田中碘泡虫的重描述及系统发育分析

基于形态学和分子数据(18S rDNA)重新描述了寄生于重庆江津地区金鱼 (Carassius auratus auratus)鳃丝的田中碘泡虫 (Myxobolus tanakai Kato, et al., 2017), 并结合系统发育分析对其近缘种进行了比较研究。形态学特征: 该虫种孢子为后端钝圆的长梨形, 大小为(14.58±0.54) μm×(6.09±0.37) μm; 两个极囊等大; 极丝与极囊长轴垂直缠绕8—10圈; 囊间突起位于极囊前端呈三角形; 具有嗜碘泡。分子特征: 共获得3个分离样本的18S rDNA序列, 其一级结构序列与日本黑川地区鲤 (Cyprinus carpio) 鳃丝寄生的田中碘泡虫的一致性达99.3%—99.6%, 且在系统发生树中聚为一支。结果表明: 本研究种与日本的田中碘泡虫为同种, 此为中国新记录; 金鱼为田中碘泡虫的宿主新记录。18S rDNA的V2、V4和V7区二级结构的比较结果表明: 田中碘泡虫已发生了明显的种内变异, 推测可能因宿主差异和地理隔离同时所致。此外, GenBank中报道的数个野鲤碘泡虫的序列是否为同种有待进一步厘清。

REDESCRIPTION AND PHYLOGENY OF MYXOBOLUS TANAKAI KATO ET AL., 2017

This study redescribed Myxobolus tanakai Kato, et al., 2017 parasitizing the gills of Carassius auratus auratus from Jiangjin District of Chongqing based on morphological and molecular data (18S rDNA), and compared M. tanakai with other genetic related species using phylogeny. Morphologically, the spores were long pear-shaped with a posterior blunt end and a size of (14.58±0.54) μm × (6.09±0.37) μm. The two polar capsules were equal; polar filaments perpendicularly to the longitudinal axis of the polar capsules wounded eight to ten coils; a large triangle intercapsular appendix was observed in front of the two polar capsules; iodinophilous vacuoles was evident. Molecularly, three 18S rDNA sequences from three different samples were 99.3%—99.6% identical and clustered in a branch of phylogenetic tree with that of M. tanakai populations from the gills of Cyprinus carpio in Yamaguchi City, Japan. The results indicated that the present organism is the same species as M. tanakai from Japan. This is a new record for Chinese M. tanakai, and goldfish is a new host record. The comparative results of secondary structure of 18S rDNA V2, V4 and V7 revealed that intraspecific variation already existed in M. tanakai, which might contribute to host differentiation and geographical isolation. In addition, whether certain sequences reported in GenBank belong to Myxobolus koi remained to be clarified.