态系统结构与功能。稳定碳同位素作为植物水分利用效率的一个间接指标,在不同水分梯度环境中,及植物不同代谢产物与水分关系中有着广泛的应用。同位素在土壤-植被-大气连续体水分中的应用,有助于了解生态系统的水分平衡。随着稳定同位素方法的使用,植物与水分关系的研究将取得更大的进展。     

Looking at the unseen: combining animal bio‐logging and stable isotopes to reveal a shift in the ecological niche of a deep diving predator

Understanding how marine top predators exploit their environment is a central topic in marine ecology. Among all methodologies used to investigate this part of ecology, electronic devices are very useful to track animals' movements and foraging habitats, but they do not provide any dietary information. Stable isotopes provide information on trophic levels but remain imprecise to identify small spatial‐scale habitats. In this study, we combined the two approaches to obtain a synoptic view of the foraging behaviour variability of southern elephant seals Mirounga leonina. Our results suggested marked differences in distribution, diving behaviour, foraging habitats, trophic levels, and dietary habits of elephant seals according to their sex and age. Thus, we characterized main foraging habitats over the Kerguelen‐Heard Plateau and the Antarctic shelf for juvenile males, while females foraged mainly in oceanic waters of the Polar Frontal Zone and the Antarctic Zone. In addition, we highlighted the ontogeny of niche partitioning in this sexually dimorphic species. While females did not exhibit a major dietary shift in relation to their age and their breeding status, a different picture emerged for males. Young males had a trophic level identical to that of all females. However, at 3–4 yr of age, males showed a progressive increase in trophic level. The inter‐annual combination of bio‐logging and stable isotopes could provide a powerful tool to investigate possible shifts in ecological niche between years according to environmental changes.     

Zinc,copper, and iron nutrition studied with enriched stable isotopes

Enriched stable isotopes were used in nutrition studies of normal, healthy adults to measure zinc, copper, and iron absorption. After obtaining baseline values for zinc, copper, and iron absorption from diets adequate in all nutrients, the effects of age, pregnancy, and deveral dietary variables were studied. Stable isotopes of zinc, copper, and iron were incorporated into diets. Complete fecal samples were collected and the unabsorbed isotopes remaining in the samples were measured by thermal ionization mass spectrometry, the most precise analytical method for the determination of stable mineral isotopes. Stable isotopes were also infused in five young men to evaluate the potential of studying mineral utilization and kinetics with stable isotopes. The results of these studies demonstrate that a number of factors can affect mineral absorption, but the specific effects differ for different minerals. Isotopic enrichments could be measured in urine and blood, so kinetic studies of utilization of essential minerals are now feasible with enriched stable isotopes. Continued use of stable isotopes to determine mineral absorption, combined with stable-isotope studies of mineral utilization, balance data, and biochemical indicators of mineral status, should result in a better understanding of mineral requirements and metabolism under a variety of conditions.     

Using stable isotopes to trace origin and host plants of an African polyphagous pest and an European beneficial insect

Crop protection against insect pests requires first a good knowledge of the biology and ecology of the different pest species and the associated beneficials, in particular the spatial distribution of the populations. But the movement of insect populations in the landscape remains often poorly known and in some cases does not make it possible to know the role of the various cultivated and wild habitats in the dynamics of pest and useful insects. Stable isotopes are a tool contributing to the knowledge of host plants (13carbon/12carbon) as well as geographical origin of insects (1hydrogen/2hydrogen). The analysis of stable isotopic ratios has been performed in south-western France on populations of the hoverfly Episyrphus balteatus, one of the most important predators of the cereal aphids in Europe and on West African populations of the bollworm Helicoverpa armigera, an important polyphagous pest attacking cotton and vegetables in the Old World. Methodology, preliminary results and perspectives given by stable isotopes are presented here.     

Avian claw morphometry and growth determine the temporal pattern of archived stable isotopes

Detailed knowledge about claw formation and growth rate is a prerequisite for the interpretation of avian claw stable isotopes, as is commonly done with feather stable isotopes to e.g. infer habitat use, dietary specialisations, and spatial occurrence. In this study, we provide basic information about claw formation and empirical evidence about the time scale of archiving isotopic information to develop a reliable assessment of archived isotopic pattern in claws of passerines. Avian claws grow conically from the tip of the bone of the phalanx. The length of the tip of an avian claw, suitable for stable isotope analysis, is about 42 ± 6.8% (SD) of total linear claw length and can also be estimated from the body mass of a given species. Claw growth rate in adult songbirds typically ranged between 0.03 and 0.05 mm d^?1, but differed between front and back toes, and varied seasonally. From the claw growth rate, the archiving period of a given claw length can be estimated. In long‐distance migrant species, δ¹³C of claws matched δ¹³C of feathers grown during the same period (wintering or breeding period). In Palaearctic‐African migrants sampled in the breeding season, δ¹³C of the distal half of the claw tip reflected the African wintering site, while the proximal half reflected a blend of African and European δ¹³C signatures, as expected. Hence there is empirical evidence that entire claw tips mirror the isotopic environments over longer periods (up to months), and over weeks when parts can be analysed. However any part of a claw contains a blend of material formed at different times due to the claw's conical (i.e. longitudinal and lateral) growth. Avian claws provide a complementary isotope archive for investigations, but its applicability may vary according to the ecology of the study species.     

Use of stable carbon and nitrogen isotopes in insect trophic ecology

Insects are the most diverse organisms and often the most abundant animals in some ecosystems. Despite the importance of their functional roles and of the knowledge for conservation, the trophic ecology of many insect species is not fully understood. In this review, I present how stable carbon (C) and nitrogen (N) isotopes have been used to reveal the trophic ecology of insects over the last 30 years. The isotopic studies on insects have used differences in C isotope ratios between C₃ and C₄ plants, along vertical profiles of temperate and tropical forest stands, and between terrestrial and aquatic resources. These differences enable exploration of the relative importance of the food resources, as well as movement and dispersal of insects across habitats. The ¹³C‐enrichment (approximately 3‰) caused by saprotrophic fungi can allow the estimation of the importance of fungi in insect diets. Stable N isotopes have revealed food resource partitioning across diverse insect species above and belowground. Detritivorous insects often show a large trophic enrichment in ¹³C (up to 3‰) and ¹⁵N (up to 10‰) relative to the food substrates, soil organic matter. These values are greater than those commonly used for estimation of trophic level. This enrichment likely reflects the prevalence of soil microbial processes, such as fungal development and humification, influencing the isotopic signatures of diets in detritivores. Isotope analysis can become an essential tool in the exploration of insect trophic ecology in terms of biogeochemical C and N cycles, including trophic interactions, plant physiological and soil microbial processes.     

Spatial and temporal variabilities of δ<Superscript>13</Superscript>C and δ<Superscript>15</Superscript>N within lower trophic levels of a large lake: implications for estimating trophic relationships of consumers

Stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N) often have unique values among lake habitats (e.g. benthic, littoral, pelagic), providing a widely used tool for measuring the structure and energy flow in aquatic food webs. However, there has been little recognition of the spatial and temporal variabilities of these isotopes within habitats of aquatic ecosystems. To address this, δ¹³C and δ¹⁵N were measured in seston, zebra mussels (Dreissena polymorpha) and young-of-year (YOY) yellow (Perca flavescens), and white perch (Morone americana) collected from four sites across the offshore habitat of the western basin of Lake Erie during June–September 2009. Values of δ¹³C and δ¹⁵N showed significant spatial and temporal variations, with month accounting for >50% of the variation, for both stable isotopes and all the species except seston. Such variation in isotope values has the potential to significantly influence or confound interpretation of stable isotopes in measures, such as trophic position (TP) which use lower trophic level organisms as their baseline. For example, TP was found to vary up to 0.7 for yellow and white perch (TP = δ¹⁵N_fish − δ¹⁵N_{zebra mussel}/diet-tissue fractionation factor) depending on the zebra mussel data used (e.g., from a different location or a different collection month). As the use of stable isotopes continues to move from qualitative to more quantitative measures of trophic structure, food web research must recognize the importance of stable isotopes' variability in lower trophic level organisms, especially in large lake systems.     

Ecomorphology of the wheatears (genus Oenanthe)

We used measurements of museum skins to assess morphological differences between the 22 currently recognized species of wheatear and to identify correlations between morphological features, behavioural traits and degrees of sympatry between species. Ground-dwelling species of steppe-like habitats have long tarsi, long claws and short tails; some are migratory and have long pointed wings and non-emarginated primaries ( O. isabellina and O. oenanthe ), while others are sedentary and have more rounded and slotted wings ( O. bottae , O. heuglini and O. pileata ). Vegetation-tolerant species ( O. pleschanka , O. hispanica , O. cypriaca and O. deserti ) have relatively long tails, short tarsi, long middle toes and long claws. The rock-dwelling species have short tarsi, long toes and short claws; they can be either relatively heavy ( O. leucura and O. monticola ) or light, like the wheatears inhabiting the most arid areas ( O. monacha , O. leucopyga and O. alboniger ). Although sedentary, the latter show intermediate characteristics between sedentary and migratory species, having relatively pointed wings with non-emarginated primaries. Together with their low wing-loadings, these traits may be related to the scarcity of resources in their habitats, which obliges them to make frequent and long flights. The clear morphological differentiation between wheatear species appears to be mainly related to their migratory and foraging habits, but seems to bear no relation to their degree of sympatry.     

Stable isotope compounds - production,detection, and application

Stable isotopes are used in wide fields of application from natural tracers in biology, geology and archeology through studies of metabolic fluxes to their application as tracers in quantitative proteomics and structural biology. We review the use of stable isotopes of biogenic elements (H, C, N, O, S, Mg, Se) with the emphasis on hydrogen and its heavy isotope deuterium. We will discuss the limitations of enriching various compounds in stable isotopes when produced in living organisms. Finally, we overview methods for measuring stable isotopes, focusing on methods for detection in single cells in situ and their exploitation in modern biotechnologies.     

Prey-induced changes to a predator's behaviour and morphology: Implications for shell-claw covariance in the northwest Atlantic

Whereas many plasticity studies demonstrate the importance of inducible defences among prey, far fewer investigate the potential role of inducible offences among predators. Here we ask if natural differences in a snail's shell hardness can induce developmental changes to a predatory crab's claw size. To do this, we fed Littorina obtusata snails from either thick- or thin-shelled populations to captive European green crabs Carcinus maenas. The crabs' shell-breaking behaviour dominated among those fed thin-shelled snails, whereas crabs fed thick-shelled snails mostly winkled flesh through the shell opening without damaging the shell itself (a.k.a. aperture-probing behaviour). Significantly, the size of crab crusher claws grew in proportion to the frequency of shell-crushing behaviour and, for a same shell-crushing frequency, crabs fed thick-shelled snails grew larger crusher claws than those fed thin-shelled snails after two experimental moults. Diet and behaviour had no effect on the growth of the smaller cutter claws of same individuals, providing good evidence that allometric changes to crusher claws were indeed a result of differential use while feeding. Findings indicate that both predation habits and claw sizes are affected by green crabs' diet, supporting the hypothesis that prey-induced phenotypic plasticity contributes to earlier accounts of shell-claw covariance between this predator and its Littorina prey in the wild.     

Stable isotope ratios indicate that body condition in migrating passerines is influenced by winter habitat

Although predicted some time ago, there has been little success in demonstrating that the overall fitness of migratory birds depends on the combined influences of their experiences over all seasons. We used stable carbon isotope signatures (delta13C) in the claws of migrating black-throated blue warblers Dendroica caerulescens to infer their wintering habitats and investigated whether winter habitat selection can be linked to condition during migration. Resident bird species with low delta13C corresponded to selection of more mesic habitats, and migrating birds with low delta13C were in better condition than conspecifics with higher delta13C signatures. These findings concur with empirical observations on the wintering grounds, where dominants (mostly males) tend to exclude subordinates from mesic areas (considered to be high-quality habitats). We believe that variation in condition during migration may be one of the key factors determining differences in arrival times and condition at the breeding areas, which in turn have a major influence on reproductive success.     

Beaver invasion alters terrestrial subsidies to subantarctic stream food webs

North American beavers (Castor canadensis) were introduced to Tierra del Fuego Island in 1946 for their fur, and have since spread across the archipelago and onto the South American mainland. We assessed the impact of invasive beavers on streams of these forested watersheds by quantifying the trophic basis of production (TBP) and consumptive organic matter flows of benthic macroinvertebrate assemblages. TBP was determined in two streams: clear- and black-water. Stable isotopes were used across four streams to further elucidate food web structure and dominant pathways. TBP and stable isotopes showed that terrestrially derived organic matter (amorphous detritus, leaves, and wood) supported a majority of secondary production in the benthic food webs at all sites (forested reaches, beaver ponds, and sections downstream of ponds with foraged riparian zones). The magnitude of these flows was enhanced in beaver-modified sites compared with forested habitats (4.0–5.3× increase g AFDM m⁻² year⁻¹ in pond habitats, 1.1–2.1× increase in downstream habitats). Diatoms were the only autochthonous resource identified in macroinvertebrate guts, but their contribution to secondary production was small. Consumptive flows mirrored trends in TBP (i.e., dominance of terrestrial sources and greater magnitude in beaver ponds). Collector–gatherer consumption of amorphous detrital material dominated food web flows in all habitats, but was higher in beaver ponds relative to other habitats. Food web structure was simplified in beaver ponds; only two of the five possible functional groups contributed >1% of total organic matter flow in ponds (collector–gatherers and predators). Consumptive flows to predators increased in ponds, and stable isotopes of nitrogen and carbon (δ¹⁵N and δ¹³C) corroborated a relatively greater importance of predators (greater trophic distance), as well as less diversity of basal resources (less variation in δ¹³C) in ponds. Our findings indicate that invasive beaver’s engineering activities resulted in greater flows of terrestrial organic matter subsidies to in-stream food webs, which had a relatively greater change in the clear-water than in the black-water stream. Owing to the fact that these streams were naturally dependent on allochthonous resources for a majority of production and material flows, changes wrought by beavers to streams in forested environments are probably less than in watersheds with inherently greater dependence on autochthonous production such as the adjacent steppe biome.     

Unravelling complexities in benthic food webs using a dual stable isotope (hydrogen and carbon) approach

1. Stable carbon isotope studies have been an essential component of research regarding the contribution of methane (CH₄)-derived carbon to freshwater food webs and results have suggested that benthic macroinvertebrates in billabongs, streams and lakes may be partially, and in some instances, significantly 'fuelled' by methanotrophic biomass. However, the singular use of carbon isotopes can lead to ambiguous interpretations concerning the origin of carbon, especially in systems where phototrophs are likely to be using carbon respired sources and hence show more ¹³C-depleted values.
2. These uncertainties can be further resolved by the inclusion of additional isotopic data. Stable hydrogen isotopes are being increasingly used in food web studies with a marked advantage that sources may be isotopically distinct by one or two orders of magnitude greater than stable carbon or nitrogen, the isotopes most commonly used to delineate trophic interactions. By using hydrogen as a second biogeochemical tracer we provide further supportive evidence for the assimilation of methanotrophic microbial biomass by chironomid larvae.
3. Moreover, the hydrogen and carbon isotope values we found in chironomid tissues appear to reflect the original substrate used during methanogenesis; either acetate fermentation or carbonate reduction. Use of the former tends to result in relatively heavy carbon and light hydrogen isotope values due to kinetic isotope effects, whereas use of the latter results in relatively lighter carbon and heavier hydrogen isotope values.
4. We provide preliminary evidence to suggest that hydrogen and carbon isotope values in macroinvertebrates may be used to distinguish between CH₄ formation pathways and help to explain inter-depth and inter-specific differences between co-existing chironomid species found in the same lake.     

Stable Isotope Analysis in Primatology: A Critical Review

Stable isotope analysis has become an important tool in ecology over the last 25 years. A wealth of ecological information is stored in animal tissues in the relative abundances of the stable isotopes of several elements, particularly carbon and nitrogen, because these isotopes navigate through ecological processes in predictable ways. Stable carbon and nitrogen isotopes have been measured in most primate taxonomic groups and have yielded information about dietary content, dietary variability, and habitat use. Stable isotopes have recently proven useful for addressing more fine‐grained questions about niche dynamics and anthropogenic effects on feeding ecology. Here, we discuss stable carbon and nitrogen isotope systematics and critically review the published stable carbon and nitrogen isotope data for modern primates with a focus on the problems and prospects for future stable isotope applications in primatology. Am. J. Primatol. 74:969‐989, 2012. © 2012 Wiley Periodicals, Inc.     

Equations for Lipid Normalization of Carbon Stable Isotope Ratios in Aquatic Bird Eggs

Stable isotope ratios are biogeochemical tracers that can be used to determine the source of nutrients and contaminants in avian eggs. However, the interpretation of stable carbon ratios in lipid-rich eggs is complicated because ¹³C is depleted in lipids. Variation in ¹³C abundance can therefore be obscured by variation in percent lipids. Past attempts to establish an algebraic equation to correct carbon isotope ratios for lipid content in eggs have been unsuccessful, possibly because they relied partly on data from coastal or migratory species that may obtain egg lipids from different habitats than egg protein. We measured carbon, nitrogen and sulphur stable isotope ratios in 175 eggs from eight species of aquatic birds. Carbon, nitrogen and sulphur isotopes were enriched in lipid-extracted egg samples compared with non extracted egg samples. A logarithmic equation using the C∶N ratio and carbon isotope ratio from the non extracted egg tissue calculated 90% of the lipid-extracted carbon isotope ratios within ±0.5‰. Calculating separate equations for eggs laid by species in different habitats (pelagic, offshore and terrestrial-influenced) improved the fit. A logarithmic equation, rather than a linear equation as often used for muscle, was necessary to accurately correct for lipid content because the relatively high lipid content of eggs compared with muscle meant that a linear relationship did not accurately approximate the relationship between percent lipids and the C∶N ratio. Because lipid extraction alters sulphur and nitrogen isotope ratios (and cannot be corrected algebraically), we suggest that isotopic measurement on bulk tissue followed by algebraic lipid normalization of carbon stable isotope ratio is often a good solution for homogenated eggs, at least when it is not possible to complete separate chemical analyses for each isotope.     

Children's health risk assessment: incorporating a lifestage approach into the risk assessment process

This overview paper provides the historical context for the incorporation of lifestage‐specific concerns in human health risk assessment, briefly explains the process employed in a lifestage framework for risk assessment, and discusses the scientific rationale for how utilizing lifestage data will strengthen the overall risk assessment process. This risk assessment approach will add value by: (1) providing a more complete evaluation of the potential for vulnerability at different lifestages, including a focus on the underlying biological events and incorporation of mode of action information related to different critical developmental periods; (2) evaluating the potential for toxicity during all lifestages after early lifestage exposure; (3) reviewing the importance of integrating exposure information and adverse health effects across lifestages; and (4) serving as a basis to extend some aspects of the children's health risk assessment framework to all lifestages. Birth Defects Res (Part B), 2008. © 2008 Wiley‐Liss, Inc.     

Giant noctule bats face conflicting constraints between roosting and foraging in a fragmented and heterogeneous landscape

Noting that some ground-dwelling passerine birds have remarkably long claws, reflected in such names as longclaw (Motacillidae) and longspur (Emberizidae), this comparative study assessed whether these features might aid movement over grassy ground vegetation. Using measurements of museum specimens, we found that, corrected for body size, larks (Alaudidae) living in grassy habitats ( n =31) had significantly longer toes and claws and hence larger footspans than species dwelling on bare substrates ( n =25). Using phylogenetically corrected contrasts, the claw result remained strongly significant, and the footspan result marginally significant, while there was no significant difference between the toes of the two groups. Among 15 matched pairs of other ground-dwelling passerines, where one member of the pair inhabits vegetated ground and the other inhabits bare ground, the former had significantly longer toes and claws and hence larger footspans. We conclude that ground-dwelling passerines living on vegetated, typically grassy ground, have larger feet, due to both longer toes and claws. This probably facilitates movement over uneven and unstable vegetation.     

Stable isotopic records of bleaching and endolithic algae blooms in the skeleton of the boulder forming coral Montastraea faveolata

Within boulder forming corals, fixation of dissolved inorganic carbon is performed by symbiotic dinoflagellates within the coral tissue and, to a lesser extent, endolithic algae within the coral skeleton. Endolithic algae produce distinctive green bands in the coral skeleton, and their origin may be related to periods of coral bleaching due to complete loss of dinoflagellate symbionts or “paling” in which symbiont populations are patchily reduced in coral tissue. Stable carbon isotopes were analyzed in coral skeletons across a known bleaching event and 12 blooms of endolithic algae to determine whether either of these types of changes in photosynthesis had a clear isotopic signature. Stable carbon isotopes tended to be enriched in the coral skeleton during the initiation of endolith blooms, consistent with enhanced photosynthesis by endoliths. In contrast, there were no consistent δ¹³C patterns directly associated with bleaching, suggesting that there is no unique isotopic signature of bleaching. On the other hand, isotopic values after bleaching were lighter 92% of the time when compared to the bleaching interval. This marked drop in skeletal δ¹³C may reflect increased kinetic fractionation and slow symbiont recolonization for several years after bleaching.