Marine ecosystems play a central role in geochemical cycling and climate regulation. These environments harbour complex and cryptic ecosystems dominated in terms of abundance and biomass by planktonic microbes including bacteria, archaea, viruses, and eukaryotic organisms (such as protists and fungi). These organisms form numerous and diverse interactions encompassing all kind of exchanges e.g. predator-prey relationships and all shades of symbiosis from commensalism to parasitism. However, this equilibrium is threatened by an un-precedent irreversible ecological transformation due to multifactorial anthropogenic changes. This phenomenon is illustrated by a variation in prevalence and severity of disease outbreaks, leading to massive die-offs events. One of the most famous examples that illustrate this effect is the oyster parasite Perkinsus marinus (Perkinsozoa) that has spread over 500km along the northeastern coast of United States during a pronounced warming in 1990 and 1991. Numerous studies then comforted these observations and Harvell et al. (2009) in Ecology argued: “a warmer world would be a sicker world”.
Perkinsozoa (Alveolata) is a group of parasites infecting molluscs, dinoflagellates and amphibians. Perkinsus marinus and P. olseni are responsible of the main cause of mortality of bivalves leading to the economically important shellfish disease ‘Dermo’, Parvilucifera spp. are known to infected dinoflagellates including the toxic ones and playing a role in species succession. Finally Rana Perkinsus has been recently identified as responsible of massive die-off of tadpole populations across the USA. The Perkinsus spp. and the Rana Perkinsus have been recently classified as “emerging disease”. However, these described species represent only clades over the 30 identified so far by their genetic signatures in the sediment through molecular environmental surveys. Hence, the major challenge of this project is now to elucidate the ecological roles of this diverse group of parasitic Perkinsozoa revealed by eDNA surveys.
In this context the PARASED project will seek 1) to evaluate phylogeography of the whole Perkinsozoa lineage through two scales, 2) to identify the seasonal variability and abundance of the Perkinsozoa lineage, 3) to decipher the life cycle and host range of the Perkinsozoa and finally 4) to describe fundamental biological process involved during the parasitic association between the Perkinsozoa and their hosts.
The research strategy that we propose here is firstly to conduct a global phylogeography study of the whole Perkinsozoa lineage, and then to target two french ecosystems to evaluate the ecological role of the Perkinsozoa parasites. We will firstly focus on the commercially important school model P. olseni, and subsequently translate these methodologies and concepts to un-described Perkinsozoa only detected by their genetic signatures. This pluri-disciplinary project will encompass classical parasitology methods as well as new state-of-art microscopy, genomic and transcriptomic techniques that lean on the expertise of the different partners of this project. Moreover, this project is innovating and challenging because it focus on 1) undescribed group of parasites, the Perkinsozoa (including P. olseni), linked with massive mass mortalities and 2) on the benthic compartment in which the protist assemblage and their ecological functions are still totally ignored in the trophic network. The data and outcomes generated will substantially increase the body of knowledge of P. olseni and others Perkinsozoa life cycle and their commercially important host range. Furthermore, the comparative transcriptomics of the infective pathways with others parasitic systems will provide informations about the evolution of parasitic mechanisms within the Alveolates and more generally across tree of life but also could help define new pathways for pharmacological target strategies. Because of the environmental issues tackled in this project, the new data generated might have implications to improve sustainably the conservation policies for managing global biodiversity.
This ambitious, innovating and highly original project, in national as well as international research landscape, will involve highly recognized scientists in the field of ecology, bioinformatics, parasitology and physiology. Moreover, this project will be fully integrated into the cluster of Excellence, the LabexMER axe 6 which will provide a strong scientific support for the success of the project. Hence, these results will then form the foundation of my new long-term scientific research thematic on the ecological significance and evolution of eukaryotic parasites in marine ecosystems within a prestigious institution as the LEMAR.
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