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USF scientist unlocks mystery of high-performance toad tongues

TAMPA, Fla. -- How do toads, perhaps the least athletic of frogs, feed on fast moving insects?

Biologists have known for decades that toads snare prey by flipping their sticky tongues out in a flash of an eye--just a few thousandths of a second--far faster than any other movements the often-sluggish creatures make.

Only in the last few years, however, have researchers determined how the slow toad is capable of such a lightning fast movement. The toad springs its mouth open using elastic recoil in a bow-and-arrow mechanism that literally whips out its tongue and catches its prey.

Now researchers have just published a study in the Journal of Experimental Biology revealing that toads have an additional trick--they can flip their tongues and feed even in the cold, at temperatures that virtually immobilize many amphibians and reptiles.

Stephen Deban, an assistant professor in the University of South Florida’s Department of Integrative Biology, and Kristopher Lappin of California State University Pomona, both study the physiology and biomechanics of feeding in animals. The scientists were intrigued by the toad’s ballistic feeding mechanism.

The researchers knew that muscle contractions are severely slowed by cold temperatures, and that ectotherms like amphibians and reptiles can't warm their bodies above the temperature of their surroundings. Deban and Lappin reasoned that the toad's elastic recoil mechanism should allow them to circumvent this limitation--"like shooting a bow and arrow," Deban said.

“It doesn't matter how long it takes the muscles to draw back the bow, the arrow always flies at the same speed,” he added.

To test their hypothesis, Deban and Lappin used high-speed digital imaging at 6,000-frames per second to capture the details of southern toads, Bufo terrestris, feeding on crickets and beetles.

They simultaneously made electromyographic recordings of the mouth opening and closing muscles, to determine when the muscles were activated by the nervous system. All this was conducted in an environmental chamber at a series of temperatures from a chilly 50°F to a sweltering 100°F. The toads' muscle temperature was measured with an infrared thermometer.

The high-speed images revealed just what Deban and Lappin predicted: the toads launched their tongues with nearly the same speed at all temperatures, even at 50°F. The time from the start of the tongue flip to the full extension of the tongue was always less than 14 milliseconds (for comparison, it takes 100 milliseconds to blink your eyes).

The images also confirmed that feeding movements that are not elastically powered, were strongly affected by cold. At 50°F it took the toads two to three times longer to retract the tongue and close the mouth than at 100°F.

The muscle activity recordings showed that there was nothing special about how the toads jaw muscles or their nervous system reacted to the low temperatures. As in all animals, their muscles needed longer to "wind up" in the cold, with the mouth opening muscles turning on earlier to stretch out the elastic elements--up to 300 milliseconds before the mouth opened, more than 20 times longer than the tongue projection itself. These results showed that it is the elastic-recoil mechanism itself that gives toads their cold-proof tongue flipping ability.

This isn’t the first time a USF scientist has been involved in unlocking the mysteries of cold-blood creatures eating.Last year, Deban's laboratory discovered that chameleons can shoot their tongues out with maximum performance whether they are cold or warm, also by virtue of an elastic mechanism.

"Finding the same phenomenon in toads, which have evolved their tongue projection independently from chameleons suggests that elastic mechanisms may be a widespread strategy among animals to maintain high performance in the cold," Deban said."


Filed under:Arts and Sciences School of Natural Sciences and Mathematics Integrative Biology Research  
Author: Vickie Chachere