To ensure their experiments were relevant to fruit flies' real-world experiences, Card teamed with fellow Janelia group leader Anthony Leonardo to record and analyze the trajectories and acceleration of damselflies natural predators of the fruit fly as they attacked. They designed their looming stimulus to mimic these features. "We wanted to make sure we were really challenging the animal with something that was like a predator attack," Card says.
By analyzing more than 4,000 flies, Card and her colleagues discovered two distinct responses to the simulated predator: long and short escapes. To prepare for a steady take-off, flies took the time to raise their wings fully. Quicker escapes, in contrast, eliminated this step, shaving time off the take-off but often causing the fly to tumble through the air.
When the scientists switched off the giant fiber neurons, preventing them from firing, flies still managed to complete their escape sequence. "On a surface level evaluation, silencing the neuron had absolutely no effect," Card says. "You can do away with this neuron that people thought was fundamental to this escape behavior, and flies still escape." Shorter escapes, however, were completely eliminated. Flies without active giant fiber neurons invariably opted for the slower, steadier escape. In contrast,
|Contact: Jim Keeley|
Howard Hughes Medical Institute