The fats associated with minke whale ears (shown here in yellow), previously seen only in toothed whales, may efficiently transmit sound waves from the external environment to ears inside of the whales’ heads (shown here in purple). (Maya Yamato, Woods Hole Oceanographic Institution) |
For
decades, scientists have known that dolphins and other toothed whales
have specialized fats associated with their jaws, which efficiently
convey sound waves from the ocean to their ears. But until now, the
hearing systems of their toothless grazing cousins, baleen whales,
remained a mystery.
Unlike
toothed whales, baleen whales do not have enlarged canals in their jaws
where specialized fats sit. While toothed whales use echolocation to
find prey, baleen whales generally graze on zooplankton, and so some
scientists have speculated that baleen whales may not need such a
sophisticated auditory system. But a new study by scientists at Woods
Hole Oceanographic Institution (WHOI), published April 10, 2012, in The Anatomical Record, has shown that some baleen whales also have fats leading to their ears.
The
scientists propose that toothed whales may not be the only whales that
use fats to transmit sound in water, as previously believed, and the
fats in both types of whales may share a common evolutionary origin.
Little
progress had been made on the auditory anatomy of baleen whales because
specimens to study are hard to get. Unlike many toothed whales, they
are large, not kept in captivity, rarely strand on beaches, and
decompose rapidly when they do.
For
the new study, lead author Maya Yamato, a graduate student in the
MIT/WHOI Joint Program in Oceanography, received seven heads of minke
whales that stranded and died, mostly on beaches on Cape Cod. She
collaborated with the International Fund for Animal Welfare’s (IFAW)
Marine Mammal Rescue and Research unit in Yarmouth Port, Mass.
The
whale heads were scanned using computerized tomography (CT) and
magnetic resonance imaging (MRI) at the Computerized Scanning and
Imaging (CSI) lab at WHOI and MRI facility at Massachusetts Ear and Eye
Infirmary in Boston. Using these biomedical techniques, the researchers
generated 3-D visualizations of the whales’ internal anatomy, with both
bones and soft tissue intact and in their undisturbed natural positions,
providing “an unprecedented view of the internal anatomy of these
animals,” the scientists wrote.
Maya Yamato examines a minke whale head in the necropsy facility at the WHOI Marine Mammal Center. For her study, Yamato used computerized tomography (CT) and magnetic resonance imaging (MRI) to scan the whale heads to generate 3-D visualizations of the whales’ internal anatomy, with both bones and soft tissue intact and in their undisturbed natural positions. Then the whale heads were dissected in the necropsy facility at WHOI’s Marine Mammal Center. (Photo by Tom Kleindinst, Woods Hole Oceanographic Insitution) |
Then
the whale heads were dissected in the necropsy facility at the Marine
Mammal Center at WHOI. Together, the studies showed that all the minke
whales had “a large, well-formed fat body” connecting to the ears,
providing a potential transmission pathway guiding sound from the
environment to their inner ears.
“This
is the first successful study of intact baleen whale head anatomy with
these advanced imaging techniques,” said WHOI Senior Scientist Darlene
Ketten, director of the CSI lab at WHOI and co-author on the paper. “It
really is an important addition to our understanding of large whale head
and auditory systems.”
Also collaborating on the study were Julie Arruda and Scott Cramer at the CSI and Kathleen Moore of IFAW.
This
research was funded by a National Science Foundation Graduate Research
Fellowship, a WHOI Ocean Life Institute Graduate Fellowship, the Joint
Industry Program, the Office of Naval Research, and the U.S. Navy.
