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进化发挥关键作用。本研究针对北美广泛分布的栎栖瘿蜂*Belonocnema treatae*（文中简称B. treatae）展开沃尔巴克氏体调查，该物种以3种栎属植物为宿主并呈现区域性宿主特化，同时存在有性生殖与无性生殖世代交替的生活史。我们旨在探究B. treatae体内沃尔巴克氏体的感染模式与多样性，是否与其地理分布、宿主植物关联、生活史以及线粒体进化历史相关。
结果：对美国南部地区取自3种宿主植物、涵盖有性与无性世代的23个种群共463个个体进行筛查，结果显示平均感染率为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。基于沃尔巴克氏体表面蛋白基因（wsp）的系统发育分析显示，上述菌株彼此无亲缘关系，大概率为独立获得的共生体。我们未发现不同宿主植物关联种群间、无性与有性世代间，或有性世代的雌雄个体间存在沃尔巴克氏体感染频率差异。部分不完全的沃尔巴克氏体传播率或许可解释未感染个体的出现。对B. treatae的线粒体细胞色素氧化酶I（cytochrome oxidase I, COI）基因进行平行分析发现，感染与未感染种群均呈现较高的线粒体DNA（mtDNA）单倍型多样性，提示沃尔巴克氏体曾发生过祖先感染；同时检测到B. treatae的mtDNA明显分为东西两个支系，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。与之形成对比的是，美国佐治亚州的种群中存在两种菌株共同感染的双重感染现象，佛罗里达州中部的2个种群则出现三重感染。
结论：B. treatae不同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存现象，凸显了该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呈现显著关联，这暗示该内共生体可能在B. treatae的生殖隔离中发挥潜在作用。