Monkey lips, junk, and melon. Much of the anatomy of dolphins and whales was named by whalers, the first group of people to become intimately familiar with the innards of these seas mammals. The phrases they used reflect their one-sided interest in the sellable products they could extract from the beasts. For instance, right whales (Eubalaena spp.)were the “right” whales to hunt.

Monkeys lips (known academically as phonic lips) are actually an integral part of sound production in toothed whales, Odontoceti. Like any mammal, whales have two nares (the nasal passages that end in our nostrils). The ends of the nares in baleen whales are fused, forming a blowhole. Toothed whales however has an asymmetrical arrangement; one naris has become dominant leading to the blowhole, while the other ends in a blind tunnel.

Vocal cords are absent in cetaceans and the nasal and oral systems are completely separate. This is where the monkey lips come in; these paired muscular structures manipulate the air flowing from the lungs toward the blowhole, like the human larynx. The resulting clicks and whistles are shaped and directed as they pass through the melon (the big bulge on a dolphin’s forehead). The ingenious uses of this asymmetrical vocal apparatus include echolocation and social communication.

A paper published early this year in the Journal of the Acoustic Society of America by researchers from Hawaii and California measured the biosonar of bottlenose dolphins (Tursiops spp.). The authors used an array of microphones positioned around the dolphins to listen to the clicks the creatures produced while echolocating. Previous experiments positioned the microphones in a single plane, but in this study microphones were placed at angles ranging up to 90 degrees, or perpendicular to the dolphin. This larger picture revealed another asymmetry in cetacean sound-production: it seems only the right phonic lip was used in propagating clicks.

The social communication repertoire of toothed whales is an area of much academic interest. A study published earlier this year in Animal Behaviour by a collaboration of Russian and Canadian researchers examined the dialects of killer whale (Orcinus orca) populations off the coasts of Alaska, Canada, and the Kamchatka peninsula of Russia. They found that the types and subtypes of various calls were consistent within populations. On the other hand, the dialect differences between populations seemed to have no relation to the geographical distances separating them. This suggests a complex interaction between selective pressure to maintain a group dialect and random events that accumulate regional differences.

This blog is about humans and other animals and the interactions between them. The “monkey lips” were named by callous whalers, but now scientists have given us a deeper understanding of the inner workings of this unique vocal structure employed by some of the animals with which we share this planet.

 

Sources:

Whitlow W.L. Au et al. “Dolphin biosonar signals measured at extreme off-axis angles: Insights to sound propagation in the head.” J. Acoust. Soc. Am. Volume 132, Issue 2, pp. 1199-   1206 (2012)

Olga A. Filatova et al. “Call diversity in the North Pacific killer whale populations: implications    for dialect evolution and population history.” Animal Behaviour,    Volume 83, Issue 3, March 2012, Pages 595–603

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