When fruit flies attack, it's usually about sex

With just a little genetic tinkering, it's possible to make a male fruit fly attack the female he just mated with, and then court a male. It turns out that changing a fly's sexual orientation also changes whom he'll attack.

A group of intrepid neurobiologists announced in PLoS Biology today that they'd figured out how to make fruit flies really angry. First, a brief introduction to fruit fly culture, such as it is. Male fruit flies attack other males, and try to have sex with females. The big problem is that it's really hard to tell who is male and female. Now, thanks to this group of researchers, we know that flies discern sex (and therefore figure out who to attack) via a combination of smell and observing other flies' behavior.

The scientists figured this out by "masculinizing" female fruit flies - first by genetically engineering them to give off male pheromones, and then by engineering the further to behave like males. What they discovered was that the males attacked the females who smelled like males, and the females who acted like males. They also tried to have sex with males who smelled or acted like females.

What's cool about this is that it reveals that flies are paying attention to each other's behavior and deciding how to act based on that. Flies have social norms. They aren't going on smell alone to figure out who is who among the flies.

When fruit flies attack, it's usually about sex

The researchers explain the genetic manipulation required:

To masculinize female pheromones, a transgene carrying dsRNA for the sex determination factor transformer (traIR) was targeted to the pheromone producing cells, the oenocytes. Shortly after copulation males attacked these females, indicating that pheromonal cues can override other sensory cues. Surprisingly, masculinization of female behavior by targeting traIR to the nervous system in an otherwise normal female also was sufficient to trigger male aggression. Simultaneous masculinization of both pheromones and behavior induced a complete switch in the normal male response to a female. Control males now fought rather than copulated with these females. In a reciprocal experiment, feminization of the oenocytes and nervous system in males by expression of transformer (traF) elicited high levels of courtship and little or no aggression from control males.

Though it's been known for a while that fruit fly sexual behavior can be changed with a simple gene tweak, nobody was sure whether the male attack instinct was aroused by pheromones or behavior. Now we know it's either one.

And no, I'm afraid this won't help you: 1) turn your best friend gay, or 2) turn your sister into a vicious attack animal. Human sexual and attack behaviors are a lot more complicated than those of fruit flies, though I know sometimes that's hard to believe.

Read the full scientific paper at PLoS Biology .