HYBRID LETHAL SYSTEMS IN THE DROSOPHILA-MELANOGASTER SPECIES COMPLEX

Lethal phases of the hybrids between Drosophila melanogaster and its s ibling species, D. simulans are classified into three types: (1) embry onic lethality in hybrids carrying D. simulans cytoplasm and D. melano gaster X chromosome, (2) larval lethality in hybrids not carrying D. s imulans X, and (3) temperature-sensitive pupal lethality in hybrids ca rrying D. simulans X. The same lethal phases are also observed when ei ther of the two other sibling species, D. mauritiana or D. sechellia, is employed for hybridization with D. melanogaster. Here, we describe genetic analyses of each hybrid lethality, and demonstrate that these three types of lethality are independent phenomena. We then propose tw o models to interpret the mechanisms of each hybrid lethality. The fir st model is a modification of the conventional X/autosome imbalance hy pothesis assuming a lethal gene and a suppressor gene are involved in the larval lethality, while the second model is for embryonic lethalit y assuming an interaction between a maternal-effect lethal gene and a suppressor gene.