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Why is this little frog so horrible to jump?

When the Pumpkin Toad leaps into the air, anything seems possible. The little frog, which is about the size of a bee and the color of a cloudberry, has no problem launching itself high off the ground. But when the Pumpkin Toad starts flying away, something is wrong.

The frog’s body, limbs spread like a starfish, begins to spin. And then he falls, tumbling gracelessly until he lands on his behind or his head and involuntarily cartwheels or turns around to stop.

“Some guys are just spinning,” said André Confetti, a graduate student at the Federal University of Paraná in Brazil, demonstrating by twirling his finger in the air during a Zoom call. “Some guys do this movement,” Confetti added, wiggling his fingers in circles like a waterwheel.

“Frogs swirling in the air, in space,” said Amber Singh, soon to 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 successful jumps that its sheer incompetence has become a subject of scientific research. A team of researchers from the United States and Brazil that includes Confetti and Singh say they have an answer: miniaturized toads are so tiny that the fluid-filled chambers in their inner ears that control their balance work rather inefficiently, dooming the brave little jumpers. to a life of crash landings.


The article confirms that many species of pumpkin toads, which belong to a genus of small frogs called brachycephalicexhibit “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 puts it, “they’re not doing anything right.”

It’s not easy being a bee-sized vertebrate. Pumpkin toads have made evolutionary compromises to be so small, such as reducing the number of digits on their legs from five to three. Frogs, which are famously moist, dry out more quickly when they get this small, said Rick Essner, functional morphologist at Southern Illinois University Edwardsville and author of the paper. But sometimes it’s worth being small: “To a pumpkin toad, an ant is a huge meal,” Essner said.

Credit: Andre 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 previously researched a group of equally clumsy tailed frogs, which jumped acceptably but landed in a full facial plant.

When Marcio Pie, then a researcher at the Federal University of Paraná in Brazil and author of the paper, learned of Essner’s research on the frog that collapses on its stomach, he emailed Essner at subject of pumpkin toads. Members of Pie’s lab began collecting toads and other miniaturized frogs from the wild to watch them jump and (try) to land.

Pumpkin toads live elusive lives. The frogs live and feed under leaf litter in the Atlantic Forest of Brazil, which, combined with their size, makes them extremely difficult to study. “These are very small and secretive organisms,” Condez said. “Most of our knowledge about their behavior comes from rare field observations.”

Finding insect-sized frogs in Brazil is a daunting task. Even though a Pumpkin Toad is as bright as a Cheeto, the leaf litter is teeming with neon mushrooms and other orange life. “It’s extremely difficult to catch under leaf litter,” Confetti said. “Especially for me, because I’m color blind.”

Instead, the researchers had to listen to the cry of the frog, which sounds a bit like a cricket. Back in Pie’s lab, the researchers placed each frog on a mirror surrounded by a few barriers and filmed their jumping efforts. (Some must have been encouraged by a light pat on their little bottom.)

When Essner saw the footage, he burst out laughing. Then he immediately became engrossed in the problem at hand. The toads were so far removed from the ventral tailed frogs on the frog family tree that the problem was not ancestral. So why didn’t they make a single jump? “It wasn’t a ‘Eureka’ moment,” Essner said. “It was a, ‘What’s going on here?’ moment.”

Credit: Rick Essner
Brachycephalus coloratus does his best.

Essner then read a slew of scientific papers, including a previous experiment where researchers altered the vestibular systems of cane toads, which are normally excellent larvae. Compromised Toads exhibited landing issues eerily similar to Pumpkin Toads.

Essner wondered if the toads’ problem came down to size. Vertebrate organisms are able to balance and orient themselves in the world thanks to our vestibular system: a complex system of fluid-filled chambers and channels in our inner ear. Moving the head causes fluid, called endolymph, to produce a force that deflects sensory hair cells and signals our central nervous system to control our posture and movement. Despite the huge range of vertebrate body sizes, the size of these canals remains fairly constant. “Between a bull frog versus a human or a whale, they don’t change as much as you might expect,” Essner said.

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

David Blackburn, curator of herpetology at the Florida Museum of Natural History, and Edward Stanley, associate scientist at the museum, took CT scans of museum specimens of 147 species of frogs, including the largest frog (the Goliath frog), the smallest frog (“there are a few frog species vying for smallest frog,” noted Stanley), and pumpkin toads. The frogs were kept in a “standard frog position, quite rigid and not super flexible”, as Stanley described it. He packed the preserved frogs in Ziploc bags of packing peanuts and scanned them with the million-dollar machine. Next, Singh rendered 3D models of the frogs’ semicircular canals from the CT scans.

The resulting measurements revealed the semicircular canals of brachycephalic and miniature frogs in pedophryne were the smallest of all adult vertebrates, resulting in loss of motor control and subsequent bumpy landings.

The researchers considered other potential explanations. Maybe the Pumpkin Toads’ three-toed feet slipped during the initial jump? Or maybe their fairing landings were meant to look like a falling leaf, tricking predators looking for a snack? But the videos didn’t show a significant amount of slippage as the toads took off, and the landed toads didn’t stay still long enough to convincingly resemble a leaf, the researchers wrote.

The CT scans also hinted that the toads may have evolved internal bony armor to make it slightly safer to crash into. “Looks like they’re carrying an all-bone backpack,” Stanley said, referring to the pumpkin toad species. Brachycephalus ephippium. Still, the pumpkin toad is probably more of a trundle than a jumper. Essner suggested that jumping is likely an escape response, a way of hastily withdrawing from a dangerous situation. Better to be bruised than devoured, says the proverb. Plus, “you don’t have to worry about breaking your bones if you’re the size of a housefly,” Essner added.

Pumpkin toads live in the Atlantic Forest of Brazil, which is one of the most biologically diverse places on earth. “Each mountain in southern Brazil has the potential to harbor a new species of brachycephalic“, Confetti said. “We don’t know how many brachycephalic we have in our garden.

But 85% of the area has been deforested and what remains is very fragmented. “It makes me wonder how many of these species were there that we’ll never know about because they’re already gone,” Essner said.

Perhaps the takeaway from Pumpkin Toad is that not everything has to be optimized. Just because you’re bad at something doesn’t mean you shouldn’t, especially if you have a secret bony backpack and toxic poison glands. Even if the pumpkin toad’s little hop is the locomotor equivalent of the horse’s drawing, that does not mean that it should not walk, jump or tumble as it sees fit, in the damp litter of a growing forest. disappearance. Each species should have the right to fail spectacularly, but on its own terms.

Credit: Rick Essner
Brachycephalus brunneus makes the effort.

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