These Toadlets Are So Tiny They Can't Balance Anymore

There are certain benefits to being little. You require less food, occupy less room, and are more elusive to predators.

A backboned mammal can only become so tiny before losing its ability to balance, according to a recent discovery by scientists. When trying to leap, pumpkin toadlets (Brachycephalus) do humorously uncomfortable gymnastics due to their extreme miniaturization.

They bounce before their Skittle-sized bodies eventually come to a halt as they crash fall on their butts, backs, tummies, and even faces. Fortunately, they don't seem to be harmed by the affects.

While frogs are renowned for their ability to leap, some have even honed this skill to the point that they can gracefully parachute through the air, pumpkin toadlets aren't the only amphibians who are skilled at belly-flopping. Previous studies have revealed that before frogs could stick their landings, they first developed the capacity to jump.

Richard Essner Jr. and colleagues at Southern Illinois University used CT scans of the inner ears of 147 different species to attempt to identify the problem after being fascinated by these toadlets' brilliantly hilarious tumbles.

"They're not great jumpers, and they're not particularly good walkers either," says herpetologist Edward Stanley of the Florida Museum of Natural History. "They sort of stomp around in a stilted, peg-like version of walking."

The scientists examined the toadlings' legs and found that even though they only have three toes that are functioning, their springing leg muscles are in excellent condition.

The way they jump also doesn't make much sense, since their spread limbs and futilely grasping posture make it more difficult for them to get as far away from the danger as possible.

Instead, their minds were where the problem lay.

When we move, our vestibular system —a network of fluid-filled chambers in our ears — uses input to inform us which way is up. Fine hairs detect the direction and speed of the liquid as it sloshes in response to our movements, giving our brain the data it needs to serve as our location system.

These frogs still have vestibular organs, but it doesn't seem like they're giving the frog enough information to allow it to alter its orientation.

"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," according to Stanley.

Some Brachycephalus face additional ear-related difficulties in addition to this one. At least two species cannot hear their own mating songs because of their poor hearing abilities.

In addition to making it difficult for them to land elegantly, their small vestibular system also causes them to move slowly and cautiously. Fortunately, pumpkin toadlings spend the most of their time in Brazil's forests, where they live under leaf litter.

"They're peculiar frogs," describes Brazil's Federal University of Paraná zoologist AndrĂ© Confetti. "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." 

These animals rely on other strategies to avoid predators instead. Others rely on concealment while some are poisonous and vividly colored.

"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 says. "They get more benefits from being small than they lose from their inability to stick a landing."

Their research was published in Science Advances