Abstract
Parasites in the genus Amoebophrya sp. infest dinoflagellate hosts in marine ecosystems and can be determining factors in the demise of blooms, including toxic red tides. These parasitic protists, however, rarely cause the total collapse of Dinophyceae blooms. Experimental addition of parasite-resistant Dinophyceae (Alexandrium minutum or Scrippsiella donghaienis) or exudates into a well-established host-parasite coculture (Scrippsiella acuminata-Amoebophrya sp.) mitigated parasite success and increased the survival of the sensitive host. This effect was mediated by waterborne molecules without the need for a physical contact. The strength of the parasite defenses varied between dinoflagellate species, and strains of A. minutum and was enhanced with increasing resistant host cell concentrations. The addition of resistant strains or exudates never prevented the parasite transmission entirely. Survival time of Amoebophrya sp. free-living stages (dinospores) decreased in presence of A. minutum but not of S. donghaienis. Parasite progeny drastically decreased with both species. Integrity of the dinospore membrane was altered by A. minutum, providing a first indication on the mode of action of anti-parasitic molecules. These results demonstrate that extracellular defenses can be an effective strategy against parasites that protects not only the resistant cells producing them, but also the surrounding community.
Highlights
Parasites, thought to account for half of species richness in some ecosystems, could constitute the unseen majority of species extinctions [1]
Exposeddinospores were mixed with the host strain ST147 at a theoretical cell ratio of 5:1 for dinospores exposed to A. minutum filtrates, and at three different ratios (1:2, 1:1, and 5:1) for dinospores exposed to S. donghaienis filtrate
Infections were mitigated by the presence of a resistant host Experiment 1 tested whether or not the co-presence of a resistant host (A. minutum or S. donghaienis) could modify Amoebophrya infection dynamics with a sensitive host (S. acuminata)
Summary
Thought to account for half of species richness in some ecosystems, could constitute the unseen majority of species extinctions [1]. Infections were initiated with 3-day-old cultures of Amoebophrya from which dinospores were collected after a gentle separation from the remaining host cells (S. acuminata ST147) using gravity filtration through nylon filter (5 μm, Whatman). These dinospores were incubated with the exponentially growing host S. acuminata (strain ST147) using a 1:2 parasite:host (vol:vol) ratio to encourage infection of host cells. Exposeddinospores were mixed with the host strain ST147 at a theoretical cell ratio of 5:1 (dinospore:host) for dinospores exposed to A. minutum filtrates, and at three different ratios (1:2, 1:1, and 5:1) for dinospores exposed to S. donghaienis filtrate These ratios were calculated according to the initial dinospore density before exposure to filtrates and did not consider the possible differential losses related to filtrates. 5 days by FCM, and prevalence was analyzed after 47 h of incubation by CARD-FISH in the controls and with the CMMI1002 and Sc39 filtrate treatments
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