Dataset for: Loss of cytoplasmic incompatibility and minimal fecundity effects explain relatively low Wolbachia frequencies in Drosophila mauritiana

Maternally transmitted Wolbachia bacteria infect about half of all insect species. Many Wolbachia cause cytoplasmic incompatibility (CI), reduced egg hatch when uninfected females mate with infected males. Although CI produces a frequency-dependent fitness advantage that leads to high equilibrium Wolbachia frequencies, it does not aid Wolbachia spread from low frequencies. Indeed, the fitness advantages that produce initial Wolbachia spread and maintain non-CI Wolbachia remain elusive. wMau Wolbachia infecting Drosophila mauritiana do not cause CI, despite being very similar to CI-causing wNo from D. simulans (0.068% sequence divergence over 682,494 bp), suggesting recent CI loss. Using draft wMau genomes, we identify a deletion in a CI-associated gene, consistent with theory predicting that selection within host lineages does not act to increase or maintain CI. In the laboratory, wMau shows near-perfect maternal transmission; but we find no significant effect on host fecundity, in contrast to published data. Intermediate wMau frequencies on the island Mauritius are consistent with a balance between unidentified small, positive fitness effects and imperfect maternal transmission. Our phylogenomic analyses suggest that group-B Wolbachia, including wMau and wPip, diverged from group-A Wolbachia, such as wMel and wRi, 6–46 million years ago, more recently than previously estimated.

母系传播的沃尔巴克氏体（Wolbachia）细菌可感染约半数昆虫物种。多数沃尔巴克氏体可引发细胞质不相容（CI），即未感染雌虫与感染雄虫交配时，卵孵化率会出现下降。尽管CI可带来频率依赖性适合度优势，使沃尔巴克氏体在种群中维持较高的平衡频率，但该机制无法助力沃尔巴克氏体从极低起始频率完成扩散。实际上，驱动沃尔巴克氏体初始扩散、以及维持非CI型沃尔巴克氏体的适合度优势机制，至今仍未阐明。感染毛里求斯果蝇（Drosophila mauritiana）的wMau株系沃尔巴克氏体，虽与引发CI的拟果蝇（D. simulans）wNo株系高度相似（在682494个碱基对的序列区域中仅存在0.068%的序列分歧），却不会引发CI，这提示其近期丢失了CI表型。本研究借助wMau的草图基因组，在一个与CI相关的基因中发现了缺失突变，这与理论预测一致：宿主谱系内的自然选择并不会促进或维持CI表型。实验室实验结果显示，wMau的母系传播效率近乎完美；但与已发表的研究数据不同的是，本研究未发现其对宿主繁殖力存在显著影响。毛里求斯岛上检测到的wMau中等频率种群，与未被发现的微弱正向适合度效应以及不完全母系传播之间的动态平衡相符。我们的系统基因组学分析表明，包括wMau与wPip在内的B组沃尔巴克氏体，与wMel、wRi等A组沃尔巴克氏体的分化时间约为600万至4600万年前，这比此前的估算结果更为新近。