Taxonomic And Phylogenetic Studies Of Sixteen Freshwater Parasitic Peritriches

The parasitic peritrichs ciliate,a complex assemblage of protozoan,is considered as one of the most common parasites on freshwater economically animals.However,little studies focus on the taxonomic,phylogenetic and pathogenetic studies on the parasitic peritrich ciliates,which causes difficulties in preventing and controlling the peritriches disease.The present study is focused on the investigation of the parasitic peritrichs based on the classical taxonomy and phylogenies to clarify the misleading species,find the new species and new record species.The investigation of pathogenesis of parasitic peritrichs based on histopathological analyses and scanning electron microscopy observation is also addressed in the present study.Additionally,the phylogenies of sessilids and mobilids are inferred on the basis of ribosomal RNA(rRNA)gene sequences to find the evolutionary relationships among species.The detail results are as follows.During a survey in Hubei province,Henan province,Hunan province,Jiangxi province,Jiangsu province and Guangzhou provice,23 populations of 16 species belonging to 6 genera are described in the present study.One new species is described based on morphological and molecular methods,and fifteen species were redescribed by providing with detail diagnosis and information.The list of parasitic sessilids is as follows: one population of Epistylis chlorelligerum Shen,1980,two populations of E.horizontalis Tai,1930,three populations of E.wuhanensis n.sp.,and one population of Vorticella cf.limnetis Foissner,1979.The list of trichodinids is as follows: one population of Paratrichodina corlissi Lom and Haldar,1977,three populations of Trichodina acuta Lom,1961,two populations of T.heterodentata Duncan,1977,one population of T.hyperparasitis Chen & Hsieh,1984,one population of T.hypsilepis Wellborn,1967,two populations of T.maritinkae Basson & Van As,1991,one population of T.modesta Lom,1970,one population of T.nobilis Chen,1963,one population of T.kazubski Van As and Basson,1989,one population of Trichodinella epizootica Raabe,1950.one population of Tripartiella lechridens Basson and Van As,1987,and one population of Tripartiella macrosoma Basson and Van As,1987.The parasitic peritrichs-host relationsip study is performed in the present study by using histologic technology and scanning electron microscope,the results revealed that the infection of peritrichs could affect the breathing,the swimming,and the feeding of the host,resulting in stress on the hosts and finally cause death of hosts.The results show that(1)the sessilids could adhere the host by their stalks or scopulae,destroying the epithelium of the host,and no evidence shows the sessilids could get nutritions from the host,but regard the host as their habitats where they get food from the environment;(2)the mobilids adhere the host colonize the surface of skin,fins or gills of the host through adhesive discs and cilia and cause moderate to serious pathologic reactions including the discrete hyperplasia of the gill filaments with lamellar epithelium lifting of secondary lamellae.Additionally,the phylogenetic relationships of groups of sessilids and mobilids are addressed based on ribosomal RNA gene sequences to verify their evolutionary relationships and phylogenetic positions and further assess the validity of morphological taxonomy.The present analyses of sessilids are conducted on the basis of 30 newly obtained sequences and available sequences in GenBank database.These sequences included SSU rRNA,ITS1–5.8S–ITS2 region,and LSU rRNA gene sequences.The phylogenetic trees generated in this study revealthe following:(1)The peristomial lip may have evolved several times and could be regarded as morphological character that reflects single evolutionary divergence,and strong evidence showing that families Epistylididae and Operculariidae are polyphyletic exists;(2)the major species of Epistylididae nested within the clades of Zoothamniidae despite clustering in a basal clade,supporting the view that the major species of Epistylididae experience secondary spasmoneme loss and are derived from Zoothamnium-like species;(3)ancestral species in order Sessilida are supposed to exhibit colonial lifestyles and possess continuous stalks without spasmonemes and loricae;(4)the phylogenetic position of the loricate family Vaginicolidae requires further validation;(5)sessilids should be subdivided into two suborders,Vorticellina and Operculariina,rather than into two orders.The results of phylogentic analyses based on SSU rRNA gene sequences of mobilids reveal that:(1)the central granule is a useful taxonomic feature,but it may not be an important phylogenetic characteristic;(2)the family Trichodinidae may not be monophyletic,and the genera Trichodina and Trichodinella should not be separated at the genus level or the genus Trichodina may be paraphyletic;(3)the phylogenetic lineage of trichodinids might not correspond with their living environments,host species or certain morphological characteristics.