Comparative genomics of Cardinium: Ascertaining genes underlying symbiont-induced reproductive manipulations

Some maternally inherited bacteria are able to alter their insect hosts’ reproduction in order to promote their own spread throughout the host population. Cardinium hertigii is such a reproductive manipulator that, like the better-known and distantly related Wolbachia pipientis, is able to induce parthenogenesis, feminize genetic males into functional females, and induce cytoplasmic incompatibility (CI). CI causes a reproductive failure between symbiont-infected males and uninfected females, and so far, has only been shown to be caused by two symbionts: Wolbachia and Cardinium. The symbiont genes responsible for CI are as yet unknown in both lineages, but current cytological and genomic evidence indicates that both symbionts have independently evolved this reproductive manipulation. I have assembled and annotated the genomes of four Cardinium strains that infect parasitic wasps in the genus Encarsia. These, along with a fifth published genome, comprise a powerful comparative framework of closely related strains that induce different reproductive manipulations– two parthenogenesis-inducing strains, two CI strains, and one non-manipulating strain. The candidate genes identified in this analysis may offer insights into the genetic underpinnings of CI in Cardinium. Further, insights into the molecular mechanism of CI Cardinium may inform the search for function in CI Wolbachia and vice versa, yielding a better general understanding of how two unrelated lineages have evolved convergent phenotypes.