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

1. 对日本3个地方种群（恩树那达湾、濑户内海和天草）的等位酶分析显示，9个多态位点中有5个存在统计学差异。但总体Fst值较小（0.007），说明群体间存在一定程度的遗传交换。基于线粒体细胞色素C氧化酶亚基I （C01）和16S核糖体RNA （16S rRNA）基因序列的分子系统发育研究，对来自青岛恩树那达湾、高kasho湾、Seto内海、天草和厦门附近的金门岛的B.belcheri进行了分子系统发育研究；b .产自泰国湾和普吉岛的马来酸；产自日本冲绳的露卡亚表鱼（外群）；e . maldise （do.）源自台湾；大西洋B.floridae和B.lanceolatum，均引自DDBJ。结果表明：(1)各地区贝氏贝氏杆菌种群间差异不显著。这是出乎意料的，因为在青岛加日本和厦门种群之间已经发现了明显的形态差异。(2)根据C01和16S rRNA基因的遗传距离，6个物种间的相邻联结树中，太平洋对（B.belcheri和b.m malayanum）和大西洋对（b.b lanceolatum和b.f oridae）分别聚为一个独立的类群，后者从聚类节点开始的枝长远短于太平洋对。(3)根据C01基因序列数据，测定了大西洋和太平洋物种的分化时间约为1.1亿年，而Branchiostoma和Epigonichthys物种的分化时间约为1.3亿年。与此相反，披针叶虫和佛罗里达虫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.