These Frogs Are So Small, They Lose Their Balance

Being tiny is more beneficial than having good gymnastic skills.

Brachycephalus coloratus pumpkin toadlet

Ribeiro et al., (2017)

It’s kind of a given that frogs can jump, and many are pretty impressive when they hop. But one tiny species is really awful at leaping.

Pumpkin toadlets are so small they can’t stay balanced during speedy maneuvers like jumping. When gently nudged, these tiny amphibians vault then lose their bearings mid-air, tumbling to the ground.

Curious why these frogs can’t easily leap, researchers investigated why these mini animals are so ungraceful when jumping.

Lead author Richard Essner, a professor in the department of biological sciences at Southern Illinois University Edwardsville, had studied uncontrolled landing behavior in a different group of frogs found in the U.S. Pacific Northwest and New Zealand. Having read his work, researchers reached out to him as they were studying jumping locomotion in different Brazilian frog species, including pumpkin toadlets in the genus Brachycephalus.

The researchers sent him data and videos from the project.

“That was when I got excited because pumpkin toadlet landing behavior was very different from other frogs, including their closest relatives which were not miniaturized,” Essner tells Treehugger.

Wanting to see the unusual leaps for himself, he used high-speed video to record the frogs jumping in a lab. Trying to explain the awkward landings, they pinpointed the cause as the amphibians’ small vestibular system.

“Specifically, the semicircular canals of the inner ear provide key information about rotational movements to a jumping frog which allows it to control its posture in mid-air in order to prepare for landing,” Essner explains. “It turns out that they don't work very well when they get too small.”

The vestibular system is a network of spiraled and twisty chambers inside the inner ear. When an animal moves its head, liquid in the chambers moves as well. This sends signals to the brain that help it keep the body balanced.

The team reached out to the Florida Museum of Natural History where a lab there provided detailed images and measurements of the semicircular canals of many different frogs, including mini species.

They found the pumpkin toadlets had the smallest measured in any vertebrate organism.

“Even though the canals are as big as they can possibly be relative to their heads, they’re still not big enough for the liquid to move at a rate that would allow them to maintain balance,” study co-author Edward Stanley, director of the Florida Museum of Natural History’s Digital Discovery and Dissemination Laboratory, said in a statement.

“The semicircular canals act as a gyroscope to detect angular acceleration. Jumping frogs use this information to assess body position and control posture,” Essner says. “If the semicircular canals become too narrow, the fluid within them called endolymph cannot flow freely. This is due to friction between the endolymph and the walls of the duct in which it is contained. This reduces their sensitivity.”

Fascinating Species

Researchers say that pumpkin toadlets are particularly intriguing for many reasons, other than their substandard gymnastics.

“There are so many things to be fascinated about, including their small size obviously. I think it's amazing how they stop development early to become so small. This gives them a reduced number of digits which are remarkable to see,” Essner says.

“I also think their habitat is amazing. They live in leaf litter in cloud forests on mountaintops where it's cool and damp. That is essential because they dry out easily due to their small size.”

Because they are so small and usually remain hidden, miniaturized frogs are very difficult to study. New species are discovered all the time.

“They’re peculiar frogs,” co-author André Confetti, a Ph.D. candidate at the Federal University of Paraná, Brazil, said in a statement. “They can’t swim, they don’t have tadpoles, and they don’t seem to get around much either. We’ve monitored the acoustic behavior of these frogs and have been able to record the same individual at the same spot over the course of a year.”

The findings were published in the journal Science Advances.

Unusual Features

Because of their poor balance and difficulty easily getting around, pumpkin toadlets don’t move all that much.

“We think it might affect their ability to move across the landscape. They seem to have small home ranges,” Essner says. “Also, they are vulnerable to predators after landing since they don't land ready to jump again like most frogs.”

That could explain why some of the species have unusual features, such as bony shields, bright colors, toxicity, or camouflage. The colors warn predators to stay away because they could be poisonous while some with drab coloration can hide more easily in leaf litter.

These features may mitigate the lack of balancing abilities.

“They’re not jumping around a lot, and when they do, they’re probably not that worried about landing, because they’re doing it out of desperation,” Stanley said. “They get more benefits from being small than they lose from their inability to stick a landing.”

View Article Sources
  1. Essner, Richard L., et al. "Semicircular Canal Size Constrains Vestibular Function in Miniaturized Frogs." Science Advances, vol. 8, no. 24, 2022, doi:10.1126/sciadv.abn1104

  2. Lead author Richard Essner, a professor in the department of biological sciences at Southern Illinois University Edwardsville

  3. "Miniature Frogs Set Record as First Vertebrates to Lose the Ability to Balance." Florida Museum, 2022.