Trichodinids (Ciliophora: Peritrichida) are one of the most common parasitic protozoan, which have special structure of adhesive disc, and can swim freely. At the present time, studies on trichodinids still concern mainly with their taxonomy especially with re-investigating or re-describing the old species using modern techniques, and very little attention has been given to the phylogenetic relationships of these ciliates. In this dissertation, we studied the phylogeny of trichodinids with both morphological and molecular markers, and compared the topologies of the two kinds of trees.
1. Phylogenetic relationships among trichodinids derived from the characteristic values of denticles. A quantitative method to illustrate denticlating characters were firstly introduced and applied to the phylogenetic studies among genera of Trichodinidae. The results showed that the trichodinids evolved as the following trend: Urceolaria → Dipartiella → (Trichodinella, Tripartiella) → (Trichdoxa Pallitrichodina, Vauchomia, Semitrichodina, Paratrichodina, Trichodina) → Hemitrichodina. We also discussed the evolutionary trend of the denticles and concluded that the denticles of the adhesive disc should be an apomorphic feature of the trichodinids and their changes could reflect the evolutionary tendencies of these ciliates.
2. Molecular phlogenetic studies among trichodinids. SSU rRNA complete gene sequences of 6 species of trichodinids, and α Tubulin partial gene sequences of 3 species of trichodinids, were sequenced. Then, the neighbor joining, maximum parsimony, maximum likelihood, and Bayesian trees for the two gene sequences were constructed separately. All the trees showed that the mobilines represented by trichodinids did not cluster with their related species, sessilines. Therefore, the peritrichs were proved to be not a monophyletic group. We considered that the similarity of morphology of mobilines and sessilines were the results of evolutionary convergence. However, maybe the peritrichs are really monophyly, and either/both long-branch attraction or under-sampling made an artifactual recovery of mobilines in the phylogenetic trees. Because we could not exclude the disturbance of the long-branch attraction or under-sampling in the present study, the position of the peritrichs in the class Oligohymenophorea needs to be studied further.
3. Comparative study between morphological and molecular phylogeny of trichodinids. ITS1 gene sequences of four species of trichodinids were sequenced to construct phylogenetic tree, and the characteristic values of denticles were calculated to generate dendrogram. By comparison the two trees, their topologies were found to be similar.
Therefore, the quantitative method to illustrate denticlating characters was proved to be feasible to study the phylogenetic relationship among trichodinids.