"Infectious speciation" as exemplified by interactions between Drosophila species and inherited, endosymbiotic Wolbachia bacteria provides another possible mechanism for the involvement of immune processes in host speciation. For a group of six related species in the D. paulistorum complex, each species has its own distinct host specific obligatory and mutualistic Wolbachia with which it has achieved accommodation. This accommodation likely involves suppression of immune pathways involving apoptosis of infected cells. In hybrids, the Wolbachia over-replicate and cause embryonic inviability and male sterility, suggesting the unique host accommodation has been lost. In addition to such postmating isolation, it has also been shown that females can detect and will reject males harboring the wrong symbiont, thus further reinforcing isolation .