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Sex‐determining modes remain unknown in numerous species, notably in fishes, in which a variety of modalities have been reported. Additionally, noninvasive individual sexing is problematic for species without external sex attributes or for early life stages, requiring cytogenetic or molecular analyses when sex chromosomes or sex‐linked markers have been characterized. Genomics now provide a means to achieve this. Here, we review common sex‐determination systems and corresponding statistical methods for identifying sex‐linked genetic markers and their use for sex assignment, focusing on single nucleotide polymorphism (SNP) markers derived from reduced representation sequencing methods. We demonstrate the dependence of expected sex assignment error on the number of sex‐linked SNPs and minor allele frequency. The application of three methods was made here: (a) identification of heterozygote excess in one sex, (b) FST outlier analysis between the two sexes and (c) neuronal net modelling. These methods were applied to a large SNP data set (4604 SNPs) for 1680 thornback rays (Raja clavata). Using method (a), nineteen putative sex‐linked SNPs were identified. Comparison with the reference genome of a related species (Amblyraja radiata) indicated that all 19 SNPs are probably located on the same chromosome. These results suggest that thornback ray has a XX/XY sex‐determination system. Method (b) identified eight SNPs probably located on different chromosomes. Method (a) led to the lowest sex assignment error among the three methods (4.2% error for females and 3.7% for males). [ABSTRACT FROM AUTHOR]

Objective: The golden color of Staphylococcus aureus is due to the synthesis of carotenoid pigments. In Gram-negative bacteria, Hfq is a global posttranscriptional regulator, but its function in S. aureus remains obscure. The absence of Hfq in S. aureus was reported to correlate with production of carotenoid pigment leading to the conclusion that Hfq was a negative regulator of the yellow color. However, we reported the construction of hfq mutants in several S. aureus strains and never noticed any color change; we therefore revisited the question of Hfq implication in S. aureus pigmentation. Results: The absence or accumulation of Hfq does not affect S. aureus pigmentation. [ABSTRACT FROM AUTHOR]

Abstract: This study investigated the effects of age (first or second summer of life) and environment (three study sites on French coasts) on summer mortality in Crassostrea gigas, using three generations of oysters produced during the Morest project. For each generation, two groups of oysters, selected either as ‘resistant’ (R) or ‘susceptible’ (S) to summer mortality at the age of 6months in Rivière d''Auray (RA, South Brittany), were evaluated. In Ronce (Marennes-Oléron Bay) and RA, R oysters had low mortality during their first and second summers, while mortality was higher during the second summer in Baie des Veys (BDV, Normandy). In RA, S oysters exhibited higher mortality during their first summer than during their second, while the opposite result was found in BDV, indicating a significant environment by age interaction. Some oysters were also protected from mortality risk factors during their first year by keeping them in a nursery; they were then deployed at the two sites the following spring. Mortality in R oysters during their second year was lower than in S oysters in RA and BDV. Interestingly, mortality of the S oysters deployed in RA during their second year was much lower than the mortality observed in S oysters deployed during their first year, suggesting that S juveniles are more susceptible to summer mortality than S adults. As a consequence, the difference in mortality between the two selected groups in RA decreased from 40–45% to 5–9% when oysters were protected from summer mortality at the juvenile stage. In BDV, the difference in mortality between the two selected groups was similar whether oysters were deployed during their first or second year. The first reproductive event in oysters, combined with genetic differences between the groups interacting with local environmental conditions can go some way to explaining summer mortality events in our study. Cumulative mortality for each generation and site was higher in the S group than in the R group, indicating a positive response to selection in oysters up to 18months old. Mortality was split into three categories: low background mortality, genetic effects from the selection and unknown mortality on which no investigation has yet concentrated. Finally, culture strategy on oyster farms is discussed with respect to oyster age and environment. [Copyright &y& Elsevier]

Marine species with high fecundity and high early mortality may also have high variance in reproductive success among individuals due to stochastic factors, making successful reproduction a "sweepstakes." In some cases, the impact is sufficient to reduce the effective number of breeders in wild populations. We tested two predictions of the sweepstakes reproductive success hypothesis in a French Atlantic population of the European flat oyster, Ostrea edulis, by evaluating (1) whether individuals belonging to temporally discrete recruitment cohorts within a single reproductive season displayed reduced genetic variation relative to the entire adult population, and (2) whether these temporal cohorts of recruits were genetically differentiated from each other. We assayed genetic variation at four nuclear microsatellites and a 12S mitochondrial fragment in four recruitment cohorts. Nuclear markers provided no evidence for differentiation between recruitment cohorts and adults or between temporal cohorts. However, mitochondrial data indicate that the first temporal cohort showed significant differentiation with the last (Fst = 0.052, P < 0.05) and with the adult sample (Fst = 0.058, P < 0.05). These differences are most likely due to the smaller effective size of the mitochondrial genome—and hence its increased sensitivity to drift compared to the nuclear genome. This slight mitochondrial signal indicates a certain limitation in the number of contributing female parents in this species. The "sweepstakes" phenomenon was therefore limited in our case. Hypothetically, this phenomenon may occur or not, with a high variance as a result of the interaction between the oyster reproductive biology and different environmental conditions. [ABSTRACT FROM AUTHOR]

In several cases, oyster taxa have been misidentified owing to their high morphological plasticity, uncertain geographical range and undocumented introductions. Recently though, molecular techniques have been efficiently applied to discriminate between oysters and to quantify genetic divergence within and among species. In the present paper, we report mitochondrial (16S and COI) and nuclear (28S) DNA sequences of presumed Crassostrea gigas and Crassostrea angulata, two taxa of aquacultural importance. Mitochondrial DNA sequences are compared with previously published sequences and PCR-RFLP haplotypes. Within C. gigas, divergence was less than 0.5% for COI, and less than 0.2% for 16S. Within C. angulata, divergence was less than 1.1% for COI and 0.2% for 16S. Our results also confirm the close genetic relationship between C. gigas and C. angulata and further document their level of divergence: 2–3% for COI and 0.5–1% for 16S. However, the initially presumed C. gigas oysters farmed in Hong Kong (Pearl River delta), presented DNA sequences strongly divergent from both C. gigas and C. angulata: 13–14% for COI, 3–4% for 16S and 1.2–1.6% for 28S. The closest related species are C. gigas and Crassostrea nippona with a divergence of 12–13% for COI, 3–4% for 16S and 1.2–1.6% for 28S. Comparisons with existing DNA sequence data available in the nucleotide sequence databases shows that this is either a new species or that it corresponds to a species for which no DNA sequence is yet available. Further studies are required to document morphological characteristics and geographical range of this putative new species. [Copyright &y& Elsevier]

1 Seven populations of Beta vulgaris ssp. maritima (wild beet) situated along a latitudinal cline were studied for their vernalization requirement and its consequences for fitness. 2 Various cold regimes were applied in glasshouses and experimental gardens with plants of different ages. Three additional experimental sites (on the French Mediterranean, Atlantic and North Sea coasts) situated near three of the sampled populations, and thus including a reciprocal transplant design, were used to evaluate the influence of latitude under natural conditions. Survival and plant size were measured over 3 years. 3 The vernalization requirement was greater in plants from more northern origins. The level of cold required to allow flowering overcompensated for the colder springs, so that northern plants in northern sites flowered less than southern plants in southern sites. 4 Young seedlings were more difficult to vernalize than plants that had already developed vegetative rosettes. 5 Differences in vernalization requirement seem to be an adaptive response to spring temperatures and season length in a particular latitude. A whole winter vernalization almost always led to flowering in the subsequent year whatever the latitude or geographical origin. 6 Plants from the Atlantic and Channel coasts showed the highest lifetime reproductive success at all sites. Southern populations were better adapted to disturbed habitats as shown by their higher first-year reproductive success. The North Sea population had a lower reproductive success than the Atlantic populations, even in its native environment. [ABSTRACT FROM AUTHOR]

Following their planktonic phase, the larvae of benthic marine organisms must locate a suitable habitat to settle and metamorphose. For oysters, larval adhesion occurs at the pediveliger stage with the secretion of a proteinaceous bioadhesive produced by the foot, a specialized and ephemeral organ. Oyster bioadhesive is highly resistant to proteomic extraction and is only produced in very low quantities, which explains why it has been very little examined in larvae to date. In silico analysis of nucleic acid databases could help to identify genes of interest implicated in settlement. In this work, the publicly available transcriptome of Pacific oyster Crassostrea gigas over its developmental stages was mined to select genes highly expressed at the pediveliger stage. Our analysis revealed 59 sequences potentially implicated in adhesion of C. gigas larvae. Some related proteins contain conserved domains already described in other bioadhesives. We propose a hypothetic composition of C. gigas bioadhesive in which the protein constituent is probably composed of collagen and the von Willebrand Factor domain could play a role in adhesive cohesion. Genes coding for enzymes implicated in DOPA chemistry were also detected, indicating that this modification is also potentially present in the adhesive of pediveliger larvae. [ABSTRACT FROM AUTHOR]

In the face of an increasing world population and a subsequent need for an increase in sustainable and healthy food production, low trophic species, such as oysters, emerge as a promising alternative. However, regional variations in oyster production techniques, market dynamics, and consumption patterns create challenges for both the global and local industry's growth. In this study, a descriptive qualitative analysis of oyster markets across seven Atlantic regions was carried out. The Pacific oyster (Crassostrea gigas) was found to be farmed in most Atlantic regions except the US but is classified as invasive in Sweden and potentially invasive in South Africa. Other farmed and/or harvested species include native species (C. gasar and C. rhizophorae) in Brazil, the American cupped oyster (C. virginica) in the US, and the European flat oyster (Ostrea edulis) in France, Sweden, and the US. In Irish farms, Pacific oysters are primarily for export to European markets. The marine aquaculture sectors of Sweden, South Africa, and Namibia, as well as Brazil's farming for C. gasar, were found to be underdeveloped. This study also observed a variation in licensing, property rights, and regulatory frameworks. Financial challenges for small businesses, ecological implications of seed production techniques, biosecurity risks, and public health considerations are emphasized as critical areas for attention. This study offers valuable insights into the selected markets and can serve as a useful resource for policymakers, aquaculture practitioners, and stakeholders in optimizing global shellfish industry strategies. [ABSTRACT FROM AUTHOR]

Farming, and thus the domestication of Haliotis tuberculata , began recently. We compared the responses of unselected farmed and wild abalone to stressors that occur on farms. The aim was to determine if the farm environment had induced differences in the behavioural or physiological performances of the abalone. Thirty hatchery-born 3.5 year-old abalone and thirty wild ones were reared under standard farm conditions for 6 months and characterised for 19 traits related to growth, survival, behaviour and immunology. Behavioural and immunological responses to stressors differed between the two stocks. Farmed abalone retracted and swivelled less in reaction to a finger contact. Phagocytosis efficiency was reduced by shaking in abalone from both origins, but the farmed stock returned to the basal level after the recovery week, while wild abalone did not, and a rise of total haemocyte count after shaking and its return to a basal level after one week was only observed for the farmed stock. This indicates that both behaviour and immune responses following a stress have been affected by the farming practices. This suggests that a domestication process has already been initiated in the farmed stock. Our results may also be important for the success of any population enhancement based on hatchery-produced abalone as they raise the question of the capacity of abalone with a farmed origin to be adapted to the wild environment. [ABSTRACT FROM AUTHOR]

Dinoflagellates of the genus Alexandrium are a major cause of harmful algal blooms (HABs) that have increasingly disrupted coastal ecosystems for the last several decades. Microalgae from the genus Alexandrium are known to produce paralytic shellfish toxins (PST) but also bioactive extracellular compounds (BEC) that can display cytotoxic, allelopathic, ichtyotoxic or haemolytic effects upon marine organisms. The objective of this experimental study was to assess the effects of PST and BEC produced by A. minutum upon juvenile great scallops Pecten maximus . Scallops were exposed for one week to two different strains of A. minutum , the first producing both PST and BEC and the second producing only BEC. Escape response to starfish, daily shell growth, histological effects, and accumulation of PST were recorded after one week of exposure, and after two subsequent weeks of recovery. Daily shell growth was delayed three days in scallops exposed to the BEC-producing A. minutum strain, probably during the three first days of exposure. An increase of reaction time to predators was observed in scallops exposed to the BEC condition, suggesting that BEC may have altered sensing processes. Scallops exposed to PST displayed a less-efficient escape response and muscular damage which could reflect the effects of paralytic toxins upon the nervous system of scallops. This study demonstrates contrasting effects of the distinct toxic compounds produced by A. minutum upon marine bivalves, thus highlighting the importance to better characterize these extracellular, bioactive compounds to better understand responses of other marine organisms. [ABSTRACT FROM AUTHOR]

The European flat oyster, Ostrea edulis, is a habitat-forming bivalve which was historically widespread throughout Europe. Following its decline due to overfishing, pollution, sedimentation, invasive species, and disease, O. edulis and its beds are now listed as a threatened and/or declining species and habitat by OSPAR. Increasing recognition of the plight of the oyster, alongside rapidly developing restoration techniques and growing interest in marine restoration, has resulted in a recent and rapid growth in habitat restoration efforts. O. edulis seed supply is currently a major bottleneck in scaling up habitat restoration efforts in Europe. O. edulis has been cultured for centuries, however, research into its culture declined following the introduction of the Pacific oyster, Crassostrea gigas to Europe in the early 1970 s. Recent efforts to renew both hatchery and pond production of O. edulis seed for habitat restoration purposes are hampered by restoration project timelines and funding typically being short, or projects not planning appropriately for the timescales required for investment, research-and-development and delivery of oyster seed by commercial producers. Furthermore, funding for restoration is intermittent, making long-term commitments between producers and restoration practitioners difficult. Long-term, strategic investment in research and production are needed to overcome these bottlenecks and meet current ambitious restoration targets across Europe. [ABSTRACT FROM AUTHOR]

In the fifty years since the introduction of the Pacific oyster Crassostrea gigas and the first reports of the parasites Marteilia refringens and Bonamia ostreae in European waters, numerous research projects dedicated to the native European flat oyster Ostrea edulis have been conducted, notably in France. Most of these projects have been dedicated to developing controlled reproduction and hatchery technology for seed production, examining pathological aspects to understand and control diseases, and using genetics to develop resistant lines. While the long-term objective of most studies has been to revive the aquaculture production of O. edulis, a smaller number have addressed the ecology of local remnant beds and reefs in France. This article provides an overview of the major outcomes of all these projects, focusing on results obtained in France and prospects for future work there, taking into account the rising interest in increasing aquaculture production and ecological motivation to restore declining populations as part of the framework of the Native Oyster Restoration Alliance (NORA) and in line with UN Decade for Ecosystem Restoration. [ABSTRACT FROM AUTHOR]

This volume of Evolutionary Applications sees the publication of two genomes for the European native flat oyster Ostrea edulis, a species of significant evolutionary, ecological and commercial value. Each is a highly contiguous chromosome‐level assembly from individuals of different genetic backgrounds, which have been benchmarked against one another. This situation has resulted from the serendipitous discovery that two independent research groups were both deep into the process of building, annotating and investigating separately produced assemblies. Due to constraints with funder requirements and the need to recognize early career researchers for their work, alongside the technical challenge of integrating assemblies from two very different genomes, there was limited capacity to merge the sequences into one publication at the stage of discovery. This issue is likely to become very common over the next few years until the technologies for working with multiple genomes at once, for example, graph genomes, become commonplace in nonmodel species. Consequently, both of our teams have decided to collaborate rather than compete, recognizing the benefit to copublishing two separate genome resources for the research community, each with distinct scientific investigations, and working collaboratively to benchmark the assemblies. [ABSTRACT FROM AUTHOR]

Cytogenetic abnormalities associated with viral infections, including from viruses of the Herpesvirales order, have been reported in vertebrate species. Ostreid herpesvirus 1 (Os HV-1) has been detected worldwide during mortality outbreaks of the Pacific oyster Crassostrea gigas. On the other hand, a high proportion of aneuploid cells in somatic tissues have been observed in C. gigas. In this study, we analysed the putative association between aneuploidy levels and the detection of Os HV-1 in gills of C. gigas, the Portuguese oyster C. angulata and their F1 hybrids cultured in Ria Formosa (Portugal). Os HV-1 was detected by PCR in 5.4% of the total of oysters analysed ( n = 111) namely in 11.1%, 8.0% and 1.7% of C. gigas, C. angulata and F1 hybrid respectively. Sequencing analysis of a viral fragment amplified with the C2/C6 primer pair revealed a high similarity with the Os HV-1 reference type. Moreover, in situ hybridization confirmed the presence of Os HV-1 in gill tissue. Oysters where Os HV-1 was detected had a significantly higher mean percentage of aneuploid cells (25%) than the ones where the virus was not detected (18%). However, the overall low percentage of positive samples contrasted with the high mean percentage of aneuploidy observed, with 50% of the oysters analysed showing a percentage of aneuploid cells between 20% and 30%. We hypothesize that somatic aneuploidy may adversely affect oysters making them more prone to Os HV-1 infection, but the virus is unlikely to be the cause of somatic aneuploidy. [ABSTRACT FROM AUTHOR]

This study elucidates to generate a linkage map for Portuguese oysters, Crassostrea angulata, and recognise potential markers linked to economical traits in C. angulata. Genome-wide association studies (GWAS) using 19,475 single nucleotide polymorphisms (SNPs) generated by a genotyping-by-sequencing approach consisting of 647 individuals in two selection generations of C. angulata, consisting of 57 full-sib family of the first generation and 33 full-sib family of the second generation. GWAS identified six significant SNPs linked to whole weight (P < 10−4). These six SNPs explained 10.2% of the total genetic variance of whole weight. Additionally, three SNPs were identified linked to meat yield (i.e., soft tissue weight) and contributed to 9.2% of the total genetic variance for this trait. By linkage analysis on the raw data, a total of 19,475 SNP markers were mapped to 10 linkage groups, with an average density of 19.1 SNPs per cM. This linkage map was developed and potential markers identified for whole weight and soft tissue weight provide a novel resource to characterise the genetic structure of economic traits in C. angulata. [ABSTRACT FROM AUTHOR]

Pathogenic bacteria are known to be one of the main factors affecting Pecten maximus larval survival in hatcheries. As a result, juvenile production often relies on the use of antibiotics during larval culture. However, limitations of the usage of chemicals such as chloramphenicol in aquaculture have been reinforced due to their negative environmental impact and alternatives are accordingly needed. Thus, the importance of bacterial transfer from oocytes to larvae has been studied here as well as procedures to limit larval mortality in P. maximus . In order to reduce bacterial contamination during larval development, we focused on two periods, broodstock conditioning and post-fertilization. The animals were conditioned for 2 months with two erythromycin treatments of 6 days, with ( SA ) or without sandy-bottom ( NSA ). The absence of sediment strongly reduced contamination by Vibrios of oocytes ( NSA : 0.003 ± 0.002 CFU oocyte − 1 SA : 0.57 ± 0.17 CFU oocyte − 1 ) and D-larvae ( NSA : 0.14 ± 0.05 CFU D-larva − 1 SA : 0.51 ± 0.002 CFU D-larva − 1 ). It also enhanced survival by 52% at 15 days post fertilization, whereas a two day antibiotic treatment of D-larvae did not improve subsequent survival, regardless of broodstock conditioning method. Furthermore, both treatments led to similar fatty acid profiles of oocytes and resulting larvae, suggesting that broodstock conditioning was physiologically similar with or without sediment. This work has shown that gamete contamination could be reduced when sandy-bottom was removed during broodstock conditioning under bacterial control with erythromycin. The present results contribute to a reduced utilization of antimicrobial agents for great scallop larval rearing in controlled condition. [ABSTRACT FROM AUTHOR]

Background: Triploidy can occur in many animal species but is often lethal. Among invertebrates, amphibians and fishes, triploids are viable although often sterile or infertile. Most triploids of the Pacific oyster Crassostrea gigas are almost sterile (named “3nβ”) yet a low but significant proportion show an advanced gametogenesis (named “3nα”). These oysters thus constitute an interesting model to study the effect of triploidy on germ cell development. We used microarrays to compare the gonad transcriptomes of diploid 2n and the abovementioned triploid 3nβ and 3nα male and female oysters throughout gametogenesis. Results: All triploids displayed an upregulation of genes related to DNA repair and apoptosis and a downregulation of genes associated with cell division. The comparison of 3nα and 3nβ transcriptomes with 2n revealed the likely involvement of a cell cycle checkpoint during mitosis in the successful but delayed development of gonads in 3nα individuals. In contrast, a disruption of sex differentiation mechanisms may explain the sterility of 3nβ individuals with 3nβ females expressing male-specific genes and 3nβ males expressing female-specific genes. Conclusions: The disruption of sex differentiation and mitosis may be responsible for the impaired gametogenesis of triploid Pacific oysters. The function of the numerous candidate genes identified in our study should now be studied in detail in order to elucidate their role in sex determination, mitosis/meiosis control, pachytene cell cycle checkpoint, and the control of DNA repair/apoptosis. [ABSTRACT FROM AUTHOR]

Crassostrea gigas originated from the Pacific coast of Asia, but was introduced into several European countries in the early 1970s. Natural populations have now spread across the length of the western seaboard of Europe. To elucidate the demographic and selective processes at play during this rapid expansion, genome-scan analysis was performed on different populations. High diversities and low differentiation were observed overall, but significant genetic differentiation was found among newly established populations and between the newly established northern group and a nearly panmictic group composed of southern European populations and a population from Japan. Loss of genetic diversity was also seen in the north, likely caused by founder events during colonization. The few strongly supported outlier loci revealed a genetic structure uncorrelated with the north/south differentiation, but grouping two samples from the Danish fjords (northern group) and one from the Dutch Scheldt estuary (southern group) with the one from Japan. These findings might reflect the following: (i) parallel adaptation to similar environmental pressures (fjord-like environment) within each of the two groups or (ii) a footprint of a secondary introduction of an alternative genomic background maintained by multifarious isolation factors. Our results call for a closer examination of adaptive genetic structure in the area of origin. [ABSTRACT FROM AUTHOR]

Clostridium difficile is an emergent pathogen, and the most common cause of nosocomial diarrhea. In an effort to understand the role of small noncoding RNAs (sRNAs) in C. difficile physiology and pathogenesis, we used an in silico approach to identify 511 sRNA candidates in both intergenic and coding regions. In parallel, RNA–seq and differential 5′-end RNA–seq were used for global identification of C. difficile sRNAs and their transcriptional start sites at three different growth conditions (exponential growth phase, stationary phase, and starvation). This global experimental approach identified 251 putative regulatory sRNAs including 94 potential trans riboregulators located in intergenic regions, 91 cis-antisense RNAs, and 66 riboswitches. Expression of 35 sRNAs was confirmed by gene-specific experimental approaches. Some sRNAs, including an antisense RNA that may be involved in control of C. difficile autolytic activity, showed growth phase-dependent expression profiles. Expression of each of 16 predicted c-di-GMP-responsive riboswitches was observed, and experimental evidence for their regulatory role in coordinated control of motility and biofilm formation was obtained. Finally, we detected abundant sRNAs encoded by multiple C. difficile CRISPR loci. These RNAs may be important for C. difficile survival in bacteriophage-rich gut communities. Altogether, this first experimental genome-wide identification of C. difficile sRNAs provides a firm basis for future RNome characterization and identification of molecular mechanisms of sRNA–based regulation of gene expression in this emergent enteropathogen. [ABSTRACT FROM AUTHOR]

As a result of aquaculture activities, Pacific oysters Crassostrea gigas (Thunberg, 1793) have invaded European coasts. Using seven microsatellites, we found virtually no genetic differentiation between natural populations throughout the European range (from the south of the Wadden Sea (the Netherlands) to the south of France) and French cultivated oysters. The genetic homogeneity of Pacific oyster samples appears to be the result of repeated transfers from same seed stocks made for aquaculture and, to a lesser extent, widespread dispersal due to specific biological traits of this species. The only genetic differentiation of Sylt population in the north of the Wadden Sea (Germany) suggests a stronger, persistent impact of ongoing supply of new genetic material from hatchery production, corresponding to seeds selection made by breeders. All of our genetic data highlighted the importance of aquaculture practices on the genetic structure of the keystone invader C. gigas in Europe. [ABSTRACT FROM AUTHOR]

Abstract: Response to divergent selection for “high” and “low” survival during the summer period, from July to October, was investigated in juvenile (six-month-old) Pacific oysters, Crassostrea gigas, by producing two sets of progenies in 2002 (Generation 2) and three sets of progenies in 2003 (Generation 3). A strict between-family approach was used and resistance of these selected progenies to summer mortality was assessed in three sites along French coasts, to determine their response to selection and estimate realized heritability of the trait. A significant difference in survival was observed between the “high” and “low” selected groups at all sites for all sets of progenies, indicating a significant genetic component. High realized heritabilities for survival obtained from Generation 2 oysters, ranging from 0.61±0.08 to 0.98±0.15, were in line with previous results from the first generation. Finally, Generation 3 realized heritability, ranging from 0.55±0.18 to 0.81±0.13, supported results from Generation 2. Our results demonstrate that selective breeding to improve survival during the first summer can be successfully implemented and should lead to rapid gains. Overall, selection on survival did not have any impact on growth, although it did have one on yield. [Copyright &y& Elsevier]

The flat oyster Ostrea edulis is native to Europe and populations have been severely depleted by the parasite Bonamia ostreae since the 1980s. Additional genetic markers are required to improve population genetics study and linkage map development for selection for B. ostrea-resistance in this species. Here, we characterized 27 novel microsatellite loci for O. edulis. Number of alleles per locus ranged from 6 to 25 and observed heterozygosity between 0.375 and 1. Null alleles were suggested at a few loci but most loci were in Hardy–Weinberg agreement enabling their reliable use in further population and mapping genetics approaches. [ABSTRACT FROM AUTHOR]

Abstract: We compared the temporal dynamics of gametogenesis in diploid and triploid Pacific oysters (Crassostrea gigas) using histology. Oysters were reared in an estuarine farming site in Brittany over 3 years and their gametogenesis was monitored over the exceptionally hot summer of 2003. Both diploids and triploids showed active gametogenesis, but a high proportion of triploids remained at early stages of gonad development. Gametogenesis of triploids was characterized by the simultaneous occurrence of gonias and immature cytes together with mature gametes rather than overall retardation, though some triploids showed complete gonad maturation. Evidence of spawning was seen in both groups, and the quantity of germinal products emitted appeared to be similar in triploids and diploids, though triploids were much heavier than diploids. Our study supports previously reported experimental observations and suggests that gonad development in triploid Pacific oysters can be enhanced when these oysters are reared in the field under unusually warm conditions. [Copyright &y& Elsevier]

Abstract: Phosphoglucomutase is a key enzyme in glycolysis and has been widely studied in vertebrates and some invertebrates but no molecular information is available in marine invertebrates despite the importance of this marker in ecological and genetical studies. In this work, we isolated a cDNA and the corresponding genomic sequence that encode PGM-2 locus in the Pacific oyster Crassostrea gigas. We used sequences drawn from the database to construct an evolutionary framework for examining the position of mollusc PGM sequences among prokaryotic and eukaryotic homologues and showed that oyster PGM gene organization was closer to vertebrates PGM genes than other invertebrates as previously found in other Lophotrochozoa species. We also investigated PGM mRNA expression in oyster tissues in response to xenobiotics (i.e hydrocarbons and pesticides). The results obtained showed that PGM mRNA expression is mostly up-regulated in the first steps of the response to pollutant exposure and is xenobiotic-dependant. [Copyright &y& Elsevier]

Investigates the effect of gamete competition on cross-fertilization success and the relative survival and growth rate of parental and F[sub1] individuals from controlled crosses at different stages of the life cycle in two species of mussels. Description on the collection and treatment of larvae; Implications for stability of the hybrid zone; Discussion on assortative fertilization.

Biosecurity, Crassostrea gigas, epidemiology, ostreid herpesvirus (OsHV-1) var, oyster farming, vertical transmission Keywords: biosecurity; Crassostrea gigas; epidemiology; ostreid herpesvirus (OsHV-1) var; oyster farming; vertical transmission EN biosecurity Crassostrea gigas epidemiology ostreid herpesvirus (OsHV-1) var oyster farming vertical transmission 4012 4017 6 07/21/21 20210801 NES 210801 In recent decades, mortality caused by ostreid herpesvirus (OsHV-1) and a variant (OsHV-1 var) has severely impacted the production of Pacific oyster, I Crassostrea gigas i , chronologically in France, New Zealand (NZ) and Australia (Jenkins et al., 2013; Keeling et al., 2014; Segarra et al., 2010). Case study of vertical transmission of ostreid herpesvirus-1 in Pacific oysters and biosecurity management based on epidemiological data from French, New Zealand and Australian hatchery-propagated seed We have collated data from the production of Pacific oysters across these countries to assess the risk associated with breeding oysters from broodstock grown in OsHV-1 var-infected waters. [Extracted from the article]

In the Archipelago Sea, pikeperch (Sander lucioperca) is an important species in both commercial and recreational fisheries. Pikeperch is caught mainly with small mesh size gillnets, and annual fishing mortality is high. The possible effects of such fisheries, as well as temperature or density on pikeperch growth have not been studied earlier. The first hypothesis of this study was that the effect of temperature on growth is positive and that of density is negative. The second hypothesis was that size-selectivity of gillnets causes the fast-growing individuals to be caught at younger ages than the slow-growing ones. The results showed that temperature had a significant positive effect on growth, and this was greater than the negative effect of year-class density, which was also significant. The gillnet selectivity caused a difference of up to 60 mm in back-calculated lengths in the fully recruited age groups within the same year class, between pikeperch caught at age 6+ and age 9+. Thus, the Rosa Lee phenomenon caused by gillnet size-selectivity led to the removal of faster growing specimens from the population at younger ages. This can potentially cause underestimation of real growth, and thus, poor fishery management. [ABSTRACT FROM AUTHOR]

Bivalve culture in Canada increased by 25% from 2000 to 2016. In Prince Edward Island (PEI), bivalves are cultivated in bays and estuaries and there is limited space for further aquaculture expansion. Thus, there is merit in developing a numerical model determining the abundance of bivalve populations in relation to their food availability in order to assess the carrying capacity of shellfish growing areas. This modelling will take into account the different bivalve species present in the bay, as the cultivated Mytilus edulis and Crassostrea virginica and wild, M. edulis, C. virginica, Mya arenaria and Mercenaria mercenaria. As a first step toward a modelling goal, this study compared the physiological differences of the 6 bivalve groups. Three physiological parameters were measured: clearance rate, oxygen consumption and assimilation to determine the energy budget or scope for growth (SFG). These measurements were carried out on individuals contained in metabolic chamber at summer and autumn temperatures (20 and 8 °C, respectively). Our results show that M. edulis is best adapted to these temperature in PEI as it maintains high SFG at both temperatures. For C. virginica and M. arenaria, high physiological parameters under summer conditions were observed, followed by a decrease in autumn. For M. mercenaria rates were low at both temperatures indicating a persistently low growth potential. These results demonstrate the adaptive physiological capacity of each species and provide insight into the underlying reasons some species such as C. virginica and M. mercenaria are at their northern distribution limit in the Gulf of St. Lawrence. Finally, no differences in the SFG between cultivated and wild bivalves have been observed. These results are discussed within the context of estimating the impact of each bivalve group in bays environment from PEI and particularly on food availability. [ABSTRACT FROM AUTHOR]

Selective breeding programs have been initiated worldwide for the Pacific oyster Crassostrea gigas to improve economically important traits such as growth and disease resistance. The emergence of genomic tools has allowed novel perspectives for using genomic selection (GS) in mixed-family breeding designs, which are cheaper and easier to develop than classical breeding schemes. In this study, we evaluated the potential of GS for different growth-related and shell colour traits in two independent commercially selected populations (P1 and P2), based on mixed-family designs. From ≈14.5K informative SNPs genotyped with the bi-species Axiom Affymetrix 57K oyster array, ≈12.5K were mapped on the reference genome. A strong heterogeneity of marker density between and within chromosomes was reported, with a low linkage disequilibrium (below 0.1 at 0.1 Mb) between pairs of SNPs. The within-population structure was homogenous for each population, with effective sizes of 107 for P1 and 76 for P2. Heritability was estimated for each trait and population and ranged from 0.08 ± 0.04 (for mean darkness intensity in P1) to 0.56 ± 0.08 (for the mean upper valve b* value in P2) for a pedigree-based model and from 0.04 ± 0.02 (for mean darkness intensity in P1) to 0.69 ± 0.04 (for the mean darkness intensity in P2) for a genomic-based model. Growth-related traits were generally highly genetically and positively correlated with each other, but weakly correlated with colour traits. Accuracy of prediction was generally higher with the genomic model (GBLUP) than with the classical BLUP model, with a maximum gain of accuracy (from 0.38 to 0.66) for flesh weight adjusted by total weight in P2. Accuracy of breeding values was slightly higher for colour traits for P2, with higher heritability estimates. Overall, our results indicate that GS has a good potential to be implemented in mixed-family breeding programs in a shellfish such as C. gigas. • Genomic selection is suitable for commercial mixed-family oyster breeding programs. • Although the SNP array quality was limited it was sufficient for genomic selection. • Growth-related traits were moderately heritable. • There were weak correlations between growth-related traits and colour traits. • Prediction accuracy was higher with the genomic model than with the pedigree model. [ABSTRACT FROM AUTHOR]

Cultivated bivalves are important not only because of their economic value, but also due to their impacts on natural ecosystems. The Pacific oyster (Crassostrea gigas) is the world's most heavily cultivated shellfish species and has been introduced to all continents except Antarctica for aquaculture. We therefore used a medium‐density single nucleotide polymorphism (SNP) array to investigate the genetic structure of this species in Europe, where it was introduced during the 1960s and has since become a prolific invader of coastal ecosystems across the continent. We analyzed 21,499 polymorphic SNPs in 232 individuals from 23 localities spanning a latitudinal cline from Portugal to Norway and including the source populations of Japan and Canada. We confirmed the results of previous studies by finding clear support for a southern and a northern group, with the former being indistinguishable from the source populations indicating the absence of a pronounced founder effect. We furthermore conducted a large‐scale comparison of oysters sampled from the wild and from hatcheries to reveal substantial genetic differences including significantly higher levels of inbreeding in some but not all of the sampled hatchery cohorts. These findings were confirmed by a smaller but representative SNP dataset generated using restriction site‐associated DNA sequencing. We therefore conclude that genomic approaches can generate increasingly detailed insights into the genetics of wild and hatchery produced Pacific oysters. [ABSTRACT FROM AUTHOR]

The Pacific cupped oyster is genetically subdivided into two sister taxa, Crassostrea gigas and Crassostrea angulata, which are in contact in the north-western Pacific. The nature and origin of their genetic and taxonomic differentiation remains controversial due the lack of known reproductive barriers and the high degree of morphologic similarity. In particular, whether the presence of ecological and/or intrinsic isolating mechanisms contributes to species divergence is unknown. The recent co-introduction of both taxa into Europe offers a unique opportunity to test how genetic differentiation is maintained under new environmental and demographic conditions. We generated a pseudochromosome assembly of the Pacific oyster genome using a combination of BAC-end sequencing and scaffold anchoring to a new high-density linkage map. We characterized genome-wide differentiation between C. angulata and C. gigas in both their native and introduced ranges, and showed that gene flow between species has been facilitated by their recent co-introductions in Europe. Nevertheless, patterns of genomic divergence between species remain highly similar in Asia and Europe, suggesting that the environmental transition caused by the co-introduction of the two species did not affect the genomic architecture of their partial reproductive isolation. Increased genetic differentiation was preferentially found in regions of low recombination. Using historical demographic inference, we show that the heterogeneity of differentiation across the genome is well explained by a scenario whereby recent gene flow has eroded past differentiation at different rates across the genome after a period of geographical isolation. Our results thus support the view that low-recombining regions help in maintaining intrinsic genetic differences between the two species. [ABSTRACT FROM AUTHOR]

Selective breeding strategies require pedigree information over generations, but many species produced in aquaculture are too small to be physically tagged at early stages. Consequently, maintaining a sufficient number of separate families is often needed but costly and logistically difficult. Alternatively, parentage assignment can be obtained using DNA markers. We developed a panel of single nucleotide polymorphism (SNP) markers for the European abalone Haliotis tuberculata using an existing transcriptomic resource. An initial set of 2,176,887 SNPs was filtered to select 500 for high throughput genotyping. Of these, 298 SNPs were amplified in at least 90% of our H. tuberculata samples, consisting of a mixed family cohort (945 offspring) generated by crossing 40 abalones, and 5 full-sib training families (70 offspring). Based on amplification success among parents, minimum allele frequency and checks carried out against the training families, a subset of 123 markers was used to carry out parentage assignment in our mixed family cohorts. Maximum likelihood and exclusion-based methods of parentage assignment yielded consistent results, allowing parentage to be assigned in 98.9% of the studied progeny. Optimization of markers suggests that the 60 most informative SNPs may be sufficient for 95% assignment success in these progeny. The panel was also used to estimate effective population size, and revealed a low N e due to high variance of reproductive success between parents. Our panel could be used to estimate genetic parameters of traits in mixed family cohorts, an essential stage to initiate selective breeding in H. tuberculata . It could also be useful tool in the context of monitoring stock enhancement and population genetics studies. [ABSTRACT FROM AUTHOR]

The seasonal changes in biochemical composition of the edible bivalve Arca noae harvested from a Mediterranean coastal lagoon (Bizerte lagoon, Tunisia) were investigated from October 2013 to September 2014. Potential food sources and nutritional quality indices (NQI) were determined by analyzing the fatty acid profiles of their tissues during an annual reproductive cycle. Results showed that A. noae had moisture (73.8–82%) and protein (24.1–58.6% dry weight) as major components, followed by lipid (10.4–28.8% dry weight) and glycogen (4.05–14.6% dry weight). A. noae accumulated lipid and glycogen for gonadal development during both maturation periods (late autumn/late spring–summer) to be used during spawning periods (winter/late summer–early autumn). However, proteins were mainly used to support reproductive allocation and played an important role on the energetic maintenance. Lipid and glycogen were found to be significantly related to temperature, salinity and chlorophyll a (p < 0.05). An increase of condition index (CI) was observed during spring and early summer when both temperature and food supply increased. The total fatty acid (TFA) profile of Ark shells was dominated by polyunsaturated fatty acids (PUFA) (33.8–49.6%), followed by saturated (SFA) (29.1–43.1%) and monounsaturated fatty acids (MUFA) (20.77–28.3%). A. noae soft tissues were also rich in macro-minerals (Na, Ca and Mg). The analysis of fatty acid trophic markers revealed that the diet of A. noae during the year of study was based on mixture food mainly on phytoplankton followed by zooplankton and other sources (bacteria, seagrass and macroalgae). Furthermore, the nutritional quality indices have revealed that A. noae is an excellent source of nutrients and a healthy food for human consumption. These data are useful to the conservation of natural stocks of A. noae and the development of sustainable aquaculture production of this shellfish species in the Bizerte lagoon. [ABSTRACT FROM AUTHOR]

Hatchery production of great scallop, Pecten maximus, remains unpredictable, notably due to poor larval survival. Large-scale flow-through systems up to 3500 L have been developed to avoid the use of antibiotics in static systems. Alternatively, small-scale flow-through systems have been successfully applied for oysters but they proved to be unsuitable to rear scallop larvae. By focusing on physical factors presumed to limit P. maximus larval development, this study aimed to optimize great scallop larvae rearing parameters under controlled conditions. First, the influence of aeration on larval performances, energetic metabolism and antioxidant defences were studied both in static and flow-through systems. Aeration depressed larval food intake, regardless of the intensities of flow tested (100 ml/min, 155 ml/min and 270 ml/min). On the other hand, antioxidant enzyme activities remained constant or decreased, suggesting that antioxidant defences were inactivated. The increase in citrate synthase activity suggested an increase in metabolic rate possibly due to a turbulent stressful environment. All larvae exposed to such turbulence died before reaching metamorphosis, whereas those reared without aeration survived well (≈ 95%). The effects of water renewal were thereafter studied in 50-L flow-through flat-bottomed tanks. No differences in survival (20.4 ± 0.5%), growth (3.8 ± 0.2 μm/d), competence (5.6 ± 0.2%), energetic metabolism level and antioxidant enzyme activities were observed when comparing 12.5 and 25 L/hr water renewal. Whereas air bubbling leads to detrimental effects, flow-through in small flat-bottomed tanks appears to be a suitable technique for scallop larvae rearing. [ABSTRACT FROM AUTHOR]

Fertilization of the oocyte is a critical process of sexual reproduction depending among other factors on spermatozoa functionality. Mitochondria participate in many crucial processes for spermatozoa motility and fertilizing ability. The Pacific oyster, Crassostrea gigas , is characterized by a high inter-individual variability of its reproductive success which has been shown to be partially due to the variability of gamete quality. The present study explored spermatozoa characteristics such as: i) relationships among mitochondrial functionality (ATP content, mitochondrial membrane potential (MMP), reactive oxygen species production); sperm viability (percentages of live, dying, and dead); and motility; and ii) their involvement in inter-oyster variability of fertilizing ability demonstrated using simple and multiple regressions. Our results showed that ATP content depends on both MMP and viability of spermatozoa. Using multiple regressions, 61% of the variability of the trochophore-larval yield was explained by a model combining the ATP content and the percentage of dying spermatozoa ( P < 0.001). Our results reveal that capacity of spermatozoa to maintain a high level of ATP via OXPHOS partly explains the inter-individual variability of fertilization success in the Pacific oyster. Sperm ATP content and viability assays will provide valuable tools for assessing sperm quality of this species in aquaculture production, cryopreservation, and bioassays. [ABSTRACT FROM AUTHOR]

The Portuguese oyster Crassostrea angulata and the Pacific oyster Crassostrea gigas are very closely related species originating from Asia that were introduced in Europe. The objectives of the present study were to determine if there is asynchrony in settlement time of C. angulata and C. gigas larvae in an area where both taxa coexist and if hybridization between the two species occurs throughout the breeding season. Oyster collectors were deployed every two weeks during one year in two different sites in Ria Formosa lagoon (Portugal) and the oysters that settled were genotyped with nuclear and mitochondrial markers. Settlement of Crassostrea sp. was observed from April to November 2004 ( n = 694), with two distinct periods. In the first period (April), when 19% of the oysters settled, the haplotypes and alleles characteristic of C. gigas were mainly observed. In the following settlement period (July to November), the frequency of haplotypes and alleles of C. gigas decreased over time while those characteristics of C. angulata reached high frequencies by the end of the settlement period. Our results suggest that C. gigas was able to reproduce at lower temperatures than C. angulata in spring. However, the non-significant allelic disequilibrium observed during almost all settlement periods suggests that hybridization is widespread in time. The results obtained in the present study show that there are differences in the reproductive behavior between C. angulata and C. gigas that may limit gene flow between the two species. [ABSTRACT FROM AUTHOR]

Abalone growth rate is often identified among important traits to improve through selective breeding. However, the rapid success of some selective breeding plans has sometimes led to negative effects in some aquaculture species due to trade-offs. One of them is the loss of homeostasis of selected animals which results in the inability to resist the stress experienced during the rearing process. In this context, this study aimed to analyze the phenotypic relationships between growth, and physiological and behavioural traits in Haliotis tuberculata under stressful conditions. Eleven traits related to growth, immunity, reproduction and behaviour were recorded under laboratory conditions. A total of 120 adults from wild or farm origin were first monitored during a 3-week stress period (high density and acute stress handling) during winter, followed by 6 months on-growing in sea-cages. Relationships between parameters were analyzed using a multi-factorial approach. Wild and farm stocks could only be discriminated on behaviour traits, confirming that the French abalone industry is in the beginning of the domestication process. After 3 weeks of chronic stress, the righting latency of an abalone was linked to better survival and faster growth. Abalones having the best growth after 6 months were characterized by higher activity during the previous winter period, whereas an early gonad maturation reduced the growth in summer. Our results provide a basis for the establishment of a multi-trait breeding program to improve the growth rate while controlling the evolution of physiological and behavioural traits. Statement of relevance The relationships of behavioural and physiological variables with survival and weight gain after application of important stressors were studied in order to provide a better understanding of Haliotis tuberculata biology during early domestication stage. This paper will give information on new targets and tools for selective breeding. [ABSTRACT FROM AUTHOR]

The strict anaerobe Clostridium difficile is the most common cause of nosocomial diarrhea, and the oxygen-resistant spores that it forms have a central role in the infectious cycle. The late stages of sporulation require the mother cell regulatory protein σK. In Bacillus subtilis, the onset of σK activity requires both excision of a prophage-like element (skinBs) inserted in the sigK gene and proteolytical removal of an inhibitory pro-sequence. Importantly, the rearrangement is restricted to the mother cell because the skinBs recombinase is produced specifically in this cell. In C. difficile, σK lacks a pro-sequence but a skinCd element is present. The product of the skinCd gene CD1231 shares similarity with large serine recombinases. We show that CD1231 is necessary for sporulation and skinCd excision. However, contrary to B. subtilis, expression of CD1231 is observed in vegetative cells and in both sporangial compartments. Nevertheless, we show that skinCd excision is under the control of mother cell regulatory proteins σE and SpoIIID. We then demonstrate that σE and SpoIIID control the expression of the skinCd gene CD1234, and that this gene is required for sporulation and skinCd excision. CD1231 and CD1234 appear to interact and both proteins are required for skinCd excision while only CD1231 is necessary for skinCd integration. Thus, CD1234 is a recombination directionality factor that delays and restricts skinCd excision to the terminal mother cell. Finally, while the skinCd element is not essential for sporulation, deletion of skinCd results in premature activity of σK and in spores with altered surface layers. Thus, skinCd excision is a key element controlling the onset of σK activity and the fidelity of spore development. [ABSTRACT FROM AUTHOR]

Oysters play an important role in estuarine and coastal marine habitats, where the majority of humans live. In these ecosystems, environmental degradation is substantial, and oysters must cope with highly dynamic and stressful environmental constraints during their lives in the intertidal zone. The availability of the genome sequence of the Pacific oyster Crassostrea gigas represents a unique opportunity for a comprehensive assessment of the signal transduction pathways that the species has developed to deal with this unique habitat. We performed an in silico analysis to identify, annotate and classify protein kinases in C. gigas, according to their kinase domain taxonomy classification, and compared with kinome already described in other animal species. The C. gigas kinome consists of 371 protein kinases, making it closely related to the sea urchin kinome, which has 353 protein kinases. The absence of gene redundancy in some groups of the C. gigas kinome may simplify functional studies of protein kinases. Through data mining of transcriptomes in C. gigas, we identified part of the kinome which may be central during development and may play a role in response to various environmental factors. Overall, this work contributes to a better understanding of key sensing pathways that may be central for adaptation to a highly dynamic marine environment. [ABSTRACT FROM AUTHOR]

Background: The Pacific oyster, Crassostrea gigas, is one of the most important aquaculture shellfish resources worldwide. Important efforts have been undertaken towards a better knowledge of its genome and transcriptome, which makes now C. gigas becoming a model organism among lophotrochozoans, the under-described sister clade of ecdysozoans within protostomes. These massive sequencing efforts offer the opportunity to assemble gene expression data and make such resource accessible and exploitable for the scientific community. Therefore, we undertook this assembly into an up-to-date publicly available transcriptome database: the GigaTON (Gigas TranscriptOme pipeliNe) database. Description: We assembled 2204 million sequences obtained from 114 publicly available RNA-seq libraries that were realized using all embryo-larval development stages, adult organs, different environmental stressors including heavy metals, temperature, salinity and exposure to air, which were mostly performed as part of the Crassostrea gigas genome project. This data was analyzed in silico and resulted into 56621 newly assembled contigs that were deposited into a publicly available database, the GigaTON database. This database also provides powerful and user-friendly request tools to browse and retrieve information about annotation, expression level, UTRs, splice and polymorphism, and gene ontology associated to all the contigs into each, and between all libraries. Conclusions: The GigaTON database provides a convenient, potent and versatile interface to browse, retrieve, confront and compare massive transcriptomic information in an extensive range of conditions, tissues and developmental stages in Crassostrea gigas. To our knowledge, the GigaTON database constitutes the most extensive transcriptomic database to date in marine invertebrates, thereby a new reference transcriptome in the oyster, a highly valuable resource to physiologists and evolutionary biologists. [ABSTRACT FROM AUTHOR]

Background: Originating from Northeast Asia, the Pacific oyster Crassostrea gigas has been introduced into a large number of countries for aquaculture purpose. Following introduction, the Pacific oyster has turned into an invasive species in an increasing number of coastal areas, notably recently in Northern Europe. Methods: To explore potential adaptation of reproductive traits in populations with different histories, we set up a common garden experiment based on the comparison of progenies from two populations of Pacific oyster sampled in France and Denmark and their hybrids. Sex ratio, condition index and microarray gene expression in gonads, were analyzed in each progeny (n = 60). Results: A female-biased sex-ratio and a higher condition index were observed in the Danish progeny, possibly reflecting an evolutionary reproductive strategy to increase the potential success of natural recruitment in recently settled population. Using multifarious statistical approaches and accounting for sex differences we identified several transcripts differentially expressed between the Danish and French progenies, for which additive genetic basis is suspected (showing intermediate expression levels in hybrids, and therefore additivity). Candidate transcripts included mRNA coding for sperm quality and insulin metabolism, known to be implicated in coordinated control and success of reproduction. Conclusions: Observed differences suggest that adaptation of invasive populations might have occurred during expansion acting on reproductive traits, and in particular on a female-biased sex-ratio, gamete quality and fertility. [ABSTRACT FROM AUTHOR]

Feeding strategies and digestive capacities can have important implications for variation in energetic pathways associated with ecological and economically important traits, such as growth or reproduction in bivalve species. Here, we investigated the role of amylase in the digestive processes of Crassostrea gigas, using in vivo RNA interference. This approach also allowed us to investigate the relationship between energy intake by feeding and gametogenesis in oysters. Double-stranded (ds)RNA designed to target the two α-amylase genes A and B was injected in vivo into the visceral mass of oysters at two doses. These treatments caused significant reductions in mean mRNA levels of the amylase genes: -50.7% and -59% mRNA A, and -71.9% and -70.6% mRNA B in 15 and 75 µg dsRNA-injected oysters, respectively, relative to controls. Interestingly, reproductive knock-down phenotypes were observed for both sexes at 48 days post-injection, with a significant reduction of the gonad area (-22.5% relative to controls) and germ cell under-proliferation revealed by histology. In response to the higher dose of dsRNA, we also observed reductions in amylase activity (-53%) and absorption efficiency (-5%). Based on these data, dynamic energy budget modeling showed that the limitation of energy intake by feeding that was induced by injection of amylase dsRNA was insufficient to affect gonadic development at the level observed in the present study. This finding suggests that other driving mechanisms, such as endogenous hormonal modulation, might significantly change energy allocation to reproduction, and increase the maintenance rate in oysters in response to dsRNA injection. [ABSTRACT FROM AUTHOR]

The Pacific oyster, Crassostrea gigas , is a species in which true male and true female well as hermaphrodite individuals have been reported. Among the latter, most are sequential, with one or more sex changes throughout their live, while a few (<2%) are simultaneous hermaphrodites (SH) which may self-fertilize. Sex determinism and its functional bases remain unclear is this species. In this study, one SH oyster was found among a mature broodstock and used to produce a progeny by self-fertilization. Several thousand offspring were obtained for this family (SF1) but only 73 SF1 oysters survived following an episode of mass mortality at the spat stage. Six of them were conditioned for reproduction and three were found to be SH, and one produced a limited but viable progeny by self-fertilization (SF2). Oysters were sampled and genotyped with 226 SNP markers, confirming that the SF1 and the SF2 oysters were produced by self-fertilization over two successive generations. To our knowledge, it is the second study reporting the feasibility of production on an inbred line of Pacific oysters by self-fertilization using a simultaneous hermaphrodite as primary genitor, and the first study to generate two successive generations of selfing. Observed mean inbreeding coefficient of SF2 oysters produced by selfing for two generations was 0.61, ranging from 0.46 to 0.80. This coefficient was lower than the expected theoretical value (0.8125), suggesting that the most homozygous offspring died at early stages due to inbreeding depression. Our study demonstrates that inbred lines of Pacific oysters can be produced by self-fertilization but may exhibit higher heterozygosity than theoretically expected due to better survival of the most heterozygous offspring. • Second evidence of oyster produced by self-fertilization beyond the larval stage. • Oysters produced by self-fertilization can produced a viable progeny. • Inbreeding rate was lower than expected. [ABSTRACT FROM AUTHOR]

AMP-activated protein kinase α (AMPKα) is a key regulator of energy balance in many model species during hypoxia. In a marine bivalve, the Pacific oyster Crassostrea gigas, we analyzed the protein content of adductor muscle in response to hypoxia during 6 h. In both smooth and striated muscles, the amount of full-length AMP-activated protein kinase α (AMPKα) remained unchanged during hypoxia. However, hypoxia induced a rapid and muscle-specific response concerning truncated isoforms of AMPKα. In the smooth muscle, a truncated isoform of AMPKα was increased from 1 to 6 h of hypoxia, and was linked with accumulation of AKT kinase, a key enzyme of the insulin signaling pathway which controls intracellular glucose metabolism. In this muscle, aerobic metabolism was maintained over the 6 h of hypoxia, as mitochondrial citrate synthase activity remained constant. In contrast, in striated muscle, hypoxia did not induce any significant modification of neither truncated AMPKα nor AKT protein content, and citrate synthase activity was altered after 6 h of hypoxia. Together, our results demonstrate that hypoxia response is specific to muscle type in Pacific oyster, and that truncated AMPKα and AKT proteins might be involved in maintaining aerobic metabolism in smooth muscle. Such regulation might occur in vivo during tidal intervals that cause up to 6 h of hypoxia. [ABSTRACT FROM AUTHOR]

We report the isolation, development and multiplex optimisation of 12 new microsatellite loci for the great scallop, Pecten maximus. Diversity was moderate to high, with number of alleles ranging from 4 to 20 and observed heterozygosity between 0.28 and 0.88. Progeny produced in a commercial hatchery was used to test locus power for parentage assignment. The percentage of offspring that was unambiguously assigned to a unique pair of parents was 97% (software package CERVUS-COLONY). Parentage assignment revealed that 22% of the studied progeny resulted from unplanned crosses. Effective population size of the study progeny was also estimated. Our study illustrates the power of microsatellites for the genetic monitoring of hatchery-produced great scallops. [ABSTRACT FROM AUTHOR]

Background: Bacterial infections are common in bivalve larvae and can lead to significant mortality, notably in hatcheries. Numerous studies have identified the pathogenic bacteria involved in such mortalities, but physiological changes associated with pathogen exposure at larval stage are still poorly understood. In the present study, we used an integrative approach including physiological, enzymatic, biochemical, and molecular analyses to investigate changes in energy metabolism, lipid remodelling, cellular stress, and immune status of Crassostrea gigas larvae subjected to experimental infection with the pathogenic bacteria Vibrio coralliilyticus. Findings: Our results showed that V. coralliilyticus exposure induced (1) limited but significant increase of larvae mortality compared with controls, (2) declined feeding activity, which resulted in energy status changes (i.e. reserve consumption, β-oxidation, decline of metabolic rate), (3) fatty acid remodeling of polar lipids (changes in phosphatidylinositol and lysophosphatidylcholine composition`, non-methylene–interrupted fatty acids accumulation, lower content of major C20 polyunsaturated fatty acids as well as activation of desaturases, phospholipase and lipoxygenase), (4) activation of antioxidant defenses (catalase, superoxide dismutase, peroxiredoxin) and cytoprotective processes (heat shock protein 70, pernin), and (5) activation of the immune response (non-self recognition, NF-κκ signaling pathway, haematopoiesis, eiconosoids and lysophosphatidyl acid synthesis, inhibitor of metalloproteinase and antimicrobial peptides). Conclusion: Overall, our results allowed us to propose an integrative view of changes induced by a bacterial infection in Pacific oyster larvae, opening new perspectives on the response of marine bivalve larvae to infections. [ABSTRACT FROM AUTHOR]

Abstract: We used a 2-DE proteomic approach to identify abundant proteins linked to oocyte quality in the Pacific oyster Crassostrea gigas, an economically important bivalve. Oocyte quality of 14 females was estimated by recording fertilisation and early developmental success until D-larval stage under controlled conditions. Proteins that were differentially expressed between females showing high or low oocyte quality were identified by nano-liquid chromatography tandem mass spectrometry. Twelve up-accumulated spots associated with low quality oocytes revealed 10 distinct proteins, including vitellogenin — breakdown products and metabolic enzymes. Eight up-accumulated spots from high quality oocytes revealed 6 distinct proteins, including chaperone molecules and cell-cycle control proteins. This is the first proteomic study dedicated to oocytes in C. gigas. Our results improve current knowledge about protein factors associated with oocyte quality in this species, and our understanding of the proteomic processes involved in their developmental competence. [Copyright &y& Elsevier]