A study by the Biology Institute (IB) at Unicamp has 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 It 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, had the collaboration of scientists from the Laboratory of Natural History of Brazilian Amphibians (Lahnab) and the Laboratory of Evolutionary Genomics of the IB, in addition to researchers from the Florida Museum of Natural History (United States), the University of New York in Abu Dhabi (United Arab Emirates), the Institute of Biosciences of the São Paulo State University (Unesp) in São Vicente and the Dacnis Project itself.
The discovery of the new frog occurred when experts at the project reserve noticed two different sounds while recording the species' song. 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 financed 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, realized that they were, in fact, two distinct species.
Finding the animal, however, proved to be a much more difficult task. In addition to being tiny, this species sings on the forest floor, hidden under leaves, and usually stops making sounds when someone approaches. When they captured the animal, the researchers found that its measurements and body shape were identical to those of the species. B. hermogenesis, not being possible 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 when describing one of the smallest frogs in the world, but when demonstrating the extremes of biology and bringing insights important for other scientists. Examples of this include understanding the smallest size a heart can have or how an animal breathes when it is so small. “These are physiological and evolutionary questions that we can ask after describing the species, in the same way that people who specialize in large animals do. How does the heart send blood to the giraffe's brain? These are dimensional limits that we are learning about and that show the size of life on Earth,” he explained.
Main features
The discovered species, named B. dacnis, has several characteristics of miniaturization, meaning that the animal has important morphological differences in relation to larger frogs. An example of this: bone fusion and loss, which results in a reduction in the number of fingers of the animal. While a large frog has four fingers on its hands and five toes on its feet, B. dacnis has one less functional finger on each limb. This characteristic shows that, due to its small size, there is no space in the animal's body to house so many anatomical elements.
On the other hand, scientists were surprised to discover that the little frog also had skeletal characteristics typical of larger frogs, such as ear parts that allow them to hear their own song. To give you an idea, the species pingo-de-ouro, which also belongs to the genus Brachycephalus, is relatively larger than the B. dacnis – reaching 2 centimeters – and does not have this characteristic. A hypothesis not yet tested by Toledo is that these groups that have fewer anatomical elements have more evolutionary derivations. In other words, they first underwent a reduction in their size and then suffered the loss of elements, showing that the B. dacnis, compared to the pingo-de-ou, would be closer to their common ancestor.
The researchers also discovered that members of this species lay only two eggs at a time, a small number for amphibians. The cururu toad, for example, can lay up to 50 eggs at a time. In addition, of the eggs of the B. dacnis frogs come out already formed – which did not go through the tadpole phase –, which could have facilitated the evolution of these amphibians towards a smaller size, as it is 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.