Fruit flies hit the gym: Tiny treadmills push flies to set 50 mm/s speed record

Researchers have turned fruit flies into tiny athletes to unlock the secrets of locomotion.

The University of Washington researchers have been working to understand the neural mechanisms behind movement.

For this, they created small-scale treadmill-like machines for fruit flies. They conducted this study to understand how fruit flies’ nervous system controls movement.

Interestingly, the treadmill experiments also led to a new revelation: the “fastest walking speed” ever recorded in fruit flies.

“They were able to surpass an instantaneous walking speed of 50 millimeters per second,” the researchers noted.

Fruit fly’s proprioception

The nervous systems of insects and humans play an important role in movement. It helps maintain balance by detecting unexpected changes and adjusting the body’s motions accordingly. This is known as proprioception, which is the body’s awareness of its own position and movement.

Animals would struggle to navigate their environment without this neurological control, putting them at risk of falling and being injured.

However, neuroscientists have struggled to understand the underlying mechanisms of how the nervous system recognizes and responds to unexpected changes. This is why researchers turned to fruit flies.

“These tiny creatures are a good model system to study the neural control of locomotion because they have a compact, fully mapped nervous system,” the researchers noted in the press release.

The team used a “linear treadmill” to train flies to walk and track their movements in 3D over a longer duration. Researchers compared walking rates in flies with and without impaired proprioception.

Decoding hidden neural control

The flies on the treadmill exhibited a burst-like walking pattern, sprinting forward and then coasting backward on the belt. They spent about half their time walking and increased their pace as the treadmill speed climbed.

The study found that fruit flies can adjust their walking patterns to maintain balance and stability, even when faced with unexpected challenges.

The key highlight came when certain neurons associated with proprioception were genetically silenced. When deprived of sensory feedback, the flies took “fewer but larger steps.”

The team noticed that the flies’ leg coordination was surprisingly unaffected by the lack of sensory feedback. This suggests that either other proprioceptive neurons are more critical for walking coordination or the nervous system can adapt to compensate.

They also compared the movement pattern using the split-belt treadmill, which has two separate belts that can move at different speeds.

“The scientists found that the split-belt treadmill had little effect on the coordination between legs. However, flies substantially changed the step distances of their middle legs when the two belts moved at different speeds,” the team noted.

“The middle legs are ideally positioned to stably pivot the body of the fly about its center of mass, like rowing a boat from its center,” the researchers added in the press release .

The study proposes that flies adjust their steps to maintain a straight path when faced with rotational disturbances. Through the split-belt treadmill experiments, researchers gained valuable insights into how fruit flies adapt to environmental changes and coordinate their leg movements for stability and locomotion.

Treadmills have a long history of being used to study the neural control of locomotion in various animals, including invertebrates like cockroaches and stick insects, as well as vertebrates like rodents, cats, and humans.

The findings were published in the Cell Press journal.