The Toxin–Antidote Model of Cytoplasmic Incompatibility: Genetics and Evolutionary Implications

Wolbachiabacteria inhabit the cells of about half of all arthropod species, an unparalleled success stemming in large part from selfishinvasive strategies. Cytoplasmic incompatibility(CI), whereby the symbiont makes itself essential to embryo viability, is the most common of these and constitutes a promising weapon against vector-borne diseases. After decades of theoretical and experimental struggle, major recent advances have been made toward a molecular understanding of this phenomenon. As pieces of the puzzle come together, from yeast and Drosophila fly transgenesisto CI diversity patternsin naturalmosquito populations, it becomes clearer than ever that the CI induction and rescue stem from a toxin– antidote(TA) system. Further, the tight association of the CI genes with prophagesprovides clues to the possible evolutionary origin of this phenomenon and the levels of selection at play.