There is such a thing as “acoustic fat” and Maya Yamato studies it. Specifically she’s interested in lipids found in whale ears.
Yamato, a Peter Buck Postdoctoral Fellow at the Smithsonian, has dedicated the past 7 years to investigating the anatomy, evolution, and biochemical properties of baleen whale ears. An understanding of how these filter-feeders—such as blue, gray, and minke whales—hear will enable us to better grasp their natural history as well as the impact of underwater noise pollution.
Hearing is one of the most important senses for whales and dolphins. However, listening underwater brings challenges. Whales, and their ears, have been evolving ever since they transitioned from a terrestrial habitat to life in the ocean some 50 million years ago. They lost their earlobes. In fact, their entire pinna—the outer wing-like part of mammalian ears—disappeared. The ear canal was also reduced, making it no longer effective for channeling sound to the middle and inner ears.
That’s where fats come in. Since the 1960s, researchers have understood that toothed whales (including dolphins and porpoises) have developed a new way of channeling sound to their ears. It involves using specialized “acoustic fats,” which are found inside their hollow lower jaws and lead to the ears. These fats are made up of lipids not found in any other mammalian tissue and were thought to be unique to the echolocating toothed whales, which hear at very high frequencies.
Thanks to Yamato, we now understand that fats are also involved in the auditory system of baleen whales. Yamato and her colleagues have published several peer-reviewed papers on the subject. One describes the discovery of fats associated with baleen whale ears, and another examines their chemical make-up.
On the spectrum of challenging things to study, baleen whales ears are at the difficult end. Yamato has focused primarily on dissecting and CT-scanning stranded minke whales, one of the smallest baleen whale species. At the Smithsonian, she is expanding her dataset to include other, larger species in collaboration with stranding networks on both the East and West Coasts of the United States.
Editor’s Note: If you’re curious about the larger realm of underwater acoustics, visit Discovery of Sound in the Sea .
By Tina Tennessen, Smithsonian's National Museum of Natural History