Of Mark Twain and Hopping Frogs

Helen Fields is a freelance science writer based in Washington, D.C.

In the Mark Twain story The Celebrated Jumping Frog of Calaveras County, a frog named Daniel Webster "could get over more ground at one straddle than any animal of his breed you ever see." Now, scientists have visited the real Calaveras County in hopes of learning more about these hopping amphibians. They’ve found that what they see in the lab doesn’t always match the goings-on in the real world.  

If you wanted to know how far the bullfrog Rana catesbeiana could jump, the scientific literature would give you one answer: 1.295 meters, published in Smithsonian Contributions to Zoology in 1978. If you looked at the Guinness Book of World Records, though, you'd find a different answer. In 1986, a bullfrog called Rosie the Ribeter covered 6.55 meters in three hops. If you divide by three, at least one of those hops had to be no shorter than 2.18 meters—about four bullfrog body lengths more than the number in the scientific paper.

The disparity matters. If bullfrogs can hop only 1.3 meters, they have enough power in their muscles to pull off the jump without any other anatomical help. But if they can jump farther, they must also be using a stretchy tendon to power their hops—an ability that other frogs have but that researchers thought bullfrogs had lost. These particular amphibians, scientists speculated, might have made some kind of evolutionary tradeoff that shortened their jumps but enabled them to swim better in the water, where they spend much of their lives.

To resolve the dispute, researchers attended the Calaveras County Fair. Since a few decades after Twain’s story came out, locals in this region 200 kilometers east of San Francisco have been hosting an annual Jumping Frog Jubilee. Now anyone can walk up, rent a bullfrog, and try to motivate it to show its jumping mettle. It's the place where Rosie the Ribeter made that record-setting series of hops.

In 2009, Henry Astley, then a Ph.D. student at Brown University, and colleagues brought a video camera in hopes of learning more about how far frogs can jump. The frogs perform their hops on the floor of a stadium, one at a time, through days of qualifying rounds. "Fortunately, it turns out we were able to measure the frog jumps without getting in anyone's way, by videotaping the arena from a seat in the stands," Astley says. During the contest, an announcer says the name of each frog. "Quite a few Kermits," Astley says. "Mr. Slimy, things like that." Then it's time for the “frog jockey” to motivate his or her amphibian. "They literally will lunge their whole body after the frogs, imitating a predator—reaching for it and yelling and everything, trying to scare it." (The local agricultural association has a frog welfare policy.)

When the researchers got back to the lab with more than 20 hours of high-definition video, they measured the length of each jump. Fifty-eight percent of the 3124 jumps they recorded were longer than 1.295 meters, the longest jump reported in the scientific literature. One athletic bullfrog covered 2.2 meters in a single bound. Unsurprisingly, frogs jumped by professionals—those committed entrants who catch their own frogs every year and screen them for jumping ability ahead of time—managed longer jumps.

The discrepancy between the longest reported jump for a bullfrog in the scientific literature and the feats pulled off by frogs at a fair shows that scientists may be wrong when they think they're getting maximal performance out of animals in the lab, Astley says. And that means their conclusions about how bullfrogs jump are wrong, too. It seems that, like other frogs, they likely jump with help from a stretchy tendon that acts like a bow and arrow, storing energy until the frog springs from the ground, the team reports online today in The Journal of Experimental Biology.

The study shows the advantages of collecting data from the real world—even if that world is a frog-jumping contest, says Steve Adolph, an animal physiological ecologist at Harvey Mudd College in Claremont, California. He can time sprinting lizards on a little racetrack in his lab, but he’s often wondered if he’s getting the lizards' peak performances. The Calaveras County Fair suggests perhaps not. "This is one of those cases,” he says, “where the general public had better data than the scientific community."

 

Posted in Biology, Plants & Animals