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In Silico Analysis of Pacific Oyster (Crassostrea gigas) Transcriptome over Developmental Stages Reveals Candidate Genes for Larval Settlement

Valentin FOULON, Pierre BOUDRY, Sébastien ARTIGAUD, Fabienne GUÉRARD et Claire HELLIO

Abstract: 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.

Schematic representation of the hypothetical molecular interactions involved in the adhesion of C. gigas pediveliger larvae, based on the selection of genes specifically expressed at the pediveliger stage.

 
REFERENCE :

Foulon, V., Boudry, P., Artigaud, S., Guerard, F., and Hellio, C. 2019. In Silico Analysis of Pacific Oyster (Crassostrea gigas) Transcriptome over Developmental Stages Reveals Candidate Genes for Larval Settlement. Int. J. Mol. Sci. 20(1): 197. doi:10.3390/ijms20010197.

 

Click here for the journal website (article in open access).

 

Modeling reproductive traits of an invasive bivalve species under contrasting climate scenarios from 1960 to 2100

Mélaine Gourault, Sébastien Petton,Yoann Thomas, Laure Pecquerie, Gonçalo M. Marques, Christophe Cassou, Élodie Fleury,Yves-Marie Paulet et Stéphane Pouvreau

HIGHLIGHTS

  • The DEB model available for the Pacific oyster was applied in a new coastal environment: the bay of Brest (France).
  • This version was successfully calibrated using a new dataset covering 6 years (from 2009 to 2014) of field monitoring.
  • The model successfully predicted in detail the complex reproductive processes of C. gigas, especially its spawning behavior.
  • Hindcasting and forecasting simulations of the reproductive phenology of C. gigas were performed using IPCC scenarios.

ABSTRACT

Identifying the drivers that control the reproductive success of a population is vital to forecasting the consequences of climate change in terms of distribution shift and population dynamics. In the present study, we aimed to improve our understanding of the environmental conditions that allowed the colonization of the Pacific oyster, Crassostrea gigas, in the Bay of Brest since its introduction in the 1960s. We also aimed to evaluate the potential consequences of future climate change on its reproductive success and further expansion.

Three reproductive traits were defined to study the success of the reproduction: the spawning occurrence, synchronicity among individuals and individual fecundity. We simulated these traits by applying an individual-based modeling approach using a Dynamic Energy Budget (DEB) model. First, the model was calibrated for C. gigas in the Bay of Brest using a 6-year monitoring dataset (2009–2014). Second, we reconstructed past temperature conditions since 1960 in order to run the model backwards (hindcasting analysis) and identified the emergence of conditions that favored increasing reproductive success. Third, we explored the regional consequences of two contrasting IPCC climate scenarios (RCP2.6 and RCP8.5) on the reproductive success of this species in the bay for the 2100 horizon (forecasting analysis). In both analyses, since phytoplankton concentration variations were, at that point, unknown in the past and unpredicted in the future, we made an initial assumption that our six years of observed phytoplankton concentrations were informative enough to represent “past and future possibilities” of phytoplankton dynamics in the Bay of Brest. Therefore, temperature is the variable that we modified under each forecasting and hindcasting runs.

The hindcasting simulations showed that the spawning events increased after 1995, which agrees with the observations made on C. gigas colonization. The forecasting simulations showed that under the warmer scenario (RCP8.5), reproductive success would be enhanced through two complementary mechanisms: more regular spawning each year and potentially precocious spawning resulting in a larval phase synchronized with the most favorable summer period. Our results evidenced that the spawning dates and synchronicity between individuals mainly relied on phytoplankton seasonal dynamics, and not on temperature as expected. Future research focused on phytoplankton dynamics under different climate change scenarios would greatly improve our ability to anticipate the reproductive success and population dynamics of this species and other similar invertebrates.

Figure 4: Oyster growth and spawning simulations obtained by the DEB model compared with observed data from 2009 to 2014 (DFM = Dry Flesh Mass). Observed DFM is represented by black dots with standard deviation bars (n = 30). Grey lines represent individual growth trajectories simulated by the model. The dark red bold line represents the mean of the 30 trajectories.

REFERENCE

Gourault, M., Petton, S., Thomas, Y., Pecquerie, L., Marques, G.M., Cassou, C., Fleury, E., Paulet, Y.-M., & Pouvreau, S. 2019. Modeling reproductive traits of an invasive bivalve species under contrasting climate scenarios from 1960 to 2100. Journal of Sea Research 143: 128–139. doi:10.1016/j.seares.2018.05.005.

Click for the journal page.

Guillaume Mitta seminar

Cracking the code of Pacific Oyster Mortality Syndrome

For decades, methodological limitations have restricted the study of infectious diseases to simplified experimental pathosystems in which the influences of host and pathogen diversity and the biotic and abiotic environments have been minimized. Such reductionist approaches have made diseases with complex etiologies difficult to characterize. This is the case for some diseases triggering recurrent mass mortalities in non-model species of ecological and/or economic interest such as pollinators, corals and marine mollusks.

The objective of the present work was to examine a disease of complex etiology affecting one of the main invertebrate species exploited in the world, the Pacific oyster Crassostrea gigas. Introduced to France in the 1970s, C. gigas suffers mass mortalities associated with complex interactions between host, environment and pathogens. The severity of these mortality outbreaks has dramatically increased since 2008They mainly affect juvenile stages decimating up to 100 % of young oysters in French farms. Over the past years, this mortality syndrome has become panzootic, being observed in numerous other countries worldwide.

By developing a holistic approach to tackle the complexity of interactions, we deciphered the complex intra-host interactions underlying the Pacific oyster mortality syndrome. Using ecologically realistic experimental infections combined with thorough molecular analyses on oyster families with contrasted susceptibilities, we demonstrated that the disease is caused by a multiple infection whose initial and necessary step is the infection of oyster hemocytes by a herpesvirus. Viral replication leads to an immune-compromised state of the host, evolving toward subsequent bacteremia by opportunistic bacteria.

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