Caltech: Angry fly study could lead to curbing human male aggression

PASADENA >> Caltech biologists are buzzing over a study that links aggression in male flies with aggression in human males.

The findings could one day lead to a solution for curbing the behavior in human males.

Researchers in the biology department found a neuropathway in the brain helps transmit a molecule that triggers male flies to get scrappy with other male flies, but be chivalrous toward lady flies. The behavior is triggered by a molecule called tachykinin (Tk), which has also been found in human males.

“One important finding was that this molecule is working in the brain to influence the activity,” said Kenta Asahina, postdoctoral fellow and lead author of the study. “One possibility is to look for drugs or small molecules that inhibit or modify the activity of the genes participating.”

The team studied fruit flies’ behavior up close. Larger flies dos-a-dose with other males, usually smaller flies, on a piece of food until the smaller one is usually bullied off.

“It’s a bit like sumo wrestlers,” said David Anderson, Caltech biologist and corresponding author of the study. “(The larger fly) just makes more aggressive displays and lunges toward the losing fly and the losing fly doesn’t fight back.”

Male flies also square off against male flies when a female is present.

“Attacks in flies require certain pheromones to be present on the opponent fly so that the fly can tell its a male and not a female because male flies don’t attack female flies generally,” said Anderson. “And, they won’t attack males if they don’t have the pheromone.”

Researchers also experimented with fly aggression by manipulating the neurons that transmit the Tk molecule, and found that flies can be triggered to attack flies and other objects that it normally wouldn’t.

“If we juice up our experimental flies to increase their aggressive arousal, we can get them to attack target flies that don’t have any pheromones on them, and we can even get them to attack a fly-sized magnet, an inanimate object as long as the magnet is moving around. And that is something we never see in a normal fly.”

When the Tk molecule was beefed up in the smaller flies, it was able to hold its own against the larger, bullying fly, Anderson said.

Scientists chose to study the nervous systems in flies instead of other mammals because of the fly’s simple nervous system, Anderson said. Since these latest findings are early, a timeline for treatment in human male aggression is not yet known.

“There’s clearly a need for clinical possibilities to work effectively and specifically to mediate and modulate the level of aggressive impulses, and I hope we can get some insight to achieve that goal,” said Asahina. “Human behavior is way more complex than society and environment, although we’re looking for an environmental basis, and hope to make use of that data.”

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