Differential δ13C and δ15N signatures among scallop tissues: Implications for ecology and physiology

International audienceThere have been several studies where the isotopic composition of organisms has been determined seasonally, but fewer have examined separate organs. In this context, separate organs (e.g. gonad, digestive gland and muscle), of a suspension-feeder, the scallop Pecten maximus, were used to assess seasonal changes of both stable isotopes and biochemical components. Our study used multiple indicators (stable carbon and nitrogen isotopes ratios, biochemical components and seston Chl a) to track nutritive activity and energy allocation in P. maximus from the Bay of Brest (France). In addition to seasonal variation in the isotopic composition of P. maximus tissues, we found strong differences in the mean isotopic signatures of different organs. This has serious implications for interpretation of animal diets and potential use in animal physiology. Furthermore, we present evidence that seasonal variations of metabolism will cause changes in the isotopic composition not related to changes in the diet. Interpretation of isotopic data may require consideration of values from several separate organs. Finally, 15N appears powerful to track metabolite fates in the scallop P. maximus

Responses of two scleractinian corals to cobalt pollution and ocean acidification

The effects of ocean acidification alone or in combination with warming on coral metabolism have been extensively investigated, whereas none of these studies consider that most coral reefs near shore are already impacted by other natural anthropogenic inputs such as metal pollution. It is likely that projected ocean acidification levels will aggravate coral reef health. We first investigated how ocean acidification interacts with one near shore locally abundant metal on the physiology of two major reef-building corals: Stylophora pistillata and Acropora muricata. Two pH levels (pH(T) 8.02; pCO(2) 366 mu atm and pH(T) 7.75; pCO(2) 1140 mu atm) and two cobalt concentrations (natural, 0.03 mu g L-1 and polluted, 0.2 mu g L-1) were tested during five weeks in aquaria. We found that, for both species, cobalt input decreased significantly their growth rates by 28% while it stimulated their photosystem II, with higher values of rETR(max) (relative Electron Transport Rate). Elevated pCO(2) levels acted differently on the coral rETR(max) values and did not affect their growth rates. No consistent interaction was found between pCO(2) levels and cobalt concentrations. We also measured in situ the effect of higher cobalt concentrations (1.06 +/- 0.16 mu g L-1) on A. muricata using benthic chamber experiments. At this elevated concentration, cobalt decreased simultaneously coral growth and photosynthetic rates, indicating that the toxic threshold for this pollutant has been reached for both host cells and zooxanthellae. Our results from both aquaria and in situ experiments, suggest that these coral species are not particularly sensitive to high pCO(2) conditions but they are to ecologically relevant cobalt concentrations. Our study reveals that some reefs may be yet subjected to deleterious pollution levels, and even if no interaction between pCO(2) levels and cobalt concentration has been found, it is likely that coral metabolism will be weakened if they are subjected to additional threats such as temperature increase, other heavy metals, and eutrophication

Stable carbon isotopic composition of Mytilus edulis shells: relation to metabolism, salinity, d13CDIC and phytoplankton.

Abstract Bivalve shells can potentially record the carbon isotopic signature of dissolved inorganic carbon (d 13 C DIC ) in estuarine waters, thereby providing information about past estuarine biogeochemical cycles. However, the fluid from which these animals calcify is a 'pool' of metabolic CO 2 and external dissolved inorganic carbon (DIC). The incorporation of respired 13 Cdepleted carbon into the skeletons of aquatic invertebrates is well documented, and may affect the d 13 C record of the skeleton. Typically, less than 10% of the carbon in the skeleton is metabolic in origin, although higher amounts have been reported. If this small offset is more or less constant, large biogeochemical gradients in estuaries may be recorded in the d 13 C value of bivalve shells. In this study, it is assessed if the d 13 C values of Mytilus edulis shells can be used as a proxy of d 13 C DIC as well as providing an indication of salinity. First, the d 13 C values of respired CO 2 (d 13 C R ) were considered using the d 13 C values of soft tissues as a proxy for d 13 C R . Along the strong biogeochemical gradient of the Scheldt estuary (The NetherlandsBelgium), d 13 C R was linearly related to d 13 C DIC (r 2 = 0.87), which in turn was linearly related to salinity (r 2 = 0.94). The mussels were highly selective, assimilating most of their carbon from phytoplankton out of the total particulate organic carbon (POC) pool. However, on a seasonal basis, tissue d 13 C varied differently than d 13 C DIC and d 13 C POC , most likely due to lipid content of the tissue. All shells contained less than 10% metabolic carbon, but ranged from near zero to 10%, thus excluding the use of d 13 C in these shells as a robust d 13 C DIC or salinity proxy. As an example, an error in salinity of about 5 would have been made at one site. Nevertheless, large changes in d 13 C DIC (>2&) can be determined using M. edulis shell d 13 C

Assimilation of shrimp farm sediment by Holothuria scabra: a coupled fatty acid and stable isotope approach

Deposit-feeding sea cucumbers are efficient nutrient recyclers and have the potential to contribute to the limitation of organic matter load in polyculture or integrated aquaculture systems. Assessing how they assimilate organic matter originating from other farmed species is therefore important for the development of such multi-species farming systems. Here, a coupled stable isotope − fatty acid approach was used to characterize the assimilation of organic matter from shrimp (Penaeus stylirostris) farming by Holothuria scabra in an experimental culture system. H. scabra were reared in mesocosms on shrimp farming-originating sediment with and without additional food sources (maize and fish meals). Although fatty acid results did indicate that shrimp-farming sediment was assimilated by holothurids, we found no evidence of maize waste and fish meal contribution to H. scabra organic carbon (no effect on δ13C, no accumulation of meal-specific fatty acids). However, a strong effect of fish meal on H. scabra δ15N was observed, suggesting that this additional food source could represent an alternative source of nitrogen for holothurids. Finally, this study supports the culture of H. scabra as a perspective to reduce sedimentary organic matter excess associated with shrimp farms, and suggest that the addition of selected food sources might contribute to increasing the content in some nitrogen organic compounds in holothurid tissues

An English cover-up: masks, murders, and English cruelty in Goncourt, Lorrain, and Schwob

Fin-de-siècle writers from diverse disciplines were drawn to the seductive potential of masks and disguise; mask-wearing characters of indefinite identity, indeterminate gender, and insecure psychology proliferate in their texts. However, when characters are designated as English in such stories, they are also, and with remarkable frequency, associated with cruelty or murder: the mask-wielding murderers of Marcel Schwob’s ‘MM. Burke et Hare, Assassins’ carry out their crimes in Britain upon British victims; Edmond de Goncourt weaves his theatrical narrative around the mask-like demeanour of Lord Annandale in La Faustin; and Jean Lorrain’s malicious Lord Ethal exacerbates the Duc de Fréneuse’s perverse obsessions with masks in Monsieur de Phocas. This article explores this unexpected correlation, and examines the ways that English masks are used as narrative devices – at once to mould and play with national distinctions, and to reflect upon the psychological state of the French subject

Sequential Isotopic Signature Along Gladius Highlights Contrasted Individual Foraging Strategies of Jumbo Squid (Dosidicus gigas)

International audienceBackground: Cephalopods play a major role in marine ecosystems, but knowledge of their feeding ecology is limited. In particular, intra- and inter-individual variations in their use of resources has not been adequatly explored, although there is growing evidence that individual organisms can vary considerably in the way they use their habitats and resources. Methodology/Principal Findings: Using d13C and d15N values of serially sampled gladius (an archival tissue), we examined high resolution variations in the trophic niche of five large (.60 cm mantle length) jumbo squids (Dosidicus gigas) that were collected off the coast of Peru. We report the first evidence of large inter-individual differences in jumbo squid foraging strategies with no systematic increase of trophic level with size. Overall, gladius d13C values indicated one or several migrations through the squid's lifetime (,8-9 months), during which d15N values also fluctuated (range: 1 to 5%). One individual showed an unexpected terminal 4.6% d15N decrease (more than one trophic level), thus indicating a shift from higher- to lower-trophic level prey at that time. The data illustrate the high diversity of prey types and foraging histories of this species at the individual level. Conclusions/Significance: The isotopic signature of gladii proved to be a powerful tool to depict high resolution and ontogenic variations in individual foraging strategies of squids, thus complementing traditional information offered by stomach content analysis and stable isotopes on metabolically active tissues. The observed differences in life history strategies highlight the high degree of plasticity of the jumbo squid and its high potential to adapt to environmental changes

A global perspective on the trophic geography of sharks

Sharks are a diverse group of mobile predators that forage across varied spatial scales and have the potential to influence food web dynamics. The ecological consequences of recent declines in shark biomass may extend across broader geographic ranges if shark taxa display common behavioural traits. By tracking the original site of photosynthetic fixation of carbon atoms that were ultimately assimilated into muscle tissues of 5,394 sharks from 114 species, we identify globally consistent biogeographic traits in trophic interactions between sharks found in different habitats. We show that populations of shelf-dwelling sharks derive a substantial proportion of their carbon from regional pelagic sources, but contain individuals that forage within additional isotopically diverse local food webs, such as those supported by terrestrial plant sources, benthic production and macrophytes. In contrast, oceanic sharks seem to use carbon derived from between 30° and 50° of latitude. Global-scale compilations of stable isotope data combined with biogeochemical modelling generate hypotheses regarding animal behaviours that can be tested with other methodological approaches.This research was conducted as part of C.S.B.’s Ph.D dissertation, which was funded by the University of Southampton and NERC (NE/L50161X/1), and through a NERC Grant-in-Kind from the Life Sciences Mass Spectrometry Facility (LSMSF; EK267-03/16). We thank A. Bates, D. Sims, F. Neat, R. McGill and J. Newton for their analytical contributions and comments on the manuscripts.Peer reviewe

A thousand-genome panel retraces the global spread and adaptation of a major fungal crop pathogen

Human activity impacts the evolutionary trajectories of many species worldwide. Global trade of agricultural goods contributes to the dispersal of pathogens reshaping their genetic makeup and providing opportunities for virulence gains. Understanding how pathogens surmount control strategies and cope with new climates is crucial to predicting the future impact of crop pathogens. Here, we address this by assembling a global thousand-genome panel of Zymoseptoria tritici, a major fungal pathogen of wheat reported in all production areas worldwide. We identify the global invasion routes and ongoing genetic exchange of the pathogen among wheat-growing regions. We find that the global expansion was accompanied by increased activity of transposable elements and weakened genomic defenses. Finally, we find significant standing variation for adaptation to new climates encountered during the global spread. Our work shows how large population genomic panels enable deep insights into the evolutionary trajectory of a major crop pathogen

Utilisation de la coquille Saint-Jacques comme traceur environnemental : approches biologique et biogéochimique

To calibrate the great salop Pecten maximus as a tool for environmental reconstruction, a multi-approach linking biology, ecology and biogeochemistry has been developped.Dans l'optique de faire de la coquille Saint-Jacques, Pecten maximus, un outil de reconstruction environnementale, une approche liant la biologie, l'écologie et la biogéochimie a été développée. Dans un premier temps, l'étude des anomalies de croissance coquillière de la coquille Saint Jacques nous a permis de révéler des dysfonctionnements de la production primaire. En effet, ces anomalies sont associées à des efflorescences de diatomées carencées en certains éléments nutritifs (acide orthosilicique et/ou phosphates), et dont les propriétés qualitatives sont modifiées (agrégation). La mesure du δ15N et du δ13C dans les tissus de P. maximus et l'application des facteurs de fractionnement moyens admis dans la littérature, montrent que le phytoplancton n'est pas une ressource trophique majoritaire. Deux hypothèses principales découlent de cette observation 1) le phytoplancton constitue une source minoritaire de nourriture 2) les facteurs de fractionnement utilisés ne sont pas valables. D'autre part, les variations saisonnières du δ15N et δ13C ont pu être mises en relation avec les différentes priorités d'allocation d'énergie de cet organisme. Ce résultat ouvre des perspectives quant à l'utilisation de ces rapports isotopiques en tant qu'outils écophysiologiques. Les variations de δ18Ocalcite permettent de tracer l'évolution saisonnière de la température à ± 0,7°C. Le δ13C de la calcite décroît au cours de l'année et au cours de la vie des individus, il semble être contrôlé par des processus biologiques. Le δ13C pourrait devenir un outil d'étude du métabolisme des coquilles Saint-Jacques. Enfin, le développement méthodologique du système LA-ICP-MS permet l'obtention de profils d'éléments traces à une échelle journalière (Mg/Ca, Mn/Ca, Ba/Ca, Sr/Ca et Pb/Ca). Ces rapports semblent cependant être influencés par plusieurs facteurs environnementaux et/ou métaboliques. Des études supplémentaires sont nécessaires pour calibrer ces proxy élémentaires