Duron O, Fort P, Weill M
Department of Biology, University College London, London, UK.
Heredity (Edinb). 2007 Jun;98(6):368-74. doi: 10.1038/sj.hdy.6800948. Epub 2007 Mar 7.
Wolbachia are maternally inherited endocellular bacteria, widespread in invertebrates and capable of altering several aspects of host reproduction. Cytoplasmic incompatibility (CI) is commonly found in arthropods and induces hatching failure of eggs from crosses between Wolbachia-infected males and uninfected females (or females infected by incompatible strains). Several factors such as bacterial and host genotypes or bacterial density contribute to CI strength and it has been proposed, mostly from Drosophila data, that older males have a lower Wolbachia load in testes which, thus, induces a lighter CI. Here, we challenge this hypothesis using different incompatible Culex pipiens mosquito strains and show that CI persists at the same intensity throughout the mosquito life span. Embryos from incompatible crosses showed even distributions of abortive phenotypes over time, suggesting that host ageing does not reduce the sperm-modification induced by Wolbachia. CI remained constant when sperm was placed in the spermathecae of incompatible females, indicating that sperm modification is also stable over time. The capacity of infected females to rescue CI was independent of age. Last, the density of Wolbachia in whole testes was highly strain-dependent and increased dramatically with age. Taken together, these data stress the peculiarity of the C.pipiens/Wolbachia interaction and suggest that the bacterial dosage model should be rejected in the case of this association.
沃尔巴克氏体是通过母体遗传的细胞内细菌，广泛存在于无脊椎动物中，能够改变宿主繁殖的多个方面。细胞质不相容性（CI）在节肢动物中普遍存在，会导致感染沃尔巴克氏体的雄性与未感染的雌性（或感染不相容菌株的雌性）杂交产生的卵孵化失败。细菌和宿主基因型或细菌密度等多种因素会影响CI的强度，并且大多从果蝇数据推测，年龄较大的雄性睾丸中的沃尔巴克氏体载量较低，因此诱导的CI较轻。在此，我们使用不同的不相容致倦库蚊品系对这一假设提出质疑，并表明在蚊子的整个生命周期中，CI以相同强度持续存在。不相容杂交产生的胚胎随着时间推移呈现出流产表型的均匀分布，这表明宿主衰老并不会降低沃尔巴克氏体诱导的精子修饰作用。当将精子置于不相容雌性的受精囊中时，CI保持不变，这表明精子修饰作用也随时间保持稳定。受感染雌性挽救CI的能力与年龄无关。最后，整个睾丸中沃尔巴克氏体的密度高度依赖于品系，并且会随着年龄急剧增加。综上所述，这些数据强调了致倦库蚊/沃尔巴克氏体相互作用的特殊性，并表明在这种关联中应摒弃细菌剂量模型。
