Data from: Diversity and distribution of Wolbachia in relation to geography, host plant affiliation and life cycle of a heterogonic gall wasp

Background: The maternally inherited endosymbiont Wolbachia is widespread in arthropods and nematodes and can play an important role in the ecology and evolution of its host through reproductive manipulation. Here, we survey Wolbachia in Belonocnema treatae, a widely distributed North American cynipid gall forming wasp that exhibits regional host specialization on three species of oaks and alternation of sexually and aseuxlly reproducing generations. We investigated whether patterns of Wolbachia infection and diversity in B. treatae are associated with the insect's geographic distribution, host plant association, life cycle, and mitochondrial evolutionary history.
Results: Screening of 463 individuals from 23 populations including sexual and asexual generations from all three host plants across the southern U.S. showed an average infection rate of 56% with three common Wolbachia strains: wTre1-3 and an additional rare variant wTre4. Phylogenetic analysis based on wsp showed that these strains are unrelated and likely independently inherited. We found no difference in Wolbachia infection frequency among host plant associated populations or between the asexual and sexual generations, or between males and females of the sexual generation. Partially incomplete Wolbachia transmission rates might explain the occurrence of uninfected individuals. A parallel analysis of the mitochondrial cytochrome oxidase I gene in B. treatae showed high mtDNA haplotype diversity in both infected and uninfected populations suggesting an ancestral infection by Wolbachia as well as a clear split between eastern and western B. treatae mtDNA clades with a
sequence divergence of > 6%. The strain wTre1 was present almost exclusively in the western clade while wTre2 and wTre3 occur almost exclusively in eastern populations. In contrast, the same strains co-occur as double-infection in Georgia and triple-infections in two populations in central Florida.
Conclusions: The diversity of Wolbachia across geographically and genetically distinct populations of B. treatae and the co-occurrence of the same strains within three populations highlights the complex infection dynamics in this system. Moreover, the association of distinct Wolbachia strains with mitochondrial haplotypes of its host in populations infected by different Wolbachia strains suggests a potential role of the endosymbiont in reproductive isolation in B. treatae.

背景：母系遗传的内共生体沃尔巴克氏体（Wolbachia）广泛分布于节肢动物与线虫体内，可通过生殖调控对宿主的生态与演化发挥重要作用。本研究针对贝洛诺克尼马瘿蜂（Belonocnema treatae）开展沃尔巴克氏体分布调查：该物种是北美广泛分布的瘿蜂科造瘿蜂，呈现出对3种橡树的区域宿主专化性，且存在有性与无性生殖世代交替的生活史。本研究旨在探究B. treatae体内沃尔巴克氏体的感染模式与多样性，是否与该昆虫的地理分布、宿主植物关联、生活周期及线粒体进化历史存在关联。
结果：对采自美国南部3种宿主植物上的23个种群（涵盖有性与无性世代）的463头个体进行筛查后发现，平均感染率为56%，共检出3种常见沃尔巴克氏体菌株wTre1~3，以及1种罕见变异株wTre4。基于wsp基因的系统发育分析表明，上述菌株间无亲缘关联，大概率为独立起源的遗传元件。本研究未观察到不同宿主植物关联种群间、无性与有性世代间，乃至有性世代雌雄个体间的沃尔巴克氏体感染频率存在显著差异。沃尔巴克氏体传递效率的不完全性，或可解释未感染个体的出现。对B. treatae线粒体细胞色素氧化酶I基因的平行分析结果显示，感染与未感染种群均具有较高的线粒体DNA单倍型多样性，提示沃尔巴克氏体存在祖先感染事件；同时发现B. treatae的线粒体支系存在清晰的东西分化，序列分歧度超过6%。菌株wTre1几乎仅存在于西部支系中，而wTre2与wTre3则几乎仅分布于东部种群。与之相反，佐治亚州的种群存在两种菌株的双重感染，而佛罗里达州中部的2个种群则出现了三重感染。
结论：B. treatae地理与遗传分化种群间的沃尔巴克氏体多样性，以及3个种群内出现的相同菌株共感染现象，凸显了该研究体系中复杂的感染动态。此外，在被不同沃尔巴克氏体菌株感染的种群中，特定沃尔巴克氏体菌株与宿主线粒体单倍型的关联模式，提示该内共生体可能在B. treatae的生殖隔离过程中发挥潜在作用。