Institute of Parasitology, Slovak Academy of Sciences, Hlinkova 3, 04001 Košice, Slovakia.
Parasitol Res. 2012 Oct;111(4):1621-7. doi: 10.1007/s00436-012-3001-z. Epub 2012 Jul 20.
The sequence structure of the ribosomal internal transcribed spacer 2 (ITS2) was determined for six species of Khawia (Cestoda: Caryophyllidea), parasites of cyprinid fish in the Holarctic Region. Homologous intragenomic ITS2 structure was found in Khawia armeniaca, Khawia baltica, and Khawia rossittensis; whereas divergent intragenomic ITS2 copies were detected in Chinese, Japanese, and Slovak isolates of Khawia sinensis and in Khawia japonensis, both parasitic in common carp, and in Khawia saurogobii, recently described from Chinese lizard gudgeon in China. Despite distinct morphological differences between K. saurogobii and K. sinensis, both species display very high level of molecular homogeneity. Variation in number of short repetitive motifs [(GCCT)(n) (GCCC)(n)], [(GTG)(n)], [(ATAC)(n)], [ACGTGT (TCGTGT)(n)], [(GT)(n)], [(GT)(n)], and [(ACCT)(n) (GCCT)(n)] resulted in assortment of ITS2 sequences in four ITS2 variants in K. saurogobii from China, three in Chinese and Japanese isolates of K. sinensis, and five ITS2 variants in K. sinensis from Slovakia. In K. japonensis, the structure and arrangement of microsatellites was different from those of K. sinensis and K. saurogobii. The heterogeneity in the number of two microsatellite regions [(TG)(n); (TTG)(n)] divided ITS2 clones into two variants-first ITS2 variant (472 bp) with (TG)(5) and (TTG)(6), and second variant with (TG)(7) and (TTG)(2) (465 bp). Sequence identity of K. saurogobii with all but one (K. sinensis) congeneric species ranged between 49.5 and 69.2%, which corresponds to the interspecific differences. In contrast, sequence identity of K. saurogobii and K. sinensis (87.6-95.0%) failed into the range of intraspecific variation determined for K. sinensis samples. This close genetic similarity indicates that recently described K. saurogobii may have undergone morphological divergence as a result of ongoing sympatric speciation by host switching.
我们测定了 6 种环凯阔节绦虫（Cestoda： Caryophyllidea）核糖体内部转录间隔区 2（ITS2）的序列结构，这些绦虫是北温带鲤鱼的寄生虫。在亚美尼亚环凯阔节绦虫、波罗的海环凯阔节绦虫和罗斯氏环凯阔节绦虫中发现了同源的种内 ITS2 结构；而在中国、日本和斯洛伐克的中华环凯阔节绦虫和日本环凯阔节绦虫以及中国石龙子泥鳅寄生的环凯阔节绦虫中检测到了不同的种内 ITS2 拷贝；在中国石龙子泥鳅寄生的环凯阔节绦虫和环凯阔节绦虫中也检测到了不同的种内 ITS2 拷贝。尽管环凯阔节绦虫和中华环凯阔节绦虫之间存在明显的形态差异，但它们都表现出非常高的分子同质性。短重复序列模体[(GCCT)(n) (GCCC)(n)]、[(GTG)(n)]、[(ATAC)(n)]、[ACGTGT (TCGTGT)(n)]、[(GT)(n)]、[(GT)(n)]和[(ACCT)(n) (GCCT)(n)]数量的变化导致了中国的 4 种环凯阔节绦虫、中国和日本的 3 种中华环凯阔节绦虫以及斯洛伐克的 5 种中华环凯阔节绦虫的 ITS2 序列的不同排列。在日本环凯阔节绦虫中，微卫星的结构和排列与中华环凯阔节绦虫和环凯阔节绦虫不同。两个微卫星区域[(TG)(n); (TTG)(n)]的数量差异将 ITS2 克隆分为两种变体——第一种 ITS2 变体（472bp）具有（TG）（5）和（TTG）（6），第二种变体具有（TG）（7）和（TTG）（2）（465bp）。环凯阔节绦虫与除一种（中华环凯阔节绦虫）同属物种的序列同一性在 49.5%至 69.2%之间，这对应于种间差异。相比之下，环凯阔节绦虫和中华环凯阔节绦虫的序列同一性（87.6-95.0%）没有落入中华环凯阔节绦虫样本确定的种内变异范围。这种密切的遗传相似性表明，最近描述的环凯阔节绦虫可能由于宿主转换的同域物种形成而经历了形态上的分化。
