Salamander jumping ability has a surprising twist

An analysis of the physics of how salamanders jump reveals a "new way to get vertical lift for animals," according to a researcher who presented the findings at a biology symposium.

Anthony Hessel, a graduate student with Northern Arizona University, describes the high-flying manoeuvres of the tiny, slender amphibians as a "hip-twist jump" that's unique in the animal world.

This is a brand new mechanism that hasn't been seen, it hasn't been used, and there's potential for designing new machines and technology to come out of it- Anthony Hessel, Northern Arizona University graduate student

Terrestrial salamanders, with their squat legs and slippery feet, may not look built to defy gravity. But their ability to launch themselves upwards as much as six to 10 times their height from a position so low to the ground fascinated Hessel.

"It's a cool little mechanism," he told CBC News. "If you consider how they lay on the ground and their only height off the ground is two or three millimetres, and they're able to get six or seven centimetres into the air, that's like us jumping 25 feet."

To deconstruct thisimpressive vaulting action, Hessel set up an apparatus with a camera for a frame-by-frame analysis and watched a salamander propel itself. Reviewing the footage in slow motion, it was clear that salamander legs don't spring or provide the kind of push that other creatures would need to achieve liftoff.

'Flat catapult' action

Instead, the desmognathus ochrophaeus salamander used in Hessel's study rotates its body so quickly that it can get airborne to evade predators. Five salamander species have been shown to use the same mechanism.

To use an analogy, Hessel said it's helpful to picture a rock climber hanging to a ledge with one hand. In order to reach above the climber's head to grab onto a crevice that's even higher, the person would need to rotate his or her shoulders.

"When you do that you're actually moving your body upwards," Hessel explained.

"The salamander, instead of doing this vertically, is doing this horizontally. But because they're using so much power, they can pull themselves towards a planted foot, pole-vault over that limb and get into the air."

Footage shot by Hessel from above shows the salamander's body bending quickly and then recoiling as it is flung upwards. The whole jumping mechanism happens in about 20 milliseconds.

Hessel calls it a "flat catapult" action in which a salamander curls into the shape of a letter C, then rapidly transfers energy from itstorso into the ground. The movement can create what's called elastic energy.

Measuring stiffness

"This is a brand new mechanism that hasn't been seen, it hasn't been used, and there's potential for designing new machines and technology to come out of it," he said, adding that engineers in the biomechanics field may draw inspiration from this kind of movement to build new robots.

Hessel noted fish also use stored elastic energy to pilot their swimming motions by way of muscle contraction in their torsos. He said he wants to do further study to find out how much energy is stored when salamanders bend.

"Are they able to channel that into their hips like fish do? That's the next question for us," he said.

He has constructed a miniature cantilever apparatus in order to measure stiffness in salamander torsos by tying a string to the amphibian's body and a transducer. The experiment uses euthanized salamanders, which are then used for other experiments.

"You bend the salamander to a certain length, and then you release it and see the force measurements on it," he said.

Hessel presented his findings at the Society for Integrative and Comparative Biology symposium earlier this month. His work attracted interest from Science magazine, which wrote about the salamander leaping abilities this month. Hessel is now writing a manuscript about his research for The Journal of Experimental Biology.