NEWS RELEASE #14623, 9/3/97
More extreme than chameleons, some salamanders literally shoot their tongues at insects, UC Berkeley scientists discover
Berkeley -- Chameleons are known for firing their tongues at insects to snatch them off a leaf, and now scientists have discovered a salamander whose tongue goes ballistic too.
While all salamanders flick their tongues out to capture insects, scientists assumed they simply push them out the way most animals do.
While photographing a lungless salamander from Sardinia, however, UC Berkeley graduate student Stephen M. Deban discovered that it actually extends its tongue so far out of its mouth that it must be shot out like a bullet.
The lungless salamander Hydromantes supramontis. (Click on photo for 51 K JPEG image.)
PHOTO CREDIT: Nature Magazine and Steve Deban
"The tongue's skeleton completely leaves the body like a little harpoon," says Deban, a doctoral student in the Department of Integrative Biology and a member of UC Berkeley's Museum of Vertebrate Zoology. "The tongue is truly ballistic, like that of a chameleon."
Deban and David B. Wake, professor of integrative biology and a specialist in frogs and salamanders, in collaboration with Gerhard Roth of the Brain Research Institute of the University of Bremen, Germany, report their find in a brief scientific correspondence in this week's issue of Nature (9/4/97).
"(The salamander) Hydromantes launches its entire tongue skeleton at prey and thus is the only vertebrate known to shoot part of its visceral skeleton completely out of its body as a projectile," the researchers conclude in their Nature note.
Deban studies the behavior of the so-called lungless salamanders -- the family Plethodontidae that includes about two-thirds of all salamander species in the world. Most lungless salamanders -- so-called because they breathe through their skin and have no lungs -- live in the New World tropics, but many live in North America and five species inhabit southern Europe, primarily France, Italy and Sardinia.
While visiting Roth in Germany, Deban spent a day trying to get better pictures of lungless salamanders with their tongues extended, using as subjects Roth's study animals, members of the species Hydromantes supramontis native to the island of Sardinia.
Upon developing the nearly 140 photos from the shoot he noticed one in which the salamander had its tongue extended almost 6 centimeters (a little over 2 inches), approximately 80 percent of the salamander's head and body length. Deban says his photo subjects often hit targets at that distance, but he was able to catch only one on film.
It soon dawned on Deban that the skeleton inside the tongue wasn't nearly that long, meaning that the supporting structure of the tongue must emerge entirely from the salamander's mouth. The implication is that the salamander doesn't merely push the tongue out but throws it out and lets its momentum carry it toward the target.
"I've been looking for evidence of this since 1982, when I was challenged to prove my suspicion that some salamanders have a ballistic tongue," Wake says. "This spectacular photograph by Steve finally proves it."
The salamander flings its tongue in the same way a melon seed is launched from between two fingers. The skeleton of cartilage in the tongue is shaped roughly like a pair of tweezers, with the two prongs facing the tail. Each prong is encased in a sheath of spiraling muscle fibers that, when they contract, squeeze the prongs and shoot the cartilage out of the mouth.
Interestingly, the chameleon achieves the same effect in the opposite manner: the cartilage remains in the head and the encircling muscle shoots out of the mouth. Apparently, Wake says, the two unrelated creatures independently evolved a similar method for capturing prey .
In both animals a sticky pad at the tip of the tongue immobilizes the insect until it can be brought into the mouth.
Deban predicts that other members of the genus Hydromantes also use a ballistic method to protract the tongue, because all have the same tongue structure and internal cartilage. Among these are the only species native to North America, all three from California: the Shasta salamander from northern California; the Mount Lyell salamander that lives in the Sierra Nevada; and the limestone salamander from the area of the Merced River.
"I have no doubt they are capable of using this mechanism," Deban says. Wake suspects that many members of the lungless salamander family do likewise.
Most members of Hydromantes live entirely on land, spending part of the year in caves or crevices, walking around on rock walls with the aid of large webbed feet, laying eggs in moist places and living off insects and other small creatures. Even before Deban's discovery they were known to have the longest tongues relative to their body of any amphibian, though none have tongues approaching the length of the much larger chameleons, members of the lizard family, Chameleonidae.
These salamanders are quick with their tongues too. They can flick them out in about a hundredth of a second, much faster than chameleons, Wake says. Also, while a chameleon's tongue falls slack and is rewound into the mouth after catching a fly, salamanders jerk their tongues back.
"These salamanders have a remarkable protraction system that heaves the tongue out of the mouth and jerks it back in so fast you don't see the tongue at all -- you just see the fly disappear," Wake says. "With a chameleon the tongue falls limp and is cranked slowly back into the mouth."
The salamander can do this because the muscle that retracts the tongue into the mouth contracts as the tongue flies outward, enabling it to pull back quickly upon hitting the insect.
Some frogs also employ ballistic protraction, Deban notes, though they have no tongue skeleton and simply throw the tongue muscle out of the mouth.
Deban and a post-doctoral student in the museum, Mario Garcia-Paris, reported two years ago that one of the related California salamanders, the Mount Lyell salamander (Hydromantes platycephalus), is unique in another way. It has adopted a novel technique for escaping predators: it curls sideways into a ball, tucks its legs and rolls downhill for up to 1 1/2 feet.
Deban soon will head off to Roth's laboratory in Germany to continue his study of how the brain coordinates the muscle contractions to shoot the tongue out, and how this coordination might have been modified from a more general tongue-pushing system. He is interested in how such an extreme system might have evolved in Hydromantes and its shorter-tongued relatives.
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