The lab in the Bryan Research Building on Duke University’s campus doesn’t look like a recording studio.
“But this is where it all happens,” says Jonathan Chabout, a neuroscientist who is studying autism in mice and its possible connection to autism in humans. “We have 12 cages with very fancy microphones that can capture ultrasound recordings, and each of those is plugged into a computer so we can record 12 channels at the same time, so this is our studio.”
The lab specializes in recording sweet, lilting and haunting love songs. There are no words in these soft, high-pitched ballads because mice sing them.
That’s right. Mice.
Everybody knows the little creatures squeak, but Duke researchers discovered that male mice sing. It’s only the males who break into song, and those songs are all about love.
“We call these sexy songs because it shows the male can produce a complex song and that makes him attractive for mating,” says Dr. Erich Jarvis, Associate Professor in the Department of Neurobiology at Duke University Medical Center. “And we’ve found that the only behavioral context to make them sing is anything related to a female, such as a female presence or even something touched by female urine. The singing is all related to courtship behavior.”
Let that sink in for a moment. Female mice can induce male mice to break into silly love songs.
And just like people, researchers found the type of love song depends on the context. Researchers recorded male mice when they were roaming around their cages, when they were exposed to the smell of female urine and when they were placed in the presence of a female mouse. It turns out the songs male mice sing are louder and more complex when the male mouse smells a female and is looking for her.
“The females prefer these more complex sounds than the simple ones,” adds Jarvis. “In fact in our experiments we found if you play the songs back through speakers, the females spend more time around the speaker playing the complex songs.”
Researchers don’t believe that attraction to more complex songs means anything semantically. They compare it to how humans react to a jazz musician, in which some songs are preferred more than others.
After showing how male mice break into complex song when females aren’t around, researchers then placed a female mouse in a cage with a male mouse. Once again, the male mouse started singing, but this was a different tune.
“You can see how the songs get shorter and simpler when the two mice are together,” says Chabout, pointing to the marks on a computer screen, which visually graph the song. “We think the male is more interested in chasing the female than in producing complex sounds.”
In fact when comparing the male mouse’s behavior to the songs, it became clear the male mouse sang complex songs when he was on the other side of the cage, but then switched to simple songs when he got close to the female mouse.
Proximity to the lady mouse is, it seems, important in song selection.
The discovery puts mice in a pretty elite group of animal vocalizers such as birds, whales, and dolphins. But don’t try to listen for the songs of love-struck mice, because the little singers harmonize in the ultra-sonic range, which is too high-pitched for the human ear.
Mouse songs start at 40 kilohertz and can go as high as 100 khz. Human hearing starts around 15 khz. Special microphones are needed to record the mouse songs, which are then played back at a lower frequency.
The mouse songs were discovered almost by accident. Mice vocalization is being studied as a model to understand human vocal behavior and the effect of autism. In humans, autism not only limits speech but also makes it very monotone. The same thing happens to autistic mice.
Researchers have already found that mice with a genetic variant sometimes seen in autism have what could be called stunted squeaks. Those stunted squeaks could be used models for studying non-verbal autistic individuals who have problems uttering words.
“We’re trying to test the limits of mouse vocalization systems as a model to understand human behavior,” explains Dr. Jarvis. “Because we are now starting to be able to characterize mouse vocal behavior, and we’re gaining a better understanding of the brain, we can be better informed of what to look for and how to study the mechanisms of autism in a mouse.”
Dr. Jarvis then looks at the mice scampering around the cage and smiles. “Plus,” he adds, "I think this discovery is also important just because it’s fascinating and it helps us appreciate and understand nature and the biology of the animals around us. It’s through that we get a better appreciation of ourselves.”