相手蟹属两种蟹类线粒体16S rRNA基因序列的比较

Sequence Comparison of Mitochondrial 16S rRNA Gene between Two Species in Sesarma sp.

测定了相手蟹属红螯相手蟹和褶痕相手蟹线粒体16S rRNA基因部分片段的序列，二者的序列长度相同，均为533bp，且A、T、D、C的含量相似，分别为198bp（37．1％），206bp（38．6％），84bp（15．8％），45bp（8．4％）和200bp（37．5％），205bp（38．5％），81bp（15．2％），47bp（8．8％）；二者的序列有49处差异，其中21个位点为转换、22个位点为颠换和6个缺失／插入位点。进一步对20种相手蟹属蟹类的长度为361bp的16S rRNA基因同源序列进行分析，发现AT的含量为78．6％～82．9％，明显高于GC的含量，且存有91个变异位点。从NJ树和遗传距离来看，在分布于中国的3种相手蟹中，无齿相手蟹和红螯相手蟹的亲缘关系最近（d=0．0151），而它们与褶痕相手蟹的亲缘关系则较远（d=0．0924／0．0923）。分布于中国的相手蟹和分布于北美的相手蟹之间存在着较大的遗传距离（差异），表明它们之间有着较远的亲缘关系，互为单系起源。

Partial sequences of the mitochondrial 16S rRNA gene were determined for two species （Sesarma haematocheir and S. plicata） in Genus Sesarma. It was found that the length of sequence was the same for S. haematocheir and S. plicata. Among the 533 nucleotides obtained, the A, T, G and C contents were all similar, 198bp （37. 1%）, 206 bp （38.6%）, 84 bp （15.8%）, 45 bp （8.4%） and 200 bp （37.5%）, 205 bp （38.5%） , 81 bp （15.2%）, 47 bp （8.8%）, respectively. There were 49 different sites between the two spe- cies, including 21 transition sites, 22 transversion sites and 6 deletion/insertion sites. Furthermore, 361 bp homologous fragment was analyzed to discuss the phylogenetie relationship among 20 Sesarma species. The results showed that there were higher A and T contents （78.6% -82.9% ） than G and C contents. There were 91 variable positions of 16S rRNA sequences among the 20 species. Among 3 Sesarma species in China, S. dehaani and S. haematocheir were the closely related （ d = 0. 0151 ） ; and there were greater genetic distances between S. plicata and S. dehaani / S. haematocheir （d = 0. 0924/0. 0923）. The average genetic distances of S. plicata, S. dehaani and S. haematocheir, compared with the North American crabs of genus Sesarma, were 0. 1032 ± 0. 0089, 0. 0783 ± 0. 0105 and 0. 0720 ± 0.011, respectively, indicating that there were greater genetic differ enees between China and North American Sesarma crabs and that they were monophyletie each other.