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Enlighten Me: In mating, mice sing as a duet

Maggie Bartlett, NHGRI

Serenading sounds like an old-fashioned way to attract a mate, but for mice, singing plays a key role in courtship. Many studies have shown that male mice sing to females they’re interested in. But until now, there hasn’t been evidence that shows that females sing back. Recently, University of Delaware scientists have published a new study that shows that these romantic solos are actually duets.

In this week’s Enlighten Me, Delaware Public Media’s science reporter Eli Chen explains this new finding and its possible significance.

Think about all the ways you’d describe a mouse: it’s small, it’s afraid of cats, it likes cheese, it’s in cartoons. But to Josh Neunuebel, a neuroscientist who studies mice all day, the most interesting thing about them is how social they are.

“They have these incredibly dynamic and rich social interactions. They fight, they chase each other. They form dominance hierarchies so when males are around and they have to compete for something, they’ll try to establish who’s the alpha male,” said Neunuebel.

And some of the richest social interactions between mice take place as they’re mating. For many years, scientists believed that in courtship, males were the only ones doing the talking. Studies have shown that when males are alone with an unconscious female, or scientists put them near a female’s urine, males will try to interact with that female presence. But reverse the situation - and females aren’t vocal.  So- the thought was maybe the females don’t talk back.

But Neunuebel says that assumption may simply be the result of working with limited technology.

“The problem with the field is that we’ve never had a way to figure out who’s vocalizing,”  said Neunuebel.

Mice are usually kept in cages made out of hard plastic and if you record sounds in a hard plastic container, it’s tricky to pinpoint who or what is making a specific sound.

“When the sound is bouncing around, it makes trying to localize where the sound is coming from very difficult," said Neunuebel. "So the first thing we thought was, we need to solve that problem. We need to get rid of some of these reflections so it’s a cleaner signal that we’re looking at.”

And to find out if they could trace some of the “songs” back to females, Neunuebel and his colleagues built a small recording studio. We walked into the laboratory next door to check it out.

“This is the animal room facility, so it’s a very secure area, we’re going to have to gown up if you don’t mind, said Neunuebel. "You’re going to get the whole lab experience.”

After we buttoned up our lab coats and wrapped cloth shower caps around our shoes, we headed inside. In one of the rooms stood a black closet on wheels, a little more than five feet tall -- it looked like a prop a magician would use to perform a disappearing act.

“So this is where the magic happens...”

He opened the door to reveal a chamber made of nylon mesh walls and foam floors -- these are materials that absorb sound rather than reflect it. Smaller walls contained the middle part of the closet, which was covered in a layer of white pellets. Small ultrasonic microphones were placed along base of the contained area, since mice vocalize at a frequency that’s well above the range of human hearing. 

“This is their studio for singing and playing. We don’t want the sound from outside to interfere with anything so we enclose it in this giant box to block out all the sound," said Neunuebel.

And based on the audio and video recordings at this studio, the scientists were able to calculate that some songs were coming from the females. As the mice chased each other, the females who talked also slowed down their pace, almost as if to send the males a message

“Hey, I’m over here, I’m interested,” said Neunuebel.

The females who weren’t interested just kept going at a normal pace.

Listening to a recording of the mice, with the frequency slowed down by 20 times, Neunuebel was also struck by how much the males and females were interacting with each other, almost like they were having conversations.

A clip of the mice "singing" in their studio at University of Delaware's Spencer Lab.

“When the females increase their vocal rates, so do males. And when males increase their vocal rates, so do females. So it looks like there might be some vocal exchange going on," said Neunuebel. "It was really incredible to see that.”

Understanding how mice interact is important for Neunuebel’s research. His lab at University of Delaware studies social behavior in mice to learn more about communication deficits that occur with autism. One of things they’re looking at is how timing plays a role in social interactions. Now that the researchers have seen that exchanges take place between male and female mice, they might focus on how quickly male and female mice respond to each other -- and see how that compares with their autistic mouse models. 

Garet Lahvis, a neuroscientist at Oregon Health and Science University, also uses mice to study brain disorders that affect communication.

“I think one of the critical features of a social interaction is the ability to both listen to the individual that you’re having an exchange with and interject at moments of silence and when the conversation dies down,” said Lahvis.

If male and female mice are capable of having exchanges, Lahvis says it would be useful in brain research to know what the underlying mechanisms are behind these social interactions.

“And that would be enormously helpful in understanding various disorders from autism to other forms of mental illness,"  said Lahvis.

Right now, knowing that female mice sing back to their gentleman callers is just the tip of the iceberg.

“We don’t know if the male or female starts it, we don’t know the fine grain details of their interactions. There’s a lot of unexplored questions which we’re starting to deal with now.” said Neunuebel.

So just like humans, communication seems to be the key to successful relationships between mice. But whether there are pick-up lines or boxes of chocolate involved -- we’ll wait for the scientists listening in to find out.

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