基于线粒体细胞色素氧化酶Ⅰ亚基(COI)基因的两种枝吻纽虫系统发育关系分析

为了探讨纽虫之间的遗传差异及亲缘关系,对取自北海和湛江的中华枝吻纽虫(Dendrorhynchus sinensis)26个样本和湛江枝吻纽虫(Dendrorhynchus zhanjiangensis)3个样本的线粒体细胞色素氧化酶Ⅰ亚基(COI)基因部分片段进行序列测定,并结合从GenBank下载的其它纽虫序列,分析它们之间的系统发育关系。结果显示,中华枝吻纽虫26个个体共检测17个单倍型,湛江枝吻纽虫3个个体共检测到2个单倍型,其长度均为615bp;枝吻纽虫个体核苷酸序列A、T、G、C的含量相近,碱基组成均表现出A+T含量偏倚,即A+T含量明显高于G+C含量。中华枝吻纽虫的17个单倍型以及湛江枝吻纽虫的2个单倍型之间的遗传距离分别为0.002~0.013和0.008;而两种枝吻纽虫COI基因序列的遗传差异很大,彼此之间的遗传距离都在0.194以上,加之分子系统树(NJ)的拓扑结构也显示,作为同属的两种枝吻纽虫没有聚成1支,而是各自成支,这些表像都支持两种枝吻纽虫分别为独立有效物种的观点。中华枝吻纽虫的17个单倍型聚为1支后,与Cerebratulus marginatus,C.lacteus聚为1大支,而湛江枝吻纽虫的2个单倍型聚为1支后,与Lineus ruber和L.longissimus聚为1大支,表明枝吻纽虫属(Dendrorhynchus)并非单系。

Molecular Phylogeny of Two Nemerteans with a Branched Proboscis based on the Sequences of Mitochondrial COI Gene

The sequences of mitochondrial COI gene of two nemerteans with a branched proboscis (Dendrorhynchus zhanjiangensis and D.sinensis) from the coast of Beihai and Zhanjiang were determined and subjected to phylogenetic analysis with other nemerteans obtained from the GenBank.The lengths of sequences of D.sinensis (seventeen haplotypes from twenty six individuals) and D.zhanjiangensis(two haplotypes from three individuals) were all 615bp.The A, T, G and C contents of them were similar, and the AT content was higher than the GC content.The genetic distances among the seventeen haplotypes of D.sinensis and the two haplotypes of D.zhanjiangensis were very small (0.002~0.013 and 0.008) whereas the genetic distances between the two nemerteans were very large (in more than 0.194), implying that they were independent effective species respectively.Topological structure of the molecular phylogenetic tree constructed by Neighbor-Joining method showed that D.sinensis and D.zhanjiangensis did not form a clade, but on the contrary, D.sinensis and two species of Cerebratulus marginatus and C.lacteus were clustered into a distinct clade.Therefore, the results indicated that the genus of Dendrorhynchus was not monophyletic.