By Sid Perkins, Science News
Frogs learned to leap long before they learned how to land smoothly, researchers suggest, based on the simple observation that the amphibians have been hopping around for hundreds of millions of years, but some species still have trouble sticking their landings.
Many people, and even many scientists, presume that frogs all jump the same way, says Richard L. Essner Jr., an evolutionary biologist at Southern Illinois University in Edwardsville. Per the conventional view of a hop, a frog rapidly extends its hind limbs to launch itself skyward, rotates forward as it soars gracefully through the air, and then uses its forelimbs to efficiently absorb the force of its landing.
Would that it were. New studies reveal that some species of primitive frogs — especially the ones in a family called Leiopelmatidae — are good jumpers but are amazingly klutzy at touching down. Essner and his colleagues report their findings online July 13 and in an upcoming Naturwissenschaften.
Few scientists have studied leiopelmatid frogs, and none have analyzed their jumping behavior, Essner says. He and his colleagues used high-speed video to scrutinize these frogs’ leaps and landings and then compared those movies to others of more evolutionarily advanced species, including Lithobates pipiens, the northern leopard frog, and Bombina orientalis, the oriental fire-bellied toad.
Both L. pipiens and B. orientalis began pulling their hind limbs back toward their bodies mid-leap, a trait that allowed them to more quickly position their legs for another jump. These frogs consistently landed on their forelimbs, with L. pipiens landing within a degree or so of -24° (a body angle approximately pointed toward 4 o’clock, if seen from the side jumping from left to right).
But the leiopelmatid Ascaphus montanus, the Rocky Mountain tailed frog, didn’t withdraw its legs midflight and had wildly inconsistent landings, with body angles at touchdown ranging from a 62° leg-dragging belly flop to a -71° near-tumbling face plant.
There’s an evolutionary reason for this, Essner and his colleagues speculate. The earliest frogs probably used leaping as a way to escape predators and return to the water, he notes. In such a scenario — previously proposed by other scientists, he adds — how a frog lands isn’t important. But as some ancient species of frogs became more adapted to life away from water, efficient landings allowed hops to come in quick succession — good for both evading predators and chasing prey.
“Not much is known about [primitive] frogs,” says Sandra Nauwelaerts, a biomechanicist at Michigan State University in East Lansing. Because no primitive frogs are fully terrestrial, the findings make sense, she adds.
There’s a spectrum of landing performance in frogs, says Gary Gillis, a biomechanicist at Mount Holyoke College in South Hadley, Mass. In toads, for instance, the feet and legs are typically the only body parts that touch the ground during or after a hop. “People rarely think of the role of the hind limbs in landing,” he notes. “Landing successfully is what makes the next hop possible.”