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.诸多母系遗传内共生体（maternally inherited endosymbionts）可通过多种方式操控宿主生殖策略以提升自身适合度，其中一类典型机制为杀雄作用（male-killing）：受感染母本所产的雄性子代在发育阶段会被内共生体杀灭。目前已有多项假说被提出用以阐释杀雄作用的演化优势，包括将受感染雌性的资源从雄性子代重新分配至雌性子代、帮助受感染雌性规避近交，以及若传播并非严格依赖母系途径则可促进向未感染雌性的水平传播。本研究以受杀雄型沃尔巴克氏体（Wolbachia）感染的食真菌物种印颖果蝇（Drosophila innubila）为实验对象，对上述假说进行了检验。结果显示，野外种群中未检测到水平传播的证据，也未观察到沃尔巴克氏体可降低近交水平的现象。资源重新分配效应确实存在：受感染雌性的平均体型略大于未感染雌性，但体型增大所带来的选择优势不足以解释自然种群中感染的发生频率。野外采集的受感染雌性（而非实验室饲养个体）的繁殖力显著高于未感染雌性。实验研究表明，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（RNA virus）感染带来的负面影响。综上，这类杀雄型内共生体除可能通过杀雄作用带来收益外，还可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。