The effect of heteroplasmy on cytoplasmic incompatibility in transplasmic lines of Drosophila simulans showing a complete replacement of the mitochondrial DNA.

Unidirectional cytoplasmic incompatibility has been observed in crosses between different strains of Drosophila simulans when the males, but not the females, involved in the crosses are infected with intracellular rickettsia-like microorganisms. In contrast to what is known about this system an unexpected partial incompatibility has been observed between two infected strains. Transplasmic lines have been constructed in the laboratory to investigate this phenomenon. The injection of a foreign infected cytoplasm into a strain which apparently shows the same kind of bacterial infection causes an incompatibility in crosses between injected heteroplasmic males, but not injected females, of the same strain. These findings suggest that several crossing types exist within the Drosophila simulans incompatibility system. The complete replacement of the original mitochondrial DNA observed in some of the transplasmic lines made it possible to analyse and exclude any link between incompatibility and mitochondrial genomes.