The Drosophila melanogaster, the fruit fly, has been well-studied for years. Scientists know its genome inside and out, have seen it develop from a single cell to full maturity and have even gone on to tease apart neurons in the fruit fly's brain. What scientists didn't realize is that it's not completely a loner, succumbing to collective behavior much like other species would.
In a study published in the journal Nature, researchers from the University of Lausanne and École Polytechnique Fédérale de Lausanne showed that fruit flies react better to situations as a group than individually. In the case of the study, fruit flies were placed in a container half-filled with carbon dioxide. When alone, fruit flies reacted to the odor of the gas timidly. But as a group, they moved away from the carbon dioxide in the container and sought clean air more decisively.
Collective behavior in fruit flies in the study is guided by three simple rules:
1. A fruit fly walks more often in the presence of carbon dioxide gas but not in a particular direction.
2. When a fruit fly encounters carbon dioxide after coming from clean air, it will turn around.
3. If a fruit fly bumps into another, the second fruit fly will move away from the first one.
Lead author Pavan Ramdya observed these rules in real life and was able to reproduce them in a computer simulation, programming virtual fruit flies to follow the same rules. However, it should be noted that fruit flies do not respond to just any kind of bump. For them to move, they have to be lightly grazed on the tips of their legs.
Researchers were also able to identify the exact neurons in the brain responsible for the fruit flies' reaction and the subsequent collective behavior. They did this by first identifying a fruit fly strain that stopped moving when bumped and then swapping a glowing green protein for the neuron-silencing toxin that made particular fruit flies stop moving. The glowing green protein is sensitive to light so neurons are fired when fruit flies see blue light, making them move.
"This is a landmark study of collective behavior. Never before has it been possible to unweave the intricate coding of social behavior during collective decision-making," said Iain Couzin, from the Max Planck Institute for Ornithology and Princeton University. Couzin was not involved in the study.
Other authors for the study include: Richard Benton, Pawel Lichocki, Dario Floreano, Steeve Cruchet, Winnie Tse and Lukas Frisch.
