Speciation and phylogeny of the lancelet, Branchiostoma belcheri (Gray) in East Asian waters, as viewed from molecular and morphological analyses

1.对日本的3个地方群体(Enshu-nada Sound、Seto Inland Sea和Amakusa)进行的等位酶分析表明，在9个多态基因座中，有5个群体间存在显著差异。然而，Fst(0.007)的总体值很小，表明种群之间应该有一定程度的遗传交换。根据线粒体细胞色素C氧化酶亚基I(C01)和16S核糖体核糖体RNA(16S RRNA)基因的核苷酸序列，对来自内州湾、戈卡索湾、内海、阿马库萨、青岛(中国北部)和厦门附近吉门(中国南部)的贝尔切鱼、泰国湾和普吉岛的马来丝虫、日本冲绳的卢卡鱼(作为外群)、马尾鱼(Do.)结果表明：(1)各地方种群间无显著差异。这是意想不到的，因为青岛和日本人与厦门人之间存在显著的形态差异。(2)根据C01和16S rRNA基因的遗传距离，在六个物种的邻接树中，太平洋对(B.belcheri和B.marayanum)与大西洋对(B.lanceolatum和B.floridae)各聚为一类，后者从聚类节的分枝长度比太平洋的短得多。(3)根据C01基因的序列数据，太平洋对(B.belCheri和B.marayanum)和大西洋对(B.floridae)各聚为一类。大西洋和太平洋物种的分化时间约为1.1亿年前，而Branchiostoma和Eigonichthys物种的分化时间约为1.3亿年。相比之下，轮纹夜蛾和斑潜蝇的分化时间估计为零。

1. Allozyme analysis for the 3 Japanese local (Enshu-nada Sound, Seto Inland Sea, and Amakusa) populations of Branchiostoma belcheri, revealed statistically significant differences among them at 5 out of 9 polymorphic loci. However, the smallness of the overall value of Fst (0.007) indicates that there should be a certain degree of genetic exchanges among the populations.2. Molecular phylogenetic studies based on nucleotide sequences of mitochondrial cytochrome C oxidase subunit I (C01) and 16S ribosomal RNA (16S rRNA) genes were performed for B.belcheri from Enshu-nada Sound, Gokasho Bay, Seto Inland Sea, Amakusa, Qingdao (North China), and Jimmnen Island, near Xiamen (South China) ; B.malayanum from Gulf of Thailand and Phuket ; Epigonichthys lucayanus (as an outgroup) from Okinawa, Japan ; E.maldivense (do.) from Taiwan ; and Atlantic B.floridae and B.lanceolatum, both cited from DDBJ.The results are :(1) No significant differences were detected among all the analysed local populations of B.belcheri. It is unexpected because marked morphological differences have been recognized between Qingdao plus Japanese and Xiamen populations.(2) In the neighbor-Joining trees among the six species based on the genetic distances in the C01 and 16S rRNA genes, the Pacific pairs (B.belcheri and B.malayanum) and the Atlantic ones (B.lanceolatum and B.floridae) were clustered each into a distinct group, with the branch lengths of the latter from the node of the cluster being much shorter than those of the Pacific.(3) On the basis of the sequence data of C01 gene, the divergence time between the Atlantic and Pacific species about was measured ca. 110 million years ago and that the Branchiostoma and Epigonichthys species ca. 130 million years. In contrast, the divergence time between B.lanceolatum and B.floridae was estimated zero.