From Wolbachiagenomics to phenotype: molecular models of cytoplasmic incompatibility must account for the multiplicity of compatibility types

•Two main mechanistic models are proposed for cytoplasmic incompatibility.•Both can explain simple cases of incompatibility as seen in Drosophila.•Mosquitoes Culex pipiensshow complex and non-transitive cytoplasmic incompatibilities.•Only the toxin–antidote model simply explains such complexity, through lock–key interactions.