相手蟹属两种蟹类线粒体16SrRNA基因序列的比较

测定了相手蟹属（Sesarma）红螯相手蟹（S．haematocheir）和褶痕相手蟹（S．plicata）线粒体16SrRNA基因部分片段的序列，二者的序列长度相同，均为533bp，且A、T、G、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16SrRNA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，无齿相手型（S．dehaani）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=0．0924／0．09231。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。

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

Partial sequences of the mitochondrial 16S rRNA gene were determined for two Sesarma species （S. haematocheir and S. pficata）, and the length of sequence of S. haematocheir and S. plicata was the same. Of the 533 nucleotides obtained, the A, T, G and C contents were similar, which were 198 bp （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 species, including 21 transition sites, 22 transversion sites and 6 deletion/insertion sites. Furthermore, 361 bp homologous fragment was analyzed to discuss the phylogenetic relationship of 20 Sesarma species. The results showed that AT content （78.6% - 82.9%） was higher than GC content and there were 91 vadable positions of 16S rRNA sequences among the 20 species. Among 3 Sesarma species in China, S. dehaani and S. haematocheir were closely related （d=0.0151）; and there were greater genetic distances between S. pficata and S. dehaani I S. haematocheir （d=0.0924/0.0923）. The average genetic distances of S. plicata , S. dehaani and S. haematocheir with the North American crabs of genus Sesarma were respectively 0.103 2 ± 0.008 9, 0.0783±0.0105 and 0.072 0± 0.011, which indicated that there were greater genetic differences between China and North American Sesarma crabs and they were monophyletic each other.