On the mechanism of Wolbachia-induced cytoplasmic incompatibility:: confronting the models with the facts

The endocellular bacterium Wolbachia manipulates the reproduction of its arthropod hosts for its own benefit by various means, the most widespread being cytoplasmic incompatibility (CI). To date, the molecular mechanism involved in Cl has not been elucidated. We examine here three different Cl models described in previous literature, namely, the lock-and-key, titration-restitution and slow-motion models. We confront them with the full range of CI patterns discovered so far, including the most complex ones such as multiple infections, asymmetrical and partial compatibility relationships and the existence of Wolbachia variants that can rescue the host from CI but not induce it. We conclude that the lock-and-key model is the most parsimonious of the models and fits the observations best. The two other models cannot be categorically invalidated, but they encounter some difficulties that make additional hypotheses necessary.