Functional ecology of parasitic protists in benthic ecosystems – PARASED

Marine ecosystems play a central role in geochemical cycling and climate regulation. These environments harbour complex and cryptic communities, 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. Numerous studies then confirmed these observations and Harvell et al. (2009) in Ecology argued: “a warmer world would be a sicker world”.
Perkinsea (Alveolata) is a group of parasites infecting molluscs, dinoflagellates and amphibians. Perkinsus marinus and P. olseni are responsible of the economically important shellfish disease ‘Dermo’, the main cause of mortality of bivalves. Parvilucifera spp. are known to infect dinoflagellates including the toxic ones. 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 three clades over the 30 recently identified by their genetic signatures in the sediment through molecular environmental surveys. Hence, the major challenge of this project is now to elucidate the ecological role of this diverse group of parasites, the Perkinsea.
In this context the PARASED project will seek 1) to evaluate global phylogeography and local seasonal genetic diversity and abundance of Perkinsea, 2) to decipher the life cycle and host range of the Perkinsea and finally 3) to describe fundamental biological processes involved during the parasitic association between the Perkinsea and their hosts.
The research strategy that we propose here is firstly to conduct a global phylogeography study of the whole Perkinsea lineage, and then to target two French ecosystems (the bays of Arcachon and Brest) to evaluate the ecological role of the Perkinsea parasites. We will firstly focus on the commercially important school model P. olseni, and subsequently translate methodologies and concepts to Perkinsea only detected so far by their genetic signatures. This multi-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 focuses on 1) poorly described group of parasites, the Perkinsea (including P. olseni), linked with shellfish mass mortalities and 2) on the benthic compartment in which the protist assemblages and their ecological functions are still totally ignored in trophic networks. The data and outcomes generated will substantially increase the body of knowledge on the functional ecology of P. olseni and others Perkinsea on host population. We will identify their life cycle and evaluate their knock-on effect on host populations that encompass species of economical/ecological interest. Ultimately, we aim to decipher the cellular mechanisms and pathways involved during the infection. Because of the environmental issues tackled in this project, the new data generated might have implications to improve sustainable conservation policies for managing global diversity.