... and discovered on Mount Kilimanjaro

The endocytoplasmic bacterium Wolbachia causes the death of arthropod embryos, when present in reproductive organs, by cytoplasmic incompatibility1. Wolbachia is harboured in both sexes but transmission is maternal only. Cytoplasmic incompatibility occurs when infected males inseminate uninfected females2 or females bearing a different variant of Wolbachia3,4. Two kinds of Wolbachia have been described1: (mod+resc+) which induces cytoplasmic incompatibility by modifying sperm but can rescue this phenotype when in the egg, and (mod−resc−) which neither induces cytoplasmic incompatibility nor rescues from it. Theory predicts a third kind (mod−resc+) that would not induce cytoplasmic incompatibility but would rescue from it5,6,7. We have found such a Wolbachia variant in a Drosophila simulans population on Mt Kilimanjaro, Tanzania. The existence of a mod−resc+Wolbachia shows that the modification and rescue functions can be dissociated with regard to the cytoplasmic incompatibility process.