Bargues M D, Mas-Coma S
Departamento de Parasitología, Facultad de Farmacia, Universidad de Valencia, Spain.
Mol Biol Evol. 1997 May;14(5):569-77. doi: 10.1093/oxfordjournals.molbev.a025794.
The 18S rDNA sequences of the six most common European Lymnaeidae species (Mollusca:Gastropoda:Basommatophora) have been obtained by direct PCR cycle sequencing and silver staining methods. The sequence alignment and secondary structures of the 18S rRNA gene of Lymnaea stagnalis, L. auricularia, L. peregra, L. palustris, L. glabra, and L. truncatula are analyzed. This gene proves to be a good marker for both specific determination and supraspecific lymnaeid phylogeny. The malacological importance is evident, considering the specific determination problems of individual snails and the present systematic chaos in Lymnaeidae due to their pronounced morphoanatomic uniformity, which makes a classification by traditional methods impossible. The majority (17) of the total of 43 nucleotide-substituted positions appears to be confined to a small region included in helix E10-1 of the variable region V2, enabling species group distinction: (1) the first sequence is common to L. auricularia and L. peregra; (2) the second sequence is unique to L. truncatula; and (3) the third sequence is identical for L. glabra, L. palustris, and L. stagnalis. The other 26 nucleotide-substituted positions are dispersed over the entire gene, although four grouped nucleotide positions in helix 6 of V1 are of interest in distinguishing L. glabra from both L. palustris and L. stagnalis. The phylogenetic trees obtained by comparison with four other molluscan species (a polyplacophoran, two bivalves, and a stylommatophoran gastropod) show the presence of four well-defined subgenera among the genus Lymnaea sensu lato: (1) Lymnaea (Radix), (2) Lymnaea (Galba), (3) Lymnaea (Leptolimnaea), and (4) Lymnaea (Lymnaea). Two branches, L. auricularia-L. peregra-L. truncatula and L. glabra-L. palustris-L. stagnalis, are worth mentioning from the parasitological point of view, since the two digenean species of large medical and veterinary impact transmitted by lymnaeids, Fasciola hepatica and F. gigantica, appear to be linked to the first branch.
通过直接PCR循环测序和银染法获得了欧洲六种最常见椎实螺科物种（软体动物：腹足纲：基眼目）的18S rDNA序列。分析了静水椎实螺、耳萝卜螺、奇异椎实螺、沼泽椎实螺、光滑椎实螺和截形椎实螺18S rRNA基因的序列比对和二级结构。该基因被证明是用于物种鉴定和超物种椎实螺系统发育研究的良好标记。考虑到单个蜗牛的物种鉴定问题以及由于椎实螺明显的形态解剖学一致性导致目前椎实螺科系统混乱，传统方法无法进行分类，其在软体动物学上的重要性显而易见。在总共43个核苷酸替换位点中，大多数（17个）似乎局限于可变区V2的螺旋E10-1中的一个小区域，从而能够区分物种组：（1）第一个序列是耳萝卜螺和奇异椎实螺共有的；（2）第二个序列是截形椎实螺特有的；（3）第三个序列是光滑椎实螺、沼泽椎实螺和静水椎实螺相同的。其他26个核苷酸替换位点分散在整个基因中，尽管V1螺旋6中的四个成组核苷酸位点对于区分光滑椎实螺与沼泽椎实螺和静水椎实螺很有意义。与其他四种软体动物物种（一种多板纲动物、两种双壳纲动物和一种柄眼目腹足纲动物）比较得到的系统发育树显示，广义椎实螺属中存在四个明确的亚属：（1）椎实螺属（萝卜螺亚属），（2）椎实螺属（豆螺亚属），（3）椎实螺属（薄唇椎实螺亚属），（4）椎实螺属（椎实螺亚属）。从寄生虫学角度来看，有两个分支值得一提，即耳萝卜螺-奇异椎实螺-截形椎实螺分支和光滑椎实螺-沼泽椎实螺-静水椎实螺分支，因为由椎实螺传播的两种对医学和兽医学有重大影响的复殖吸虫物种肝片吸虫和巨片吸虫似乎与第一个分支有关。
