文蛤属(Meretrix)16S rRNA基因及ITS1序列的系统学分析

MOLECULAR PHYLOGENY OF MERETRIX (MOLLUSCA, BIVALVIA) BASED ON 16S rRNA GENES AND ITS1 SEQUENCES

利用线粒体16SrRNA基因片段及核糖体DNA转录间隔区ITS1序列分析的方法,以近缘属的青蛤(Cyclinasinensis)为外群,对文蛤属的文蛤(M.meretrix)、丽文蛤(M.lusoria)、帘文蛤(M.lyrata)和斧文蛤(M.lamarckii)4种贝类进行了系统学研究。经ClustalX多重比对及DNAsp软件分析后,用PAUP4.0分析软件,计算出种间序列的碱基转换/颠换频率,利用邻接法NJ构建系统发育树。结果表明,帘文蛤与该属其他三种的分歧时间较早,两类序列与其他种类间的相对遗传距离分别在0.25866—0.28218和0.15644—0.20104之间。文蛤与丽文蛤间的16SrDNA及ITS1序列间的遗传距离仅为0.04805和0.04201,拓扑结构图显示关系很近,并且二者的分布区大面积重叠,其序列间的转换/颠换频率接近种内单元型(haplotype)间的序列变化,鉴于它们的贝壳形态有一定差别,应归为同一个种内的不同地理亚种比较恰当。

Members of the Genus Meretrix are commercially important marine fishery seashells in China. Some of species have already become regional economic mainstay in coastal areas of China. However, the tax- onomy of Meretrix is still in argument over several discrepancies among scientists in the world. This paper deals with the mitochondria partial 16S rRNA genes and ITS1 （ Internal Transcribed Spacerl, between 18S ribosomal RNA gene and 5.8S ribosomal RNA gene） sequences from 4 Meretrix species, including M. meretrix, M. lusoria, M. lyrata and M. lamarckii common in Chinese coastal zones. At the target sequences with universal primers, we investigated and amplified 16S rRNA and ITS1 of the four species and obtained fragments of 16S rRNA between 590bp and 648bp and ITS1 between 781bp and 825bp, as well as the alignment with software Clustal-X and the sequences variations with DNAsp4. 171 mutation sites in 16S rRNA fragment with polymorphism at 0.17, and 251 nucleotide mutation sites in ITS1 sequence with polymorphism at 0.20 were determined. Setting Cyclina sinensis as the outgroup in phylogeny, with PAUP 4.1 Beta, we calculated the rate of base pair transition/transversion and constructed the system tree with neighbor-joining （NJ） method for the four species. The results show that the genetic distance of M. lyrata to other three were between 0. 258-0. 282 and 0. 156-0. 201, suggesting a significant differentiation of M. lyrata from other species, but closer to M. lamarckii. In addition, M. meretrix is closer to M. lusoria, as the distances in-between were 0. 048 and 0. 042 in 16S rRNA and ITS1 respectively, and the areas of distribution were largely superimposed for each other. By ignoring inserted and missing sites, the two species＇ transition/transversion can be bracketed as inter-species haplotype. Minor morphological difference between the two could be due to geographical reasons and may described as two subspecies, which agree with the taxonomy for genus Meretrix proposed by Prashad （1932） and Fischer-Pierre （ 1941 ）.