Nature’s engineers

Our good colleague, Dr. David Hu at Georgia Tech and his students are often at Zoo Atlanta. Setting up their expensive hi-tech and high-speed cameras, or a just a GoPro, all around the Zoo to record—quite simply—what the animals do. Then the subject the videos to months of analyses and mathematical models that would stump most of us. The results wind up revealing truly fascinating insights into how animals do what they do. Have you ever thought for too long about eyelashes? I didn’t think so. How about cat tongues? The Hu lab has worked with nearly every variety of animal at the Zoo, including our cats, goats, elephants, frogs and snakes. In a blog posting last year, I highlighted their work with frog tongues and saliva. At a recent conference I attended, I saw Dr. Hu’s graduate student, Alexis Noel, deliver a fascinating update on her research on the functionality of cat tongues.

At the same conference, the Hu lab also presented an update on their work with a Zoo favorite, Kelly the African elephant, and her amazing trunk. As a backstory to their research, let’s consider elephant trunks for a moment. The trunk is a unique structure across all vertebrates. Most moveable appendages in nature contain bones to serve as underlying anchors for muscle attachment and to form hinges. Can you imagine your arm functioning without bones, and hinges in your wrist and elbow? Or how about a giraffe’s neck with no bones in it? The trunks are an exceptional example of a muscular hydrostat that operate under the principle that water (for example, the fluid inside those thousands of muscle cells) cannot be compressed. So, any muscular force that attempts to compress the fluid in the opposing sets of muscle cells will produce an equal force in the opposite direction. In other words, because the fluid inside those cells cannot be squirted to a different place when force is applied, the fluid acts in the same manner as a rigid bone would do. This is the same principle to explain how an earthworm moves and how an octopus manipulates its arms.

In fact, your own tongue is also a muscular hydrostat. There are no bones in your tongue, correct? If there are, you might want to see a specialist. But a peculiar arrangement of three sets of muscles in the trunk allows it to be far more powerful, yet also dexterous than animal tongues, worms, or even octopi can accomplish. Series of long muscles, many attaching to the skin itself, extend along the length of the trunk to raise, lower, or move it side-to-side. Another series of many shorter muscles are oriented perpendicular to the length of the trunk, and series of unusual helical muscles are wrapped barber-pole style along the length of the trunk. These latter muscles produce the unique twisting abilities of the trunk. Note that the extreme twisting motions of elephant trunks would not be possible if the trunk contained bones. Even snakes, with hundreds of vertebrae along their length, are very limited in their abilities to twist. Applied together, under very fine nervous control, this array of muscular orientations accomplishes both astonishing strength and delicate manipulations of even small objects. The fleshy trunk is an extension of the fused upper lip and the nostrils. At the tip are two opposing tips that are under muscular control and used to grasp smaller objects, in much the way we would use our forefinger and our thumb to pick up a coin. Dr. Hu and his students have been studying the forces that Kelly applies to different varieties of small treats in order to grasp them and transfer them to her mouth.

Check it out here.

Watch for Dr. Hu and his students during your next visit to the Zoo!
Joe Mendelson, PhD
Director of Research