The diminutive size —less than 1 centimeter in length, in certain cases — and the vibrant colors make Brazilian frogs of the genus brachycephalus are among the most interesting vertebrates in the world. But the charm comes at a price: they’ve shrunk so much that they’ve been unable to hop in a controlled and elegant way, unlike any other self-respecting frog.
“They can jump, but not orient themselves during the descent of the jump”, says André Confetti, a doctoral student at UFPR (Federal University of Paraná) and co-author of a new study on mini frogs that is being published in the specialized journal Science Advances.
The research team, coordinated by Brazilian Marcio Pie, from Edge Hill University (United Kingdom), showed that the culprit for the animals’ poor acrobatic skills is the inner ear. To be more exact, the problem starts with the size of the semicircular canals, structures in the inner ear that are essential for vertebrates like frogs and us to be able to orient themselves in space.
These channels, whose shape resembles donuts glued together in different orientations, are filled with a liquid with a density similar to that of water. When we turn our head in a certain direction, the fluid moves and touches cells that act as sensors, which allows the brain to capture the patterns of our movement and posture.
It turns out that there is a size limit for semicircular canals to function properly, because of the way fluid circulates within them. So much so that, in most vertebrates, the size variation of the structure does not depend much on the body size of the species. But the Brazilian thrush has shrunk so much throughout its evolution that the canals had to partially accompany this miniaturization — and ended up losing efficiency. In this, who paid the duck was the precision of the jumps.
“The idea of investigating this came precisely because of the size of the frogs, because when we do field research, the impression is that they jump normally, it is even difficult to follow the jumps”, explains Confetti.
Things change, however, when footage of the jumps is analyzed in slow motion, especially when comparing the frog jumping style with that of other full-sized amphibians. “When you jump, you know that you’re going to land on your feet in the same place or, if you’re jumping into a pool, you know that you have to go forward to fall into the water. In the case of these frogs, none of that happens”, he compares. the researcher. “Usually, frogs [sapos, rãs e pererecas] jump already directed to where they want to go, which is not the case with these animals.”
The species of the genus brachycephalus are exclusive to the highest mountainous stretches of the Atlantic Forest, in the Serra do Mar and Serra da Mantiqueira. They are restricted environments, with less availability of resources, which may partly explain why the animals have become miniaturized (smaller bodies require less food to sustain themselves, after all).
Frogs are adapted to life in the leaf litter (the thick layer of leaves that covers the forest floor) and feed mainly on ants and mites, compatible with their minimal size. Their skin has a considerable amount of toxins, which serve as a defense against predators. Their very specific habitat makes them especially vulnerable to climate change.
