Unidirectional incompatibility between populations of Drosophila simulans

Drosophila simulans females from a strain collected at Watsonville, CA produce very few offspring when mated with males from a strain collected at Riverside 510 km away. This incompatibility does not exist in the reciprocal cross. In the incompatible cross, mating and oviposition are normal, but eggs fail to hatch. A survey of other California populations indicates that unidirectional incompatibility is widespread. The incompatibility is maternally inherited over one generation. Using older Riverside males or rearing the strains at 28⚬C suppresses incompatibility. Culturing the strains on medium with tetracycline restores compatibility, suggesting the involvement of a microorganism.