Endosymbionts interacting with sex-determining genes and processes

Insects are rich in reproductive diversity and in maternally inherited symbionts. Maternal inheritance has selected for a suite of microbial mechanisms that enhance host fitness and skew sex ratios in favor of females. Recently, there has been significant progress in characterizing the genetic and cellular mechanisms that these maternally transmitted symbionts use to manipulate insect sex. Significant advances include the identification of specific microbial effector proteins that lead to male-killing, parthenogenesis, and feminization in a range of model and nonmodel insects. Many of these effectors target similar host processes, such as dosage compensation and the sex determination cascade that leads to sex-specific splicing of genes, including transformer and doublesex. The independent origins of these endosymbionts and their induced phenotypes facilitate an enhanced understanding of convergent evolution and offer opportunities to investigate the mechanisms driving insect reproductive diversity.