Limited female dispersal predicts the incidence of Wolbachia across ants (Hymenoptera: Formicidae)

The endosymbiotic bacterium Wolbachia is perhaps the greatest panzootic in the history of life on Earth, yet remarkably little is known regarding the factors that determine its incidence across species. One possibility is that Wolbachia more easily invades species with structured populations, due to the increased strength of genetic drift and higher initial frequency of infection. This should enable strains that induce mating incompatibilities to more easily cross the threshold prevalence above which they spread to either fixation or a stable equilibrium infection prevalence. Here, we provide empirical support for this hypothesis by analysing the relationship between female dispersal (as a proxy for population structure) and the incidence of Wolbachia across 250 species of ants. We show that species in which the dispersal of reproductive females is limited are significantly more likely to be infected with Wolbachia than species whose reproductive ecology is consistent with significant dispersal of females, and that this relationship remains after controlling for host phylogeny. We suggest that structured host populations, in this case resulting from limited dispersal, may be an important factor in determining how easily Wolbachia becomes successfully established in a novel host, and thus its occurrence across a wide diversity of invertebrate hosts.

内共生细菌沃尔巴克氏体（Wolbachia）或许是地球生命史上宿主范围最广的跨物种共生体，然而目前人们对决定其在不同物种中感染发生率的因素却知之甚少。一种可能性是，由于遗传漂变强度更高、初始感染频率也更高，沃尔巴克氏体更易入侵具有结构化种群的物种，这一效应应能使诱导交配不相容性的菌株更易突破临界感染率阈值，进而传播至固定感染状态或达到稳定的平衡感染率。本文通过分析250种蚂蚁的雌性扩散能力（作为种群结构的替代指标）与沃尔巴克氏体感染率之间的关联，为该假说提供了实证支持。研究表明，繁殖雌性扩散受限的物种，其感染沃尔巴克氏体的概率显著高于繁殖生态符合雌性广泛扩散特征的物种，且在控制宿主系统发育关系后，该关联依然成立。我们据此提出，由有限扩散所形成的结构化宿主种群，或许是决定沃尔巴克氏体能否成功在新宿主中定殖的关键因素之一，进而影响其在多种无脊椎动物宿主中的分布格局。