A novel clade of alphaproteobacterial endosymbionts induces complete cytoplasmic incompatibility in the coconut beetle

Maternally inherited bacterial endosymbionts in arthropods manipulate host reproduction to increase the fitness of infected females. Cytoplasmic incompatibility (CI) is one such manipulation in which uninfected females produce few or no offspring when they mate with infected males. Only Wolbachia induces complete CI, which causes 100% offspring mortality in incompatible crosses. Here we report on a third CI inducer that belongs to a novel clade of Alphaproteobacteria detected within the coconut beetle, Brontispa longissima. This beetle comprises two cryptic species, the Asian and Pacific clades, which show incompatibility in hybrid crosses. Different bacterial endosymbionts, a novel clade of Alphaproteobacteria in the Pacific clade and Wolbachia in the Asian clade, induced bidirectional CI between them. The former induced complete CI and the latter induced partial CI. We performed Illumina MiSeq sequencing to confirm the responsibility of the novel Alphaproteobacteria for the complete CI and the diversity of Wolbachia.