Lukes J, Jirkû M, Dolezel D, Kral'ová I, Hollar L, Maslov D A
Institute of Parasitology, Czech Academy of Sciences, 370 05 Ceské Budejovice, Czech Republic.
J Mol Evol. 1997 May;44(5):521-7. doi: 10.1007/pl00006176.
To further investigate the phylogeny of protozoa from the order Kinetoplastida we have sequenced the small subunit (SSU) and a portion of the large subunit (LSU) nuclear rRNA genes. The SSU and LSU sequences were determined from a lizard trypanosome, Trypanosoma scelopori and a bodonid, Rhynchobodo sp., and the LSU sequences were determined from an insect trypanosomatid, Crithidia oncopelti, and a bodonid, Dimastigella trypaniformis. Contrary to previous results, in which trypanosomes were found to be paraphyletic, with Trypanosoma brucei representing the earliest-diverging lineage, we have now found evidence for the monophyly of trypanosomes. Addition of new taxa which subdivide long branches (such as that of T. brucei) have helped to identify homoplasies responsible for the paraphyletic trees in previous studies. Although the monophyly of the trypanosome clade is supported in the bootstrap analyses for maximum likelihood at 97% and maximum parsimony at 92%, there is only a small difference in ln-likelihood value or tree length between the most optimal monophyletic tree and the best suboptimal paraphyletic tree. Within the trypanosomatid subtree, the clade of trypanosomes is a sister group to the monophyletic clade of the nontrypanosome genera. Different groups of trypanosomes group on the tree according to their mode of transmission. This suggests that the adaptation to invertebrate vectors plays a more important role in the trypanosome evolution than the adaptation to vertebrate hosts.
为了进一步研究动质体目原生动物的系统发育，我们对小亚基（SSU）和大亚基（LSU）核核糖体RNA基因的一部分进行了测序。SSU和LSU序列是从一种蜥蜴锥虫——斯氏锥虫（Trypanosoma scelopori）和一种波豆虫——Rhynchobodo sp.中测定的，LSU序列是从一种昆虫锥虫——康氏锥虫（Crithidia oncopelti）和一种波豆虫——类锥波豆虫（Dimastigella trypaniformis）中测定的。与之前的结果相反，之前发现锥虫是并系的，其中布氏锥虫（Trypanosoma brucei）代表最早分化的谱系，而我们现在发现了锥虫单系性的证据。添加细分长分支（如布氏锥虫的分支）的新分类单元有助于识别导致之前研究中并系树的同塑性。尽管在最大似然法的自展分析中，锥虫类群的单系性得到了97%的支持，在最大简约法中得到了92%的支持，但最优单系树和次优并系树之间的对数似然值或树长只有很小的差异。在锥虫亚树中，锥虫类群是一个非锥虫属单系类群的姐妹群。不同组的锥虫在树上根据它们的传播方式进行分组。这表明，对无脊椎动物媒介的适应在锥虫进化中比适应脊椎动物宿主发挥着更重要的作用。
