Amphibian uses agony song to defend itself from predators – 03/31/2024 – Science

A study published in the journal Acta Ethologica recorded, for the first time in South America, the use of ultrasound by amphibians. This is also the first record of the use of this sound frequency to defend against predators, the so-called agony song.

“Some potential predators of amphibians, such as bats, rodents and small primates, are able to emit and hear sounds at this frequency, which is inaudible to humans. One of our hypotheses is that the agony song is directed at some of them, but it is possible that the broad frequency be a generalist, to scare away as many predators as possible”, says Ubiratã Ferreira Souza, first author of the work, carried out as part of his master’s degree at the Institute of Biology at the State University of Campinas (IB-Unicamp) with a scholarship from Fapesp.

Another hypothesis is that the song is used to attract another predator, which in turn would attack the animal that was about to prey on the amphibian, in this case, the leaf frog (Haddadus binotatus), endemic species of the Atlantic forest.

The researchers recorded the agony song on two occasions. When analyzed by special software, the sound presented frequencies from 7 to 44 kilohertz, and from 20 kilohertz it is inaudible to humans.

During singing, the leaf frog makes a series of typical defense movements against predators. The animal raises the front part of its body and opens its mouth, throwing its head back. Then, it partially closes its mouth, thus emitting the song with part of the frequency audible to us, from 7 to 20 kilohertz, and part inaudible, from 20 to 44 kilohertz.

“Since Brazil has the greatest diversity of amphibians in the world, with more than 2,000 described species, it would not be surprising that other frogs also emit sounds at this frequency”, says Mariana Retuci Pontes, co-author of the study and doctoral student at IB-Unicamp , with a scholarship from Fapesp.

Another species

The use of this strategy by a second species may have been discovered by chance by the researcher herself. In January 2023, during a visit to the Alto Ribeira State Tourist Park (Petar), in the municipality of Iporanga (SP), Pontes saw an individual on a rock that was probably a little forest frog (Ischnocnema henselii), although he did not collect the animal for precise identification of the species.

As she wanted to take a photo, the researcher tried to better position the animal by holding it by the legs. Pontes was then surprised by the behavior of the little frog, which made the same defensive body movement and the same sound as the leaf frog (H. binotatus). About a meter away from her, there was still a jararaca (Bothrops jararaca), which reinforces the evidence that the behavior is carried out in front of predators

It was not possible to analyze the audio, extracted from a video that the researcher managed to make, and verify the presence of ultrasound in Petar’s frog. However, the stimulus of pulling the legs is precisely one of those that researchers use to simulate an attack by a predator, used in recordings of Haddadus binotatus.

“Since both species live in similar environments, the leaf litter [camada de folhas sobre o solo]are small [entre 3 e 6 centímetros] and have similar predators, it is possible that Ischnocnema henselii also make use of this agony song with ultrasound to protect yourself from natural enemies”, explains Luís Felipe Toledo, professor at IB-Unicamp who supervised the study and coordinates the project From natural history to the conservation of Brazilian amphibians, supported by Fapesp.

The first time Toledo suspected that Haddadus binotatus emitted sounds at a frequency inaudible to humans in 2005, when he was carrying out his doctorate at the Institute of Biosciences at the Universidade Estadual Paulista (IB-Unesp), in Rio Claro. However, due to limitations of the equipment used at the time, it was not possible to verify frequencies above 20 kilohertz.

The other records of ultrasound use by amphibians were made in three species from Asia. However, frequency is used for communication between individuals of the same species. In mammals, ultrasound is common among whales, bats, rodents and small primates. The use for defense against predators was something unheard of until then among amphibians.

Now, the researchers want to answer a series of questions raised by the discovery, such as which predators are sensitive to the distress call and how they react to this behavior and whether the sound is aimed at them or to attract the predators’ natural enemies. . “Does the frog call an owl to attack the snake that wants to eat it?”, speculates Souza.

The study was also supported by Fapesp through a doctoral scholarship for Guilherme Augusto Alves and another project coordinated by Toledo.