Interspecific hybridization between Drosophila species group melanogaster sibling species: isozymic patterns and reproductive relationships

In spite of previous consensus that no F1 fertile hybrids (of both sexes) could be produced between any mating combination of Drosophila melanogaster, D. simulans, and D. mauritiana, the present data indicate that such hybrids were obtained. Thus, some crosses between D. mauritiana females and D. simulans or D. melanogaster males yield F1 fertile hybrids (of both sexes) which have been named Masi (or Masi-2 and Masi-3) and Mame, respectively. Electrophoretic studies, using the species-diagnostic genes for 6-phosphogluconate dehydrogenase, alcohol dehydrogenase, and aldehyde oxidase (6-Pgd, Adh, and Aldox, respectively), were used to investigate the hybrid status, taking into consideration (i) their reproductive relationships, (ii) the coexistence of electromorphs from different species in the same hybrid, within the same generation, and (iii) the expression of the above electromorphs in the hybrids as well as in progeny from backcrosses, where unexpected irregularities and abnormalities were observed. These interspecific hybrids have been kept in our laboratory (as stocks) for 50 generations, to date, and have also been tested for various characteristics that contributed to the verification of their hybrid status (mating abilities, enzyme activities, hybrid sex ratio, the morphology of male genital arches and other fitness components). The finding of major genetic phenomena (e.g., allozymic repression) in these hybrid genomes gives some idea of the nature of events that could be associated with strong evolutionary changes, thus controlling speciation processes.Key words: Drosophila, electrophoresis, electromorphs, interspecific hybrids.