Morgan J A, Blair D
Department of Zoology and Tropical Ecology, James Cook University, Townsville, Queensland, Australia.
Parasitology. 1998 Mar;116 ( Pt 3):289-97. doi: 10.1017/s0031182097002217.
Cryptic species, belonging to the 37 collar-spine Echinostoma group, were distinguished using nuclear rDNA ITS (884 bases) and mtDNA CO1 (257 bases) and ND1 (530 bases) sequences. Sequences were obtained from five 37 collar-spine species, Echinostoma trivolvis, E. paraensei, E. caproni, E. revolutum and E. sp.I, a parthenogenetic isolate from Africa. Three geographic isolates of E. caproni were compared. Average sequence divergence among the 37 collar-spine species range from 2.2% in the rDNA ITS through 8% for the CO1 and 14% for the ND1. In addition, genes were sequenced from 2 non 37 collar-spine species, E. hortense and an undescribed Australian species, E. sp. (Aus). For each gene, distances of terminals from a predicted ancestral sequence were calculated. These indicated that ND1 is diverging significantly faster than the other 2 regions. In the CO1 gene most substitutions are synonymous and saturation has been reached for the majority of pairwise comparisons. The ND1 gene exhibits greater pairwise divergence but less evidence of saturation due to weaker conservation of first and second codon positions. The ITS has no amino acid coding constraints and displays no evidence of saturation. Although all 3 regions successfully distinguished the nominal species, ND1 appears to be the most informative region for investigating relationships within the 37 collar-spine group.
利用核核糖体DNA ITS（884个碱基）、线粒体DNA CO1（257个碱基）和ND1（530个碱基）序列，区分了属于37棘口吸虫属颈棘组的隐存种。序列取自5种37棘口吸虫属物种，即三岐棘口吸虫、帕氏棘口吸虫、卡氏棘口吸虫、卷棘口吸虫和棘口吸虫sp.I（一种来自非洲的孤雌生殖分离株）。对卡氏棘口吸虫的3个地理分离株进行了比较。37棘口吸虫属物种之间的平均序列差异在rDNA ITS中为2.2%，在CO1中为8%，在ND1中为14%。此外，还对2种非37棘口吸虫属物种（霍氏棘口吸虫和一种未描述的澳大利亚物种棘口吸虫sp.（Aus））的基因进行了测序。对于每个基因，计算了与预测祖先序列的末端距离。结果表明，ND1的分化速度明显快于其他2个区域。在CO1基因中，大多数替换是同义的，并且大多数成对比较已达到饱和。ND1基因表现出更大的成对差异，但由于第一和第二密码子位置的保守性较弱，饱和证据较少。ITS没有氨基酸编码限制，也没有饱和证据。虽然所有3个区域都成功区分了指名物种，但ND1似乎是研究37棘口吸虫属组内关系最具信息性的区域。
