Massive spring mortality outbreaks have been reported in Mytilus spp. in France since 2014. The main areas affected are the Pertuis Charentais Sounds and the coast of the Pays de la Loire, which ...cultivate mainly M. edulis, and the putative causal agents remain unknown. We report the results of the first generation of mass selection focused on survival and resistance to the spring mortality in M. edulis. Two stocks of mussels were sampled in the Pertuis Charentais Sounds in 2014; one of these went through a spring mortality outbreak and the survivors were used to produce the selected stock, while the second stock was M. edulis considered to be naïve against the putative causal agents of the mortality outbreak and was used to produce the control stock. A first cohort was produced in 2015 and tested at one site in the Pertuis Charentais Sounds. In April and May 2016, a spring mortality outbreak was observed when seawater temperature ranged from 10 to 15 °C. In October 2016, the selected stock had a lower mortality (44%) than the control stock (78%). To confirm this result and investigate genotype by environment interaction, a second cohort was produced in 2016 and tested at six sites. Although no significant mortality was reported at the four sites in the Pertuis Charentais Sounds in 2017, the selected stock had a lower mortality (17–27%) than the control stock (61–74%) at the two sites along the coast of the Pays de la Loire. The survival had increased of 34–48% after one generation of mass selection and the realized heritability was high, ranging from 0.55 to 1.15, but further generations of selection are required to obtain a better estimation of the heritability. Our study showed a positive response to selection in three environments that were different to the site from which mussels were selected, suggesting the absence of strong genotype by environment interaction in sites where spring mortality outbreaks occurred. Selection to enhance M. edulis survival of the spring mortality should be efficient and should be capable of easy implementation through mass selection. Apparently, selection to enhance the survival of M. edulis did not affect the mussel growth in comparison with the controls, but automatically improved the yield of M. edulis in sites affected by the spring mortality outbreaks.
•Mass selection to enhance the resistance to the spring mortality outbreak in M. edulis was successful.•Significant genetic improvement after one generation of selection (+34–48%)•No significant strong genotype by environment interaction•Most of the mortality occurred at temperature ranging from 10 to 15 °C
Marine organisms are threatened by the presence of pesticides in coastal waters. Among them, the Pacific oyster is one of the most studied invertebrates in marine ecotoxicology where numerous studies ...highlighted the multiscale impacts of pesticides. In the past few years, a growing body of literature has reported the epigenetic outcomes of xenobiotics. Because DNA methylation is an epigenetic mark implicated in organism development and is meiotically heritable, it raises the question of the multigenerational implications of xenobiotic-induced epigenetic alterations. Therefore, we performed a multigenerational exposure to an environmentally relevant mixture of 18 pesticides (nominal sum concentration: 2.85 μg·L–1) during embryo–larval stages (0–48 hpf) of a second generation (F1) for which parents where already exposed or not in F0. Gene expression, DNA methylation, and physiological end points were assessed throughout the life cycle of individuals. Overall, the multigenerational effect has a greater influence on the phenotype than the exposure itself. Thus, multigenerational phenotypic effects were observed: individuals descending from exposed parents exhibited lower epinephrine-induced metamorphosis and field survival rates. At the molecular level, RNA-seq and Methyl-seq data analyses performed in gastrula embryos and metamorphosis-competent pediveliger (MCP) larvae revealed a clear F0 treatment-dependent discrimination. Some genes implicated into shell secretion and immunity exhibited F1:F0 treatment interaction patterns (e.g., Calm and Myd88). Those results suggest that low chronic environmental pesticide contamination can alter organisms beyond the individual scale level and have long-term adaptive implications.
Early life stages are crucial for organism development, especially for those displaying external fertilization, whose gametes and early stages face environmental stressors such as xenobiotics. The ...pacific oyster, Crassostrea gigas, is considered a model species in ecotoxicology because of its ecological characteristics (benthic, sessile, filter feeding). So far studies have investigated the impact of xenobiotics at embryotoxic, genotoxic and physiological endpoints, sometimes at the multigenerational scale, highlighting the role of epigenetic mechanisms in transmitting alterations induced by exposure to single xenobiotics. However, to date, little is known about the impact of environmentally-mimicking contaminants cocktails. Thus, we examined the impact of an early exposure to environmentally relevant mixture on the Pacific oyster life history. We studied transcriptomic, epigenetic and physiological alterations induced in oysters exposed to 18 pesticides and metals at environmental concentration (nominal sum concentration: 2.85 μg.L−1, measured sum concentration: 3.74 ± 0.013 μg.L−1) during embryo-larval stage (0–48 h post fertilization, hpf). No significant differences in embryo-larval abnormalities at 24 hpf were observed during larval and spat rearing; the swimming behaviour of exposed individuals was disturbed, while they were longer and heavier at specific time points, and exhibited a lower epinephrine-induced metamorphosis rate as well as a higher survival rate in the field. In addition, RNA-seq analyses of gastrula embryos revealed the differential expression of development-related genes (e.g. Hox orthologues and cell cycle regulators) between control and exposed oysters. Whole-genome DNA methylation analyses demonstrated a significant modification of DNA methylation in exposed larvae marked by a demethylation trend. Those findings suggest that early exposure to an environmentally relevant pesticide mixture induces multi-scale latent effects possibly affecting life history traits in the Pacific oyster.
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•Crassostrea gigas embryos were exposed to an environmental pesticide mixture for 48 h.•Carry-over effects were observed along the lifecycle of the oysters.•The expression of developmental genes was modified during the exposure.•Exposed oysters exhibit a global DNA demethylation during and after the exposure window.•Some phenotypic endpoints were impaired: swimming behavior, metamorphosis, field survival.
•Exploration of energy density sources of variability: species, season, region, size.•Relationships between dry mass content and ED are strong but species specific.•Larger length, mass and ED at age ...in the English Channel than in the Bay of Biscay.•Sardine display larger energy reserves than anchovy.•Larger reserves are likely in link with larger spawning or maintenance costs.•A strong scaling of ED with size with a dome shape pattern for sardine.•Decrease of ED with size is discussed in link with feeding and spawning behaviours.
There is a growing interest in monitoring body condition of marine organisms in the context of the ecosystem approach to fisheries and global change. Fish condition is under the influence of environmental variability on seasonal scale, but also on longer timescales. It represents a good indicator of habitat quality or individual fitness, and is also a relevant parameter to evaluate energy transfer through the trophic chain. However, the sources of variability in fish condition need to be accurately understood and the significance of existing indices has to be correctly assessed. Here, we measured the energy density, a precise and global indicator of fish bioenergetic condition, for anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) in the Bay of Biscay and the English Channel, based on an extensive sampling design in 2014. First, we investigated the well-documented relationship between percent dry mass and energy density, and showed that such relationship is species specific. Second, we observed distinct patterns in bioenergetic condition between anchovy and sardine. Both species display similar minimum values at size or age but maximum are significantly higher for sardine, reflecting a higher energy storage capacity that scales more strongly with size. Third, we confirmed the large seasonal variability in energy density of both species. In the Bay of Biscay, energy density values for anchovy and sardine (age 1+) are 5.7 and 5.9 kJ g−1 (wet weight) in spring and 6.8 and 7.9 kJ g−1 in autumn, respectively. Our results revealed that fish from the English Channel display significantly higher energy density values in autumn (9.8 kJ g−1 for anchovy and 10.5 kJ g−1 for sardine) than those from the Bay of Biscay. When combined with size and weight at age it appears clearly that, after age 1, fish from the northern region display larger growth and energy reserves. This likely results from a higher zooplankton productivity in the English Channel or/and a selection pressure towards faster growing and faster reserve building individuals, to be able to survive a longer winter than in the Bay of Biscay. Finally, we described a dome shaped evolution of energy density with body size in case of sardine. Increase with size has been well documented but not the decrease at largest sizes. Several mechanisms may explain such a pattern, i.e. increasing investment in spawning, shift in diet or a metabolic trade-off between temperature and food availability, with regard to maintenance requirements.
Functional groups are sets of species that play a similar role in a food web. We defined functional groups of fish species based on their morphological characteristics, while using expert knowledge ...for invertebrates. We measured 9 morphological traits of 72 fish species, and carried out multivariate analyses to assign fish species to functional groups. The analysis identified 9 trait-based fish functional groups to which were added 3 expert-based invertebrate functional groups. The habitat (position in the water column) and potential diet of each group were identified from the literature. Using the MEDITS bottom trawl survey data collected at 10 to 800 m depth, we calculated relative change in the 12 fish and invertebrate functional group biomasses for 12 Mediterranean areas over the period 1994 to 2012. Multiple regression trees identified 4 regions with similar changes: (1) the Adriatic and the Ionian Sea; (2) the Tyrrhenian Sea and the Strait of Sicily; (3) the Balearic Islands and other enclosed areas such as the Gulf of Lions and Aegean Sea; and (4) the Ligurian Sea and Sardinia. The biomass of all functional groups increased or remained stable in the first 2 regions, while around half the functional group biomasses decreased in the other 2 regions. These regional differences in functional group biomass changes were mainly associated with regional variations in the time trends of bottom water temperature (37%), bottom water dissolved oxygen (23%) and mean catch levels (9%). This study contributes to the EU Marine Strategy Framework Directive by proposing food web indicators based on morphologically and habitat defined functional groups.
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