Heneberg Petr, Sitko Jiljí, Bizos Jiří, Kocková Lucie, Malá Milena, Literák Ivan
Third Faculty of Medicine, Charles University in Prague, Ruská 87, 100 00, Prague, Czech Republic,
Parasitol Res. 2014 Sep;113(9):3211-20. doi: 10.1007/s00436-014-3982-x. Epub 2014 Jun 25.
Collyriclum faba (Plagiochiida: Collyriclidae) adults occur in pairs within subcutaneous cysts. Here, we tested the extensive C. faba infrapopulation for five DNA loci known to display variability among Central European C. faba individuals. The infrapopulation tested shared 100% similarity in four of the five mitochondrial and nuclear DNA loci tested. Contrariwise, the internal transcribed spacer 1 (ITS1) loci in all but one individual differed from each other. We found only 0.0-1.5 base substitutions per 1,000 sites within the cysts, while we found 0.7-9.0 substitutions between the cysts of the single host and 3.0-9.0 substitutions when comparing C. faba individuals isolated from different host individuals. We observed the most of the ITS1 variability within 48 bp repetitive sequences featured by the chi-like sequence 5'-GCTTGTCTGCC-3' at their beginning. Similarly to the extensive C. faba infrapopulation examined, we determined the presence of highly variable number of repetitive sequences within the ITS1 locus of C. faba isolated from multiple host species and from various geographic locations. While similar variability was observed earlier in mutually unrelated specimens of several Schistosomatidae and Microphallidae species, here, we for the first time document it among multiple individuals of a single infracommunity possessing single mitochondrial haplotype. Lower ITS1 evolutionary divergence rates observed between individuals within the cysts when compared to those between the cysts suggest that the recombination occurs at multiple stages of the life cycle. We propose DNA recombination involving chi-like sequences to serve as a general feature shared by multiple families of digenetic trematodes to increase genetic diversity of their polyembryonic populations infecting their definitive hosts.
豆状嗜眼吸虫（斜孔目：嗜眼吸虫科）成虫成对寄生于皮下囊肿内。在此，我们检测了大量豆状嗜眼吸虫种群中五个已知在中欧豆状嗜眼吸虫个体间存在变异性的DNA位点。所检测的种群在五个线粒体和核DNA位点中的四个位点上具有100%的相似性。相反，除一个个体外，所有个体的内部转录间隔区1（ITS1）位点彼此不同。我们在囊肿内每1000个位点仅发现0.0 - 1.5个碱基替换，而在单个宿主的囊肿之间发现0.7 - 9.0个替换，在比较从不同宿主个体分离出的豆状嗜眼吸虫个体时发现3.0 - 9.0个替换。我们观察到ITS1的大部分变异性存在于48 bp重复序列中，这些序列开头具有类似chi的序列5'-GCTTGTCTGCC-3'。与所检测的大量豆状嗜眼吸虫种群相似，我们确定从多个宿主物种和不同地理位置分离出的豆状嗜眼吸虫ITS1位点内存在高度可变数量的重复序列。虽然之前在几种裂体吸虫科和微茎科彼此不相关的标本中也观察到了类似的变异性，但在此我们首次在具有单个线粒体单倍型的单个群落的多个个体中记录到这种情况。与囊肿之间的个体相比，囊肿内个体间观察到的较低ITS1进化分歧率表明重组发生在生命周期的多个阶段。我们提出涉及类似chi序列的DNA重组是复殖吸虫多个科共有的一个普遍特征，以增加感染其终末宿主的多胚种群的遗传多样性。
