中国9种嗜子宫线虫系统发育的初步研究

A PRELIMINARY STUDY ON PHYLOGENY OF NINE SPECIES OF PHILOMETRIDS IN CHINA

为了探讨鱼类寄生嗜子宫线虫的系统发育关系,测定了8种嗜子宫线虫的ITS rDNA(核糖体转录内间隔区核 糖核酸)序列和9种嗜子宫线虫的18S rDNA(小亚基核糖体核糖核酸)部分序列,并构建了18S rDNA序列的系统发 育树。在比较和分析ITS rDNA和18S rDNA两种分子标记对嗜子宫科线虫系统发育适用性的基础上,分析了嗜子 宫线虫的系统发育关系。结果表明:中国嗜子宫线虫是单系起源;黄颡鱼似嗜子宫线虫、赣州似嗜子宫线虫和棍头 嗜子宫线虫亲缘关系非常接近,可能是较晚形成的种;似嗜子宫线虫属可能应该被细分为更多的属。

Because of difficulties in finding males of philometrids, they are usually recognized by females only. The character of the female is lacking, so many arguments arise on the present classification system of this nematode. To reveal the phylogenetic relationships of the philometrids collected in China, the intemal transcribed spacer region rDNA（ ITS rDNA）of 8 species and the partial small subunit rDNA（ 18S rDNA）of 9 species were sequenced. Due to great divergence in the sequences, ITS rDNA was not considered suited for the phylogentic studies in philometrids. Regarding 18S rDNA, an alignment of 943 nucleotide sites was obtained, of which, variable sites were 140 including 69 parsimony informative sites. Sequence divergence among the philometrids analyzed ranged from 0 between close species to 11.99% between distant species. In contrast with ITS rDNA, 18S rDNA was the more reliable marker for analyzing the phylogenetic position of the philometrids, thereby a phylogenetic tree based on the sequences of 18S rDNA was constructed. It was found that the tree strongly supported the philometrids in China to be a monophyly. The three species, Philometroides fulvidraconi, P. ganzhounensis and Philometra clavaeceps were very close in relationship, and might be appeared lately in history. The structure of the Cuticular bosses of philometrids was suggested to be lost easily in rapid evolution of the nematodes, thus it should not to be regarded as one of the most important distinct characteristics of the genus Philometrodes from other genera. According to the present data and the previous opinions of other researchers, it was suggested that the genus Philometroides should be divided into different genera.