Bidirectional cytoplasmic incompatibility caused by Wolbachia in the terrestrial isopod Porcellio dilatatus

• We characterized a new CI Wolbachia strain infecting Porcellio dilatatus dilatatus.
• We showed that P. dilatatus can be infected by 2 different bidirectional CI strains.
• CI level is not dependent on the bacterial load but on each strain properties.
• These CI-Wolbachia strains may participate to the divergence of their host.

In the terrestrial isopod species Porcellio dilatatus, unidirectional Cytoplasmic Incompatibility (CI) between two morphs (P. d. dilatatus and P. d. petiti) caused by a Wolbachia strain (wPet) infecting the morph P. d. petiti has been previously described by experiments initiated four decades ago. Here, we studied another Wolbachia that has been recently detected in a population of the morph P. d. dilatatus. The MLST markers reveal that this Wolbachia is a new strain called wDil distinct from wPet also belonging to the isopod clade of Wolbachia. Quantifications of both Wolbachia strains in the gonads of the two P. dilatatus morphs revealed that all males exhibit similar Wolbachia titers while the titers in females depend on the Wolbachia strain they host. Crossing experiments showed that both wDil and wPet induced partial unidirectional CI with different intensities. Moreover, these two strains induced bidirectional CI when individuals were both infected with one of the two different Wolbachia strains. This way, we demonstrated that P. dilatatus can be infected by two closely related Wolbachia strains (wDil and wPet), that seem to have different modification-rescue systems.

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