荆州碘泡虫(粘体动物门,碘泡虫科)重描述及其基于18S rDNA系统发育关系分析

本实验利用现行主流分类衍征,重新对荆州碘泡虫(Myxobolus kinchowensis)进行了详细描述,其分类特征如下:包囊圆形,寄生于鲫肌肉与肾脏,肌肉包囊大小(126.7±1.8)μm,肾脏包囊直径为94.2μm;两寄生部位各形态参数无显著差异,成熟孢子正面观呈梨形,缝面观呈纺锤形,含一大一小两梨形极囊;无明显囊间突起,孢子后端无褶皱,无粘液膜。组织病理显示在两寄生部位均未引起严重的炎性反应,且感染强度不高,推测该种对宿主无显著影响。基于18S r DNA进化分析发现荆州碘泡虫与寄生在肌肉部位的碘泡虫属种类聚为一个大枝,然后该大枝又根据地理位置远近分为北美枝、欧洲枝以及亚洲枝。通过形态比较研究以及分子分析可确定荆州碘泡虫为有效种,其寄主为鲫,寄生部位为肌纤维间和肾小囊。此外,两组织差异明显的寄生部位出现说明荆州碘泡虫相应的放射孢子虫在宿主鲫体内存在不同的发育与移行途径,而肌肉可能为其常规寄生部位,肾脏为其异常寄生部位,这种寄生部位的转移与宿主转变可能是粘孢子虫物种多样性形成的机制。

Redescription and phylogenetic analysis based on 18 S rDNA of Myxobolus kinchowensis ( Myxozoa: Myxobolidae)

Myxobolus kingchowensis Ma & Chen, 1963 was originally described from multi-organs of several cyprinid fi-shes with insufficient data which should be supplemented and validated by current taxonomic criteria. The morphological fea-tures of the concerned species are as follows: plasmodia dwelling in trunk muscle and renal capsule, with diameter of 126. 7 ± 1. 8 μm and 94. 2μm in maximum, respectively; no significant differences among all taxonomic parameters of two isolates; mature spores were pyriform in frontal view and fusiform in sutural view, with tapering anterior end and round posterior end; spore surface smooth with thick straight sutural ridge; polar capsule, unequal, locating in the anterior part of spores; no significant intercapsular process, edge marking on the spore posterior end and mucus envelope surrounding the spore valves. Histopathological observations showed that no significant inflammatory responses occurred in both kidney and muscle, so it can be assumed that the infection of this species has no significant detrimental effects on host taking the low infection intensity into account. Phylogenetic analysis showed that M. kingchowensis clustered with several muscle-in-fecting Myxobolus species and formed an independent clade among cyprinid-infecting species, and showing a tendency to cluster according to the geographical distribution of their fish hosts. In addition, the occurrence of two infection sites for M. kingchowensis indicated that there are two routes of migration and development after the invasion of the fish host by infec-tive actinospores. However, muscle is the primary infection site and kidney the secondary site. We thought that this infec-tion site-shift and host-shift are the possible mechanisms of the occurrence of high species diversity of fish myxosporean parasites.