Leaping Lizards! Gary Gillis’s New Research
Posted: February 18, 2009
Lizards have the ultimate quick release escape system. When in a predator’s grips, they drop their tails to escape, leaving the twitching body part to distract the predator as they scamper to safety. But what price do tree-dwelling lizards pay for freedom?
A team led by MHC biology professor Gary Gillis tested the effect the loss had on the lizards’ mobility and agility, and he found they were compromised: The lizards could no longer jump without tumbling backwards, making it difficult to land safely when jumping between branches. The results of his study were published February 13 in the Journal of Experimental Biology, and the research has already attracted international media coverage from the Canadian Discovery Channel and the Toronto Star, as well as publications in Germany, India, and Thailand.
Up to 50 percent of some lizard populations seem to have traded part of their tails in exchange for escape, according to Gillis. While the tails typically grow back in three to six months, he wondered how the loss might impact a branch-hopping, tree-dwelling lizard’s mobility and ability to survive in the interim. Teaming up with then-undergraduate student Lauren Bonvini '07, he began recording lizard leaps to observe how well the reptiles coped without their tails.
Bonvini--now a graduate student at Dartmouth College--remained on campus the summer following her graduation to continue working with Gillis on the project. Together they constructed a jumping arena from boxes and fine sandpaper, then gently encouraged arboreal Anolis carolinensis (anole) lizards to launch themselves from an 11-centimeter-high platform while filming the animals’ jumps. The lizards performed well, launching themselves by pushing off with their back feet and landing gracefully, covering distances ranging from 14.9 to 29.9 centimeters.
But how well would the animals perform without their tails? After holding the lizards' tails to encourage them to drop them, just as they would with a predator, Bonvini then persuaded the tailless reptiles to jump as Gillis filmed. As soon as the first animal took to the air, Gillis knew something was different.
"It looked weird," he said. "The animals became blurred as they jumped."
Replaying the animal's jump in slow motion, they could see the lizard was tumbling backwards, out of control, as its tail stump flailed. As he filmed other tailless anoles, four backflipped out of control, although two others seemed to manage their trajectories better.
Teaming up with Duncan Irschick of the University of Massachusetts, Amherst, to analyze the reptiles’ leaps, Gillis found that everything about the tailless lizards’ takeoff was exactly the same as it had been before they lost the appendage--until they left the jump stage. The lizards then began flipping back by more than 30 degrees; some tumbled so far that they landed on their backs. The team also realized that when the lizards with whole tails took off, they raised the base of their tails as the rest of the appendage trailed along the ground, as if it was somehow stabilizing the takeoff.
"If jumping and landing are important for lizards, they are clearly compromised after losing their tails. Coordinated landing on a branch is out of the question when spinning backwards," said Gillis. Escaping lizards pay a significant ecological cost for their life-saving quick-release system, he concluded.
So how do the lizards use their tails to ensure a safe touchdown? Gillis isn’t sure whether they push down with their tails at takeoff to prevent themselves from spinning, or whether the trailing tail passively stabilizes the animal’s departure. He is continuing his research to determine how lizards adjust to life without their tails, with differential degrees of tail loss, and after the tails have grown back.
That said, the lizards who participated in the most recent study have all found happy endings--despite their trials.
"They were all were adopted as pets by friends," Gillis reported.