Les amoebophryidae (Syndiniales) parasitoïdes de dinoflagellés : cycle de vie, dynamique et spécificité in situ

Abstract : Syndiniales are marine parasitoids infecting a wide range of planktonic hosts, from dinoflagellates, decapods, to fish larvae. One family, the Amoebophryidae mostly infects dinoflagellates. In the Penzé estuary (North of Brittany, France), all species of dinoflagellates observed were infected by these pathogens, including the toxic species Alexandrium minutum, which produces paralytic shellfish poisoning. A strong specificity has been detected : a dinoflagellate species being infected by a genetically distinct parasitoid clade, the same clade infecting the same host species year after year (from 2004 to 2006). These pathogens have the capacity to control their host populations, resulting in the rapid host successions from field. This host population control was studied by integrating an Anderson-May model with the predation pressure. The parasitoid infecting the non-toxic Scrippsiella trochoidea was obtained in pure culture. The presence of the pathogen induced the host sexuality, resulting in the production of diploid resistant cysts. However, a few of them were also infected by the parasitoid. After a dormancy of two months, both the host and the parasitoid were able to germinate, and a new infectious cycles were observed. This behaviour strongly links in time and space both partners, and explains the recurrence of infections. We hypothesized that blooms can only occur when parasitic controls are absent, explaining the toxic blooms of A. minutum in the Penzé estuary that began in the 80' suddenly ended in 2001. This hypothesis was also tested in the Thau lagoon (Mediterranean Sea), where the blooming Alexandrium catella species arise from the 90'. This dinoflagellate species was the only one to not be infected by Amoebophryidae during toxic blooms that occurred in spring and autumn 2007.
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Aurélie Chambouvet. Les amoebophryidae (Syndiniales) parasitoïdes de dinoflagellés : cycle de vie, dynamique et spécificité in situ. Parasitologie. Paris 6, 2009. Français. ⟨tel-01111122⟩

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