Researchers have designed a complex experiment to study the mysterious wing structure of fruit flies, capturing muscle and wing movement simultaneously to explore the biomechanics of their flight. Flies’ wings evolved with a complex hinge system hundreds of millions of years ago, allowing minute muscle movements to translate into flight. This unique adaptation continues to puzzle biologists and remains an evolutionary enigma.
Michael Dickinson, a researcher and professor of bioengineering and aeronautics at the California Institute of Technology (Caltech), studies insect flight. He describes the wing hinge as one of the most significant and remarkable structures in the evolution of life.
To better understand the role each muscle plays in controlling the wing hinge, Dickinson and his team designed an experiment to simultaneously record muscle movement and the resulting wing motion in fruit flies. The setup itself is as complex as the wing hinge it studies, allowing researchers to gather high-resolution data on all 12 tiny wing muscles and capture three-dimensional wing movement patterns.
Creating a Video Game-Like Environment for Flies
The fly was surrounded by a series of panoramic LED screens designed to simulate environmental cues. Dickinson explains that these cues created a “video game” atmosphere for the fly, influencing its flight behavior. The panoramic screens could change to make the fly move left, right, up, or down, as well as accelerate or decelerate.
Flies can detect up to 200 light flickers per second, giving them some of the fastest visual systems on Earth. In comparison, most videos are shot at a frame rate of 24 frames per second. Dickinson notes that flies might view these videos like a slideshow, demonstrating their highly responsive visual perception.
Capturing Muscle Movements and Wing Dynamics
To capture muscle movements, the researchers used genetic engineering to make the muscles glow when active. A microscope was set to reflect specific wavelengths of light onto the fly, triggering fluorescence in the active muscles. The emitted light was then recorded, allowing researchers to track muscle activity.
For wing movement, three high-speed cameras capable of capturing 15,000 frames per second were used. The cameras needed high spatial resolution to detect subtle changes in muscle movements that could affect the fly’s flight. Because of the extremely short exposure times, a large amount of light was required to produce images. To avoid blinding the flies, the researchers used infrared cameras.
Finally, the experiment included a third camera that provided real-time feedback on each wing beat’s amplitude, enabling the researchers to adjust the LED simulations based on the fly’s response.
The experiment collected terabytes of data, including 72,000 wing beats, which were divided into training and testing datasets. The training data was then used to develop a neural network to predict wing movement based on muscle activity. Dickinson explains, “To capture the richness of what this muscle system can do, we needed a wide variety of flight patterns and a lot of data.”
Challenges and Future Directions
Working with live animals presented additional challenges in the experiment’s development. For example, because lights and electronic devices generate heat, the researchers had to ensure the room remained cool enough for the flies to remain active. The fruit flies used in the experiment were reluctant to fly in conditions above 25°C (77°F).
Currently, researchers are working with laboratory fruit flies, the only species whose muscles can be visualized with genetic modifications. They hope to compare their results with other experiments involving mosquitoes in the future. Looking ahead, they plan to develop a computer simulation to design physical structures based on the principles of insect wings, potentially unlocking new applications in engineering and robotics.
