Female Mice Sing During Courtship

They don’t use microphones or seranade like Don Quixote. But scientists have known for a long time that male mice belt out something like love songs to females when the time seems right to them.

What they didn’t know, until a University of Delaware researcher developed a sophisticated array of microphones and a sound analysis chamber, was that female mice were singing back.

No one knows if the females are singing “It Had To Be You” or “Blurred Lines,” but mouse “songs”, as neuroscientist Joshua Neunuebel, assistant professor of psychological and brain sciences, calls them, apparently are quite the thing with these little rodents.

No Obvious Signs

You can’t tell that a mouse is singing or shouting. There is no obvious physical sign.

And their voices during these interactions register in a range far beyond the reach of human ears, Neunuebel said.

The highest range the human ear can detect is about 20 kilohertz. The high-pitched voice of a mouse registers at about 35 to 125 kilohertz, he said.

It takes special microphones to pick that up and Neunuebel and his collaborators have worked on collecting, analyzing and interpreting all sorts of mouse sounds and related data.

Singing Back

Neunuebel developed a sound system and analysis equations that allowed researchers to figure out – with up to 97 percent accuracy – which sound came from which mouse.

That’s when they discovered that female mice weren’t just listening to male voices. They were singing back.

With the new sound analysis capacity – and especially the ability to pinpoint which mouse the vocals are coming from – a platform for much broader research now is available.

The work could lead to advances in understanding autism, for example, and deficits that may exist in the neural circuits of the brain that underlie social communication, Neunuebel said.

Studying mouse communication and behavior can produce great insight into brain mechanics and systems and possibly give researchers valuable insight into how human brains work.

“We are just scratching the surface,” he said.

Studio Recordings

Neunuebel and his collaborators developed a fascinating system. They rigged up an acoustically precise chamber, surrounded by foam, that had nylon mesh walls to reduce “reflections” – the phenomenon of sound bouncing around an enclosed space and off walls.

They installed an array of four microphones, illuminated the chamber with infrared light, and linked each mouse to a tracking system.

They also developed a calculation to divide the sound into smaller pieces and then estimated the source location for all the small pieces, correcting for delays caused by the speed of sound in air at room temperature and at standard atmospheric pressure.

A theoretical grid was laid across the floor of the chamber, spaced at a quarter of a millimeter. From each point on the grid, they calculated the estimated delay between each possible pair of microphones and used this to analyze sounds and estimate their sources.

The system gathered data as four mice – two males, two females – were observed interacting and often detected vocal exchanges during chases when a male pursued a female.

The data showed that females who responded vocally to a male’s “song” also slowed down, making it easier for the male to catch up to them. Unresponsive females kept up their pace.

That makes researchers think these songs may be communicating important social information – but that is another study, yet to come.

Joshua P Neunuebel, Adam L Taylor, Ben J Arthur, SE Roian Egnor
Female mice ultrasonically interact with males during courtship displays
eLife 2015;4:e06203 DOI: http://dx.doi.org/10.7554/eLife.06203

Illustration: Jeff Chase, University of Delaware