Morgan Jess A T, DeJong Randall J, Jung Younghun, Khallaayoune Khalid, Kock Sonja, Mkoji Gerald M, Loker Eric S
Department of Biology, University of New Mexico, Albuquerque 87131, USA.
Mol Phylogenet Evol. 2002 Dec;25(3):477-88. doi: 10.1016/s1055-7903(02)00280-4.
The Planorbidae represent one of the most important families of freshwater snails. They have a wide distribution and are significant both medically and economically as intermediate hosts for trematode worms. Digenetic trematodes of the genus Schistosoma cause schistosomiasis, a disease that infects 200 million people, and domestic animals throughout the tropics. Three of the four recognized species groups of Schistosoma rely on snails of the family Planorbidae to complete their life cycles. Each species group requires a specific planorbid genus-Bulinus, Biomphalaria, or Indoplanorbis. Our understanding of the relationships among the genera within the Planorbidae is rudimentary and based solely on internal anatomy and shell morphology. Two molecular markers, ribosomal 28S and actin exon 2, were sequenced and a phylogeny constructed for 38 taxa representing 16 planorbid genera. The phylogeny supports the division of the Planorbidae into two subfamilies, the Bulininae and Planorbinae. Interestingly, two representatives of the family Ancylidae fall within the Planorbidae highlighting the need for further analysis and possible reclassification of this group. A molecular based phylogeny of the genus Schistosoma was then mapped against the snail tree. The trees indicate that planorbid-transmitted Schistosoma appear not to be co-speciating with their current snail host lineages. Rather, host switching was prominent, including a switch involving two distantly related planorbid genera, Biomphalaria and Bulinus. Our study of the Planorbidae poses fundamental questions regarding how and when Schistosoma acquired new snail hosts, including how switches to relatively distant hosts are accomplished and why some available planorbids were not colonized.
扁卷螺科是淡水螺类中最重要的科之一。它们分布广泛，作为吸虫的中间宿主，在医学和经济方面都具有重要意义。血吸虫属的复殖吸虫会引发血吸虫病，这种疾病在热带地区感染了2亿人以及家畜。已确认的血吸虫四个物种组中的三个依赖扁卷螺科的螺类来完成其生命周期。每个物种组都需要特定的扁卷螺属——泡螺属、双脐螺属或印度扁卷螺属。我们对扁卷螺科各属之间关系的了解还很初步，仅基于内部解剖结构和壳的形态。对核糖体28S和肌动蛋白外显子2这两个分子标记进行了测序，并为代表16个扁卷螺属的38个分类单元构建了系统发育树。该系统发育树支持将扁卷螺科分为两个亚科，即泡螺亚科和扁卷螺亚科。有趣的是，椎实螺科的两个代表物种归入了扁卷螺科，这凸显了对该类群进行进一步分析和可能重新分类的必要性。然后，将基于分子的血吸虫属系统发育树映射到螺类树上。这些树表明，由扁卷螺传播的血吸虫似乎并未与其当前的螺类宿主谱系共同进化。相反，宿主转换很突出，包括涉及两个亲缘关系较远的扁卷螺属——双脐螺属和泡螺属的一次转换。我们对扁卷螺科的研究提出了关于血吸虫如何以及何时获得新的螺类宿主的基本问题，包括如何实现向相对较远宿主的转换以及为什么一些可用的扁卷螺未被定殖。
