Penn researcher identifies “superfast” muscles in bats

Bat

Bats survive because of their amazing perceptive abilities. Working in total darkness, they catch tiny insects that can quickly fly in any direction.

The phrase “blind as a bat” is a little unfair to the nocturnal mammals. Bats actually survive because of their amazing perceptive abilities. Working in total darkness, they catch tiny insects that can quickly fly in any direction. But this ability stems not from their eyes. It comes from their vocal chords and echolocation. By bouncing sound waves off objects in their environment and pinpointing the position of their prey using echoes, some bats can catch hundreds, even thousands, of insects a night.

A researcher at Penn has shown that bat echolocation is made possible by the fastest muscles ever seen in mammals.

Andrew Mead, a graduate student in the Department of Biology in the School of Arts and Sciences, collaborated with a team of researchers at the University of Southern Denmark to see how fast the muscles used in echolocation truly are.

Mead

Andrew Mead, a graduate student in the Department of Biology in the School of Arts and Sciences.

Mead and his colleagues had previously studied the so-called “superfast” muscles that help some birds precisely control their singing. Although the sounds produced by a bat during echolocation aren’t beautiful—they are too high-pitched for humans to hear—they are critical to a bat’s way of life. It’s the speed with which a bat makes a succession of calls that allows it to hunt in the dark.

With vision, animals receive a more-or-less continuous stream of information about the world. With echolocation, however, bats get only a snapshot of their environment with each call and echo. That means while they are hunting, bats need to receive the most rapid updates on their prey's position at the instant before the catch. At that point, they produce as many as 190 calls a second in what is known as the “terminal buzz.”

In their experiments, Mead and colleagues attached a bat vocal chord muscle to an oscillating motor and electrically stimulated it to twitch. By increasing the speed of the motor, the researchers could determine how fast the muscle could fully contract and relax before seizing up. They found that these bat muscles are the fastest of any mammal and are 20 times faster than the fastest muscles in the human body.



“You can think of a muscle like a car engine,” Mead says. “It can be tuned to be efficient or tuned to be powerful, depending on what you want it to do. It turns out that bats trade off a lot of force to be able to get these rapid oscillations. In a way, it’s like an engine that’s been tuned for extremely high RPM.”

To date, superfast muscles have been identified in fish, reptiles, birds and mammals, and now Mead and his colleagues plan on studying the molecular and genetic aspects of their mechanics and development.

Originally published on October 6, 2011