When a male fruit fly wants to track down a gal, he follows his nose along her attractive scent trail. Jean-François Ferveur explains that this alluring bouquet is a complicated mixture of 16 hydrocarbon compounds, but it wasn't clear which of the cocktail's components turns a female fruit fly into a femme fatale. He adds that two of the female's scent components were suspected of being sex pheromones but `testing the allure of dummy females scented with these chemicals may not tell us much about the sexual advances of male flies towards live females'. Ferveur needed to test the aphrodisiac effects of the two mysterious substances on flesh and blood flies. Teaming up with Fabrice Marcillac, their idea was simple: create mutant flies lacking both hydrocarbons, apply a dab of scent to one and allow a male fruit fly to decide which takes his fancy; scented or unscented females(p. 3927).
But the team needed to find a way of applying the natural females' aroma to the mutants. Fortunately, the mutants quickly picked up the natural flies'scent when crowded together in a tiny jar. After spending a day together, the mutant females' pheromone scent was indistinguishable from the wild-type females'. Ferveur was ready to see how the males responded to the mutants'topped up scent.
Selecting a perfumed female and her unperfumed sister, Ferveur waited to see which of the two would prove irresistible to a waiting male. The aphrodisiac properties of the substances were abundantly clear; the perfumed sisters won the male's affections almost every time. `When we saw the first males courting the perfumed mutant, we knew we were on to something', says Ferveur. But what really astonished the two researchers was that the two pheromones appeared to act both as a `start' button for male mating behaviour,triggering earlier copulation, as well as an `off' button, terminating copulation. `The males began mating more rapidly with the perfumed females and copulation lasted longer than with the unperfumed females', says Ferveur. So the hydrocarbons don't simply send out a sexy signal; they also have a dramatic effect on the male's sexual performance.
But there was an unexpected twist to the story; the fruit fly Viagra had some interesting side-effects. Ferveur was surprised to find that the perfumed females had fewer daughters than the unperfumed females. `There appears to be a trade-off', explains Ferveur, `a female with these two pheromones may attract more males, but also leave behind fewer female progeny'. Although he admits that he is not sure why this is happening, these tantalising results certainly hint at conflict between the sexes.