A study by the Institute of Biology (IB) at Unicamp described a new species of frog that inhabits dense, humid, leafy forests. Discovered in the environmental reserve of the Dacnis Project, in Ubatuba, in the state of São Paulo, the amphibian of the genus Brachycephalus is only 7 millimeters long, making it the second smallest vertebrate species on the planet.
The article detailing the animal's characteristics, published today in the scientific journal PeerJ , involved the collaboration of scientists from the Laboratory of Natural History of Brazilian Amphibians (Lahnab) and the Laboratory of Evolutionary Genomics at IB, as well as researchers from the Florida Museum of Natural History (United States), New York University Abu Dhabi (United Arab Emirates), the Institute of Biosciences at São Vicente, and the Dacnis Project itself.
The discovery of the new frog occurred when experts from the project's reserve noticed two different sounds while recording the call of the species *Brachycephalus hermogenesi* , originally described in Picinguaba, also in Ubatuba. Dacnis, a non-governmental organization, conducts research and educational projects on the biodiversity of the Atlantic Forest and funded the study together with the São Paulo Research Foundation (FAPESP), the Coordination for the Improvement of Higher Education Personnel (CAPES), and the National Council for Scientific and Technological Development (CNPq). When he received the audio recorded in the field, Professor Luís Felipe Toledo, coordinator of Lahnab and leader of the research, found that they were, in fact, two distinct species.
Finding the animal, however, proved to be a much more difficult task. Besides its diminutive size, this genus sings on the forest floor, hidden beneath the leaves, and generally stops emitting sounds when someone approaches. Upon capturing the creature, the researchers found that its measurements and body shape were identical to those of the species B. hermogenesi , making it impossible to distinguish them by their physical characteristics.
“We call this a cryptic species when there are morphologically identical species. The song helps a lot to distinguish, but we can’t always make the recording and sometimes it may be a female that doesn’t sing,” said Toledo.
To describe the new species, the team conducted studies on the morphological, anatomical, bioacoustic and molecular characteristics of the animal. One of the main innovations was the use of cutting-edge tools such as high-resolution computed tomography techniques that allowed them to “zoom in” on the frog’s body and visualize in detail even the small beings ingested by the amphibian.
According to the professor, the most relevant aspect of the research was not in describing one of the world's smallest frogs, but in demonstrating the extremes of biology and providing important insights for other scientists. Examples of this include understanding the smallest size a heart can be or how an animal breathes when it is so small. “These are physiological and evolutionary questions that we can ask after describing species, in the same way that specialists in large animals do. How does the heart pump blood to the giraffe's brain? These are dimensional limits that we are discovering and that show the scale of life on Earth,” he explained.
Main features
The newly discovered species, named B. dacnis , possesses several miniaturization characteristics, meaning that the animal has significant morphological differences compared to larger frogs. One example is bone fusion and loss, resulting in a reduced number of toes. While a large frog has four fingers on its hands and five toes on its feet, B. dacnis has one less functional toe on each limb. This characteristic demonstrates that, due to its small size, there is not enough space in the animal's body to accommodate so many anatomical elements.
On the other hand, scientists were surprised to discover that the frog also exhibited skeletal characteristics typical of larger frogs, such as ear parts that allow them to hear their own calls. To give an idea, the golden frog species, which also belongs to the genus Brachycephalus , is relatively larger than B. dacnis – reaching 2 centimeters – and does not possess this characteristic. A hypothesis not yet tested by Toledo is that these groups with fewer anatomical elements have more evolutionary derivations. That is, they first underwent a reduction in size and then suffered the loss of elements, showing that B. dacnis , compared to the golden frog, would be closer to their common ancestor.
Researchers also discovered that members of this species lay only two eggs at a time, a small number for amphibians. The cane toad, for example, can lay up to 50 eggs at once. Furthermore, the eggs of B. dacnis hatch into fully formed frogs – which did not go through the tadpole stage – which could have facilitated the evolution of these amphibians towards a smaller size, due to a simpler system.
“But they are quite abundant in nature. You can hear hundreds of them singing at once. Even with few eggs, they must lay several times a year, because they reproduce whenever it rains, and it rains a lot in the Ubatuba region,” commented the professor.
