Monday, October 17, 2016

Ultrasonic Love Songs You Can’t Hear: Mice Sing Like Jet Engines to Find A Mate

Mice court one another with ultrasonic love songs that are inaudible to the human ear. New research shows they make these unique high frequency sounds using a mechanism that has only previously been observed in supersonic jet engines.

Wild mice, rats and also many other rodents produce ultrasonic songs that they use for courting and territorial defense. These love songs are often studied in mice to find cures for stuttering and autism. However, until now it was not established how mice can make such ultrasonic sounds, which is important if you want to explain why drug treatments or gene mutations change songs.

"We found that mice make ultrasound in a way never found before in any animal", says Elena Mahrt, lead author on the study and graduate student at Washington State University Vancouver, USA.

"Mice don't use vibrating vocal folds in their larynx to make these ultrasonic sounds. Instead they point a small air jet coming from the windpipe against the inner wall of the larynx", says Dr. Coen Elemans, senior author on the study and head of the Sound Communication and Behavior group at the University of Southern Denmark.

The deer mouse is just one type of mouse that is known to sing.
 Photo credit: Thomas Kitchin and Victoria Hurst/Design Pics Inc./Alamy

The international group of researchers found mice use a mechanism similar to that of a jet engine inside their throats in order to make high frequency whistles – the first time such a mechanism has been observed in any animal.

These ‘singing’ mice are often used to study communication disorders in humans, such as stuttering. However, until now it was not understood how mice can make these ultrasonic sounds, which may aid in the development of more effective animal models for studying human speech disorders.
Hear a mouse love song lowered in pitch to make it audible to humans. 
Credit: University of Cambridge/ back to back news

Now, new research co-authored at the University of Cambridge and published in the journal Current Biology has found that when mice ‘sing’, they use a mechanism similar to that seen in the engines of supersonic jets.

Previously, it had been thought that these ‘Clangers’-style songs were either the result of a mechanism similar to that of a tea kettle, or of the resonance caused by the vibration of the vocal cords. In fact, neither hypothesis turned out to be correct. Instead, mice point a small air jet coming from the windpipe against the inner wall of the larynx, causing a resonance and producing an ultrasonic whistle.

Using ultra-high-speed video of 100,000 frames per second the researchers showed that the vocal folds remain completely still while ultrasound was coming from the mouse’s larynx.
Credit: ElectricScienceNews

“This mechanism is known only to produce sound in supersonic flow applications, such as vertical takeoff and landing with jet engines, or high-speed subsonic flows, such as jets for rapid cooling of electrical components and turbines,” said Dr Anurag Agarwal, study co-author and head of the Aero-acoustics laboratories at Cambridge’s Department of Engineering. “Mice seem to be doing something very complicated and clever to make ultrasound.”

“It seems likely that many rodents use ultrasound to communicate, but very little is known about this - it is even possible that bats use this cool mechanism to echolocate,” said the study’s senior author Dr Coen Elemans from the University of Southern Denmark. “Even though mice have been studied so intensely, they still have some cool tricks up their sleeves.”

"Interestingly this mechanism is known only to produce sound in supersonic flow applications, such as vertical takeoff and landing with jet engines, or high-speed subsonic flows, such as jets for rapid cooling of electrical components and turbines", says Dr. Anurag, co-author and head of the Aero-acoustics laboratories at the University of Cambridge, UK. "Mice seem to be doing something very complicated and clever to make ultrasound", he continues.

"It seems likely that many rodents around the globe use ultrasound to communicate, but very little is known about this... It is even possible that bats use this cool mechanism to echolocate", Elemans says, " Even though mice has been studied so intensely they still have some cool tricks up their sleeves".

"The more we understand how mice make their social sounds, the easier it will be to understand what happens in a mouse brain that has the same genetic mutation as a human with a speech or social disorder", Mahrt concludes.



Contacts and sources:
Sarah Collins
University of Cambridge

Dr. Coen Elemans
Sound Communication & Behavior Group, Department of Biology
University of Southern Denmark,

Citation: Elena Mahrt et al. ‘Mice produce ultrasonic vocalizations by intra-laryngeal planar impinging jets.’ Current Biology (2016) DOI: 10.1016/j.cub.2016.08.032.

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