Data from: “Darwin’s corollary” and cytoplasmic incompatibility induced by Cardinium may contribute to speciation in Encarsia wasps (Hymenoptera: Aphelinidae)

The potential importance of cytoplasmic incompatibility (CI) – inducing bacterial symbionts in speciation of their arthropod hosts has been debated. Theoretical advances have led to a consensus that a role is plausible when CI is combined with other isolating barriers. However, the insect model systems Nasonia and Drosophila are the only two experimental examples documented. Here we analyzed the components of reproductive isolation between the parasitoid wasp Encarsia suzannae, which is infected by the CI-inducing symbiont Cardinium, and its uninfected sibling species Encarsia gennaro. Laboratory crosses demonstrated that: 1) sexual isolation is incomplete; 2) hybrid offspring production is greatly reduced in the interspecific CI cross; 3) viable hybrids may be produced by curing E. suzannae males of Cardinium with antibiotics; 4) hybrid offspring production in the reciprocal cross is greatly reduced by hybrid inviability due to genetic incompatibilities; 5) hybrid sterility is nearly complete in both directions at the F1 stage. Thus, asymmetrical hybrid incompatibilities and CI act as complementary isolating mechanisms. We propose a new model for contributions of CI symbionts to speciation, with CI reducing gene flow between species in one direction, and in the other, a symbiont sweep resulting in accelerated mtDNA evolution, negative cytonuclear interactions and hybrid incompatibilities.

诱导细胞质不相容（cytoplasmic incompatibility, CI）的细菌共生菌在其节肢动物宿主的物种形成过程中所具备的潜在重要性，长期以来存在学术争议。理论研究的进展已形成共识：当CI与其他生殖隔离屏障结合时，其作用具备合理性。然而目前仅在昆虫模式系统金小蜂属（Nasonia）与果蝇属（Drosophila）中记录到相关实验例证。本研究针对被诱导CI的共生菌卡氏体菌（Cardinium）感染的寄生蜂苏珊恩蚜小蜂（Encarsia suzannae），及其未感染的近缘姐妹种詹纳罗恩蚜小蜂（Encarsia gennaro）的生殖隔离组分开展了系统分析。实验室杂交实验证实如下结论：1）性隔离并不完全；2）种间CI杂交中的杂交后代产出量大幅降低；3）通过抗生素清除苏珊恩蚜小蜂雄蜂体内的卡氏体菌后，可获得可育杂交后代；4）反交组合中，遗传不相容引发的杂种致死会大幅降低杂交后代的产出量；5）两个杂交方向的F1代杂种均几乎完全不育。综上，不对称的杂种不相容性与CI共同构成了互补型生殖隔离机制。本研究提出了一套全新模型，用以阐释CI共生菌对物种形成的贡献：CI可在一个方向上降低物种间的基因流；而在另一方向上，共生菌的选择性清扫可加速线粒体DNA的进化进程，引发负向核质互作与杂种不相容性。