Wolbachia are obligately intracellular alphaproteobacteria that infect approximately half of all insect species. Maternal inheritance of these endosymbionts produces selection to enhance female fitness. In addition to mutualistic phenotypes such as nutrient provisioning, Wolbachia produce various reproductive manipulations that favor infected females. Most common is cytoplasmic incompatibility, namely reduced embryo viability when Wolbachia-infected males fertilize Wolbachia-uninfected females. The regular loss of cytoplasmic incompatibility indicates this phenotype is not favored by natural selection among Wolbachia variants within host populations.
Turelli, M., Katznelson, A., & Ginsberg, P. S. (2022). Why Wolbachia-induced cytoplasmic incompatibility is so common. Proceedings of the National Academy of Sciences, 119(47), e2211637119.