Carnal Knowledge | Fruit flies imbibe - it's males gone wild

It can be sobering to contemplate all our recent discoveries revealing the abilities of the humble fruit fly. Fruit flies sleep, they learn, and their pinhead-size brains hold memories both happy and traumatic.

The latest research out of Pennsylvania State University shows that fruit flies also have sexual inhibitions.

The discovery was made by loosening them up with, what else, alcohol. It had the most profound effect when male flies were penned up with, what else, other males.

Lead author Kyung-An Han said bottled-up male flies typically "just sit there and don't do anything."

When the neuroscientist added some ethanol-soaked cotton, however, they sprung into an orgy of activity - chasing, mounting and collapsing into heaps. Han and colleagues published their findings last week in the journal PLoS ONE.

Drosophila melanogaster under normal conditions are almost exclusively heterosexual. Males mate only with virgin females, Han said, although in the fly world a female effectively regains her virginity after laying eggs and starting a fresh reproductive cycle.

Researchers in recent years have observed that when a male spots a virgin (or reformed virgin) female, he follows her and taps her abdomen with a foreleg. Then he sings a mating song by vibrating his wings. The male then "licks" the female's genitals, possibly to determine if she is of his species.

Female fruit flies refuse to mate with males that do not perform all these steps in the proper order.

Once in a while, a male will try this routine on another male. And under normal circumstances, Han said, "the other male gets upset and rejects him and he runs away."

Two years ago scientists announced they had created homosexual fruit flies through genetic engineering. The feat required changing the sequence of just one gene, called fru, that comes in a male and female version.

Males engineered with the faux female fru were passive, behaving like normal female flies. Females given the male version used the male courtship ritual on other females.

Han said her inebriated male flies, on the other hand, were not exclusively gay. When held in mixed groups, they still preferred females. Their behavior seemed more like an extreme version of human beer goggles - the tendency of alcohol to make everyone look sexier.

In an interview, Han said the most interesting part to her was the effect of repeatedly getting her flies drunk. At first, the males got frisky for just a few minutes before they started falling off the side of the container and passing out. (She can tell when they're unconscious because they're lying on their backs, which they don't generally do.)

But after a few days of forced bingeing, they jumped on each other with increasing ardor and also took longer to pass out.

To illustrate this, she sent me a short video (posted at http://go.philly.com/science) of the flies after repeated exposures. By the third time, they were forming what looked like conga lines that quickly collapsed as each fly jumped on the one ahead.

Yes, Han said, the males were trying to copulate with each other. "Of course, they can't do it because their gonad is different," she said. "They tend to fall."

It reminded me of certain beer-fueled, quasi-homoerotic hazing rituals I'd witnessed among college students, most of which culminated in men dragging other men into showers.

Female flies under the influence were far less interesting. They typically wait to be courted by a male, so even if they became less discriminating, it was hard to tell.

Han said her ultimate research goal is to understand how memory works. In humans, she said, drug addiction involves an extreme sort of remembered pleasure; addicts often have enhanced memories of anything associated with their habits.

The male fruit flies pursued one another faster and faster as their alcohol exposures added up despite dry periods in between. Does that mean they remembered their previous drunken exploits and enjoyed them? Were they embarrassed when they got sober?

Perhaps these answers will come from Han's next round of experiments.