2种相手蟹线粒体12S rRNA基因序列分析

Sequence Analysis of Mitochondrial 12S rRNA Gene between Two Species of Sesarmid Crabs

测定了红螯相手蟹和褶痕相手蟹线粒体12SrRNA基因部分片段的序列，前者为572bp，后者为576bp。二者的核苷酸序列A、T、G、C的含量相似，分别为42．5％、37．6％、11．9％、8．0％；42．0％、37．0％、12．5％、8．5％；不包括8处插Ⅳ缺失位点，两序列间有48个变异位点，核苷酸差异率为8．42％，其中转换30个、颠换18个，转换与颠换比约1．67。对国内外相手蟹长度为383bp的12SrRNA基因同源序列进行分析，A＋T含量为76．6％～81．4％，明显高于G＋C的含量，且存有84个多态位点。系统发生树的拓扑结构显示，所有的相手蟹分别聚为3大支，代表着3个不同的属即相手蟹属、栉齿蟹属和仿相手蟹属；这与形态学分类结果相一致。

Partial sequences of the mitochondrial 12S rRNA gene were determined for two Sesarma species （S. haematocheir and S. plicata）. The result indicated that there was length variation between two sesarmid crabs, which was 572 bp and 576 bp, respectively. The A, T, G and C contents were similar, which were 42.5%, 37.6%, 11.9%, 8.0% and 42.0%, 37.0%, 12.5%, 8.5% for S. haematocheir and S. plicata, respectively. There were 48 different sites （except 8 deletion/insertion sites） between the two species, including 30 transition sites and 18 transversion sites. The ratios of different sites and si/sv were about 8.42% and 1.67, respectively. Furthermore, 383 bp homologous segment was analyzed to discuss the phylogenetic relationship of correlative sesarmid crabs in the world. The results showed that A ＋ T content （76.6% ～81.4% ） was higher than G ＋ C and 84 polymorphic positions of 12S rRNA sequences were found among them. Topological structure of the molecular phylogenetic tree, constructed by 12S rRNA gene with Neighbor-Joining method, revealed that all species of sesarmid crabs were clustered into three distinct branches, respectively, which correspond to the genera Sesarrna, Chiromantes and Parasesarma. The molecular data showed consistence with the classified result of sesarmid crabs by morphological characters.