从18S rRNA基因序列探讨盾腹吸虫的系统发育关系

PHYLOGENETIC SYSTEMATIC INFERENCE IN THE ASPIDOGASTREA(PLATYHELMINTHES,TREMATODE) BASED ON THE 18S rRNA SEQUENCE

盾腹亚纲吸虫被认为是寄生扁形动物中古老的类群,包括盾腹科、多萼科、裂杯科和皱腹科,科间系统发育关系尚存争议。本研究收集GenBank数据库中所有的盾腹吸虫18S rRNA基因序列,测定了三种盾腹吸虫的相应序列,分别采用最大简约法和最大似然法构建分子系统发育树。结果显示,多萼科的分类地位不成立,多萼属应还原到盾腹科;盾腹科的盾腹亚科和杯盾亚科均非单系,吸槽列数可能是平行进化特征,不能反映盾腹科各亚科间的系统发育关系。建议将具有边缘器的吸槽型腹吸盘,以及不具边缘器的吸杯型和皱褶型腹吸盘分别鉴定为盾腹科、裂杯科和皱腹科种类的共裔性状。

The subclass Aspidogastrea（Platyhelminthes,Trematoda） is an archaic and minor group among parasitic platyhelminths,and comprises 4 families,of which the Aspidogastridae Poche,1907 is divided into three subfamilies,and other three families,i.e.Stichocotylidae Faust ＆ Tang,1936,Rugogastridae Schell,1973,and Multicalycidae Giboson ＆ Chinabut,1984 only contains a single genus each.However,there are still arguments on the phylogenetic relationships among these four families.In the present study,the 18S rRNA sequences of three aspidogastrean species,i.e.Aspidogaster conchicola,Aspidogaster ijimai and Multicalyx elegans were determined,and all published 18S rRNA gene data for aspidogastreans in the GenBank database were downloaded,in order to examine the phylogenetic relationships within the Aspidogastrea.According to the molecular data,nucleotide variations of 18S rRNA sequences across all eight species of aspidogastreans ranged from 1.1% to 9.1%,among 6 species of the Aspidogastridae from 1.1% to 7.7%,between Rugogaster hydrolagi of the Rugogastridae and six aspidogastrid species from 8.2% to 9.1%,whereas between Multicalyx elegans of the Multicalycidae and six aspidogastrid species only from 2.7% to 6.8%.Phylogenetic analyses of the 18S rRNA with the digenean species Paragonimus westermani as outgroup by the maximum parsimony（MP） and the maximum likelihood（ML） methods produced two identical topological trees.R.hydrolagi of the Rugogastridae locating at the base of phylogenetic trees,appears to be the sister group of all other aspidogastrean species,which form two main clades,the first comprising the Aspigogaster and the Lobatostoma of the Aspidogastrinae,and M.elegans,the second the Multicotyle of the Aspidogastrinae,and the Cotylaspis and the Cotylogaster of the Cotylaspidinae.Recognizing Multicalycidae,however,would make the Aspidogastidae paraphyletic.It suggested that the genus Multicalyx should revert to the family Aspidogastridae,and the Multicalycidae be invalid family name;furthermore,the adhesive disc,with marginal organ,consisting of alveoli,the adhesive disc,without marginal organ,consisting of well separated sucker,and of rugae,shoud be identified as the synapomorphy of the Aspidogastridae,the Stichocotylidae,and the Rugogastridae,respectively.In addition,both the Aspidogastrinae and the Cotylaspidinae were shown to be non-monophyletic,implying that the number of longitudinal rows of alveoli is the parallel evolution character,and being unrelevant to subfamilial relationships in the Aspidogastridae.Therefore,the subfamilial classification of the Aspidogastridae needs to be revised by examining more genera and species of aspidogastrids.