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.

寄生虫的宿主范围对生态与演化过程具有重要影响，但其推断难度颇高。成功的感染依赖于多步骤进程的结果，而感染过程中仅部分环节是决定寄生虫宿主范围的关键。为验证该假说，我们以水蚤（Daphnia）寄生虫——腊氏芽孢杆菌（Pasteuria ramosa）为研究对象，探究其宿主范围，并明确了该寄生虫在感染过程不同阶段的侵染成功率。我们采用感染实验与测定寄生虫吸附宿主食道能力的检测方法，针对4株腊氏芽孢杆菌基因型，分别测试了蚤状溞（Daphnia pulex）、长刺溞（Daphnia longispina）与大型溞（Daphnia magna）的多个基因型样本。研究发现，寄生虫的吸附过程并不具有宿主物种特异性，却具有宿主基因型特异性。这或表明，调控吸附过程的基因座上的等位基因，在距今1亿年分化的不同宿主物种间存在共享。但在本实验中，腊氏芽孢杆菌始终无法在非本土宿主物种体内繁殖，这提示侵染不同宿主物种的腊氏芽孢杆菌属于不同变种，每个变种仅具有狭窄的宿主范围。本研究方法凸显了拆解感染过程各环节的解释力，并解决了此前关于寄生虫宿主范围的潜在矛盾研究结论。