The Pumpkin Toadlet’s Miniature Size Makes It a Lousy Hopper

These amphibians’ tiny inner ear canals make balancing mid-jump a challenge

A close-up image of a tiny orange colored frog
In total, researchers made CT scans of the inner ears of 147 frog species. With these scans, the team determined that Brachycephalus toads' semicircular canals are the smallest ever recorded for adult vertebrates. Ariovaldo Giaretta via Wikimedia Commons under CC BY-SA 2.5

Frogs are known for graceful jumps and precise landings. However, not all frogs are as elegant jumpers as others. The pumpkin toadlet, belonging to the genus Brachycephalus, a tiny, orange-colored amphibian found among leaf litter in the forests of southeastern Brazil, is the clumsiest of them all. After flinging itself into the air, the frog, about the size of a Skittle, tumbles and cartwheels before flopping to the ground on its back or belly, reports the Atlantic's Katherine J. Wu.

Researchers suspect that the frog’s crash landing may be due to its inability to balance mid-leap, a consequence of its miniature stature, and even more miniature ears. The study was published this week in Science Advances.

“They’re not great jumpers, and they’re not particularly good walkers either. They sort of stomp around in a stilted, peg-like version of walking,” says Edward Stanley, study co-author and director of the Florida Museum of Natural History's Digital Discovery and Dissemination Laboratory, in a statement.

Using CT scans of the brightly colored toadlet, researchers found that their vestibular system, the structures within the ear that guide balance in vertebrates, is so small that when the frogs spring into the air, they quickly lose their balance and simply fall gracelessly to the ground, reports Isaac Schultz for Gizmodo. The CT scans were part of a larger project called oVert, a four-year initiative across 18 institutions to create 3-D models of more than 20,000 fluid-preserved museum specimens.  

In total, researchers made CT scans of the inner ears of 147 frog species. With these scans, the team determined that Brachycephalus toads’ semicircular canals are the smallest ever recorded for adult vertebrates. The fluid inside the bony tubes in the inner ear normally aids vertebrates in sensing their body position, and lets them orient themselves for a smooth sailing and proper landing. The flow of fluid within the semicircular canals as the head and body move up and down, side to side or forward and back gives the brain information about positioning. Because the tiny frog’s tubes are so small, it’s harder for fluid to flow freely, and causes reduced sensitivity to changes in the body’s orientation, reports Meghan Rosen for Science News.  

“We think that without the necessary vestibular feedback, they remain in their launch posture rather than folding up their hindlimbs in mid-air like other frogs,” says study co-author Richard Essner, a herpetologist at Southern Illinois University Edwardsville, to Gizmodo.

The team also recorded the frogs jumping and analyzed the footage to find that the change in rotation speed was lowest when they were mid-air. This suggests that the toadlets find this stage the hardest to track with their insensitive ear canals and end up flopping to the ground instead of landing on their feet, New Scientist’s Jake Buehler reports.

While the pumpkin toadlet will likely never win gold in a gymnastics competition, the frog compensates with enhanced defenses against predators. A variety of pumpkin toadlet species are poisonous to eat, excreting from their skin the same tetrodotoxin as puffer fish. They can also camouflage extremely well among the leaf litter, and have a thickened bone in their skulls and backs, per New Scientist.  

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