Data from: Evidence for a recent horizontal transmission and spatial spread of Wolbachia from endemic Rhagoletis cerasi (Diptera: Tephritidae) to invasive Rhagoletis cingulata in Europe

The widespread occurrence of Wolbachia in arthropods and nematodes suggests that this intracellular, maternally inherited endosymbiont has the ability to cross species boundaries. However, direct evidence for such a horizontal transmission of Wolbachia in nature is scarce. Here, we compare the well-characterized Wolbachia infection of the European cherry fruit fly, Rhagoletis cerasi, with that of the North American eastern cherry fruit fly, Rhagoletis cingulata, recently introduced to Europe. Molecular genetic analysis of Wolbachia based on multilocus sequence typing and the Wolbachia surface protein wsp showed that all R. cingulata individuals are infected with wCin2 identical to wCer2 in R. cerasi. In contrast, wCin1, a strain identical to wCer1 in R. cerasi, was present in several European populations of R. cingulata, but not in any individual from the United States. Surveys of R. cingulata from Germany and Hungary indicated that the frequency of wCin1 infection increased dramatically in just a few years with at least two independent horizontal transmission events in Germany and Hungary. This is further corroborated by the analysis of the mitochondrial cytochrome oxidase II gene that showed linkage of wCin1 with two distinct haplotypes in Germany, one of which is also infected with wCin1 in Hungary. In summary, our study provides strong evidence for a very recent interspecific Wolbachia transmission with a subsequent spatial spread in field populations.

沃尔巴克氏体（Wolbachia）在节肢动物与线虫中的广泛分布表明，这种胞内、母系遗传的内共生体具备跨物种界限的能力。然而，自然界中沃尔巴克氏体发生此类水平传播的直接证据却十分匮乏。本研究将已得到充分表征的欧洲樱桃实蝇（Rhagoletis cerasi）沃尔巴克氏体感染情况，与近期传入欧洲的北美东部樱桃实蝇（Rhagoletis cingulata）的感染情况进行了对比。基于多位点序列分型（multilocus sequence typing）以及沃尔巴克氏体表面蛋白（Wolbachia surface protein, wsp）对沃尔巴克氏体开展的分子遗传学分析显示，所有R. cingulata个体均感染了与R. cerasi中的wCer2完全一致的wCin2。与之形成对比的是，wCin1——一种与R. cerasi中的wCer1完全一致的菌株——存在于R. cingulata的多个欧洲种群中，但未在美国的任何个体内被检出。对德国与匈牙利的R. cingulata种群的调查显示，wCin1的感染频率在短短数年内大幅上升，且在德国与匈牙利至少发生了两起独立的水平传播事件。线粒体细胞色素氧化酶II（cytochrome oxidase II）基因的分析进一步佐证了这一结论：该分析显示wCin1与德国种群中的两种不同单倍型（haplotype）存在连锁关联，其中一种单倍型在匈牙利种群中也同时感染了wCin1。综上，本研究为近期发生的种间沃尔巴克氏体传播及其后续在野外种群中的空间扩散提供了强有力的证据。