Bats Have Fastest Known Mammal Muscle
September 30, 2011

Bats Have Fastest Known Mammal Muscle

Bats derive their ability to use echolocation, the bouncing of sound waves off objects to produce an accurate representation of the environment in total darkness, from so-called “superfast” muscles, researchers reported in latest issue of the journal Science.

These superfast muscles, which are located in the bats´ larynx, are a physical trait never before seen in mammals, and allow the bate to make a rapid series of calls as they home in on their prey.  

They are the fastest known mammal muscle.

"We discovered that Daubenton's bat (found throughout Eurasia) controls its echolocation calls with the fastest-contracting muscle type described," said Coen Elemans, assistant professor in biology at the University of Southern Denmark and lead author of the study.

Bats using echolocation emit a high-pitched call, and then listen for the echoes that tell them how far away objects are and what they are.   After a bat identifies an insect, it calls more frequently, eventually calling up to 190 times a second as it goes for the kill in something known as the “terminal buzz”.

"It was unknown how bats are able to produce calls so quickly", said University of Southern Denmark Assistant Professor John Ratcliffe, senior author on the study.

"We figured that this rate would be limited by the bats ability either to process the returning echoes or produce the calls themselves", he said.

Superfast muscles have amazing adaptations making them capable of contractions about 100 times faster than our normal body muscles and up to 20 times faster than human's fastest muscles -- those that move our eyes.  Until now, superfast muscles have only been observed in rattlesnakes, which have them in their tails, and certain other species of reptiles, birds and fish.

"But recently we also found them in birds who use them to sing their beautiful songs. And now we have discovered them in mammals for the first time", Elemans said, "suggesting that these muscles — once thought extraordinary — are more common than previously believed."

In conducting their study, the biologists measured when echoes returned to the ears of free flying bats.

"Our data suggest that bats could theoretically produce calls much faster - up to 400 calls a second - before the returning echoes would become confusing to the bat,” Ratcliffe said.

Next, the researchers looked at how bats make their calls and measured the performance of their vocal muscles.

"We determined the power the muscles can deliver, much like how you measure a car's performance,” Elemans said.

"We were surprised to see that bats have the superfast muscle type and can power movements up to 190 Hertz (times per second), but also that it is actually the muscles that limit the maximum call rate during the buzz.”

"Before the bats evolved more than 50 million years ago, the night skies were full of flying moths and other insects.”

"Next to flight and echolocation, we now think that it is the buzzes powered by superfast muscle that allowed bats to better track the often erratic movements of insects in the dark and made them so successful,” Ratcliffe concluded.

The researchers also did an experiment in which bats hunted insects in a chamber wired with microphones in order to determine the theoretical maximum frequency for a buzz without overlapping echoes, which could confuse the bat.

“We determined the power the muscles can deliver, much like how you measure a car´s performance,” Elemans said.

Biologist Andrew Mead, a University of Pennsylvania graduate student who took part in the study, explained how bats fine-tune their ability to achieve their goals.

“You can think of it like a car engine,” Mead said.

“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.”

Mead and Elemans plan further study of superfast muscles from a molecular and genetic perspective.

“With more and more genomes being sequenced, including one species of bat, and one from a bird we´ve studied,´ Mead said, “we have some powerful tools to start pick apart whether or not similar genes are involved in various important roles.”

The research is published in the September 30 issue of the journal Science. 


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