Koala Bellows Deciphered

The pitch of male koalas' mating calls is about 20 times lower than it should be, given the Australian marsupial's relatively small size. Now, researchers reporting in the journal Current Biology have discovered their secret: koalas have a specialized sound-producing organ that has never before been seen in any other land-dwelling mammal. The key feature of this newly described organ is its location outside the voice box, what scientists call the larynx (Figure 1).

Koala_anatomy

Figure 1. The velar vocal folds (dark red) of male koalas are located at the intersection between the oral and nasal portions of the pharynx just opposite to the laryngeal entrance. Oral tract in light blue, nasal tract in yellow, soft palate in light red, laryngeal vocal folds in green, and arytenoid cartilage in blue. (From Charlton et al., 2013).

"We have discovered that koalas possess an extra pair of vocal folds that are located outside the larynx, where the oral and nasal cavities connect," says Benjamin Charlton of the University of Sussex. "We also demonstrated that koalas use these additional vocal folds to produce their extremely low-pitched mating calls."

The koala's bellow calls are a continuous series of sounds produced on inhalation and exhalation, similar to a donkey's braying, Charlton explains. On inhalation, koala bellows sound a bit like snoring. As the animals exhale, the sound is more reminiscent of belching. And, as Charlton says, "they are actually quite loud."

They are also incredibly low-pitched, more typical of an animal the size of an elephant. Size is related to pitch in that the dimensions of the laryngeal vocal folds normally constrain the lowest frequency that an animal can generate. As a result, smaller species will typically give calls with higher frequencies than larger ones.

Koalas have bypassed that constraint by putting those vocal folds in a new location. Charlton describes the folds as two long, fleshy lips in the soft palette, just above the larynx at the junction between the oral and nasal cavities. They may not look all that different from the laryngeal vocal folds of other mammals, but their location is highly unusual.

"To our knowledge, the only other example of a specialized sound-producing organ in mammals that is independent of the larynx are the phonic lips that toothed whales use to generate echolocation clicks," Charlton says.

The combination of morphological, video, and acoustic data in the new study represents the first evidence in a terrestrial mammal of an organ other than the larynx that is dedicated to sound production. Charlton says that he and his colleagues will now look more closely at other mammals to find out whether this vocal adaptation is truly unique to koalas.

Source: Modified from materials provided by Cell Press.

Reference

Charleton, B.D., Frey, R., McKinnon, A.J., Fritsch, G., and D. Reby. 2013. Koalas use a novel vocal organ to produce unusually low-pitched mating calls. Current Biology, 23:R1035-R1036.
http://dx.doi.org/10.1016/j.cub.2013.10.069

Read More...

Vaccine Could Save Tasmanian Devils From Extinction.

New research paves the way for the development of a vaccine for the Tasmanian devil, Sarcophilus harrisii (Figure 1), currently on the brink of extinction because of a contagious cancer.
Read More...

Opportunistic Torpor Down Under

Seasonal torpor is well known in northern latitudes. Placental mammals, including some rodents and many bat species, enter torpor to conserve energy when ambient temperatures fall and food becomes scarce. Prolonged torpor is characterized by highly Read More...

Caller ID in Koala Calls

The phone rings, you answer, the caller says “hello, and” you instantly recognize the caller’s voice. This ability to recognize other individuals by their voice is also relatively common in baboons and other non-human primates. Until recently, Read More...

Housing Bubble in Marsupial Tree Hollows

Extended families often live together under the same roof. Indeed, in many human societies even distant relatives (aunts, uncles, cousins) share the same dwelling. Less common (except for college students) is house sharing among unrelated individuals. Under what circumstances Read More...

Marsupial radiations revealed

Living metatherians exist in two strongholds: the Neotropics (Mexico, Central America, and South America) and the Australasian region (Australia, Tasmania, New Guinea, and nearby islands). One hypothesis to explain this odd distribution proposes that metatherians Read More...