The Distribution,diversity And Infection Of Parasitic Dinoflagellate Amoebophrya In The Coastal Waters Of China

The parasitic dinoflagellate in the genus of Amoebophrya infects broad range hosts of planktonic dinoflagellates,ciliates and radiolarians in eutrophic and oligotrophic waters wordwidely.Its ecological significance was gradually recognized in recent years by researchers around the word.Lately,scattered evidences indicated that this type of parasitic dinoflagellates is widely distributed in the coastal waters of China;however,we have very limited understanding on the biological characteristics and ecological roles of Amoebophrya in the coastal waters of China due to the difficulty of establishing in vitro culture in laboratory and rare research conducted in field.Thus,this dissertation systematically explored the distribution and genetic diversity of Amoebophrya in the coastal waters of China through large-scale ecological survey.A typical strain of the parasites was isolated and cultured in laboratory,its infectivity and effects to host dinoflagellates were further investigated to assess the impacts of Amoebophrya infections during dinoflagellate blooms.This research will facilitate our understanding on the role of Amoebophrya during the succession of harmful algal blooms.The major findings were listed as following:1.The hematoxylin and eosin(H & E)staining assay was successfully adopted to detect Amoebophrya infection in planktonic dinoflagellates.The H & E staining assay provided reliable diagnosis of Amoebophrya infection by identifying the characteristic “beehive” of the multinucleate trophonts.The H & E staining assay is easy to use,that can be routinely performed within 3 h(up to 20 samples/batch).With suitable calculation,the modified H & E assay can be applied to assess the prevalence of Amoebophrya infection in planktonic dinoflagellates.Overall,the H & E staining assay offered reliable and convenient detection of Amoebophrya infection in planktonic dinoflagellates,meeting the demands of large-scale ecological surveys.2.During the investigation period(from February 2015 to January 2016,10 cruises),planktonic dinoflagellate community structure was relatively stable in the Changjiang estuary and adjacent sea and totally 39 dinoflagellate taxa were identified.The species richness of Gonyaulacales ranked first,followed by Gymnodiniales and Peridiniales.The average yearly abundance of planktonic dinoflagellates was 6.62 × 105 cells/L,ranged from 9.06 × 103 to 6.10 × 106 cells/L.Fourteen free-living marine dinoflagellates served as hosts for Amoebophrya in the investigated area.The host dinoflagellate species and the prevalence of Amoebophrya infection had obvious seasonal variation,of which summer and fall was obviously higher than spring and winter.The primary peak occurred in June,when eleven species of dinoflagellates were infected,with prevalence up to 5.77 %.3.Amoebophrya was widely spread in coastal waters of China,which showed a complex distribution pattern and high genetic diversity.Nine species of dinoflagellates were found to be infected by Amoebophrya spp.,with prevalence varied between 0.03 and 2.5 %.Amoebophrya sp.ex Gymnodinium instriatum and Amoebophrya sp.ex Karlodinium micrum were commonly observed in the coastal waters of China and Wenzhou Bay had the most Amoebophrya species.All Amoebophrya spp.18 S rDNA gene sequences formed into three major clades.However,sequences of the same area did not form a single cluster,indicating that Amoebophrya populations had not form a pattern of obvious geographical distribution.Thirteen species of Amoebophrya spp.were identified in the water column,of which the Kimura-2-parameter genetic distance ranged between 0.0252 and 1.5745,with a mean of 0.5672,indicating high genetic diversity among Amoebophrya spp..4.An Akashiwo sanguinea-Amoebophrya sp.in vitro culture was established in laboratory,the biological interactions of Amoebophrya sp.were explored.Amoebophrya sp.ex A.sanguinea was aggressive and short in duration,which can induce mortality to its hosts,preventing its normal growth and proliferation.The prevalence of parasitic infection increased sharply with increasing dinospore: host ratios.The prevalence of parasitic infection was 91 ± 2.10 % when the dinospore: host cell was 20:1,becoming saturated at the dinospore: host ratio of 40: 1.The life span of Amoebophrya sp.ex.A.sanguinea was approximately 58 ± 1.2 hours.The dinospores can survive up to 78 hours in environment waters,but gradually lose their infectivity.Amoebophrya sp.ex.A.sanguinea cannot infect other dinoflagellate species,suggesting that the parasite has a high preference for specific host,with a single parasitic clade preferentially infecting a single dinoflagellate host species.In conclusion,this dissertation presented the first comprehensive study on Amoebophrya spp.infections in planktonic dinoflagellates in the coastal waters of China and explored its primary ecological roles through series of field surveys and laboratory studies.The major finding of this dissertation will contribute to better understanding on the impact of parasitism by Amoebophrya to its host dinoflagellate populations as well as the ecological significance of the parasitic dinoflagellate in coastal environments of China.