Cross-species infection trials reveal cryptic parasite varieties and a putative polymorphism shared among host species.

A parasite's host range can have important consequences for ecological and evolutionary processes but can be difficult to infer. Successful infection depends on the outcome of multiple steps and only some steps of the infection process may be critical in determining a parasites host range. To test this hypothesis, we investigated the host range of the bacterium Pasteuria ramosa, a Daphnia parasite, and determined the parasites success in different stages of the infection process. Multiple genotypes of Daphnia pulex, Daphnia longispina and Daphnia magna were tested with four Pasteuria genotypes using infection trials and an assay that determines the ability of the parasite to attach to the hosts esophagus. We find that attachment is not specific to host species but is specific to host genotype. This may suggest that alleles on the locus controlling attachment are shared among different host species that diverged 100 million year. However, in our trials, Pasteuria was never able to reprod...

寄生虫的宿主范围（host range）对生态与进化过程具有重要影响，但其宿主范围往往难以准确推断。成功的感染取决于多个步骤的协同结果，而感染过程中仅部分环节是决定寄生虫宿主范围的关键因素。为验证这一假说（hypothesis），我们针对溞属（Daphnia）的寄生细菌，即巴斯德芽孢杆菌（Pasteuria ramosa）的宿主范围展开研究，并明确了该寄生虫在感染过程不同阶段的侵染成功率。我们采用感染试验与一种可检测寄生虫吸附宿主食道能力的检测方法，利用4株巴斯德芽孢杆菌基因型（genotype），对蚤状溞（Daphnia pulex）、长肢溞（Daphnia longispina）和大型溞（Daphnia magna）的多种基因型开展了测试。研究结果显示，寄生虫的吸附作用并不具有宿主物种特异性，而是仅对宿主基因型具有特异性。这或许表明，控制吸附作用的基因座（locus）上的等位基因（allele），在分化时间达1亿年的不同宿主物种间存在共享。然而在本试验中，巴斯德芽孢杆菌始终未能完成繁殖（原文结尾截断为"reprod..."）。