Wolbachia are obligate intracellular bacteria that are globally distributed in half of all arthropod species. As the most abundant maternally inherited microbe in animals, Wolbachia manipulate host reproduction via reproductive parasitism strategies, including cytoplasmic incompatibility (CI). CI manifests as embryonic death when Wolbachia-modified sperm fertilize uninfected eggs but not maternally infected eggs. Thus, CI can provide a relative fitness advantage to Wolbachia-infected females and drive the infection through a population. In the genetic model Drosophila melanogaster, the Wolbachia strain wMel induces variable CI, making mechanistic studies in D. melanogaster cumbersome. Here, we demonstrate that sons of older paternal D. melanogaster grandmothers induce stronger CI than sons of younger paternal grandmothers, and we term this relationship the "paternal grandmother age effect" (PGAE). Moreover, the embryos and adult sons of older D. melanogaster grandmothers have higher Wolbachia densities, correlating with their ability to induce stronger CI. In addition, we report that Wolbachia density positively correlates with female age and decreases after mating, suggesting that females transmit Wolbachia loads that are proportional to their own titers. These findings reveal a transgenerational impact of age on wMel-induced CI, elucidate Wolbachia density dynamics in D. melanogaster, and provide a methodological advance to studies aimed at understanding wMel-induced CI in the D. melanogaster model.IMPORTANCE Unidirectional cytoplasmic incompatibility (CI) results in a postfertilization incompatibility between Wolbachia-infected males and uninfected females. CI contributes to reproductive isolation between closely related species and is used in worldwide vector control programs to drastically lower arboviral vector population sizes or to replace populations that transmit arboviruses with those resistant to transmission. Despite decades of research on the factors that influence CI, penetrance is often variable under controlled laboratory conditions in various arthropods, suggesting that additional variables influence CI strength. Here, we demonstrate that paternal D. melanogaster grandmother age influences the strength of CI induced by their sons. Older D. melanogaster females have higher Wolbachia densities and produce offspring with higher Wolbachia densities that associate with stronger CI. This work reveals a multigenerational impact of age on CI and expands our understanding of host-Wolbachia interactions and the biology of CI induced by the Wolbachia strain infecting the most widely used arthropod model, D. melanogaster.

中文翻译：

---

父祖母年龄影响果蝇果蝇Wolbachia诱导的细胞质不相容性的强度。

沃尔巴氏菌是专性的细胞内细菌，全球分布在所有节肢动物物种的一半中。作为动物中母体遗传最丰富的微生物，沃尔巴克氏菌通过生殖寄生策略（包括细胞质不相容性（CI））操纵宿主的繁殖。当Wolbachia修饰的精子使未感染的卵受精但未受母体感染的卵受精时，CI表现为胚胎死亡。因此，CI可以为感染Wolbachia的女性提供相对的健身优势，并通过人群推动感染。在遗传模型果蝇（Drosophila melanogaster）中，Wolbachia菌株wMel诱导了可变CI，使得对D. melanogaster的机理研究繁琐。在这里，我们证明，长老的父亲D. melanogaster的祖母的儿子比年轻的老父亲的祖母的儿子具有更高的CI，我们将此关系称为“祖母年龄效应”（PGAE）。此外，黑腹果蝇年龄较大的祖母的胚胎和成年儿子具有较高的沃尔巴克氏菌密度，这与它们诱导较强CI的能力有关。此外，我们报告说，沃尔巴克氏菌密度与雌性年龄呈正相关，并且在交配后降低，这表明雌性传递的沃尔巴克氏菌负荷与自己的滴度成正比。这些发现揭示了年龄对wMel诱导的CI的跨代影响，阐明了D. melanogaster中的Wolbachia密度动态，并为旨在了解wMel诱导的D. melanogaster模型的研究提供了方法论上的进展。重要信息单向细胞质不相容性（CI）导致受Wolbachia感染的雄性和未感染的雌性之间的受精后不相容性。CI有助于在密切相关的物种之间进行生殖隔离，并在全世界的媒介控制计划中用于大幅降低虫媒病毒的种群数量或用对传播具有抵抗力的虫媒替代那些传播虫媒病毒的种群。尽管对影响CI的因素进行了数十年的研究，但外露率在各种节肢动物的受控实验室条件下通常是可变的，这表明其他变量会影响CI的强度。在这里，我们证明了父亲D. melanogaster的祖母年龄会影响其儿子诱导的CI的强度。较旧的D。黑腹黑猩猩的雌性具有更高的沃尔巴克氏菌密度，并产生具有更高的沃尔巴克氏菌密度的后代，从而与较强的CI相关。这项工作揭示了年龄对CI的多代影响，并扩展了我们对宿主-Wolbachia相互作用以及由Wolbachia菌株感染最广泛使用的节肢动物模型D. melanogaster诱导的CI生物学的理解。