中文摘要：

犁头鳅属为中国的特有属,包括犁头鳅和长鳍犁头鳅两个物种。犁头鳅广泛分布于长江中上游,而长鳍犁头鳅则局限分布于闽江水系。该研究对采自长江中上游的犁头鳅20个个体和闽江水系的长鳍犁头鳅8个个体的线粒体细胞色素b（cytb）基因序列进行分析,以期对犁头鳅属鱼类的物种地理分化过程进行研究。结果显示,犁头鳅不同单倍型之间的遗传变异水平为0.1%～1.8%,平均为0.7%;长鳍犁头鳅各单倍型之间的遗传变异水平为0.6%～1.3%,平均为0.7%;犁头鳅和长鳍犁头鳅单倍型之间的遗传差异也较小,仅为0.2%～1.8%,平均为0.9%。采用邻接（NJ）法和贝叶斯（BI）法构建的分子系统发育树都一致显示,该研究中的犁头鳅属鱼类构成一个单系;所有长鳍犁头鳅样本构成一个单系,位于系统发育树的顶部位置;犁头鳅的样本不构成单系,而是形成并系。从形态上看,犁头鳅和长鳍犁头鳅均为有效种。由此推测,在第四纪冰期,长江中下游的犁头鳅沿东海大陆架向南扩散到东南沿海水系,长鳍犁头鳅可能是犁头鳅的一个种群扩散到闽江水系后,由于适应新的环境条件而分化成的一个新物种,剩下的长江流域的犁头鳅种群则构成一个并系类群。该文对于类似的地理物种形成方式也进行了讨论。

英文摘要：

The genus Lepturichthys is endemic in China, including two valid species, L. fimbriata and L. dolichopterus. The former is widely distributed in the Upper and Middle Yangtze River, while the latter only in Minjiang River. In the present study, the mitochondrial cytochrome b gene sequences were analyzed for 20 individuals of L. fimbriata collected from the Upper and Middle Yangtze River and eight individuals of L. dolichopterus collected from Minjiang River. This paper aimed to investigate the geographical speciation process of the genus Lepturichthys. The results showed that the genetic variations among different haplotypes of L. fimbriata ranged from 0.1% to 1.8%, with an average of 0.7%, and from 0.6% to 1.3%, with an average of 0.7% among different haplotypes of L. dolichopterus. The variations between L. fimbriata and L. dolichopterus were also very low, ranging from 0.2% to 1.8%, with an average of 0.9%. Two methods, Neighbor Joining （NJ） and Bayesian analysis （BI）, were used for constructing the molecular phylogenetic trees. Both NJ and BI trees indicated that all Lepturichthys specimens formed as a monophyletic group; the L. dolichopterus samples also formed as monophyletic group, having a derived position in the phylogenetic trees, while the L. fimbriata samples formed as a paraphyletic group. Both L. fimbriata and L. dolichopterus are valid species in morphology. Based on molecular and morphological data, we presumed that the geographical speciation process of the genus Lepturichthys could be as following： during the Quaternary Glacial period, L. fimbriata in the Middle and Lower Yangtze River dispersed to the drainages of Southeast China along the Continental Shelf of East China Sea, one population spread to the Minjiang River and envolved as a new species （L. dolichopterus） because of considerable environmental difference, while the remaining L. fimbriata populations in the Yangtze River formed as a paraphyly. The other similar geographical speciation patterns are discussed in the present