Modelling paralytic shellfish toxins (PST) accumulation in Crassostrea gigas by using Dynamic Energy Budgets (DEB)

As other filter-feeders, Crassostrea gigas can concentrate paralytic shellfish toxins (PST) by consuming dinoflagellate phytoplankton species like Alexandrium minutum. Intake of PST in oyster tissues mainly results from feeding processes, i.e. clearance rate, pre-ingestive sorting and ingestion that are directly influenced by environmental conditions (trophic sources, temperature). This study aimed to develop a mechanistic model coupling the kinetics of PST accumulation and bioenergetics in C. gigas based on Dynamic Energy Budget (DEB) theory. For the first time, the Synthesizing Units (SU) concept was applied to formalize the feeding preference of oysters between non-toxic and toxic microalgae. Toxin intake and accumulation were both dependent on the physiological status of oysters. The accumulation was modelled through the dynamics of two toxin compartments: (1) a compartment of ingested but non-assimilated toxins, with labile toxins within the digestive gland eliminated via faeces production; (2) a compartment of assimilated toxins with a rapid detoxification rate (within a few days). Firstly, the DEB-PST model was calibrated using data from two laboratory experiments where oysters have been exposed to A. minutum. Secondly, it was validated using data from another laboratory experiment and from three field surveys carried out in the Bay of Brest (France) from 2012 to 2014. To account for the variability in PST content of A. minutum cells, the saxitoxin (STX) amount per energy units in a toxic algae (ρPST) was adjusted for each dataset. Additionally, the effects of PST on the oyster bioenergetics were calibrated during the first laboratory experiment. However, these effects were shown to depend on the strain of A. minutum. Results of this study could be of great importance for monitoring agencies and decision makers to identify risky conditions (e.g. production areas, seawater temperature), to properly assess detoxification step (e.g. duration, modalities) before any commercialization or to improve predictions regarding closing of shellfish areas

Why should you manage your research data following FAIR principles: Réutiliser les données des autres et rendre les siennes réutilisables… tout un défiAtelier 6 - DOCTIS-COPE

IntroductionCycle de vie des données de rechercheDonnées de rechercheMétadonnéesJeu de donnéesFAIR is in the airWe should CAREFAIR-Réutilisable- Différence entre réutilisable et réplicable- Documentation détaillée- Normes de qualité- Accessibilité- Entrepôts et catalogues de données- l'importance des formats- Licences et restrictions- Interopérabilité- Normes et vocabulaire contrôléPhase de pratiqueDoctoralLa formation DOCTIS-COPE s’adresse aux doctorants de l’EDSML (école doctorale des Sciences de la Mer et du Littoral). L’enjeu de cette formation est de transmettre aux futurs chercheurs et enseignants-chercheurs les bonnes pratiques et les valeurs de l’intégrité scientifique, en leur donnant les outils, les méthodes et les ressources nécessaires. La formation vise également à stimuler une prise de conscience et un auto-questionnement critique de leur part en faveur de pratiques professionnelles exemplaires, notamment pour publier de manière intègre.https://isblue.fr/actualites/doctis-cope-formation-doctorale-integrite-scientifique-comment-publier-de-maniere-integre/La formation se déroule en 6 ateliers en présentiel de 3 heures, animés par des experts, sur le thème de la publication : #1 Analyse d’un article rétracté #2 Droits d’auteurs, propriété intellectuelle, plagiat #3 Conditions d’autorat #4 Science ouverte et publication #5 Choix d’une revue scientifique #6 Gestion des données et principes FAIRLa présentation partagée ici correspond à l'atelier numéro 6.Le but de cet atelier est de :1- Rappeler les définitions de base: données, métadonnées, jeux de données, cycle de vie... dans le contexte de la recherche pour des doctorants2- Expliciter le concept de réutilisabilité pour les données de rechercheIl se décompose en une partie théorique (diapo 1 à 28) suivit d'une partie pratique (diapo 28 à 39

Factors influencing disease-induced mortality of Pacific oysters Crassostrea gigas

Mortalities of oyster Crassostrea gigas seed associated with ostreid herpesvirus OsHV-1 μVar have been observed in many oyster-producing countries since 2008. The present study, comprised of 4 complementary experiments, aimed to identify factors associated with disease-induced oyster mortality in order to propose mitigation strategies. Our first experiment compared survival of oysters from natural spatfall with others sampled from nurseries, after thermal elevation in the laboratory from <14 to 21°C. A total of 60% of the tested wild seed batches (n = 51) were infected by OsHV-1, exhibited mortality and were able to transmit the disease to cohabited naïve oysters. Comparatively, only 1 out of the 32 tested batches sampled from nurseries presented similar characteristics. In a second experiment, we studied the effects that timing and duration of exposure to field conditions had on risk of infection and mortality in the laboratory at 21°C. Naïve oysters deployed in the field during winter and spring, when seawater temperatures were <14.7°C, showed no mortality in the laboratory, and OsHV-1 DNA was not detected by PCR. However, in oysters transferred to the field, OsHV-1 was observed when seawater temperature reached ~15.3°C. Our third experiment showed that the odds of mortality decreased with age of oysters when facing the disease. Further, we observed that odds of disease mortality decreased with water renewal and increased with the biomass of neighbouring infected oysters under controlled conditions. Based on these findings, we propose mitigation strategies in terms of the regulation of oyster movements between sites, timing of seeding and spatial planning, taking into account seawater temperature and seed origin

Effet de la quantité de nourriture sur la dynamique du δ13C et du δ15N dans les tissus mous du bivalves Crassostrea gigas dans le contexte de la théorie des Budgets d'Energie Dynamiques (DEB)

Nous avons utilisé un modèle basé sur la théorie des Budgets d'Energie Dynamiques, paramétré pour l'espèce Crassostrea gigas et calibré sur des données de la littérature, afin de quantifier l'impact de la quantité de nourriture f sur le fractionnement isotopique Δ. Une augmentation d'un facteur 5 de f entraîne une diminution de 35 % et 43 % du Δ13C et Δ15N respectivement. Ces résultats devraient permettre d'améliorer l'outil isotopique et de mieux comprendre les relations proies/prédateurs dans les écosystèmes côtiers

Increased growth metabolism promotes viral infection in a susceptible oyster population

The magnitude of an epidemic depends on host susceptibility to the disease, a trait influenced by the genetic constitution of the host and its environment. While the genetic basis of disease susceptibility is often associated with immune capacities, environmental effects generally reflect complex physiological trade-offs. We suggest here that in the case of obligate pathogens whose proliferation depends on the cellular machinery of the host (e.g. viruses), disease susceptibility is directly influenced by host growth. To test our hypothesis, we focussed on a viral disease affecting an ecologically relevant model exploited worldwide, the Pacific oyster Crassostrea gigas. Oysters originating from 3 lines with contrasting resistance to the disease were divided into 3 groups displaying different growth rates and acclimated to 3 food levels and 2 temperatures to generate different growth rates. These oysters were then exposed to the virus, and survival and viral shedding were measured. Finally, we developed a risk model to rank the relative importance of temperature, food, genetic selection and growth on disease-induced mortality. We found that increasing growth through temperature, food level or selection of fast-growing animals all increased mortality, especially in host populations where susceptible phenotypes dominated. Food provisioning was the most influential factor associated with higher viral shedding, followed by temperature, resistance phenotype and growth rate. We suggest that growth-forcing factors may promote the development of obligate intracellular pathogens and epidemic risk, thus opening up avenues for disease management based on the manipulation of host metabolism

Understanding the dynamics of δ13C and δ15N in soft tissues of the bivalve Crassostrea gigas facing environmental fluctuations in the context of Dynamic Energy Budgets (DEB)

International audienceWe studied the dynamics of stable isotopes δ13C and δ15N of an opportunistic suspension feeder the Pacific oyster (Crassostrea gigas) to better understand the factors that influence the trophic enrichment (trophic-shift, Δ) between primary producers and consumers. Most of the previous studies on this topic do not quantify mass fluxes or isotopic discrimination phenomena in the organism, which are two pillars in isotope ecology. We used a dynamic energy budget (DEB) approach (Kooijman, 2010) to quantify i) the fluxes of elements and isotopes in C. gigas soft tissues and ii) the impact of the scaled feeding level, the organism mass and the isotopic ratio of food on the "trophic-shift" Δ, and isotope turnover in tissues. Calibration and parametrization modelling were based on data from the literature. We showed that a five-fold increase in scaled feeding level leads to a decrease of the trophic-shift value of 35% for carbon and 43% for nitrogen. This can be explained by the molecule selection for the anabolic and/or catabolic way. When f increases due to the reserve dynamic formulation in the standard DEB model, the half-life of the isotopic ratio tδ 1/2 in tissues also decreases from 13.1 to 7.9 d for δ13C and from 22.1 to 10.3 d for δ15N. Organism mass also affects the trophicshift value: an increase of the individual initial mass from 0.025 g to 0.6 g leads to an enrichment of 22% for δ13C and 21% for δ15N. For a large individual, these patterns show that a high structural volume has to be maintained. Another consequence of the mass effect is an increase of the half-life for δ13C from 6.6 to 12.0 d, and an increase of the half life for δ15N from 8.3 to 19.4 d. In a dynamic environment, the difference in the isotopic ratios between the individual tissues and the food (δ13CW − δ13CX) exhibits a range of variation of 2.02‰ for carbon and 3.03‰ for nitrogen. These results highlight the potential errors in estimating the contributions of the food sources without considering the selective incorporation of isotopes. We conclude that the dynamic energy budget model is a powerful tool to investigate the fate of isotopes in organisms

Variability in particle retention efficiency by the mussel Mytilus edulis

International audienceSeasonal variation in blue mussel, Mytilus edulis, retention efficiency (RE) responses to natural seston concentrations were investigated in the Lysefjord, Norway. The smallest particles shown to be effectively retained (100%) were approximately 7 μm and this was observed on only one occasion. The most common response was for RE to progressively increase from small to large particles with maximum RE at 30 to 35 μm (8 of 12 experiments). Temporal changes in the seston size distribution towards a dominance of smaller particles coincided with a decrease in the RE maxima to particles between 7 and 15 μm diameter. The RE of 1 μm and 4 μm diameter particles ranged between 14–64% and 12–86%, respectively, showing that small particles occasionally serve as a significant dietary component. The observed temporal variations in particle capture suggest a capacity of M. edulis to control particle retention mechanisms based on exogenous dietary cues that are directly or indirectly related to the ambient particle size distribution. Indirect clearance rate (CR) measurements require that all particle sizes under study are effectively retained and this has widely been assumed for particles larger than 4 μm. CR was calculated for particles ranging in size from 5 to 35 μm and the percentage reduction in CR, relative to particle sizes shown to be effectively retained, ranged from 11% to 87%. CR calculations that included all particle counts between 5 and 35 μm diameter were underestimated by a mean of 26% (0–48% range). Similar errors in diet characterization may be expected to affect particle selection and absorption efficiency measurements and the compounding of errors may become extreme when a number of physiological rates and efficiencies are integrated (e.g. scope for growth).Highlights► Particle retention efficiency (RE) of natural seston was investigated in M. edulis. ► The smallest particles shown to be effectively retained (100%) were close to 7 μm. ► RE most often increased progressively from small to large particles. ► Maximum RE was reported at 30 to 35 μm in 8 of 12 experiments. ► Temporal changes in particle size distribution coincided with changes in RE maxima

A DEB model to predict accumulation and detoxification of paralytic shellfish toxins by the Japanese Oyster (Crassostrea gigas)

France being the largest consumer of oysters in Europe, oyster farming is deeply rooted in French heritage. The Japanese oyster (Crassostrea gigas) is the oyster species the most exploited in France, and in the world. Due to filter-feeding, these bivalves are sensitive to toxic algal blooms. Although not always lethal, toxic algae can affect oyster physiology and make it unfit for human consumption. Phytoplankton toxins can be classified in several groups: amnesic, neurotoxic, diarrhetic and paralytic. For the latter group, saxitoxins are synthesized by the microalgae of genus Alexandrium that can accumulate bivalve tissues. In recent years, number of studies have been performed on the interactions between C. gigas and saxitoxins. In order to better understand these interactions, mathematical models have been developed but they did not allowed to describe accurately the kinetics of accumulation and detoxification of paralyzing toxins (PSTs). Models on DEB theory (Dynamic Energy Budget) (Kooijman, 2000) have been widely applied to the study of bivalve bio-energetics. This type of model already allowed to quantify growth and reproduction of C. gigas under different environmental forcing. These models have also been applied to study host-pathogen interactions (Flye-Sainte-Marie et al., 2009) and kinetics of accumulation and detoxification of contaminants (Bodiguel et al., 2009; Echinger et al., 2010). The aim of this PhD work is to develop a model based on DEB theory, that describes the interactions between PSTs and oysters. Indeed, different effects of PSTs contamination on oyster physiology have been shown. For example, paralytic toxins alter the immune response (overproduction and phagocytosis of hemocytes), behavior (modification of valve rhythms, production of pseudo-faeces) or organ integrity (myoatrophy, inflamed gills). In this PhD project, we will focus first on describing the accumulation and detoxification kinetics of PSTs in C. gigas and second on quantifying the effects of PSTs on the physiology of C. gigas

Tire rubber chemicals reduce juvenile oyster (Crassostrea gigas) filtration and respiration under experimental conditions

International audienc