指环虫属的早期辐射及其与宿主鲤科鱼类的协同进化关系

Initial radiation of Dactylogyrus and coevolution with the dactylogyrid-cyprinid association

本研究利用28SrDNAC1-D2区序列分析采自鲤科鱼类中6亚科宿主和寄生在花鲈、梅花鲈上的共17种指环虫的系统发育关系。同时,通过比较宿主鲤科鱼类与指环虫的系统发育树,检验指环虫与其宿主是否存在协同进化关系。结果表明:17种指环虫形成5个进化支(Clade),其中寄生在团头鲂(亚科)和鲢、鳙(鲢亚科)上的6种指环虫聚为一支(Clade1),而它们的宿主鱼类在系统发育分析中也表现为近缘关系;寄生在鲮鱼(野鲮亚科)上的D.quanfami(Clade5)位于系统树最基部,鲫鱼和鲤鱼(鲤亚科)的寄生指环虫处在系统树的次基部位置,而鲤亚科与野鲮亚科组成的姐妹群在宿主系统树上同样处在基部位置,寄生虫和宿主在进化上较为原始的地位得到了很好地相互印证。因而,本研究首次利用分子系统学手段分析指环虫属远缘物种间的系统关系,揭示了指环虫属与宿主鱼类之间存在协同进化关系。另外,本研究首次发现,野鲮亚科鱼类也可能是指环虫类的早期宿主,这与先前认为鲤亚科鱼类为指环虫类的祖先宿主的推测有所不同。

Dactylogyrus Diesing, 1 850 is the most diversified group within the Monogenoidea mainly restricted to freshwater fish of the Cyprinidae. In this study, the C1-D2 domains of 28S rDNA sequences were used to infer the phylogenetic relationships among 17 Dactylogyrus species from Lateolabrax japonicus, Gymnocephalus cernuus and species of six subfamilies of the Cyprinidae. Meanwhile, the recombination activating gene 2 （RAG2） sequences were used to infer the phylogenetic relationships among nine infested cyprinid hosts. Phylogenies of host and parasite were compared to examine host-parasite coevolution. Five Dactylogyrus clades were recognized from all phylogenetic trees. Parasites from Megalobrama amblycephala, M. terminalis （Cuhrinae）, Hypophthalmichthys molitrix and Aristichthys nobilis （Hypophthalmichthyinae） were clustered together, and fish of the Cuhrinae and Hypophthalmichthyinae were identified as a sister group in the phylogenetic tree. Dactylogyrus quanfami, which was from Cirrhinus moliorella （Labeoninae）, was placed at the most basal of the tree, and parasites from Cyprinus carpio and Carassius auratus （Cyprininae） were at the next basal portion of the tree. Correspondingly, the position of the Labeoninae and Cyprininae was also put at the most basal part of their phylogenetic tree. The ancestral statuses of both parasite and host were proved by each other. Cyprinids may represent more suitable models for studying host-parasite coevolutionary patterns, considering that evolution of freshwater fish is more constrained than that of marine fish （i. e., it is correlated to the history of freshwater movements and dispersals. ）. Furthermore, the present study indicated that the Labeoninae could also be the ancestral hosts of Dactylogyrus, which was incongruent with the previous hypothesis that Asiatic Cyprininae could be the ancestral hosts .