Mice sing. The question is, where do they learn their songs?
How do mice learn to sing?
That’s the question plaguing two sets of scientists in the U.S. and Japan, whose independent mouse-song studies were published on the same day in the peer-review journal PLoS ONE.
But even though their fascination with the vocal contortions of mice are similar; the results of their studies are not.
While not engaged in a choral competition in your cupboards, there’s no dispute between researchers that mice are big singers. So why can’t you hear them?
“Mice communicate at frequencies that are above 50 kHz,” Dr. Jasmine Grimsley of Northeastern Ohio Universities and co-author of one of the studies told the Star. “To put that into the human perspective, speech is spoken at frequencies below 4 kHz. Sounds are considered to be ultrasound, inaudible to humans, if they are above 20 kHz. So these mouse songs are more than two times the top of a person’s hearing range.”
That puts the calls of mouse pups at a higher frequency than those emitted by bats.
Song made by BALB/c mice:
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Adult mice use their song, which resembles the tweeting of birds, to get the attention of mates, while pups sing to let their parents know they are hungry, cold or have fallen out of the nest.
What scientists don’t yet know is where mice get their tunes from. Are they genetically prone to hum a particularly ditty or do they pick it up from the harmonious hordes around them?
In separate studies, teams at universities in the U.S. and Japan examined the syllables emitted by mice pups from their birth to maturity.
“One way to think about mouse syllables is this: If a mouse song were like our sentence, a mouse syllable would be like our word,” explained Grimsley.
The team in Ohio monitored pups from birth to adolescence and found that newborn mice were able to emit 11 of the 12 syllables used by their parents. The patterns the pups used, though, were simple and repetitious in comparison to their elders.
“As they grew older, they started to use the other syllables more and more, producing song that was a lot more complex,” said Grimsley. “The songs of the older pups, and more so the adults, had more order to them because the syllables were likely to be produced in set patterns. So, it’s like they were developing tunes to sing.”
Focusing on the differences between the songs adult and newborn mice produce, the paper out of Ohio suggests that mouse song is both learned and innate: Pups are born with the notes, but learn from the more complex singing of their grown peers.
“We found many differences that seem likely result from both genetics and learning. But as yet, it is unclear which of the changes are learned and which are innate,” Grimsley says.
But in Japan, the link between what a mouse sings and its genes was found to be absolute.
Dr. Takefumi Kikusui, from Japan’s Azabu University, and a team at the RIKEN Brain Science Institute swapped the mouse pups from two strains of mice at birth.
Different strains of mice emit very different songs. The Japanese team wanted to see if mice would learn to hum the tune of the strain they grew up with or keep to the musical stylings of their particular breed.
“If the mice could learn the songs from the parents, and maintain the template of the songs, like song birds, they would the cross-fostering effects,” Kikusui explained to the Star.
But what they found instead was the adopted mouse pups continued to sing the song associated with their strain, despite never hanging out with other native singers.
“A small difference was observed,” noted Kikusui, with a few of the syllables’ harmonics resembling those of the host parents, but an “all over analysis of the song composition showed no significant effects of cross fostering.”
Grimsley and her team accept that genetics are significant when it comes to mouse song, but believe the Japanese study is stretching too far with its claim that mouse song is utterly innate.
“In birds, where vocal learning is best understood, they often learn song from their fathers when they are juveniles, not chicks,” says Grimsley. “The time period they tested the mice in is equivalent to being a chick. A comparable time for learning songs in mice would be when they are adolescent, between 21 and 40 days of age.”
With both teams of scientists set to continue their research, you can be sure you haven’t heard the last of singing mice.
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