Guys have a way of laying on the charm when a relationship starts. The man does his best to show only his finest attributes while wooing his girl. This is quite a common theme in virtually all animal courtship. Even the male fruit fly taps into all the magnetism he can muster in luring a mate. One of the many rituals that the male fruit fly performs during the courtship dance is the vibration of his wings. By quivering his wings just so, he sings to entice his chosen mate. Only the male serenades while only the female consents to the`come on'.
What is surprising is that both male and female flies appear to be hardwired with the ability to sing. This ability may be controlled like an`on–off' switch in appropriate neurons. Females may contain the necessary song neurons but they remain dormant without the trigger necessary to turn them `on'.
In the April 18, 2008 issue of Cell, Gero Miesenbock from the University of Oxford and Yale University School of Medicine, and his postdoctoral fellow, J. Dylan Clyne, address the question, `What accounts for the uniquely male propensity for producing song?' Maybe male wiring is slightly different from the females'.
Knowing that certain genes are expressed differently between the sexes, the team began by targeting fruitless (fru), a regulatory gene in the nervous system that is expressed differently in males (FruM)and females (FruF). By labeling fru neurons with green fluorescent protein (GFP), the team was able to illuminate a key subset of singing neurons and directly compare male and female brain circuitry. Lighting up Fru to display the song circuit allowed Clyne and Miesenbock to visualize the way the neurons are wired to one another in the brain and to find that male and female fly brains contain a similar network of the song-producing neurons, termed the song generator.
If both sexes contain the basic anatomical equipment to produce song, what allows the male to sing while the female remains silent? To answer this question, Clyne and Miesenbock subtly modified the fru gene so that expression of the gene could be artificially turned on in females' neurons with a flash of light, and listened for song. The team filmed flies and showed that by switching on selected neurons they were able to trigger singing in females. However, the flash of light needed to be brighter than that required to activate the males' song generator. And when the duo listened to the songs of males and females they found that the females sang out of tune. It appears that, in terms of courtship song, males remain the showy experts.
The authors suggest that differences in the males' and females' abilities to vibrate their wings and sing may be explained by one of two scenarios. Either, (1) very subtle differences in brain anatomy ensure male behavior remains exclusively male (and female behavior remains exclusively female), or(2) the critical on–off switch in key subsets of neurons are set in opposite configurations within the two sexes (male song-generator neurons are switched `on' by FruM, while the generator is turned `off' in females). Still, it is remarkable that a principally male behavior can even be elicited from females. By simply modifying a single gene's expression within a subset of neurons, scientists are able to evoke an unnatural behavior. Deeper insight into the behavioral differences between the sexes (in flies) will be revealed when the downstream genes that are regulated by Fru are uncovered.
