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DENMARK: Bats have fastest muscles

When a bat hunts its prey, it emits sounds that are sent back as echoes when the sounds hit an object. In this way the bat forms an acoustic image of its surroundings that it can use for navigation. The ability to hunt insects with the aid of sounds has made the bat a formidable predator in the night sky.

Researchers at the University of Southern Denmark have found another reason why the bat is such a good hunter. Extremely fast muscles in the bat's larynx can contract 200 times a second, emitting a sound every time. These muscles are the fastest ever found in mammals.

"The bat's super-quick muscles are 100 times faster than the muscles humans use when blinking," says Assistant Professor Coen Elemans of the Institute of Biology at the University of Southern Denmark, who led the research. "These muscles are still 20 times slower than the muscles in the bat's larynx."

The new finding means scientists now have a clear picture of how many sounds or calls a bat can emit per second, and how many it can hear per second. Previously, researchers believed the frequency of a bat's call was limited by the ability of the bat's ears to hear the many echoes produced every second.

But the researchers reject that because bats can hear 400 echoes a second. The limiting factor is the number of sounds the bat's larynx can emit.

In a laboratory, the researchers placed an insect on a line in the middle of a room and released a bat into the room, recording its call sounds using numerous microphones placed throughout. This enabled the researchers to see where the bat was in the room at all times while also calculating the time it took for the sound to travel from the bat to the insect and back again.

On the basis of the microphone study, the researchers determined that bats could hear 400 echoes a second. To find out how quick the bat's muscles were, they activated individual muscles using electric impulses. The muscles had been removed from the bats so they could be tested under controlled conditions and they found the muscle was 'only' able to contract 200 times a second, the fastest ever seen in mammals.

Although this is the first time that super-quick muscles have been found in a mammal, similar muscles have previously been found in other parts of the animal kingdom.

Rattlesnakes have super-quick muscles in their tails and they use them to make their rattling sounds to frighten and warn other animals. Toadfish also have quick muscles they use when they make their calls, as do pigeons and songbirds.

"When we find extremely quick muscles in several different animal species that are only distantly related, we must ask ourselves: have super-quick muscles developed individually several times? Or were these muscles developed many millions of years ago and subsequently transmitted in several different branches of the animal kingdom?" Elemans wondered.

He said the sarcoplasmic reticulum, or SR, is the calcium store of the muscle cells and comprises a complex network of membranes that form a structure within the cell but not in direct contact with the rest of the cell fluid. The SR contains many pumps that regulate the transport of calcium and other substances during muscle activity.

It was the development of super-quick muscles that made the bat a successful species when the first bats conquered the night sky some 50 million years ago. At that time the air was filled with insects and nothing ate them. The bats found a niche in the eco-system and this resulted in an explosion in the number of bats.

"Until now, people thought that the success of the bats was the result of two factors: their ability to fly and their ability to emit sounds and hear the echoes," Elemans said. "But it has been necessary for bats to develop super-quick muscles for them to be able to use the echoes to catch their prey.

"Many other animals use echoes to orientate themselves in their surroundings but that is a slow form of echo that can't be used for catching prey. The super-quick muscles in the bat's larynx are the reason why bats have been so successful as a species."

A report of the research was published in Science.
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