"Come at Me Bro" Mentality Explained Using Fruit Fly Brains

"It’s strangely reminiscent of guys who are about to get into a fight at a bar."

A bro with his arms spread and chest out doesn’t even have to say, “Come at me, bro.” His threat is clear. As research published Thursday in the journal Neuron shows, the same can be said for male fruit flies when they’re pissed off enough.

When these ubiquitous bugs want to guard their resources or territory, they stare down their rivals, pump their wings, and charge, all while quickly changing direction in a way that can make them look bigger than they are. If a rival doesn’t want to bother with a fight, he takes off. The study shows that this “Come at me, bro” behavior of fruit flies is actually driven by a very small set of neurons that operates independently of other aggressive behaviors.

Brian Duistermars, Ph.D., a neurobiology postdoc at Caltech and the study’s first author, admits the fly behavior looks all too familiar.

"It’s strangely reminiscent of guys who are about to get into a fight at a bar.

“It’s strangely reminiscent of guys who are about to get into a fight at a bar,” Duistermars tells Inverse. “They freeze and stare at each other.” Then they charge their targets, raise their wings, and even track them around the area before lowering their wings again.

In the paper, Caltech and Howard Hughes Medical Institute researchers identified a small cluster of about three neurons that, when activated, makes the fruit fly (Drosophila melanogaster) more likely to engage in threat behaviors. That in itself is a noteworthy finding, but they took it a step further and figured out how to alter these neurons and activate them in isolation, both with rivals present and even without any other flies around. In other words, they got fruit flies to buck at a decoy and threaten an empty room.

A small cluster of neurons activated when flies threatened each other. Activating these neurons could make flies threaten each other.

Neuron/ Duistermars et al

Before the researchers could manipulate flies’ brains, they had to get a good idea of how the flies acted. So they put male flies, who had been raised in isolation, in a chamber with food, one of the main triggers of threatening behavior. These solo flies are well-known to be much more aggressive than flies raised in groups. By observing over 400 of these confrontations, they found what threatening behavior looked like.

“It’s like a guy puffing out his chest and mad-dogging you and throwing his arms out,” says Duistermars.

"It’s like a guy puffing out his chest and mad-dogging you and throwing his arms out.

Next, they investigated what was going on at the cellular level. First, they figured out which neurons were activated when the flies displayed threatening behavior. With this knowledge in hand, they genetically modified flies so that those neurons could be activated by either light or heat.

When the flies with heat-activated neurons were exposed to warmer temperatures, the ion channels in their threat behavior neurons opened, and they suddenly became super aggressive. “We put the flies in a hot room, and we let the neurons turn on and run these experiments as I sit there and sweat,” says Duistermars.

Those hot, aggro flies readily threatened their neighbors, despite being accustomed to the other flies. This behavior is shown in the second and third encounters in the video above. In another step of the experiment, the researchers passed a dummy object by a heat-activated fly, which is when things got really wild: The fly threatened the inanimate object, as shown in the fourth encounter.

“That was one of the more exciting findings,” says Duistermars, “when I first saw a fly threaten an object.”

The same thing happened with the light-activated flies when they were exposed to the right wavelength of light. Their neurons activated, the flies threatened the dummy, as shown in encounter five.

Duistermars is careful to point out that the light and hea didn’t activate behavior so much as the mood that enables the behavior.

“It’s almost like an internal state,” he explains. “When we’re angry we lash out at things that didn’t make us angry.” Likewise, when flies are primed to be threatening, they’ll come after anything nearby — whether or not it was an actual threat.

While there’s no cluster of activated neurons implicated in human fistfights with strangers just yet, Duistermars points out that such behaviors are common among all sexually reproducing animals. As such, he is optimistic that he and others in his field could one day unlock the brain-bar fight connection.

“The fact that flies have a small set of neurons that basically govern this whole behavioral repertoire, it suggests that other animals do too.”

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