用16S rDNA序列初步探讨部分真虾类的系统发育关系

利用DNA序列测定技术测定了真虾下目7科8个种的线粒体16S rDNA部分序列，与从GenBank检索得到的12个相关种的16S rDNA部分序列进行同源性比对，探讨其系统发育关系及16S rDNA在真虾类系统发育研究中的应用。比对序列长353bp，其中变异位点221个、简约信息位点180个。碱基转换替代速度比颊换替代速度慢。以螯虾下目的Austropotamobius pallipes为外群构建了这20种真虾的系统发育关系分支图，结果展示：（1）长臂虾科隐虾亚科的Awhistus custos远离长臂虾亚科分支。而且它的16S rDNA序列在Genbank中，首先与六足纲（Hexapoda）的昆虫比对上。（2）长臂虾科长臂虾亚科的两个近缘属Palaemon和Palaemonetes问的4个种混合相聚，说明传统形态分类中以大颚有无触须作为这两个属的属级形态鉴定特征尚需进一步审定。（3）鼓虾总科藻虾科的Exhippolysmata ensirostris与褐虾总科褐虾科的Crangon affinis处在同一分支，而没与鼓虾科的种类形成姐妹群。研究结果表明，16S rDNA片段的序列很适合研究真虾类的属间系统发育关系，而在研究属上高级阶元或种下阶元间的系统发生关系时较不敏感，因其变异对于种级水平显得过于保守，而对于科级以上阶元又显得太快。

The molecular phylogeny of infraoder caridea based on 16S rDNA sequences

The molecular phylogeny of infraorder caridea was revealed by partial 16S rDNA sequences amplified from 8 species (belonging to 7 families) in our study, and other 12 species sequences were cited from Genbank. Alignment of the sequences showed a considerable variation in 221 nucleotide sites and 180 parsimony informative sites. The variation rate of transversion was higher than transition. A dendrogram of the 20 ca-ridean shrimps was reconstructed based on the 16S rDNA sequences with Austropotamobius pallipes as out-group. The results were as fellow: (1) Anchistus custos of Pontoniinae, Palaemonidae located far away from the branch of Palaemonidae. Its 16S rDNA sequences, blasted in Genbank, was firstly aligned with insects in Hexapoda. (2) The four species in the two close genera Palaemon and Palaemonetes were clustered in one composite branch, but the species in the two different genera were not separated correspondingly. (3) Exhip-polysmata ensirostris of Hippolytidae, Alpheoidea were not the sister group of Alpheidae in the dendrogram, but located with Crangon affinis of crangonidae, crangonoidea. The study revealed that the fragment of 16S rDNA was very suitable to analyze the relationship among genera in the caridea. But for family or higher level taxa and for species or lower taxa, the sequence was not very applicable. The sequence variation was over-conservative for species or lower taxa, and it was too fast for family or higher level taxa.