A few frog species inhabit the jungles of East Asia and take hopping to an extreme. These daredevil amphibians, dubbed parachute frogs, leap from treetops and soar through the rain-forest canopy to evade predators. Some can cover more than 50 feet in a single glide.
Although they lack the true wings of birds and bats, these frogs use extensive webbing between their toes as a winglike surface to slow their descent. They have large feet and flaps of skin between their toes to help them land safely.
University of Texas at Austin evolutionary biologist David Hillis and his Chinese colleagues at China’s Chengdu Institute of Biology gathered several specimens of black webbed tree frogs – a lime-green parachute species with black webbing – from rain forests in southern China to determine the genetics behind these remarkable adaptations.
The researchers compiled the genome of the tree frog and compared it to a closely related frog that is incapable of gliding. For a study in the Proceedings of the National Academy of Sciences USA, they pinpointed 455 modified genes. Hillis states that many of the genes they identified were associated with different aspects of webbing and foot development. “All of them are consistent with flying frogs’ strong morphological adaptation for gliding behavior.” Hillis says that some genes produce longer limbs and more sticky toe pads for climbing. The researchers also identified the network genes that are likely to produce extra webbing by following foot development in each species of tadpoles.
To see these differences in action, researchers conducted a controlled flight experiment. The researchers placed frogs of each species on perches, recorded their jumps, and then positioned soft sponges below to help them if they did not do well in the air. This was important for non-gliding frogs as they plummeted into sponges. The parachute frogs, however, splayed their webbed toes horizontally to glide horizontally before touching to land.
According to Mimi Koehl, a biomechanist at the University of California, Berkeley who has studied flying Frogs’ biodynamics but was not involved in the research, the extra webbing slows down their fall and helps them navigate through the rain-forest canopy. Frogs use their large back feet as rudders to avoid trees and descend towards puddles on forest floor where they congregate to mate and lay eggs. Koehl states, “If they can’t maneuver through this complex environment, they’re going to miss their orgy.”
The researchers believe that understanding the frogs’ adaptations could help reveal how other animals, such as flying squirrels or flying lizards, took to the skies. Koehl and her colleagues have even used flying frogs to help model dinosaur flight. She says that flying dinosaurs had feathered tails, and feathers on the hind legs. “They had the same maneuverable body design as flying frogs.”