Data from: Rapid spread of a Wolbachia infection that does not affect host reproduction in Drosophila simulans cage populations

Wolbachia endosymbionts that are maternally inherited can spread rapidly in host populations through inducing sterility in uninfected females, but some Wolbachia infections do not influence host reproduction yet still persist. These infections are particularly interesting because they likely represent mutualistic endosymbionts, spreading by increasing host fitness. Here we document such a spread in the wAu infection of Drosophila simulans. By establishing multiple replicate cage populations, we show that wAu consistently increased from an intermediate frequency to near fixation, representing an estimated fitness advantage of around 20% for infected females. The effective population size in the cages was estimated from SNP markers to be around a few thousand individuals, precluding large effects of genetic drift in the populations. The exact reasons for the fitness advantage are unclear but viral protection and nutritional benefits are two possibilities.

母系遗传的沃尔巴克氏体（Wolbachia）内共生体，可通过诱导未感染雌性不育的方式在宿主种群中快速扩散；但部分沃尔巴克氏体感染并不会影响宿主生殖过程，却仍能稳定存续。这类感染尤为引人关注，因为它们大概率属于互利共生内共生体，通过提升宿主适合度实现种群传播。本研究针对拟果蝇（Drosophila simulans）中的wAu感染株，记录了这类符合互利共生特征的传播过程。通过构建多组重复笼养种群实验，我们证实wAu的感染频率始终从中等水平逐步攀升至近乎固定，据此估算感染雌性的适合度提升约20%。本研究通过单核苷酸多态性（Single Nucleotide Polymorphism, SNP）标记，估算得到笼养种群的有效种群规模约为数千个个体，由此排除了遗传漂变对种群产生显著影响的可能性。该适合度优势的确切机制尚不明确，但病毒防护与营养增益是两种较为合理的潜在解释方向。