Sorensen R E, Curtis J, Minchella D J
Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907-1392, USA.
J Parasitol. 1998 Oct;84(5):992-7.
The recent finding of the 37-collar-spined Echinostoma revolutum in North America prompted rDNA nucleotide sequence comparisons between this worm and the sympatric Echinostoma trivolvis. Three isolates of E. revolutum from distinct sites and 2 isolates of E. trivolvis collected from a single site were used in this analysis. Sequence data were compared to those from previously sequenced members of the 37-collar-spine group. The 3 North American isolates of E. revolutum were found to be identical, but they differed from Eurasian isolates of E. revolutum at 9 of the 1,006 sites sequenced. Further, 1 of the E. trivolvis isolates studied herein was identical to the published sequence for this species, but 6 nucleotide changes were observed in the second E. trivolvis isolate. Restriction fragment length polymorphisms at this locus support the nucleotide differences found between the E. trivolvis isolates. The degree of intraspecific variation detected raises questions regarding the utility of the internal-transcribed spacer regions of the ribosomal DNA repeat for taxonomic diagnosis and in phylogenetic studies for poorly differentiated groups, such as the 37-collar-spined congeners.
近期在北美发现了具37个颈棘的卷棘口吸虫，这促使人们对该吸虫与同域分布的三歧棘口吸虫进行核糖体DNA核苷酸序列比较。本分析使用了来自不同地点的3株卷棘口吸虫分离株以及从单个地点采集的2株三歧棘口吸虫分离株。将序列数据与37个颈棘组先前测序的成员的数据进行了比较。结果发现，北美地区的3株卷棘口吸虫分离株完全相同，但在1006个测序位点中的9个位点上，它们与欧亚地区的卷棘口吸虫分离株存在差异。此外，本文研究的1株三歧棘口吸虫分离株与该物种已发表的序列相同，但在另一株三歧棘口吸虫分离株中观察到了6个核苷酸变化。该位点的限制性片段长度多态性支持了在三歧棘口吸虫分离株之间发现的核苷酸差异。所检测到的种内变异程度引发了关于核糖体DNA重复序列的内转录间隔区在分类诊断以及在分化程度较低的类群（如具37个颈棘的同属吸虫）的系统发育研究中的效用的问题。
