基于18S rDNA与ITS-5.8S rDNA对重庆地区网状车轮虫的种内分化研究

Study on Intraspecific Differentiation of Trichodina reticulata from Chongqing Based on 18S rDNA and ITS-5.8S rDNA

本研究基于形态和分子数据对采自重庆地区5个地理株系的网状车轮虫(Trichodina reticulata)进行了比较研究及重描述。研究结果表明,网状车轮虫不同株系表现出不同的表型分化,含形态略有不同的齿体及有或无中央颗粒,因而具有明显的种内形态多样性。不同地理株系网状车轮虫的18S rDNA序列相似度在99.0%~100%之间,遗传距离为0.000~0.008,并在三大变异区(V4、V5与V7)均具一致的二级结构,表明不同株系的18Sr DNA相似度与遗传距离均属种内水平。综合18SrDNA和ITS-5.8S rDNA的变异位点和系统发育对种内分歧的研究分析显示,来自不同地理分布和宿主的网状车轮虫株系皆因相同的变异位点而聚为一枝,以此推断网状车轮虫的种内分化主要受其基因的影响,地理分布与宿主差异等环境影响在目前的种群分化阶段暂未突显。此外,本研究进一步验证了中央颗粒不能作为网状车轮虫的主要鉴别性特征的观点。

Based on the comparative morphological and molecular characteristics of five strains of Trichodina reticulate, redescription of this species was conducted in the present study(Fig. 1﹣3, Table 2). The results indicated that these five strains showed different phenotype differentiation patterns including different denticle morphologies and the presence or absence of central granules, thus this species has dominant intraspecific morphological diversity. However, the sequence similarity and genetic distance among the five strains of T. reticulata were 99.0%﹣100% and 0.000﹣0.008, respectively, and their major variation areas(V4, V5 and V7)of 18 S rDNA possessed a consistent secondary structure(Fig. 6, 7), which suggests that genetic distances among these different strains are within the intraspecific level. Furthermore, the analysis of intra-species divergence on the basis of 18 S rDNA and ITS-5.8 S rDNA variation site and phylogenetic tree(Bayesian inference, BI tree and maximum likehood, ML tree) showed that these strains of T. reticulata with different geographical distributions and hosts were clustered into one clade mainly due to the same mutation site(Fig. 4, 5 and 8, 9), suggesting that the intraspecific differentiation for T. reticulata probably is mainly influenced by their genes, rather than the environmental factors including geographic distribution and host type. Besides, the present study confirmed that central granules should not be the main characteristics for species identification in T. reticulata.