Data from: 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 reproduce in nonnative host species, suggesting that Pasteuria infecting different host species are different varieties, each with a narrow host range. Our approach highlights the explanatory power of dissecting the steps of the infection process and resolves potentially conflicting reports on parasite host ranges.

寄生虫的宿主范围可对生态与进化过程产生重要影响，但其宿主范围的推断往往颇具难度。成功的寄生感染取决于多阶段的过程走向，且感染过程中仅部分步骤可能是决定寄生虫宿主范围的关键因素。为验证这一假说，我们针对水蚤（Daphnia）寄生菌——噬夏孢芽孢杆菌（Pasteuria ramosa）的宿主范围展开研究，并明确该寄生虫在感染过程不同阶段的侵染成功率。我们采用感染实验与一种可检测寄生虫附着宿主食管能力的检测方法，利用4株噬夏孢芽孢杆菌基因型，对蚤状溞（Daphnia pulex）、长刺溞（Daphnia longispina）与大型溞（Daphnia magna）的多个基因型开展了测试。研究结果显示，寄生虫的宿主附着并不具有宿主物种特异性，但却表现出显著的宿主基因型特异性。这一发现或提示，控制附着过程的基因位点等位基因在分化于1亿年前的不同宿主物种间存在共享。然而在本实验中，噬夏孢芽孢杆菌从未在非本土宿主物种体内完成繁殖，这表明侵染不同宿主物种的噬夏孢芽孢杆菌属于不同变种，各自仅拥有狭窄的宿主范围。本研究方法凸显了拆解感染过程各步骤的研究价值与解释效力，并解决了此前关于寄生虫宿主范围的潜在矛盾报道。