Data from: Maintenance of a male-killing Wolbachia in Drosophila innubila by male-killing dependent and male-killing independent mechanisms

Many maternally inherited endosymbionts manipulate their host’s reproduction in various ways to enhance their own fitness. One such mechanism is male-killing, in which sons of infected mothers are killed by the endosymbiont during development. Several hypotheses have been proposed to explain the advantages of male-killing, including resource reallocation from sons to daughters of infected females, avoidance of inbreeding by infected females, and, if transmission is not purely maternal, the facilitation of horizontal transmission to uninfected females. We tested these hypotheses in Drosophila innubila, a mycophagous species infected with male-killing Wolbachia. There was no evidence of horizontal transmission in the wild and no evidence Wolbachia reduced levels of inbreeding. Resource reallocation does appear to be operative, as Wolbachia-infected females are slightly larger, on average, than uninfected females, although the selective advantage of larger size is insufficient to account for the frequency of infection in natural populations. Wolbachia-infected females from the wild – though not those from the lab – were more fecund than uninfected females. Experimental studies revealed that Wolbachia can boost the fecundity of nutrient-deprived flies and reduce the adverse effect of RNA virus infection. Thus, this male-killing endosymbiont can provide direct, male-killing-independent fitness benefits to infected female hosts in addition to possible benefits mediated via male-killing.

许多母系遗传的内共生体（maternally inherited endosymbionts）会通过多种方式调控宿主的生殖过程，以提升自身的适合度（fitness）。其中一类典型机制为杀雄作用（male-killing）：受感染母本的雄性子代在发育阶段会被该内共生体杀灭。目前已有多项假说被提出，用以阐释杀雄作用的演化优势，包括将资源从受感染母本的雄性子代重新分配给雌性子代、避免受感染母本发生近交（inbreeding），以及若传播并非严格母系时，促进向未感染母本的水平传播（horizontal transmission）。我们以林下果蝇（Drosophila innubila）——一种受杀雄型沃尔巴克氏体（Wolbachia）感染的食真菌物种——为实验对象，对上述假说开展了验证。野外种群调查未发现水平传播的相关证据，也未观察到沃尔巴克氏体能够降低近交水平的迹象。资源重分配假说似乎具备合理性：受沃尔巴克氏体感染的雌性个体平均体型略大于未感染个体，但体型增大带来的选择优势，尚不足以解释自然种群中感染发生的频率。野外采集的受感染雌性个体（而非实验室饲养的个体），其繁殖力（fecundity）显著高于未感染个体。实验研究结果显示，沃尔巴克氏体可提升营养匮乏果蝇的繁殖力，并减轻RNA病毒感染（RNA virus infection）带来的负面效应。综上，这类杀雄型内共生体除了可能通过杀雄作用介导相关收益外，还能为受感染的雌性宿主提供直接的、不依赖杀雄作用的适合度提升益处。