Zhang Gaotian, Chen Jue, Yang Yingyuan, Liu Nan, Jiang Weibin, Gu Sunlong, Wang Xiaoming, Wang Zhenghuan
School of Life Sciences, East China Normal University, 200062 Shanghai, China;
J Parasitol. 2014 Aug;100(4):542-6. doi: 10.1645/13-224.1. Epub 2014 Mar 10.
The family Taeniidae comprises many parasitic species, which cause serious zoonoses. However, effective identification of Taeniidae species is a long-standing problem, especially in samples from wild hosts with mixed infections of different Taeniidae species. DNA barcoding analysis of small fragments of the cytochrome c oxidase subunit I (COI) gene has been confirmed as an effective and useful method for identifying Taenia species. We therefore performed DNA barcoding analysis using a 351-bp region of the COI gene to identify 27 taeniid species including 9 in the genus Echinococcus, 2 in Hydatigera, 15 in Taenia, and 1 in Versteria. A total of 484 COI sequences were used to calculate genetic divergence expressed by the Kimura 2-parameter (K2P) distance. The mean intra-specific K2P distance in the family Taeniidae was 0.71 ± 0.17% (±SE), while inter-specific divergences were considerably higher. We found that, generally, a 2.0% optimal barcoding threshold could be set to distinguish taeniid species. Taenia polyacantha and Hydatigera taeniaeformis were the only 2 false-positive species identification cases in this study for their intra-specific divergences above the 2.0% optimal threshold. Their high intra-specific divergences coincided with fact that cryptic divergences exist in these 2 species, to which new taxa were recommended. On the other hand, sister species T. asiatica and T. saginata showed a 2.48 ± 0.83% inter-specific divergence, which was the smallest among all the taeniid species. Although fitting the 2.0% optimal species barcoding threshold, the close genetic relationship between T. asiatica and T. saginata implies that longer mitochondrial DNA sequences like the complete COI sequence are needed to strictly distinguish them. Therefore, we concluded that the barcoding technique based on a 351-bp region of the COI gene is able to distinguish taeniid species except for cryptic T. polyacantha and H. taeniaeformis and should be carefully used in distinguishing the closely related species T. asiatica and T. saginata .
带科包含许多寄生性物种，可引发严重的人畜共患病。然而，有效鉴定带科物种一直是个长期存在的问题，尤其是在来自不同带科物种混合感染的野生宿主的样本中。细胞色素c氧化酶亚基I（COI）基因小片段的DNA条形码分析已被确认为鉴定绦虫物种的一种有效且有用的方法。因此，我们使用COI基因的一个351bp区域进行DNA条形码分析，以鉴定27种带科物种，包括9种棘球绦虫属、2种泡状带绦虫属、15种绦虫属和1种韦氏绦虫属。总共484条COI序列用于计算以Kimura双参数（K2P）距离表示的遗传差异。带科内种内K2P距离的平均值为0.71±0.17%（±标准误），而种间差异则明显更高。我们发现，一般来说，可以设定一个2.0%的最佳条形码阈值来区分带科物种。多棘绦虫和泡状带绦虫是本研究中仅有的2例假阳性物种鉴定案例，因为它们的种内差异高于2.0%的最佳阈值。它们较高的种内差异与这2个物种中存在隐存分化这一事实相符，因此建议为其划分新的分类单元。另一方面，姊妹物种亚洲带绦虫和牛带绦虫的种间差异为2.48±0.83%，这是所有带科物种中最小的。尽管符合2.0%的最佳物种条形码阈值，但亚洲带绦虫和牛带绦虫之间密切的遗传关系意味着需要更长的线粒体DNA序列（如完整的COI序列）来严格区分它们。因此，我们得出结论，基于COI基因351bp区域的条形码技术能够区分除隐存的多棘绦虫和泡状带绦虫之外的带科物种，在区分亲缘关系密切的亚洲带绦虫和牛带绦虫时应谨慎使用。
