June 13, 2014
Horned Frogs Use Adhesive Tape-Like Tongues To Lift Three Times Their Own Bodyweight
redOrbit Staff & Wire Reports - Your Universe Online
The tongues of horned frogs are capable of lifting up to three times their own bodyweight, thanks to a biological mechanism comparable to adhesive tape, according to a new study published Thursday in the journal Scientific Reports.
Dr. Thomas Kleinteich of the University of Kiel in Germany and his colleagues conducted a series of experiments in which they placed a horned frog in front of a glass slide, and then tempted it by placing a cricket on the other side. When the amphibian’s tongue shot out in order to seize the prey, the forces exerted by the tongue were recorded by a transducer attached to the slide.
In the wild, South American horned frogs (also known as the Pacman frog) have proven themselves capable of snatching whole mice, though the adhesive performance of their tongues and the mechanism of the contact formation with its prey were unknown. They also consume lizards, snakes, small birds and other frogs – all of which would normally be large enough to escape being swallowed without the special adhesive apparatus on the creatures’ tongues.
Dr. Kleinteich used four specimens obtained from local pet shops, explained Amanda Onion of Discovery News, but even those creatures demonstrated “incredible tongue power and speed,” with the forces from their tongues averaging more than the weight of the tongues themselves, and over three times bigger in the case of one younger frog.
Frog tongues produce an average of just 1/15 the adhesive strength of a gecko’s feet, the researcher told National Geographic’s Jennifer S. Holland, but “in terms of prey capture, frog tongue adhesive forces are enormous – on average 1.4 times their body weight.” That would be the equivalent of a 176-pound human lifting 246 pounds using only his or her tongue, and doing so within “milliseconds” of first making contact, she added.
After each of the experiments, Dr. Kleinteich and his colleagues removed the equipment and allowed them to consume the cricket, ensuring that the creatures would be satisfied and able to continue participating. A total of 20 measurements were collected from each frog, with scientists analyzing tongue prints left behind on each glass slide, said BBC News science reporter Jonathan Webb.
“It's the first time we've ever measured how well frog tongues stick,” Dr. Kleinteich told Webb. “The common belief is... that the mucus acts as some sort of superglue. But what we found was actually that we got higher adhesive forces in trials where we found less mucus. That was quite interesting.”
The mucus appeared to accumulate over time, the BBC News writer noted, but the study authors found mucus coverage tended to be on the low side during initial contact. While they said that the mucus is certainly a wet adhesive system and plays a role in the phenomenon, it does not act like superglue. The key is the combination of structure and the mucus, which is what led the researchers to make the adhesive tape comparisons.
Dr. Kleinteich and his team will now use microscopes as part of an in-depth examination of the surface of the horned frogs’ tongue, Webb said. The researcher should have few complaints about doing so, as he told BBC News that working on the experiments was “fun… I used to do a lot of morphological, descriptive work with amphibians - I used to study dead, museum specimens. For me it was quite exciting to work with the living frogs.”