First superfast muscles in mammals help bats catch prey

Daubenton's bats produce a terminal buzz of up to 190 calls per second

Bats are able to locate their prey using echolocation produced by a special kind of "superfast" muscle, scientists have found.

These specially adapted muscles can contract 100 times quicker than most of the muscles in human bodies.

This is the first time such muscles have been seen in mammals, although they had previously been found in rattlesnakes, some fish and birds.

The Danish findings are published in the journal Science.

Bats use echolocation to navigate in total darkness, as well as to catch flying insects in mid air.

In order to pinpoint the insects with enough accuracy and speed to catch them before they fly away, the bats need to make a lot of calls in rapid succession.

As the bat approaches its prey target, the frequency of calls increases up to about 190 calls per second, creating what is known as the "terminal buzz".

Researchers at the University of Southern Denmark, led by Prof Coen Elemans, designed tests to investigate just how fast the terminal buzz could be.

They discovered that the maximum frequency of the buzz was not limited by the echo return time, but was controlled by the muscles in a bat's throat.

These muscles contracted once to produce each call, totalling nearly 200 contractions, or one every five milliseconds.

Such rapid contractions made these "superfast muscles", a type of muscle which has previously only been seen in the sound-making organs of rattlesnakes, the humming Oyster Toadfish, and many songbirds.

They had not been identified in mammals, but Prof Elemans said: "I had a hunch, that if they were in mammals, they would be in bats".

Fast but weak

The superfast muscles seen in these bats can contract 100 times faster than most muscles in the human body, and 20 times quicker than the fastest muscles we have - those that control the movement of our eyes.

Muscles that can contract so quickly need cells that have special adaptations.

The extra energy needed to power the cells comes from a much higher density of mitochondria - the energy producing machines within the cell. Compared with a "normal" cell, the superfast muscle cells have 30% more of these mitochondria.

They may be quick, but they are not strong. Prof Elemans explained: "You have a force for speed tradeoff, these muscles are very strong, but very weak".

"You couldn't use them to run with," he said.

"They may even be too weak to power our large larynxes".

Bats use high speed echolocation to pinpoint their prey

The discovery of superfast muscles in the Daubenton's bats that Prof Elemans and his team studied is the first time they have been seen in mammals.

While they expect that all bats that produce a terminal buzz will have these superfast muscles, their appearance in other mammals will be limited.

While other mammals, and also oilbirds and cave swiftlets, have been known to use echolocation, they do this only for navigation and location of slow-moving prey, so there is no need for high frequency calls.

Prof Elemans explained: "When bats evolved around 45 million years ago, they were the first animal to be hunting at night. They entered an empty niche so they evolved very quickly."

"Flight would have come first, then echolocation to allow them to navigate, and then the very high rate echolocation that allowed them to locate and catch flying insects that move erratically," he said.

Prof Elemans said finding the superfast muscles in bats "spreads open the classes of animals that has them", with potential for investigating when they first appeared and how they evolved.