Scientists have known for decades that female lab mice or their pheromones cause male lab mice to make ultrasonic vocalizations. But a new paper from researchers at Washington University School of Medicine in St. Louis establishes for the first time that the utterances of the male mice are songs.
This finding, to be published Nov. 1 online by the journal Public Library of Science Biology, adds mice to the roster of creatures that croon in the presence of the opposite sex, including songbirds, whales and some insects.
"In the literature, there's a hierarchy of different definitions for what qualifies as a song, but there are usually two main properties," says lead author Timothy E. Holy, Ph.D., assistant professor of neurobiology and anatomy. "One is that there should be some syllabic diversity—recognizably distinct categories of sound, instead of just one sound repeated over and over. And there should be some temporal regularity—motifs and themes that recur from time to time, like the melodic hook in a catchy tune."
The new study shows that mouse song has both qualities, although Holy notes that the ability of lab mice to craft motifs and themes isn't quite on a par with that of master songsmiths like birds.
"Perhaps the best analogy for mouse song would be the song of juvenile birds, who put forth what you might call proto-motifs and themes," he explains. "It's not yet clear whether singing conveys an advantage to male mice during courtship, as it appears to do in birds."
Holy and study co-author Zhongsheng Guo, a programmer in his lab, came to be interested in the mice's vocalizations via the Holy lab's studies of the response evoked in the male mouse's brain by female mouse pheromones. Pheromones are chemical signals emitted by many different species that are frequently linked to mating.
"Studying this kind of response in mice lets us model higher-level tasks such as pattern recognition and learning in a brain where the neuroanatomy is much simpler than it is in humans," he explains. "The idea is to help us lay a foundation on which we can eventually construct a very concrete understanding of how these tasks are accomplished in the human brain."
According to Holy, scientists have not previously recognized mice vocalizations as song because they are unusually difficult to record and analyze. Only with the advent of improved technology for recording and analyzing the sounds and more powerful computers did it become possible to finally subject the vocalizations to careful analysis.
"We started recording the vocalizations to assess the factors that lead to recognition of female pheromones, but the vocalizations turned out to be much more complicated and interesting than we expected," he says. "That led us to decide to study them in their own right."
Likely areas for follow-up investigation include the question of whether wild mice vocalize in the same manner as laboratory mice, which have been kept and bred inside laboratories for more than a century.
"It's easy to imagine the wild mouse vocalizations will be different, since 'domestication' has changed many aspects of mouse behavior," Holy says. "So it would be intriguing to find out if their songs are more or less birdlike than the lab mouse songs."
Holy also wonders if mice learn singing from a tutor, as birds do.
"If these processes occur in mice, it may be a little bit easier to study the genetic factors that underlie song-learning in mice, because we already have a completed mouse genome, and the mouse is well-suited for genetic studies," he says.
The Washington University Genome Sequencing Center was a major contributor to the completed mouse genome, which makes it easier for scientists to draw links between genes in mouse DNA and proteins and processes they observe in the mouse. Comparative genomics can then be used to look for genes in human DNA that are likely to be linked to similar functions.
Holy T and Guo Z. Ultrasonic songs in male mice. Public Library of Science Biology, Nov. 1, 2005.
This study is currently available at: http://www.plos.org/press/plbi-03-12-holy.pdf
Funding from the National Institutes of Health and the Pew Scholars Program supported this research.
Materials provided by Washington University School of Medicine in St. Louis. Note: Content may be edited for style and length.
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