17February2019

Food makes male flies frisky

Courtship in a classic lab insect is driven by fruity smells

It’s the smell of food that gets male fruit flies in the romantic mood, says a new study exploring the sexual habits of Drosophila melanogaster.

When trying to woo an attractive female the sexually excited male fruit fly becomes a kind of troubadour, playing a love song with one wing as it waltzes behind its object of desire. But what exactly provokes this courtly behavior has been a mystery.

New experiments reported online September 28 in Nature show that removing the gene for an olfactory protein called IR84a makes male flies less apt to perform their song and dance. Found amid nerve cells that spur reproductive activity in fruit flies, the protein is primarily stimulated by two aromas — phenylacetic acid and phenylacetaldehyde. Strangely, these aphrodisiacal odors are given off not by femaleflies, but by the fruit and plant tissues the flies eat and use for laying eggs.

Most insects become amorously inclined when they sense sex pheromones — a natural biochemical perfume — coming from a potential mate. Being turned on by the scent of food instead could provide an evolutionary advantage for a species whose newborn spend several days eating and growing before they leave home. “Fruit fly larvae eat constantly, and they need a good supply of food to support this growth,” says Richard Benton of the Center for Integrative Genomics in Lausanne, Switzerland, who performed the work with colleagues in Switzerland, France and England. Being sexually stimulated by food odors ensures that flies will couple near a nutrient source, enabling them to raise their offspring where the whole family will remain well-fed.

Male fruit flies aren’t guided exclusively by food odors, though. “Their reproductive circuitry is complex,” Benton says, “and responds to many different sensory cues.” For example, randy flies will “taste” potential mates by touching them, acquiring information through contact pheromones. However, getting a whiff of fruit plays an essential role in driving Drosophila courtship behavior.

And it may not just be flies that get a rise from the essence of fruit. The same two sweet, honey-like aromas that drive flies wild are often used in perfumes, making Benton wonder if they have a similar effect on humans.

Though the aphrodisiacal effect of foods like chocolate and oysters boast more anecdotal hearsay than hard scientific evidence, researchers aren’t totally willing to discount the possibility that some foods could inspire amorous impulses in humans. “A similar pathway could potentially promote feelings of arousal in humans,” says Barry Dickson of the Research Institute of Molecular Pathology in Vienna, Austria.

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