九种绢丝昆虫线粒体12S rRNA基因的序列特征和系统发育分析

为探讨鳞翅目中绢丝昆虫之间的系统发育关系和分子进化特征，本研究测定了中国柞蚕Antheraea pernyi野生型和放养型的线粒体12S rRNA基因的部分序列，结合来自GenBank数据库的17条序列，对总共9种绢丝昆虫（2科3属）的12S rRNA基因序列进行了分析。利用软件MEGA 3.1进行碱基组成、变异位点的统计和分子进化分析，分别用类平均聚类法（UPGMA）、邻接法（NJ）、最小进化法（ME）、最大简约法（MP）重建系统发生树。测定的中国柞蚕野生型的12S rRNA基因序列（427 bp）与放养型“豫早1号”的序列完全一致。序列对齐后共鉴定80个变异位点，50个简约信息位点。碱基组成分析显示在科属间具有明显差异，AT含量蚕蛾科高于大蚕蛾科；在A和T碱基的使用上，大蚕蛾科偏好使用T，而蚕蛾科则偏好使用A。与动物中常见的以转换为主的碱基替换模式不同，所分析的9种昆虫中除桑蚕属内部为转换与颠换基本一致外，其余物种间均是颠换多于转换。进化分析支持柞蚕属、樗蚕属和桑蚕属的单系。基于UPGMA法的进化树支持琥珀蚕是柞蚕属的较原始类型，而NJ、ME和MP法则支持印度柞蚕是较原始的类型，因此，柞蚕属种间的进化关系尚需进一步研究。

Characterization and phylogenetic analysis of the mitochondrial 12S rRNA gene sequences from nine species of silk-producing insects

The nucleotide composition and substitution pattern of the partial mitochondrial 12S rRNA gene from nine species of silk-producing insects were investigated.The phylogenetic relationships among the nine species were then assessed by the methods of unweighted pair group method using arithmetic averages(UPGMA),neighbor-joining(NJ),minimum evolution(ME),and maximum parsimony(MP).The 12S rRNA gene sequences of 427 bp of the wild Antheraea pernyi are identical to the semi-domestic A.pernyi(Yuzao No.1).The genera Antheraea,Samia,and Bombyx show obviously different nucleotide composition:i)the AT content of Bombycidae family is higher than that of Saturniidae;ii)the nucleotide of Antheraea and Samia(Saturniidae)contains more Ts than As,while more As than Ts exist in Bombyx(Bombycidae).By analyzing the nucleotide substitution pattern,more transitions than transvertions were found among these species except Bombyx.All of the phylogenetic trees showed monophyly for the three genera,and the confidence limits were measured more than 96% for the clades.However,the phylogenetic tree based on UPGMA method supported the ancestral position of A.assama within Antheraea species,whereas all the trees using NJ,ME,and MP methods backed up the ancestral position of A.mylitta,suggesting that the phylogenetic relationship among Antheraea members need to be further studied with more molecular markers.