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What a Frog Needs to Make That Leap




Frogs are terrific jumpers. Ask any child who has tried to catch one. Or read Mark Twain’s story, “The Celebrated Jumping Frog of Calaveras County.” It helped make his name as a writer.

Like Twain, Chris Richards, a researcher at the Royal Veterinary College at the University of London, came to frogs early, as a first-year graduate student. Like Twain, he writes about frogs, although it’s fair to say his publications don’t get as many chuckles.

Still, “The dynamic role of the iliosacral joint in jumping frogs,” in the journal Biology Letters, goes further to explain the evolution and importance of jumping in frogs than anything Twain ever wrote.

The interesting thing about frogs, Dr. Richards pointed out in an interview, is that the ones that jump do so with power and accuracy.

It has always been known that the hinge-like iliosacral joint in the pelvis, which is unique to frogs, was significant in jumping. The joint opens to let the frog unfold like a flip phone, so that in the air the animal’s long, powerful legs and stubby rigid torso align like a straight, flying arrow.

The question Dr. Richards and his colleagues asked was whether the joint was necessary for the evolution of frog jumping.

To look at the role of the joint, they recorded jumping frogs with high-speed video (Twain was stuck with words alone) and measured the forces involved in real jumps. The scientists created a computer model to fiddle with, modifying the action of the joint, for instance, to see what would happen.

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Their calculations and virtual experiments suggest that the frog can jump without such a joint, since the legs still have plenty of power, but not as accurately.

And while frogs on a riverbank may leap anywhere to avoid predators, some frogs, like those in trees, can be highly accurate.

There are signs of the joint in frog fossils, said Dr. Richards, although it’s not clear how mobile that joint was. “There’s also evidence just looking at the frogs that exist today, which are thousands of species, that this hinge mechanism evolved multiple times independently,” he added.

What Dr. Richards and his colleagues suggest is that jumping evolved first and the flexible joint evolved later for finesse, accuracy and control of the jumping process.

This finding may even have some application to prosthetics. It took Dr. Richards years to realize the similarity “between a jumping frog and a reaching arm.”

“We can do that motion with extreme speed and accuracy,” he said. We can throw a ball, he said, but we can also reach for a piano key.

Frogs, too, can go for power, distance and accuracy.

Frogs have been good to Dr. Richards, and he plans to keep studying them. Early on, when people pegged him as a frog guy, he would tell them, “I’m not a frog guy — I’m a muscle guy. I study the muscles.”

But after a while, he realized that everything he wanted to learn in biology he could observe in frogs and their movements.

“They’re just so diverse, and they do so many things, and they’re just cool animals, so I’ve become endeared to them. Now I do feel like I’m a frog guy.”

No doubt Twain would approve.


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