Ballistic Tongues Launching when Cold
Chameleons, toads, and some salamanders can project their tongues ballistically using elastic recoil, like shooting a bow and arrow. Collagen connective tissue is in line with muscle fibers and gets stretched when the muscle fibers contract, storing elastic energy. This energy can be released extremely quickly, far faster than the muscle fibers contracted while stretching it, which means that the tongue can be launched with more power—a higher rate of energy release—than if it were powered directly by muscle contraction. The rapid recoil of the collagen is decoupled temporally from the contraction of the muscle fibers that stretched it, so the rate at which the muscle stretches the collagen is irrelevant to the speed of tongue projection. When chameleons, toads, salamanders and other ectotherms cool down, the speed of muscle contraction slows and so do their movements. Ballistic movements such as tongue projection that make use of elastic recoil, however, are able to circumvent this thermal handicap, because the rate of recoil of collagen is independent of temperature.
This movie shows a Chamaeleo calyptratus, the veiled chameleon, capturing a suspended cricket at two different temperatures, 35°C (top) and 15°C (bottom), slowed down 100 times. You can see that tongue projection is similar at these two temperatures, but tongue retraction is much slower at the colder temperature. Tongue retraction does not use elastic recoil and depends upon direct muscle contraction. Our paper in PNAS provides details of our temperature experiments on chameleon tongue projection.
Here a southern toad, Bufo terristris, capture crickets at two temperatures, 24°C (top) and 17°C (bottom), slowed down 100 times. Notice that ballistic mouth opening and tongue projection—which are elastically powered—are nearly identical, but that tongue retraction and mouth closing are slower in the cold. Like the chameleon above, the toad is able to circumvent the slowing effects of cold on muscle contraction using elastic recoil. See our paper in JEB for more details.
Like the toad and chameleon, the ballistic-tongued Hydromantes platycephalus can shoot its tongue at cold temperatures. This species lives at high elevation (~3000 m) in the Sierra Nevada mountains of California and is active at freezing temperatures, so a cold-proof tongue projection mechanism is an asset. This movie shows an individual feeding at two temperatures. See our "Cold-blooded snipers" paper in JEZ.
See more feeding movies on our YouTube channel
This material is based upon work supported by the National Science Foundation under Grant No. IOS 0842626.