Why is this little frog so awful to jump?

The moment the pumpkin toad jumps into the air, everything seems possible. The tiny frog, which is about the size of a honey bee and the color of a cloudberry, has no problem sitting high up on the ground. But when the pumpkin toad begins to soar, something goes wrong.

The frog’s body, limbs scattered like a starfish, begin to spin. And then it falls, overturns mercilessly until it lands on its back or head and inadvertently rolls or spins to a stop.

“Some boys are just spinning,” said André Confetti, a doctoral student at the Federal University of Paraná in Brazil, demonstrating by spinning his finger in the air over a Zoom call. ‘Some boys do this movement, ‘Confetti added, waving her fingers in circles like a water wheel.

“Frogs blowing in the air, in space,” said Amber Singh, who will soon be a master’s student at San Jose State University.

The pumpkin toad, which is a frog but not a toad, is so terrible at landing the mare that its sheer incompetence has been the subject of scientific research. A team of researchers from the US and Brazil that includes Confetti and Singh say they have an answer: The miniaturized toads are so small that the fluid-filled chambers in their inner ears that control their balance function quite inefficiently, judging the brave little jumpers. to a lifetime of crash landings.

The paper confirms that many species of pumpkin amphibians, which belong to a genus of tiny frogs called Brachycephaluspresents “a very unusual jump with uncontrolled landing behavior,” said Thais Condez, a researcher at Carleton University in Canada, who was not involved in the research.

Or, as Confetti put it, “they do nothing right.”

It is not easy to be a vertebrate the size of a bee. Pumpkin toads have made evolutionary considerations for being so small, such as reducing the number of digits on their legs from five to three. Frogs, which are known to be moist, dry out faster when they are small, said Rick Essner, a functional morphologist at Southern Illinois University Edwardsville and author of the paper. But sometimes it pays to be small: “For a pumpkin toad, an ant is a big meal,” Essner said.

Credit: André Confetti
The pumpkin toad, Brachycephalus coloratus.

Frogs developed the ability to jump before they developed the ability to land, which means that not all frogs have mastered the second part of the process. Essner has previously studied a group of equally clumsy tail frogs, which jumped acceptably enough, but landed in a whole face plant.

When Marcio Pie, then a researcher at the Federal University of Paraná in Brazil and an author on paper, found out about Essner’s stomach frog research, he sent an e-mail to Essner about the pumpkin toads. Members of Pie’s laboratory began collecting amphibians and other miniaturized frogs from the wild to see them jump and (try to) land.

Pumpkin toads live elusive lives. The frogs live and search under fallen leaves in Brazil’s Atlantic Forfest, which together with their size make them very difficult to study. “They are very small and secretive organisms,” said Condez. “Most of our knowledge of their behavior comes from rare sightings in the field.”

Finding insects the size of insects in Brazil is a difficult task. Although a pumpkin toad is as light as a Cheeto, the leaf litter is teeming with neon mushrooms and other orange-colored life. “It’s extremely difficult to catch under the charcoal,” Confetti said. “Especially for me, because I’m color blind.”

Instead, the researchers had to listen to the frog’s cry, which sounds a bit like cricket. Back in Pie’s laboratory, the researchers placed each frog on a mirror surrounded by some barriers and filmed their jumping attempt. (Someone had to be encouraged with a gentle pressure on the small buttocks.)

When Essner saw the footage, he burst out laughing. Then he was immediately engrossed in the problem. Toadlets were so far from the belly-flapping tail frogs on the frog’s family tree, meaning the problem was not ancestral. So why could they not land a single jump? “It was not a ‘Eureka’ moment,” Essner said. “It was a, ‘What the hell is going on here?’ moment.”

Credit: Rick Essner
Brachycephalus coloratus trying their best.

Essner went on to read a number of scientific articles, including a previous experiment in which researchers weakened the vestibular systems of toads, which are usually excellent jumpers. The compromised toads showed eerily similar landing problems as the pumpkin toads.

Essner wondered if the problem with toadlets came down to size. Vertebrate organisms are able to balance and orient us in the world because of our vestibular system: an intricate system of fluid-filled chambers and channels in our inner ear. Moving the head causes the fluid, called the endolymph, to produce a force that diverts sensory hair cells and signals our central nervous system to control our posture and movement. Despite the huge range of body sizes for vertebrates, the size of these channels remains fairly consistent. “Between an ox frog versus a human or a whale, they do not change as much as you expect,” Essner said.

The researchers suspected that the toad’s small body and smaller skull could limit the size of the semicircular canals in the inner ear and prevent the fluid inside from flowing freely. “When you take a pipe and make it smaller and smaller and smaller, the resistance to liquid flow increases,” Essner said.

David Blackburn, curator of herpetology at the Florida Museum of Natural History, and Edward Stanley, an associate scientist at the museum, took CT scans of museum samples of 147 species of frogs, including the largest frog (the Goliath frog), the smallest frog (” there are a couple of frog species in the competition for the smallest frog, “Stanley remarked, and the pumpkin toads. The frogs were kept in a “standard froggy position, fairly stiff and not superfloppy,” as Stanley described it. He packed the preserved frogs in Ziploc bags of packaged nuts and scanned them with the million-dollar machine. Singh then rendered 3D models of the frogs’ semicircular channels from the CT scan.

The resulting measurements revealed the semicircular channels to Brachycephalus and miniature frogs in Paedofryne was the smallest of all adult vertebrates, resulting in loss of motor control and subsequent chaotic landings.

The researchers considered other possible explanations. Maybe the pumpkin toads’ three-toed feet caused them to slip during the first jump? Or maybe their scary landings were meant to be like a falling leaf, fooling predators in search of a bite to eat? But the videos did not show a significant amount of slippage at the start of the toads, and the landed toads did not remain motionless long enough to look convincing on a leaf, the researchers wrote.

CT scans also suggested that toilets may have developed an inner bone armor to make it a little safer to crash. “It looks like they’re wearing a backpack that’s completely bone,” Stanley said, referring to the pumpkin species Brachycephalus ephippium. Still, the pumpkin toad is probably more of a trundler than a leaper. Essner suggested that jumping is probably an escape response, a way to quickly get away from a dangerous situation. Better to be beaten than consumed, it is said. In addition, “you do not have to worry about breaking bones if you are the size of a housefly,” Essner added.

Pumpkin toads live in Brazil’s Atlantic forest, which is one of the most biologically diverse places on the planet. “Every mountain in southern Brazil has the potential to have a new species of Brachycephalus“We do not know how much,” said Confetti Brachycephalus we have in our backyard. ”

But 85 percent of the region is deforested, and what remains is very fragmented. “It makes me wonder how many of these species were there that we never get to know about, because they are already gone,” Essner said.

Perhaps the takeaway of the pumpkin toad is that not everything needs to be optimized. Just because you’re bad at something does not mean you should not do it, especially if you have a secret bony backpack and toxic venom glands. Although the pumpkin’s small leap is the locomotive equivalent of the horse drawing, it does not mean that it should not walk, jump or tumble as it pleases, in the damp leaf litter in a disappearing forest. Each species should have the right to fail spectacularly, but on its own terms.

Credit: Rick Essner
Brachycephalus brunneus made the effort.