Research Director: Dr. Daisuke Yamamoto
(Professor, School of Human Sciences, Waseda University)
Research Term: 1994-1999

When studying the relationship between genes and behavior, a good place to start is with sexual behavior, similarities of which extend across all species of animals. One of the best organisms for this purpose is the fruit fly, Drosophila, because from egg to adult it takes ten days, after which the mature fruit fly lives for only a month or so. It is thus easy to observe the lifetime behavior over a short time, and to generate mutations. Mutations and their related phenotypes, physical expressions, provide a powerful way to identify the genes related to behavior. This project used sexual behavior as a good starting point for researching the genetics of behavior, while concentrating on the fruit fly Drosophila melanogaster.

Research Results

New Drosophila mutant: A new Drosophila mutant, satori, was isolated, the males of which do not court or copulate with female flies.The mutations were identified in the fruitless gene which is responsible for bisexual and homosexual behavior in the satori mutant. It was demonstrated that this mutation in the fruitless gene causes a brain sexual transformation with a concomitant change in sexual orientation.
In the case of the spinster gene, of which mutation in female Drosophila results in extraordinarily strong rejection against courting males, mouse and human homologues were cloned. These genes were mapped on the chromosome, and were used to create a gene knock-out mouse for examining its effect on behavior in mammals.

Evolutionary implications of sexual dimorphism in Drosophila: For the first time sexual dimorphism was found in the brains of several species of Hawaiian Drosophila., in which the male possesses a significant enlargement of one of the glomeruli of the antennal lobe, the olfaction center in the brain. The most conspicuous sexual dimorphism was found in the adiastola species group. The origin of this group is the species ornata in the oldest island, Kauai, which does not exhibit sexual dimorphism of the glomerulus. The moderate sexual difference is found in descendent species cilifera and adaistola, each from the Molokai and Maui islands.The most extreme sexual dimorphism is observed in setosimentum, the youngest species established in the newest island, Hawaii. Therefore, it is likely that the brain sexual dimorphism occurred for the first time in the Maui/Molokai island complex that raised 10-20 million years ago, then further exaggerated in the divergent species through evolution. It is thus possible to demonstrate diverging mating behavior and it’s related physiological anatomy during evolution of the Hawaiian Drosophila.

Investigating the Instinctive Behavior and Integration Mechanism at the Individual, Cellular and Molecular Levels

Homosexual Activity of Mutants