Marine biology researchers from the University of British Columbia (UBC), Stanford University, and the Smithsonian Institution's National Museum of Natural History have discovered a unique nerve structure that allows massive rorqual whales to fish effectively. The nerves within the tongues and mouths of these whales can "stretch" to more than twice their resting length and then snap back into position effortlessly, just like a bungee cord.
The results, published this week in the journal Current Biology, illustrate that these highly extensible oral nerves are what make the largest of Earth's creatures able to create huge pockets between their insulating layer of blubber and the wall of their bodies in order to trap their food. The whales dive as their tongues invert and their mouths open, and in essence fill an internal water balloon full of prey. They then press the water back out of their bodies through their baleen plates, retaining their food.
The category of rorqual whales includes the enormous blue whale and its slightly smaller cousins the fin whale and the humpback whale. These creatures, which weigh from 40 to 80 tons, are among the planet's largest vertebrates, and the volume of a large whale's single feeding dive gulp can exceed the volume of the whale itself.
Wayne Vogl of University of British Columbia (UBC)'s Cellular and Physiological Sciences department remarked: "This discovery was totally unexpected and unlike other nerve structures we've seen in vertebrates, which are of a more fixed length."
The researchers first thought the dull white cord-like structure they had discovered was a blood vessel, as these are typically elastic. However, when they discovered the cord was not hollow, they observed that it had the characteristic thick white coating and yellowish central core of a nerve.
Human nerves do not typically stretch without sustaining damage. Stretching them by even 10 percent can cause permanent conductive problems. In fact, injuries from stretched nerves can cause loss of sensation, shooting pains, and paralysis, and are the most common type of human nerve damage.
In rorqual whales, however, the unique arrangement of nerve cells within a central core permits individual nerve fibers to unfold rather than stretch. This allows them to feed on tiny crustaceans by the millions as they dive. Since the rest of the whale's mouth must stretch to accommodate this kind of feeding, it stands to reason that their oral nerve structures must also somehow be flexible.
This discovery may someday yield benefits for people suffering from nerve damage. : "Our next step is to get a better understanding of how the nerve core is folded to allow its rapid unpacking and re-packing during the feeding process" UBC zoologist Robert Shadwick says.
It is not yet clear to the team whether other animals such as frogs whose throats expand or chameleons whose tongues snap out and back with lightning speed will share this anatomical trait. Other nerve structures in different parts of the same kinds of whales do not unfold and recoil back into shape in the same way.
"This discovery underscores how little we know about even the basic anatomy of the largest animals alive in the oceans today" postdoctoral fellow from UBC and the curator at the Smithsonian's National Museum of Natural History, Nick Pyenson says. "Our findings add to the growing list of evolutionary solutions that whales evolved in response to new challenges faced in marine environments over millions of years."
