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）可通过多种方式调控宿主繁殖，以提升自身演化适合度。其中一类机制为杀雄作用（male-killing）：受感染母本所产生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，用于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至雌性子代、避免受感染母本发生近交，以及若传播并非完全依赖母系途径，则可促进内共生体向未感染个体进行水平传播。我们在隐棒果蝇（Drosophila innubila）——一种可被杀雄型沃尔巴克氏体（Wolbachia）感染的食真菌物种——中对上述假说开展了验证。野外种群中未检测到水平传播的迹象，也未发现沃尔巴克氏体可降低近交水平的证据。资源重新分配效应确实存在：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，但体型增大所带来的选择优势，不足以解释其自然种群中的感染频率。野外采集的受感染雌性个体（而非实验室饲养种群）的繁殖力高于未感染个体。实验研究显示，沃尔巴克氏体可提升营养匮乏果蝇的繁殖力，并减轻RNA病毒感染带来的负面影响。综上，这种杀雄型内共生体除了可能通过杀雄作用介导相关益处外，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收益。