Studies On The Phylogeny Of Trichodinids

Trichodinids (Ciliophora: Peritrichida) are one of the most common parasiticprotozoan,which have special structure of adhesive disc, and can swim freely. At thepresent time, studies on trichodinids still concern mainly with their taxonomyespecially with re-investigating or re-describing the old species using moderntechniques, and very little attention has been given to the phylogenetic relationshipsof these ciliates. In this dissertation, we studied the phylogeny of trichodinids withboth morphological and molecular markers, and compared the topologies of the twokindsoftrees.1. Phylogenetic relationships among trichodinids derived from the characteristicvalues of denticles. A quantitative method to illustrate denticlating characters werefirstly introduced and applied to the phylogenetic studies among genera ofTrichodinidae.Theresultsshowedthatthetrichodinidsevolvedasthefollowingtrend:Urceolaria→Dipartiella→(Trichodinella, Tripartiella)→(TrichdoxaPallitrichodina, Vauchomia, Semitrichodina, Paratrichodina, Trichodina)→Hemitrichodina. We also discussed the evolutionary trend of the denticles andconcluded that the denticles of the adhesive disc should be an apomorphic feature ofthe trichodinids and their changes could reflect the evolutionary tendencies of these ciliates.2. Molecular phlogenetic studies among trichodinids. SSU rRNA complete genesequences of 6 species of trichodinids, andαTubulin partial gene sequences of 3species of trichodinids, were sequenced. Then, the neighbor joining, maximumparsimony, maximum likelihood,and Bayesiantrees for thetwo gene sequences wereconstructed separately. All the trees showed that the mobilines represented bytrichodinids did not cluster with their related species, sessilines. Therefore, theperitrichs were proved to be not a monophyletic group. We considered that thesimilarity of morphology of mobilines and sessilineswere the results of evolutionaryconvergence. However, maybe the peritrichs are really monophyly, and either/bothlong-branchattractionor under-samplingmadean artifactual recoveryofmobilines inthe phylogenetic trees. Because we could not exclude the disturbance of thelong-branch attraction or under-sampling in the present study, the position of theperitrichsintheclassOligohymenophoreaneedstobestudiedfurther.3. Comparative study between morphological and molecular phylogeny oftrichodinids. ITS1 gene sequences of four species of trichodinids were sequenced toconstruct phylogenetic tree, and the characteristic values of denticles werecalculated to generate dendrogram. By comparison the two trees, their topologieswerefoundtobesimilar.Therefore,the quantitativemethodtoillustratedenticlatingcharacters was proved to be feasible to study the phylogenetic relationship amongtrichodinids.