Data from: Phenotypic shift in Wolbachia virulence towards its native host across serial horizontal passages

Vertical transmission mode is predicted to decrease the virulence of symbionts. However, Wolbachia, a widespread vertically transmitted endosymbiont, exhibits both negative and beneficial effects on arthropod fitness. This ‘Jekyll and Hyde’ behaviour, as well as its ability to live transiently outside host cells and to establish new infections via horizontal transmission, may reflect the capacity of Wolbachia to exhibit various phenotypes depending on the prevailing environmental constraints. To study the ability of Wolbachia to readily cope with new constraints, we forced this endosymbiont to spread only via horizontal transmission. To achieve this, we performed serial horizontal transfers of haemolymph from Wolbachia-infected to naive individuals of the isopod Armadillidium vulgare. Across passages, we observed phenotypic changes in the symbiotic relationship: (i) The Wolbachia titre increased in both haemolymph and nerve cord but remained stable in ovaries; (ii) Wolbachia infection was benign at the beginning of the experiment, but highly virulent, killing most hosts after only a few passages. Such a phenotypic shift after recurrent horizontal passages demonstrates that Wolbachia can rapidly change its virulence when facing new environmental constraints. We thoroughly discuss the potential mechanism(s) underlying this phenotypic change, which are likely to be crucial for the ongoing radiation of Wolbachia in arthropods.

据预测，垂直传播模式会降低共生体的毒力。然而，广泛分布的垂直传播内共生体沃尔巴克氏体（Wolbachia），对节肢动物适合度兼具负面与有益影响。这种“杰基尔与海德式”的双重行为，加之其可在宿主细胞外短暂存活、并通过水平传播建立新感染的能力，或许反映出沃尔巴克氏体可根据当前环境约束条件，呈现多种表型的能力。为探究沃尔巴克氏体应对新约束条件的能力，我们强制该内共生体仅通过水平传播进行扩散。为此，我们将沃尔巴克氏体感染个体的血淋巴连续进行水平传代，接种至未感染该共生体的潮虫（Armadillidium vulgare）个体体内。传代过程中，我们观察到共生关系出现表型变化：(i) 沃尔巴克氏体在血淋巴与神经索中的滴度均有所上升，但在卵巢中保持稳定；(ii) 实验初期沃尔巴克氏体感染呈良性状态，但仅经过数轮传代后便呈现强致病性，致使多数宿主死亡。这种经反复水平传代后出现的表型转变，证明沃尔巴克氏体在面临新环境约束时，可快速改变其毒力。我们深入探讨了驱动该表型变化的潜在机制，这类机制或许对沃尔巴克氏体在节肢动物中的持续辐射演化至关重要。