Reproduction patterns of the bloody cockle Senilia senilis (Linnaeus 1758) in the Sine-Saloum inverse estuary

Understanding the reproductive biology of a species is an important means of determining the renewal capacity of natural stocks, especially in the case of heavily exploited species. It is a fundamental element in supporting the implementation of management measures. Here, we studied the bloody cockle (S. senilis) in the Sine-Saloum, with the aim of describing its seasonal and spatial reproductive cycle. S. senilis reproduction was studied over an annual cycle at two sites chosen for their contrasting situations along the upstream-downstream gradient. The reproductive cycle was studied by histological analysis of a pool of individuals maintained in-situ and sampled throughout the year. Our results showed that gamete maturation is asynchronous within and between individuals. Gametogenesis mostly occurred in October. The maturation stage showed a seasonal pattern with continuous reproduction throughout the year, with two preferred periods between May and July and December and February. The reproductive cycle is highly dependent on temperature and salinity variations, resulting in a seasonal cycle and spatial heterogeneity. The temperature induces gametogenesis and salinity synchronizes the spawning periods

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

Generation and analysis of a 29,745 unique Expressed Sequence Tags from the Pacific oyster (Crassostrea gigas) assembled into a publicly accessible database: the GigasDatabase

Background: Although bivalves are among the most-studied marine organisms because of their ecological role and economic importance, very little information is available on the genome sequences of oyster species. This report documents three large-scale cDNA sequencing projects for the Pacific oyster Crassostrea gigas initiated to provide a large number of expressed sequence tags that were subsequently compiled in a publicly accessible database. This resource allowed for the identification of a large number of transcripts and provides valuable information for ongoing investigations of tissue-specific and stimulus-dependant gene expression patterns. These data are crucial for constructing comprehensive DNA microarrays, identifying single nucleotide polymorphisms and microsatellites in coding regions, and for identifying genes when the entire genome sequence of C. gigas becomes available. Description: In the present paper, we report the production of 40,845 high-quality ESTs that identify 29,745 unique transcribed sequences consisting of 7,940 contigs and 21,805 singletons. All of these new sequences, together with existing public sequence data, have been compiled into a publicly-available Website http://public-contigbrowser.sigenae.org:9090/Crassostrea_gigas/index.htm l. Approximately 43% of the unique ESTs had significant matches against the SwissProt database and 27% were annotated using Gene Ontology terms. In addition, we identified a total of 208 in silico microsatellites from the ESTs, with 173 having sufficient flanking sequence for primer design. We also identified a total of 7,530 putative in silico, single-nucleotide polymorphisms using existing and newly-generated EST resources for the Pacific oyster. Conclusion: A publicly-available database has been populated with 29,745 unique sequences for the Pacific oyster Crassostrea gigas. The database provides many tools to search cleaned and assembled ESTs. The user may input and submit several filters, such as protein or nucleotide hits, to select and download relevant elements. This database constitutes one of the most developed genomic resources accessible among Lophotrochozoans, an orphan clade of bilateral animals. These data will accelerate the development of both genomics and genetics in a commercially-important species with the highest annual, commercial production of any aquatic organism

Origine et développement des cellules germinales chez l'huître Crassostrea gigas : intérêt pour le contrôle de la reproduction en écloserie

Membres du jury : Fostier Alexis, Favrel Pascal, Nonnotte Liliane, Goulletquer Philippe, Cochard Jean-ClaudeA comprehensive knowledge of Crassostrea gigas oyster reproduction processes is essential to optimize controlled reproduction in hatchery. This study aimed to determine the origin and the mechanisms of annual renewal of germ cells, still unknown in oysters, and the influence of temperature and photoperiod parameters on the regulation of the reproductive cycle. We characterized an orthologue of the vasa gene, the Oyvlg (Oyster vasa-like gene), the first germ cell specific marker isolated in molluscs. This marker was used to study C. gigas germline development. Oyster germ cells appeared specified during early development from mesentoblast 4d, as primordial germ cells (PGCs) determined by maternal cytoplasmic determinants, including Oyvlg mRNA. In adult oysters, the annual renewal of germ cells results from a proliferation of germinal stem cells (GSCs), self-renewing cells, scattered in the conjunctive tissue during the resting period. One-year experimental conditionings were realized to determine temperature and photoperiod parameter effects on oyster gametogenesis. Experimental conditionings consisted in (1) natural temperature and photoperiod conditions corresponding to Marennes-Oléron bay values, (2) accelerated conditions, twice faster than natural cycles and (3) constant wintering conditions adjusted to 8°C and 8 hours day-length. These analyses revealed a high plasticity of C. gigas reproduction since the rhythm of the reproductive cycle was entirely modelled by temperature and photoperiod variations. Decreasing photoperiod may regulate GSCs proliferation while low temperature (8°C-11°C) would enhance gonial mitosis and high temperature would accelerate germ cell maturation. As a result, manipulation of temperature and photoperiod conditions allows effective controlled reproduction all over the year.Le renouvellement annuel de la population de cellules germinales chez l'huître creuse Crassostrea gigas est une étape clé de son cycle de reproduction. La compréhension de ces mécanismes est essentielle à la maîtrise de la reproduction contrôlée de C. gigas, indispensable pour répondre à une demande croissante des ostréiculteurs, de naissain produit en écloserie. Les objectifs de cette étude étaient de déterminer l'origine et les mécanismes de renouvellement annuel des cellules germinales de C. gigas et de comprendre l'infuence des facteurs environnementaux sur ces processus. Le gène Oyster vasa-like gene (Oyvlg), premier marqueur spécifique des cellules germinales découvert chez les bivalves a été caractérisé. Ce gène, exprimé spécifiquement dans les cellules de la lignée germinale, nous a permis de déterminer que les cellules germinales de C. gigas, d'origine mésodermique, étaient différenciées dès le stade embryonnaire sous la forme de cellules germinales primordiales (PGCs). Ces PGCs seraient spécifiées par la localisation de déterminants cytoplasmiques transmis maternellement à l'embryon, dans une structure équivalente à un cytoplasme germinal. Les ARNm Oyvlg seraient l'un de ces déterminants germinaux. Au stade adulte, la population de cellules germinales apparaît renouvelée annuellement par la prolifération, au début du cycle de reproduction, de cellules germinales souches (GSCs), dispersées en petits groupes dans le tissu conjonctif pendant la période de repos sexuel. La différenciation des GSCs en gonies et la multiplication de ces gonies marque le début de la gamétogenèse. Afin de tester l'effet de la température et de la photopériode sur la gamétogenèse, des huîtres adultes ont été conditionnées expérimentalement pendant un an en écloserie, dans trois conditions de température et de photopériode différentes : (1) conditions dites "naturelles" reproduisant les cycles de température et de photopériode moyens enregistrés à Marennes-Oléron, (2) conditions "accélérées", deux fois plus rapides que les cycles naturels, (3) conditions "hivernales" constantes à 8°C et 8 heures de jour. Ces expérimentations ont mis en évidence une grande plasticité physiologique de la reproduction de C. gigas, dont le rythme se synchronise parfaitement sur celui des facteurs température / photopériode. Des photopériodes décroissantes pourraient stimuler la prolifération des cellules germinales souches alors que la température apparaît comme le facteur prédominant dans la régulation des mitoses goniales et de la maturation. Les températures basses (8°C – 11°C) semblent déclencher les mitoses goniales et les températures élevées accélèrent le processus de maturation des cellules germinales. L'utilisation de cycles de température et de photopériode modifiés (accélérés ou hivernaux) permettraient d'obtenir des pontes toute l'année en écloserie, y compris en période automnale généralement considérée comme réfractaire pour le conditionnement

Origine et développement des cellules germinales chez l'huître Crassostrea gigas (intérêt pour le contrôle de la reproduction en écloserie)

La connaissance parfaite de la reproduction de Crassostrea gigas est essentielle à l'optimisation de la production de naissain en écloserie. Les objectifs de cette étude étaient de déterminer l'origine et les mécanismes de renouvellement annuel des germinales chez C. gigas et de comprendre l'influence des facteurs environnementaux sur ces processus. Le gène Oyster vasa-like gene (Oyvlg), premier marqueur spécifique des cellules germinales découvert chez les bivalves a été caractérisé et utilisé pour l'étude de la lignée germinale chez C. gigas. Ces cellules germinales, d'origine mésodermique, apparaissent différenciée dès le stade embryonnaire sous la forme de cellules germinales primordiales (PGCs), spécifiées par des déterminants cytoplasmiques maternels, dont les ARNm Oyvlg. Au stade adulte, la population de cellules germinales apparaît renouvelée annuellement par la prolifération de cellules germinales souches (GSCs) dispersées dans le tissu conjonctif pendant la période de repos sexuel. Trois conditionnements expérimentaux ont été réalisés pendant un an en écloserie afin de tester l'effet de la température et de la photopériode sur la gamétogenèse : conditionnements (1) " naturel " reproduisant les cycles de température et de photopériode enregistrés à Marennes-Oléron, (2) " accéléré ", deux fois plus rapides que les cycles naturels, (3) " hivernal ", constant à 8C et 8h de jour. Ces expérimentations montrent que le rythme de reproduction de C. gigas, d'une grande plasticité, se synchronise parfaitement sur celui des facteurs température/photopériode. Des photopériodes décroissantes stimuleraient la prolifération des GSCs et les températures basses (8C-11C) déclenchent les mitoses goniales. La modification des cycles de température et de photopériode permet d'obtenir des pontes toute l'année en écloserie.The perfect knowldege of Crassostrea gigas oyster reproduction processes is essential to optimize controlled reproduction in hatchery. The aims of this study were to determine the origin and the mechanisms of annual renewal of germs cells, still unknown in oysters, and the influence of temperature and photoperiod parameters on the regulation of the reproductive cycle. We characterized an orthologue of the vasa gene, the Oyvlg (Oyster vasa-like gene), the first germ cell specific marker isolated in molluscs this marker was used to study C gigas germline development. Oyster germ cells appeared specified during early development from mesentoblast 4d, as primordial germ cells (PGCs) determined by maternal cytoplasmic determinants, including Oyvlg mRNA. In adult oysters, the annual renewal of germ cells, scattered in the conjunctive tissue during the resting period. One-year experimental conditionings were realized to determine temperature and photoperiod parameter effects on oyster gametogenesis. Experimental conditionings consisted in (1) natural temperature and photoperiod conditions corresponding to Marennes-Oléron bay values, (2) accelerated conditions, twice faster than natural cycles and (3) constant wintering conditions adjusted to 8ʿC and 8 hours day-lenght. These analyses revealed a high plasticity of C. gigas reproduction since the rythm of the reproductive cycle was entirely modelled by temperature and photoperiod variations. Decreasing photoperiod may regulate GSCs proliferation while low temperature (8ʿC-11ʿC) would enhance gonial mitosis and high temperature would accelerate germ cell maturation. As a result, manipulation of temperature and photoperiod conditions allows effective controlled reproduction all over manipulation of temperature and photoperiod conditions allows effective controlled reproduction all over the year.BREST-BU Droit-Sciences-Sports (290192103) / SudocSudocFranceF

L'huître, cette sentinelle témoin d’un littoral à préserver

Dans la catégorie des mollusques marins, l’huître est une espèce essentielle de nos côtes françaises et à forts enjeux économique et patrimonial. Espèce ingénieure, elle rend de nombreux services dans les écosystèmes côtiers. Pourtant, les huîtres subissent de fortes pressions dont les pollutions d’origine humaine. Parmi ces pollutions que nous détaillerons dans cet article : les pollutions chimiques, les pollutions biologiques comme les microalgues toxiques naturelles -dont les recrudescences peuvent avoir une origine anthropique-, et de nouveaux contaminants chimiques et particulaires, les microplastiques, complétant ainsi le précédent article montrant l’importance écologique des huîtres et les menaces liées au réchauffement climatique qui pèsent sur elles (Lire Les huîtres : ces architectes méconnus des milieux côtiers). L’huître en tant qu’espèce sentinelle indicatrice de l’état de santé (ou de dégradation) de l’écosystème côtier, se retrouve donc à la place du lanceur d’alerte exigeant des mesures fortes de protection des habitats littoraux

Study of the antioxidant capacity in gills of the Pacific oyster Crassostrea gigas in link with its reproductive investment.

International audienceEnergy allocation principle is a core element of life-history theory in which "the cost of reproduction" corresponds to an acceleration of senescence caused by an increase in reproductive investment. In the "theory of aging", senescence is mainly due to the degradation of lipids, proteins and DNA by reactive oxygen species (ROS), by-products of oxidative metabolism. Some studies have shown that oxidative stress susceptibility could be a cost of reproduction. The present study investigates the effect of reproductive investment on antioxidant capacity in the gills of a species with a very high reproductive investment, the Pacific oyster Crassostrea gigas. We used RNA interference targeting the oyster vasa-like gene (Oyvlg) to produce oysters with contrasted reproductive investment. Antioxidant capacity was studied by measuring the mRNA levels of genes encoding major antioxidant enzymes, and the activity of these enzymes. The highest reproductive investment was associated with the highest transcript levels for glutathione peroxidase and extra-cellular and mitochondrial superoxide dismutase. In contrast, lipid peroxidation did not show any sign of oxidative damage whatever the reproductive investment. Up-regulation of certain genes encoding enzymes involved in the first step of ROS detoxification could therefore be a part of the organism's strategy for managing the pro-oxidant species produced by heavy reproductive investment

Characterization of a gonad-specific transforming growth factor-beta superfamily member differentially expressed during the reproductive cycle of the oyster Crassostrea gigas.

International audienceThrough differential screening between oyster families selected for high and low summer survival, we have characterized a new transforming growth factor-beta (TGF-beta) superfamily member. This novel factor, named oyster-gonadal-TGFbeta-like (og-TGFbeta-like), is synthesized as a 307 amino acid precursor and displays 6 of the 7 characteristic cysteine residues of the C-terminal, mature peptide. Sequence comparison revealed that og-TGFbeta-like has a low percentage of identity with other known TGF-beta superfamily members, suggesting that og-TGFbeta-like is a derived member of this large superfamily. Real-time PCR (RT-PCR) analysis in different oyster tissues showed that og-TGFbeta-like is specifically expressed in both male and female gonads, at distinct levels according to the reproductive stage. Og-TGFbeta-like relative expression was the lowest at the initiation of the reproductive cycle and increased as maturation proceeded to achieve a maximal level in fully mature female and male oysters. In situ hybridisation demonstrated that expression was exclusively detected in the somatic cells surrounding oocytes and spermatocytes. The role of this newly-characterized TGFbeta member in the reproduction of cupped oyster is discussed in regard to the specificity and the localization of its expression, which singularly contrasts with the pleiotropic roles in a variety of physiological processes commonly ascribed to most TGF-beta family members identified so far

Effect of the antioxidant N-acetylcysteine on the depuration of the amnesic shellfish poisoning toxin, domoic acid, in the digestive gland of the king scallop <i>Pecten maximus</i>

International audienceDomoic acid (DA) is a potent neurotoxin produced by worldwide distributed diatoms of the genus Pseudo-nitzchia (PSN) and is responsible for Amnesic Shellfish Poisoning (ASP) in humans. King scallop Pecten maximus, a bivalve species of high commercial interest, is regularly subjected to blooms of Pseudo-nitzschia sp., thus accumulating and retaining high levels of DA for extended periods, leading to prolonged fisheries and aquaculture closures and important economic losses following increasingly recurrent toxic PSN blooms. The underlying mechanisms behind this accumulation and long toxin retention remain poorly understood so far. Fishermen and the aquaculture industry ask for methods to accelerate DA depuration in contaminated scallops, which has led to investigate the effect of some substances such as the antioxidant N-Acetylcysteine (NAC), which was previously found to improve up to four-fold DA depuration in P. maximus adductor muscle. Our study investigated the potential of NAC to accelerate DA depuration in all scallop tissues, including the digestive gland (DG), where most of the toxin is accumulated. Twenty-four contaminated adult scallops were collected following a toxic P. australis bloom in the Bay of Brest (France) and half were treated with the antioxidant NAC (250 mg L À1) for 6 days. HPLC toxin quantification analyses did not revealed any significant differences in the DA burdens in the DG between treated scallops and the control group. DA amounts in the adductor muscle and gonads were below the HPLC detection limit in both groups. Our results revealed that NAC does not thus appear as a commercially suitable solution for fisheries and aquaculture industries as DA depuration enhancer in the tested conditions