Quality over quantity: unraveling the contributions to cytoplasmic incompatibility caused by two coinfecting Cardinium symbionts

Cardinium hertigii is a common maternally-inherited bacterial endosymbiont of arthropods. Some Cardinium strains spread by increasing female fitness through the induction of cytoplasmic incompatibility (CI), which kills offspring of crosses between infected males and uninfected female hosts. CI is a two-step manipulation: first, sperm from male hosts are modified by the symbiont in a manner that causes offspring death. Second, when females are also infected, the symbiont reverses sperm modification in the egg cytoplasm, allowing offspring of infected females to survive and spread the symbiont. While Cardinium causes CI in many arthropod hosts, most of what is known about Cardinium CI stems from the symbiosis between the Cardinium strain cEper1 and its minute parasitoid host, Encarsia suzannae. Here, we study a second Cardinium CI system in the wasp Encarsia partenopea. Encarsia partenopea harbors two Cardinium strains, cEina2 and cEina3, with the cEina3 present at a much lower density t...