The genome sequence of the variegated scallop, Mimachlamys varia (Linnaeus, 1758).

We present a genome assembly from an individual Mimachlamys varia (the variegated scallop; Mollusca; Bivalvia; Pectinida; Pectinidae). The genome sequence is 975.4 megabases in span. Most of the assembly is scaffolded into 19 chromosomal pseudomolecules. The mitochondrial genome has also been assembled and is 21.78 kilobases in length.

The variegated scallop, Mimachlamys varia, undergoes alterations in several of its metabolic pathways under short-term zinc exposure.

The variegated scallop (Mimachlamys varia) is a filter feeder bivalve encountered in marine regions of the Atlantic coast. In particular, it is present in the La Rochelle marina (France), where it is used for the biomonitoring of marine pollution, due to its ability to strongly bioaccumulate pollutants. In this semi-closed environment, contamination generated by port activities leads to an accumulation of both organic and metal pollutants. Zinc is one of these pollutants, present at a dose of up to 150 µg.L-1. This study investigated the effects of 48 h zinc exposure upon the metabolic profiles of Mimachlamys varia using UHPLC/QToF (ultra-high performance liquid chromatography-quadrupole time-of-flight) tandem mass spectrometry metabolomics. After acclimation in mesocosms recreating in situ conditions, both controls and exposed with Zn2+ (150 µg.L-1) bivalves were dissected to recover the gills after 48 h and stored at -80 °C before metabolites extraction. UHPLC/QToF tandem mass spectrometry was performed to study metabolite composition of samples. Statistical analysis of results using multivariate techniques showed a good classification between control and exposed groups. Eleven identified metabolites were found to be down-modulated in exposed scallops. These variations could reflect potential zinc effects on several of the biological processes, such as energy metabolism, osmoregulation and defense against oxidative stress. Among the eleven metabolites highlighted, four were reported for the first time in an aquatic organism exposed to Zn. This study demonstrates once again the diversity of interactions between bivalves and metals and the complexity of the physiological response of marine bivalves to pollutants.

Metabolomics based on UHPLC-QToF- and APGC-QToF-MS reveals metabolic pathways reprogramming in response to tidal cycles in the sub-littoral species Mimachlamys varia exposed to aerial emergence.

Mimachlamys varia is a sub-littoral bivalve encountered from Norway to the Mediterranean Sea, which lives mostly byssally attached to rocks. During the low tide period, M. varia individuals, located highest on the shore, may experience short time of aerial exposure and face a low availability of oxygen. Here we report a comparative metabolomic profiling of gill samples of M. varia obtained by both LC-QToF and APGC-QToF mass spectrometry, to analyze metabolic changes occurring during emersion in comparison with immersion. Scallops were grown in aquaria with a simulated intertidal environment mimicking short-duration air exposure that they might experience during extreme tides: alternating 2 h emersion and 10 h immersion. Our results show a switch from aerobic to anaerobic metabolism after only 2 h of emersion, with the resort to different pathways: glucose-lactate, glucose-succinate and aspartate-succinate pathways. Furthermore, carnitine-conjugated metabolites were found to accumulate during emersion, as well as urate. The level of tyrosine on the contrary was found to decrease. These findings indicate a complex metabolic reprogramming that occurs after a two hour emersion period and upon re-immersion. Furthermore, M. varia is used as sentinel species in pollution biomonitoring, through the assay of biomarkers to evaluate the effects of pollutants. Here we show that emersion induces a significant decrease of superoxide dismutase activity, an enzyme developed by bivalves to face oxidative stress and used as biomarker. These findings have to be taken into account to normalize sampling during campaigns of environmental monitoring, by taking in situ, as far as possible only immersed individuals.

What is the relationship between the bioaccumulation of chemical contaminants in the variegated scallop Mimachlamys varia and its health status? A study carried out on the French Atlantic coast using the Path ComDim model.

Increasing activity along the French Atlantic coast has led to chronic pollution with, in particular, mixtures of contaminants such as hydrocarbons, phytosanitary products, PCBs and heavy metals. Based on previous research, pollution biomarkers were used in this study as they can indicate health status when monitoring the impact of pollutants on coastal species such as the marine bivalve Mimachlamys varia. Mollusc bivalves were sampled in March 2016, in open and semi-open areas (a harbour zone), from thirteen sites which differed in terms of their level of pollution, and were located along the Atlantic coast from Brittany down to the Nouvelle-Aquitaine region. First, analyses of heavy metals and organic contaminants (e.g. pesticides, polycyclic aromatic hydrocarbons, polychlorobiphenyl) in the digestive gland of bivalves were performed. Second, biochemical assays were used to study defence biomarkers: oxidative stress with Superoxide Dismutase (SOD), detoxification of organic compounds with Glutathione-S Transferase (GST), lipid peroxidation with Malondialdehyde (MDA), and immune processes with Laccase. In addition to the biochemical assays, a genetic approach was used to measure genetic diversity (haplotype and nucleotide diversity) at each site. Biomarker assays and genetic diversity were correlated with the chemical contaminants in bivalves using the Path-ComDim statistical model. Our results showed specific correlations between biochemical assays in the digestive glands with heavy metal contaminants, and between genetic diversity and organic pollution. Blocks of responses were analysed for correlations in order to develop standardized tools and guidelines that could improve our understanding of the short-term and long-term impact of contaminants on physiological parameters.

In situ evaluation of oxidative stress and immunological parameters as ecotoxicological biomarkers in a novel sentinel species (Mimachlamys varia).

Although the variegated scallop Mimachlamys varia seems to be a suitable sentinel species for contaminant monitoring, no study has identified biomarkers in this species. In order to fill this gap, this study conducted an in situ biomarker approach. M. varia were collected in contaminated and uncontaminated areas and responsiveness of oxidative stress and immunological biomarkers was evaluated in the digestive gland. In parallel, 14 trace element concentrations were evaluated in the same organ. Superoxide dismutase activity and malondialdehyde content responded efficiently to in situ contamination when a certain degree of contamination was reached. Laccase-type phenoloxidase showed a high sensitivity but saturation of the response was highlighted for the highest contaminations. Additionally, correlations were found between biomarkers and trace element concentrations. Taken together, results showed that biomarker approach conducted in the digestive gland of M. varia represents a sensitive analytical tool to highlight ecotoxicological issues in coastal marine ecosystems.