Lickin' Lizards

USF scientists shed light on hunting proficiency of chilly chameleons.

 

By Vickie Chachere

 

Tampa, Fla. (March 9, 2010) – Chameleons are known for their changing colors, their ability to look in two different directions at the same time and the distinctive digits on their feet. Now, a pair of USF researchers has unmasked the reptile for another attribute: their high-performance hunting even under chilly conditions.

Biologists Christopher V. Anderson and Stephen M. Deban are the authors of a new study which documents that chameleons can hunt – and do it well – at temperatures as low as 15˚C, a temperature that would immobilize many other reptiles. (Watch a video of their deft hunting here.)

So while chameleons seem in no hurry, their bug-lashing tongues certainly are at all hours of the day with the help of an elastic recoil mechanism that is insensitive to temperature in a way muscle tissue isn’t.

The study found that this ability has given the slow-moving, sit-and-wait predator an advantage in feeding on early morning insects with a sure element of surprise. Their research is published this week in the new issue of the Proceedings of the National Academy of Sciences.

Using high-speed cameras to analyze how chameleons under temperature-controlled laboratory conditions feed on crickets, the duo found that chameleons use a “bow and arrow” mechanism that decouples muscle contraction, allowing elastic recoil to launch the chameleon’s tongue at its prey, which is then snapped back into the reptile’s hungry jaws.

The chameleon tongue accelerates at more than 41 G’s, making them particularly stealthy hunters in their native habitats, which range from sub-Saharan Africa to Madagascar to southern Europe and even India. Chameleons can be found in the searing desert sand dunes of Namibia to high altitudes where nighttime lows drop to freezing temperatures.

The chameleons are faster tongue-flickers at warmer temperatures, the scientists noted, but exhibited high-performance hunting skills at temperatures as low as 15 ˚C – demonstrating physical abilities more powerful than animals such as quail in a vertical takeoff, sprinting lizards and jumping frogs.

For Anderson, who has studied chameleons and kept them as a hobby for 13 years, the discovery adds a new dimension to an animal which has thrived with more than 200 species worldwide. Understanding their ability to hunt when other reptiles must wait to be warmed by the sun to get moving may explain some of their success, Anderson said.

Scientists had long observed that chameleons would be active during early morning hours – when some insects also are active – but had no explanation for how or why the reptile was an outlier when it came to morning temperatures. Like all reptiles, chameleons elevate their body temperatures by basking in the sun.

It took a specialized high-speed digital camera shooting 3,000 frames a second, five Chamaeleo calyptratus and a specially-chilled room to find out.

The team carefully monitored the chameleon’s body temperature and allowed the room to chill before dangling crickets in front of their study subjects.  They found the chameleon’s tongue projection occurred in phases in which the temperature-dependent muscle used to wind up the chameleon’s tongue spring is temporally decoupled from the recoil of the collagen connective tissue that is used to launch the tongue. They measured the feeding episodes for peak velocity, peak acceleration and peak power, finding that chameleons are at their peak hunting prowess in warmer temperatures but fend for themselves quite well when the mercury dips.

Anderson and Deban likened the chameleon’s tongue to a bow and arrow – one in which the bow is pulled back slower when it’s cold, but it’s still an efficient way to hunt.

“They don’t have to chase their prey,” Deban said. “They can hunt their prey in the branches, even when it’s cold.”

 

Photo by Christopher V. Anderson

 

The University of South Florida is one of the nation's top 63 public research universities and one of only 25 public research universities nationwide with very high research activity that is designated as community engaged by the Carnegie Foundation for the Advancement of Teaching.  USF was awarded $380.4 million in research contracts and grants in FY 2008/2009. The university offers 232 degree programs at the undergraduate, graduate, specialist and doctoral levels, including the doctor of medicine. The USF System has a $1.8 billion annual budget, an annual economic impact of $3.2 billion, and serves more than 47,000 students on institutions/campuses in Tampa, St. Petersburg, Sarasota-Manatee and Lakeland. USF is a member of the Big East Athletic Conference.

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