About 50 million years ago, the ancestors of whales, like those of today's cows, left the Earth's surface to return to the sea. With them they took with them their system for producing sound, which is not very different from the human one. However, it doesn't work the same way underwater, and more fundamentally, opening your mouth to produce it means drowning. As they adapt to their new environment, some whale species have refined their vocalizations to the point where it appears to humans as if they are singing.
Now a group of scientists have dissected specimens of three of them to reveal the secrets of their song. Over the course of evolution, they have redesigned their larynx so that it can communicate over long distances. But their study also shows how the noise generated by people affects their ability to communicate. They continue to sing, but can no longer be heard.
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The different groups of whales developed adaptations to the new environment: Odontocetes (such as dolphins, killer whales and sperm whales) evolved to have a nasal vocal organ that was capable of producing high-frequency sounds and, in the case of the dolphinids, used these for echolocation to use ; Meanwhile, mystics (such as the blue whale, the humpback whale, and the fin whale) have almost completely remodeled their larynxes. This organ, one of the most complex in mammals, has two functions: protection of the airways and lungs and phonation.
In most land dwellers, this phonation involves the vibration of the vocal folds caused by the flow of air through the space between them, the glottis. But the water forced radical adjustments. The result, particularly for some baleen whales, far exceeded the communication of their terrestrial ancestors: they are capable of emitting sounds that travel tens or even hundreds of kilometers. But most of what was known about the phonation system of these mystics was based on assumptions and inferences.
Between 2018 and 2019, a group of scientists specializing in whale phonation organized the collection of the larynx of some whales. They needed them to be as fresh as possible so that they could be studied thoroughly. They contacted environmental organizations to inform them of any strandings. So they removed this organ from three Mysticetes species, a minke whale, a northern whale and an impressive humpback whale. The latter is one of the few species that have enchanted sailors with their calls for centuries.
Next, they dissected them to understand their anatomy in depth. In principle, they have all the elements that are present in other mammals, for example several basic cartilages for laryngeal articulation and sound production. However, they do not have vocal cords like humans and other land animals, and some of these cartilages have hardened and lost their original function. Instead, they have evolved a U-shaped structure (seen from above) parallel to the trachea, which has a horizontal orientation in these animals rather than vertically as in the human species. And above this shape there is a pad of fat.
What the researchers did, which they detailed in the journal Nature, was to mechanically blow air into the larynxes to confirm their theory. They saw the air vibrating the U's arms, producing low-frequency sounds similar to those of these whales as they came into contact with the accumulation of fat above. To do this, they used the air that entered the lungs through the nostrils and breathed it out from there to produce the sound. Up to here, like land animals do. But in whales, they have the ability to reuse the flow they seem to send back to the lungs and make new sounds again.
“They developed new structures because the vocal cords on the surface would hinder rapid breathing.”
Coen Elemans, an expert in whale communication and acoustics at the University of Southern Denmark
“We think they developed new structures because the vocal folds would hinder rapid breathing on the surface,” explains Professor Coen Elemans from the Sound Communication and Behavior Group at the University of Southern Denmark and lead author of this innovative research. “These structures allow baleen whales to emit the very low-frequency sounds they all make,” he adds. Although the physical mechanisms underlying sound production (vibrations induced by airflow) are the same as human speaking and singing, researchers have confirmed that “only a few species (humpbacks and bowhead whales) have the ability to repair the cartilage of whales move, have redeveloped.” Larynx and the thick tissue over these structures together. How [hacemos los humanos con] “our vocal cords,” complete. This also allows them to emit high-frequency sounds, “the songs that most people know well,” he concludes.
In a second part of the work, after scanning the humpback whale's larynx, they modeled it to study its behavior under different physical and acoustic conditions. “Our model includes precise 3D shapes of the larynx and its muscles, which allowed us to simulate, for example, how frequency is controlled by muscle modulation,” says Qian Xue, a professor in the Department of Mechanical Engineering at the University of Michigan. in a note: Rochester Institute of Technology in Rochester (USA) and co-author of the study. His institutional colleague Weili Jiang added that their model accurately predicted the results of our experiments, “but we were also able to calculate acoustic properties that we could not measure in the laboratory, such as frequency range.”
Among the results they obtained was a piece of information of great importance: the sounds they emit on the surface can reach the deepest part of the sea, but below 100 meters these whales cannot emit them. It's physically impossible for them. The problem is that this area is increasingly filled with noise generated by human activities (ships, underwater mining, prospecting, etc.). By combining these experiments and models, the researchers showed that baleen whales are physiologically unable to escape anthropogenic noise because it masks their voices and therefore limits their communication range. Elemans complains: “The limited frequency range (between 10 and 300 hertz) and depth (0 to 100 meters) at which they can emit noise overlap with human-generated noise; That’s why they can’t sing louder or deeper to avoid our noise.”
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