Scientists have found the pheromone which promotes aggression in flies.
The study, published in Nature, also identified the neurons in the fly's antenna that detect this pheromone and relay the information to the brain to elicit aggression.
According to biologists from the California Institute of Technology (Caltech), the findings could help unravel the mystery of how aggression is hardwired into the brain by an animal's genes.
Study coauthor David Anderson, Caltech's Seymour Benzer Professor of Biology and a Howard Hughes Medical Institute investigator, said: "Obtaining such proof required the ability to experimentally interfere with the insects' capacity to sense the pheromone.
"And that, in turn, necessitated identification of the receptor molecules that detect aggression pheromones, and of the olfactory sensory neurons that express these receptors."
Liming Wang, a graduate student in Anderson's lab and the Nature paper's first author, pointed out that the only insect in which these conditions could be met was the vinegar fly, Drosophila melanogaster.
The boffins looked at the effect donor flies had on the aggressiveness of a pair of "tester" male flies placed on top of a cage.
Anderson said: "Remarkably, the presence of the caged donor flies strongly increased aggression between the tester flies, and this aggression-promoting effect increased with a higher number of donor male flies."
Wang added: "These experiments suggested that the presence of high densities of male flies in a local environment can indeed promote aggression through their release of cVA and its detection by other flies."
Surprisingly, says Anderson, the flies with the hyperactive neurons quickly dispersed, leaving the food resource behind. "They fought one another until a dominant fly became 'king of the hill' and drove the other flies away," he explains.
"In contrast," Anderson adds, "flies whose genes weren't manipulated in this way ate happily together, like cows grazing placidly on an alpine meadow."