To gain insights into the genes that contribute to the unique singing behaviour researchers are examining singing mice. The information they obtain could help them understand and identify genes that affect language in humans.
Singing mice (scotinomys teguina) are not your average lab rats. Their fur is tawny brown instead of the common white albino strain; they hail from the tropical cloud forests in the mountains of Costa Rica; and, as their name hints, they use song to communicate.
"We can choose any number of traits to study but we try and choose traits that are not only interesting for their own sake but also have some biomedical relevance," University of Texas at Austin researcher Steven Phelps said.
"We take advantage of the unique property of the species," he said.
The song of the singing mouse song is a rapid-fire string of high-pitched chirps called trills used mostly used by males in dominance displays and to attract mates.
Up to 20 chirps are squeaked out per second, sounding similar to birdsong to untrained ears. But unlike birds, the mice generally stick to a song made up of only a single note.
"They sound kind of soft to human ears, but if you slow them down by about three-fold they are pretty dramatic," Phelps said.
Most rodents make vocalizations at a frequency much too high for humans to hear. But other rodents typically don't vocalize to the extent of singing mice, which use the song to communicate over large distances in the wild, said Andreas George, a graduate student working in Phelps' lab.
Phelps's newest research projects is examining the genetic components that influence song expression. Center stage is a special gene called FOXP2.
"FOXP2 is famous because it's the only gene that's been implicated in human speech disorders specifically," Phelps said.
Having at least one mutated copy of the gene has been associated with a host of language problems in humans, from difficulty understanding grammar to an inability to make the precise mouth movements needed to speak a clear sentence.
The FOXP2 gene is remarkably similar overall between singing mice, lab mice and humans, said Phelps.
To find parts of the gene that may contribute to the singing mouse's songs, Phelps is searching for sequences unique to the singing mouse and testing them for evidence of natural selection, which weeds out mutations with no likely observable effect from those that are likely to contribute to singing behaviour.
"Those two things go a long way," Phelps said.
"And when you look at the intersection of those two things they give us a really good set of candidate regions for what might be causing species differences," he said.
Most genetic mutations don't cause serious problems. They are often a part of the genome that is not expressed, still make a functional product, or are simply drowned out by the amount of genes and gene products that are working correctly.
FOXP2 mutations, on the other hand, can have significant effects on speech because of the gene's role as a transcription factor-a gene product that helps control the expression of other genes.
This means a mutation in the FOXP2 gene can start a chain of events that can lead to reduced expression, or possibly even no expression, of a number of other genes.
Phelps and his team are figuring out what activates FOXP2 expression and the genes that are expressed after its activation by playing singing mice recording of songs from their own species and neighbouring species and observing the gene expression patterns.
Learning what activates FOXP2 and what genes are activated by it could provide clues into how outside stimuli affects gene expression and what genes are important in the understanding and integration of information, said Phelps.