Analyses on Species Diversity on Parasitic Helminths based on Molecular Phylogeny

分析了寄生蠕虫多样化的机制，重点分析了寄生蠕虫广泛存在于小型鲸类中的拟线虫科(线虫科)，主要来源于线虫科。在日本附近海域，有3种海豚寄生，它们分别是达尔江豚、江豚和港口江豚，其中前两者分别寄生于5种伪寄生线虫，而后者也寄生于同一科的多种线虫。本研究以线粒体DNA(MDNA)上编码的细胞色素C氧化酶亚基I(COI)基因约1.2kbps的部分序列为基础，利用分子分析方法，结合寄主的系统发育，研究了寄主在共进化、宿主交换和共域物种形成三种类型下的物种形成过程。用于分析的线虫是达尔氏江豚的2属5种，…的2种江豚有2个属，港口江豚有1个种。邻接树表明，这些假别名分为两类，一类是来自达尔江豚的Parurus Dalli、Stenurus truei和S.yamagutii，另一类是由江豚的S.minor和来自达尔江豚和江豚的三种Halocercus组成。传统上，狭口吸虫属(Stenurus)、狭口吸虫属(Pharurus)和假狭口吸虫属(Pseudotenurus)被归为狭口吸虫亚科，主要分布于颅窦和鼻腔，而盐藻属(Halocercus)也寄生于肺内的支气管。因此，这是一个相当意想不到的结果。另一方面，江豚的孙美氏吸虫与达尔氏鼠类的S.truei有密切的亲缘关系，这些结果提出了几个物种形成的过程：港豚由裸鼠祖先进化而成的伪科一分为二的类群，Halocercus属的共同祖先是由小海豚等颅窦栖息者通过改变栖息地到支气管，以及后代寄生在其他裸鼠身上而形成的；三种伪异物共同栖息在达尔江豚的颅窦中，尽管繁殖隔离的机制尚不清楚；通过将宿主从多尔的江豚转变为江豚，发生了来自S.truei的P.sunameri。较少

Mechanisms of diversification on parasitic helminths were analyzes focusing on the family Pseudaliidae (Nematoda), which widely infest in the small cetaceans mainly from the family Phocoenidae. In the waters around Japan three members of the phocoenids distribute, Dall's porpoise Phocoenoides dalli, finless porpoise Noephocaena phocaenoides and harbour porpoise Phocoena phocoena, of which the former two are parasitized by five species of pseudaliid nematodes each and the latter is also infested by several species of the same family. In this study, the processes of speciation were investigated, considering the host's phylogeny, under three categolies i. e., co-evolution, host exchange and sympatric speciation by using molecular based analyses.The partial sequences of about 1.2 kbps from cytochrome c oxidase sub-unit I (COI) gene encoded on mitochondrial DNA (mDNA) were used for analyses. The nematodes used for analyses were five species of two genera from Dall's porpoise, two species of … More two genera from finless porpoise and one species from harbor porpoise. The neighbor-joining tree indicated that these pseudaliids were divided into two clusters, one contained Parurus dalli, Stenurus truei and S.yamagutii derived from Dall's porpoise, and Pseudostenurus sunameri from finless porpoise; and the other was constructed by S.minor from harbour porpoise and surprisingly three species of the genus Halocercus from Dall's porpoise and finless porpoise. Conventionally, the genus Stenurus, Pharurus and Pseudostenurus are classified into the subfamily Stenurinae mainly inhabit in the cranial sinus and nasal cavity, while the genus Halocercus also makes the subfamily Halocercinae parasitic in the bronchi of lung. Thus, this is a quite unexpected result. On the other hand, P.sunameri from finless porspose was closely related with S.truei from Dall's porpoise.So far these results are concerned, several processes of speciation are suggested, the clusters dividing the family Pseudaliidae into two was made by co-evolution when harbour porpose was derived from the phocoenid ancestor, the common ancestor of the genus Halocercus was derived from the cranial sinus inhabitants such like S.minor by changing their habitat to the bronchi, and the descendants infested in other phocoenids; three species of pseudaliids inhabit in the cranial sinus of Dall's porpoise speciated sympatrically, although the mechanism of the reproductive isolation is unknown ; P.sunameri occurred from S. truei by changing a host from Dall's porpoise to finless porpoise. Less