Studies On Molecular Phylogeny And Evolution In Some Critical Ciliates

Because of special nuclear dualism,complicated morphogenetic process and uniquesexual reproduction (conjugation),ciliates play important roles in molecular biology,cell biology and researches on relationships between nucleus and cytoplasm,especiallyin the eukaryotic biological evolution.Systematics and phylogenetics on the ciliatedprotozoa have been carried out for over 20 years.However,its phylogeny still remainsconfusing as regards the evolutionary relationships and systematic positions of manywell-known groups.This is due to the high diversity of their morphology,the difficultyin recognizing which similarities are due to convergent evolution,the loss ofintermediate forms during the long period of time and insufficient molecularinformation.Molecular marker genes were chosen e.g.SSU rRNA gene and ITS 1-5.8S-ITS2 geneas to study systemetics,phylogenetic position or relationships and evolutionary historiesof some key and / or ambiguous taxa of ciliated protozoa.Based on the gene sequenceing and analyses,our work resolved some confusions ofmorphological taxonomy and phylogenetic positions of some key taxa within threecalsses at the genetical level,which included,SSU rRNA gene sequences for 25 species,and ITS1-5.8S-ITS2 gene sequences for 13 species were determined,and submitted tothe GenBank/EMBL database.We used multiple computer-assisitent algorithms inferredfrom combinations of molecular sequences and morphological and morphogeneticcharacterizations to supply important basis and parameters for molecular systematics,areconstruction of phylogenetic positions and evolutionary relationships of key taxaciliated protozoa.The conclusions were confirmed:1.Spirotrichea(1) Gastrocirrhus and Euplotidium form a monophyletic group,namely the familyGastrocirrhidae,and appear to be intermediate taxa bridging the evolution of theDiophrys-Uronychia and Euplotes-complexes (i.e.,Euplotes,Certesia and Aspidisca);(2) Caryotricha,together with Kiitricha,diverges at the deep level from all othermembers of the spirotrichs.Its branching position is between Phacodiniidia andLicnophoridia.It is strongly support the distinct separation of the Kiitricha-Caryotrichaclade,which always branches basal to the Stichotrichia-Hypotrichia-Oligotrichia -Choreotrichia assemblage;(3) The monophyly of pseudoamphisiellids and discocephalines was supported,bothof which were separated between the other stichotrichs and hypotrichs by a deep split.The order Discocephalida,representing an ancestral group,should contain twosuborders:Discocephalina and Pseudoamphisiellina.(4) Monophyly of the class Spirotrichea and its subclasses included were discussedseveral times,and some of questions were cleared.2.Oligotrichea(1) After morphological investigations and molecular analyses,an organism isbelieved as an undescribed family and a new genus:i.e.Eurystomatidae n.fam.,Eurystoma n.gen.According to phylogenetic analyses of SSU rRNA gene sequences,Eurystoma clusters with the genus Cyclidium,as a sister group to the familyPleuronematidae;(2) Philaster falls into the clearly outlined order Philasterida and it is most closelyrelated to Uronema-Paranophrys assemblage,which groups then with clustersconsisting of uronematids,parauronematids,entorhipidiids etc;the family Philasteridae,including Philaster and Philasterides,appears to be polyphyletic;(3) The secondary structure of ITS2 region in eleven representative scuticociliates andtwo ambiguously related genera are analyzed for the first time.It is found that thesecondary structure information can help to improve alignment and utilize appropriatelyphylogenetic strategies.Clearly,the variable ITS2 regions are more likely to accumulatemutations that could potentially record the divergence of the major (e.g.fmily level)lineages.3.Phyllopharyngea(1) It has a strong support for the monophyly of the class Phyllopharyngea andsubclass Phyllopharyngia;(2) Suctorian budding types are monophyletic,and exogenous budding appears to bebasal to evaginative and endogenous budding.4.Heterotrichea(1) The"traditional"heterotrichs (sensu Corliss,1979) consist of several paraphyleticgroups,including the current classes Heterotrichea,Armophorea and part of theSpirotrichea;(2) Secondary structures of SSU rRNA gene for"traditional"heterotrichs arepredicted and analysed; (3) The class Heterotrichea is confirmed as a monophyletic assemblage,and the genusPeritromus is demonstrated to be a peripheral group;Condylostentor is more closelyrelated to Condylostoma than to Stentor;Folliculina,Eufolliculina,and Maristentoralways cluster together;Climacostomum occupies a paraphyletic position distant fromFabrea,showing a close relationship with Condylostomatidae and Chattonidiidaedespite of modest support.5.Unknown species(1) The genus Mesodinium had numerous deletions and substitutions in its SSU rRNAgene,which is very divergent from all other ciliates;(2) Maximum likelihood analysis places Mesodinium on the basal subphylumIntramacronucleata,following removal of ambiguously aligned regions.In addition,secondary structure model of 5.8S rRNA gene for ciliated protozoa isrepredicted,compared with the previous model established before.