A group of frogs alternately called pumpkin toads and flea toads have become so small that they are no longer able to maintain balance during quick maneuvers, such as jumping, researchers report.
“They’re not great jumpers, and they’re not very good walkers either.”
Amphibians are exceptionally good at being small. There are salamanders the size of your thumbnail, pygmy newts that live in patches of moss and feast on microscopic insects, and inch-long African tree frogs that spend their entire lives in and around the banks of small puddles.
In fact, the title of world’s smallest vertebrate is currently held by a species of frog that could comfortably perch on the head of a pencil eraser. But a new study shows that all this downscaling is not without serious downsides.
The researchers studied four species of the genus brachycephalicshowing that these miniature frogs are able to jump when gently pushed, but invariably lose control of their trajectory mid-jump, pirouette gracelessly through the air before crash-landing.
“They’re not great jumpers, and they’re not great walkers either. They sort of stomp in a stilted version of walking,” says Edward Stanley, director of the Digital Discovery and Dissemination Lab at the Florida Museum of Natural History and co-author of the study in Scientists progress.
Researchers were able to identify the probable cause of this inconvenient mode of transportation thanks to oVert, a four-year initiative between 18 institutions to create 3D models from CT scans for more than 20,000 museum specimens across the United States. United.
Co-author Amber Singh assembled hundreds of frog scans while working with the oVert project as an undergraduate student at the University of Florida. Pumpkin toads stand out in these scans as having the smallest vestibular system ever measured in any vertebrate organism.
The vestibular system is a fluid-filled network of spiraling chambers inside animals’ inner ears that somewhat resembles a nautilus. When an animal moves its head, the fluid in these chambers moves with it, brushing against tiny hairs that send electrical impulses to the brain that allow it to maintain balance, distinguish up from down, and detect acceleration. .
Natural selection, however, has imposed strict constraints on the vestibular system. Baleen whales, a group that includes the largest mammals on earth, have chambers that are only slightly larger than those of humans.
This does not seem to be a problem for large vertebrates, but for organisms at the smaller end of the size spectrum, the vestibular system takes up proportionally more and more space inside the skull. The chambers in pumpkin toads’ skulls look like overinflated balloons.
“Even though the channels are as tall as they can be relative to their heads, they’re still not tall enough for the liquid to move at a speed that would allow them to maintain equilibrium,” Stanley says.
It is not the first time brachycephalic frogs have aroused the interest of scientists. Pumpkin toads treble mating calls that look like chirping crickets. However, at least two species have underdeveloped auditory systems and are completely deaf to the love songs of amorous males.
Then there are the glowing skeletons. In 2019, scientists found that the same two species with males that tuned out also fluorescent boneswhich are visible under their thin skin when viewed under black light.
“These are peculiar frogs,” says co-author André Confetti, a doctoral student at the Federal University of Paraná, Brazil. “They can’t swim, they don’t have tadpoles and they don’t seem to move much either. We monitored the acoustic behavior of these frogs and were able to record the same individual in the same location over the course of a year.
This tendency to stick around is probably one of their greatest strengths. brachycephalic the frogs live under the leaf litter of the tropical Atlantic forest of Brazil. Some are brightly colored – a warning to potential predators of their toxicity – while others are coated in dull colors that help camouflage.
In each case, their main tactic to avoid being eaten does not involve high-speed jaunts, but rather staying in one place and being as unappetizing or as stealthy as possible.
Stanley suspects that these visual cues, or lack thereof, may have created a tenuous balancing act for brachycephalic.
“They don’t jump up a lot, and when they do, they’re probably not that worried about landing, because they’re doing it out of desperation,” he says. “They gain more from being small than they lose from their inability to land successfully.”
Richard Essner Jr. of Southern Illinois University Edwardsville is the lead author of the study. Other co-authors are from the Federal University of Paraná, Brazil; the Florida Museum of Natural History; and Mater Natura – the Institute for Environmental Studies.
The National Science Foundation and Southern Illinois University Edwardsville Graduate School funded the work.
Source: University of Florida
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