- Pumpkin toadlets are very bad at jumping, often losing balance mid-air and crash landing awkwardly.
- Researchers have determined that this is due to the size of their inner ear canals, the area of the body that regulates balance and orientation: their semicircular ear canals are the smallest recorded in vertebrates.
- The toadlets live in the leaf litter of Brazil’s Atlantic forest, where being small enough to burrow is an advantage.
- But the frogs are so small that the balancing mechanisms in their ears can’t respond to quick movements, resulting in some ungraceful antics.
Frogs usually land on their feet, but one group of tiny toadlets from Brazil are so small they can’t stick a landing.
Pumpkin toadlets (Brachycephalus spp.) are teensy, about the size of an M&M. These miniaturized frogs will jump when given a nudge or a scare, but lose their balance as they tumble through the air, often landing with a graceless thud on their backs, bellies or wherever they fall.
“They’re not great jumpers, and they’re not particularly good walkers either,” Edward Stanley, director of the Florida Museum of Natural History’s Digital Discovery and Dissemination Laboratory, said in a statement. “They sort of stomp around in a stilted, peg-like version of walking.”
Researchers discovered that this clumsy hopping has to do with a part of the inner ear that regulates balance. When frogs (and many other animals) move, fluid inside the spiraling chambers of the inner ear flows over microscopic hairs. As they’re moved, these hairs trigger electrical impulses to the brain that tell the animal how to distinguish up from down, balance, and position its body upright.
However, because toadlets are so minuscule, these fluid-filled chambers don’t send a strong enough signal to help the frog out during its daring leaps. Pumpkin toadlets, it turns out, have the smallest semicircular ear canals recorded in any vertebrate animal, according to a newly published study in the journal Scientific Advances.
“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,” said Stanley, a co-author of the study.
The scientists uncovered the frogs’ minuscule semicircular canals through oVert, a four-year project involving 18 institutions to create 3D models from CT scans for more than 20,000 museum specimens across the U.S. Four species of pumpkin toadlets were included in the project.
The miniature frogs have traded balance for stature (or a lack thereof), scientists say. Their wee bodies can easily nestle down in the leaf litter of the forest floor in Brazil’s tropical Atlantic Forest, where they live.
Some Brachycephalus are brightly colored, a warning to would-be predators that they’re poisonous. Others are camouflaged, mimicking the brown and black colors of their leafy surroundings. Either way, the toadlets tend to stand their ground and stay put rather than attempt any sudden moves in the face of danger, or attraction.
“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,” said study co-author André Confetti, a Ph.D. candidate at the Federal University of Paraná, Brazil. “They get more benefits from being small than they lose from their inability to stick a landing.”
A 2017 study found that at least two species of Brachycephalus frogs have underdeveloped auditory systems, making them deaf to the high-pitched mating calls of admiring males. This diminished system may be another trade-off for their small size.
One of the species, Brachycephalus ephippium, has received a lot of attention over the past few years after scientists found that its bones glow through their skin under UV light. They may be using this as a visual cue for mating, since they’re deaf to the love songs of their own kind.
“They’re peculiar frogs,” Confetti said. “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 only “spot” for the pumpkin toad is in Brazil’s Atlantic Forest, one of the most endangered forests on the planet. Only around 3.5% of its primary forest remains, after mass clearing for soy and sugarcane farming and cattle ranching, which began in the 1940s. Fortunately, many of the pumpkin toadlets still thrive in a network of protected areas, where they can safely, albeit awkwardly, stomp forward.
Banner image: Pumpkin toadlets live in the leaf litter of Brazil’s Atlantic forest, where being small enough to burrow is an advantage. Image by Carol Manzano via Wikimedia Commons (CC BY-SA 4.0).
Essner, R. L., Pereira, R. E., Blackburn, D. C., Singh, A. L., Stanley, E. L., Moura, M. O., … Pie, M. R. (2022). Semicircular canal size constrains vestibular function in miniaturized frogs. Science Advances, 8(24). doi:10.1126/sciadv.abn1104
Goutte, S., Mason, M. J., Christensen-Dalsgaard, J., Montealegre-Z, F., Chivers, B. D., Sarria-S, F. A., … Felipe Toledo, L. (2017). Evidence of auditory insensitivity to vocalization frequencies in two frogs. Scientific Reports, 7(1), 1-9. doi:10.1038/s41598-017-12145-5
Goutte, S., Mason, M. J., Antoniazzi, M. M., Jared, C., Merle, D., Cazes, L., … Thoury, M. (2019). Intense bone fluorescence reveals hidden patterns in pumpkin toadlets. Scientific Reports, 9(1). doi:10.1038/s41598-019-41959-8