The sex lives of fruit flies are making almost as many headlines these days as the Spears sisters. Last month scientists at the University of Chicago caused a stir when they said they had induced homosexual courtship in male fruit flies by changing levels of a neurochemical. And now researchers from Penn State University have looked into how a male fruit fly's sexual behavior changes when he consumes alcohol every day.
The findings probably won't come as a surprise to the average bartender: When guy fruit flies become alcoholics they dramatically increase their attempts to copulate with other flies. The study, published Wednesday in the peer-reviewed online journal of the Public Library of Science, PLoS ONE, is one of the first to take a scientific look at the physiological relationship between alcohol consumption and sexual behavior. And it might just reveal a thing or two about the science of human sexual behavior under the influence of alcoholism. Previous research on fruit flies and intoxication had looked at one-time exposure to alcohol, but Kyung-An Han, an associate professor of biology at Penn State and the study's lead author, wanted to use daily exposure to mimic the habits of chronic alcohol users and abusers.
But where does a fruit fly go for a good drink? The closest analog that Han and her team could come up with was administering ethanol vapors that induced intoxication. The flies did have the option of moving in or out of the vapors, to moderate alcohol consumption. As they became acclimated to consuming ethanol--the intoxicating ingredient of alcoholic drinks--their behavior started to change.
In the two experimental setups, one with only male fruit flies and the other with both sexes, the drunken male fruit flies increased their attempts to court and copulate with other fruit flies--"ethanol-enhanced courtship disinhibition" was one way the researchers described it. In the environment with females, male fruit flies more than tripled their attempts to mate with the females (the attempts were largely unsuccessful--Han explains that, perhaps unsurprisingly, male fruit flies have difficulty copulating under the influence). In an all-male environment, they began courting each other, a behavior that Han says is very unusual among fruit flies. "In normal circumstances, they usually do not court males at all," says Han. By the sixth day of ethanol exposure, the number of fruit flies who attempted intermale courtship had gone from none to more than a third. Han and her students also discovered that ethanol-induced intermale courtship is affected by aging; under the influence of ethanol, middle-aged and old male flies (2 to 4 weeks old) have a higher propensity for intermale courtship compared to 4-day-old flies.
Han says that's one of the more important findings of her research: that behavior changes in a situation of daily alcohol consumption versus one-time exposure. She says that as the male fruit flies acclimated to the effects of alcohol through daily exposure, they became significantly less inhibited in their courtship behaviors. "These findings represent the first demonstration of enduring behavioral changes induced by recurring ethanol exposure in a fly model," says Han. While the research is preliminary, it could open doors to understanding how addiction develops and how repeated imbibing of a drug or alcohol induces changes that are different from a single episode.
Han cautions against drawing too many parallels between humans and fruit flies, particularly between alcohol consumption and homosexual behavior. But she does say that information from this animal model could be a good baseline for similar studies in other animals, including humans. And Han admits that when humans and fruit flies drink, they do fall into an awfully similar pattern of behavior. "When they get intoxicated, first they become more hyper," says Han, describing the progressive behavior of fruit flies under the influence. "Then, when they get more drunk, they lose motor control and often fall off the container. They have trouble coordinating their six legs. When they get really sedated then they lie on their backs." The study did not, however, determine whether fruit flies woke up with regrets and a hangover.
To see video of flies under the influence, click here.