In a study that sheds light on the biology of aggression, scientists swapped genes in gender-bending fruit flies to make boys fight like girls, and girls fight like boys.
Researchers from Harvard Medical School and the Institute of Molecular Pathology in Vienna focused on a gene in fruit flies dubbed "fruitless," an important player in behavioral differences between the sexes of these insects.
The gene is known for its role in male courtship, but also controls another sex-specific behavior — how flies fight, according to the research appearing Sunday in the journal Nature Neuroscience.
When they fight, female fruit flies rely on maneuvers like shoving and head butts to an opponent's body. Males use tactics that include lunging, boxing and rearing up on their back legs and snapping down their forelegs to flatten an adversary.
The researchers swapped the male and female versions of the gene in fruit flies and observed the consequences. Males with the feminine gene used female fighting tactics, while the females with the masculine gene fought like the boys.
People have a lot to learn about the biological basis of aggression, said Harvard neurobiologist Edward Kravitz, one of the study's authors.
"It goes without saying aggression, as well as violence, in society is a serious problem. It has to have biological roots. And the biological roots will have genetic components and experiential components," Kravitz said in an interview.
It is important to learn about such complex behaviors in a simple organism, and then apply this knowledge to higher and higher forms while ultimately trying to gain insight into human behavior, Kravitz said.
People do not have an exact equivalent to the "fruitless" gene, Kravitz added, but probably have other human genes serving similar functions.
Steel-cage match
Kravitz said his team, pondering how to instigate fruit fly fights, settled on food and mating — or, in this case, necrophilia.
They set up the insect world's equivalent to a steel-cage match — a chamber with glass walls and a lid with air holes, a dish of fly food and a mate — and sent in the combatants. But when they used a live female fly as a lure for the males, she often would just fly off.
"My student discovered when he transferred the female to the dish and accidentally crushed her head that the males didn't care whether she had a head or not. That's a true story of what led us to cutting the heads of the females off in subsequent studies," Kravitz said. "They'll court the dead, headless female fly, and try to copulate with her sometimes."
Winners and losers
In a related study in the Proceedings of the National Academy of Sciences last week, Kravitz and colleagues wrote that flies developed "winner" or "loser" mentalities in these fights, which amounted to a series of nonlethal skirmishes.
Kravitz acknowledged some of the nutty aspects of the experiments.
"When you're trying to explain this to your children -- 'Dad, what did you do today?' 'Well, I had these two fruit flies, son, and I was trying to figure out how to get them to fight.' Just think of that."