LEAPIN' LIZARDS--UC IRVINE RESEARCH SHOWS SOME REPTILES BREATHING EASIER
Can Lizards on Treadmills Shed Light on How We Breathe?
Irvine, Calif. -- They are the bionic beasts of lizardom, the Michael Jordans of the reptile realm.
Speedy reptiles known as monitor lizards have an anatomical advantage most other lizards can't claim, according to research done at UC Irvine. Monitor lizards can breathe while they run by pumping air through sacs in their throats, researchers report in the June 4 issue of Science. Other types of lizards can't breathe and run at the same time.
Mammals are believed to have evolved from reptilian ancestors. The study suggests that the evolution of increased, sustainable aerobic capacity in animals required the development of muscles that could power the lungs to move air in and out quickly, independently of whether an animal was running.
Studies of the locomotor and ventilatory systems of lizards also are important in providing a framework for ultimately understanding how humans breathe and the primary functions of human trunk muscles.
Tomasz Owerkowicz, a graduate student at Harvard University, and Beth Brainard, an assistant professor at the University of Massachusetts, observed that monitor lizards were pumping air through their throats. They came to UCI to better understand how the pumping contributes to breathing, and turned to James Hicks, UCI professor of ecology and evolutionary biology, and UCI postdoctoral fellow Colleen Farmer for help. Hicks is a leading expert in the heart-and-lung systems of vertebrates, especially reptiles, and researchers from across the country and world come to Hicks' lab to perform studies on animals from rattlesnakes to alligators.
Lizards scamper ahead by twisting their bodies from side to side as they move their feet forward. Muscles in a lizard's trunk make it possible to move forward this way. Those same muscles also control how a lizard rotates its ribs and expands its lungs to breathe.
Dave Carrier, an associate professor at the University of Utah, observed in earlier studies that lizards cannot use the same muscles for two actions--running and breathing--at the same time. So, most lizards cannot run far without getting out of breath. After a burst of speed, they must rest to recover the normal level of oxygen in their blood. But monitor lizards can run quickly and for some distance, and their blood oxygen levels remain high and constant while they're moving. This inconsistency has puzzled scientists.
The new study in Science shows that monitor lizards use a "gular pump"--a rapid pumping of sacs in the throat--to push air into the lungs while they run. It is a backup system that keeps air entering the lungs, even when the lungs cannot expand the ordinary way.
"The monitor lizard, the aerobic king of the lizard world, has circumvented the basic constraint of its breathing and walking apparatus by having an accessory ventilatory pump," Hicks said. "This would be analogous to the evolution of the diaphragm in mammals, which ventilates the lung independently of locomotion."
To do their study, the researchers compared the 12-inch long monitor lizards to another lizard, the green iguana. They put three iguanas and six monitor lizards through their paces on a treadmill. Each lizard ran at the maximum speed it could steadily scamper on the treadmill for one to three minutes, and the scientists shot x-ray videos of the creatures.
Next, they examined the videos frame by frame for evidence of gular pumping. (See pictures of the lizards at
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