This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Limbs evolved as a means of locomotion. From the primitive rotating flagella of bacteria to the wings of flies and even our own legs, animals use these appendages to travel to find food or mates or escape predators.
But in countless species across the animal kingdom, limbs are repurposed to create elaborate social displays: Birds of paradise fan out their wings and hop around in courtship dances, while crabs wave their claws to communicate to potential mating partners. As humans, we use our limbs to dance, gesture while talking, wield tools and conduct a remarkable diversity of behaviors. How does the brain control and coordinate its body parts for such distinct purposes?
A new study from Caltech neuroscientists has discovered how social behaviors—specifically aggressive displays of intimidation—are wired in the brain of the fruit fly Drosophila melanogaster, a commonly used model organism. The team discovered two brain "modules" that are connected to the wings and to the legs, respectively, that govern the animal's threat displays. The research was led by Caltech graduate student Shuo Cao and conducted in the laboratory of David Anderson, the Seymour Benzer professor of biology, leadership chair and director of the Tianqiao and Chrissy Chen Institute for Neuroscience at Caltech, and a Howard Hughes Medical Institute investigator.
A paper describing the work was published on Oct. 15 in the journal Current Biology. Male Drosophila exhibit four specific behaviors when trying to intimidate other fruit flies with threat displays. A fly will leap forward in rapid, stuttering bursts of activity; throw up its wings at a 45-degree angle to form a V; repeatedly turn to face the recipient of its aggression; and pump its wings forward in a movement too fast for the human eye to see.
Altogether, it's not dissimilar from the actions of an aggressive man who puffs up his chest and throws out his arms in a show of intimidation. The flies will not conduct these behaviors unless confronted with another male fly. In 2018, the Anderson lab discovered that a tiny patch of fly brain cells, called AIP neurons, controls these threat displays.
When AIP neurons are optogenetically activated by researchers in experiments, the study showed, flies will exhibit a threat display even when no other fly is present. If the neurons are silenced, a fly is still physically able to attack another fly it comes into contact with, but it no longer performs the preamble to the fight—the threat display. Curiously, the fly's brain contains very few AIP neurons—only five to seven are present in each of the insect's two brain hemispheres.
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