Research by UMass Amherst Biologist Suggests that Lizards Offer Evolutionary Freeze-Frame

June 4, 1999


AMHERST, Mass. - Research by Elizabeth Brainerd, of the biology department at the University of Massachusetts, addresses a long-standing disagreement among scientists regarding how lizards breathe. The study, conducted along with colleagues at Harvard University and the University of California, is detailed in the current issue of the prestigious journal, Science. The work was funded by the University of Massachusetts, the National Science Foundation, and a Chapman Fellowship.

Brainerd''s specialty is biomechanics with an emphasis on evolution. Her work focuses on breathing in lizards. This particular study focused on breathing in green iguanas and monitor lizards. Researchers took X-ray videos of the lizards while the animals walked on treadmills.

For years, researchers have disagreed about whether lizards can run and breathe at the same time. The iguana uses chest muscles for both running and breathing, and so is unable to run and breathe simultaneously. This results, Brainerd says, in "a skittering-type locomotion." Many other kinds of lizards are believed to face the same constraint.

The monitor lizard, however, has the ability to run and breathe simultaneously. Brainerd and her colleagues discovered that monitor lizards, when they run, are able to use a large pump in the throat, called a gular pump, for breathing. The mouth and throat cavity are used, Brainerd says, "like a bicycle pump," as the lizard squeezes air into its lungs. This back-up system enables the monitor lizard to overcome the anatomical limitations of other lizards, she says.

Researchers believe that the monitor lizard has circumvented the basic constraint of its breathing and walking apparatus by having this accessory ventilatory pump. The development would be analogous to the evolution of the diaphragm in mammals, which ventilates the lung independently of locomotion, the scientists say. This would suggest that the monitor lizard is at an evolutionary midpoint, relying on both forms of breathing, Brainerd says.