Giant whales use highly elastic nerves like bungee cords to open their mouths wide as they sweep through the water hunting for fish, new research reveals.

Fin, humpback and blue whales, along with others in the rorqual whale family, were found to possess nerves in their mouths and tongues that can double in length, allowing the jaw to open wide for feeding. These newly recognized nerves are able to fold and unfold as the mouth of the cetacean opens and closes during the hunt.

This is a highly unusual finding, as nerves are not normally capable of stretching due to the possibility of being damaged by any significant stress. Pulling a typical vertebrate nerve by 10 percent can prevent it from transmitting signals, while a pull of 30 percent of its length will snap the fiber. Such damage can often result in serious pain, and extreme cases can even lead to paralysis.  

Bundles of nerve fibers within the core of the nerve cores are covered in a layer of collagen and elastin. These segments unfold as the mouth expands, allowing the collection of vast quantities of water and feed. At a critical length, collagen stiffens, preventing the nerve from further stretching. Finally, elastin, acting like a bungee cord, snaps the nerve back to its relaxed length.

The nerves were discovered next to a muscle during a dissection of a fin whale. The team examined the fiber, determining it was not a blood vessel.

"It was then that we realized it must be a nerve, unlike anything we had seen before," A. Wayne Vogl of the University of British Columbia said.

Blue whales are the largest animal that ever lived, weighing up to 200 tons. The fin whale is also a massive beast, topping out about 130 tons. Researchers believe the highly stretchable nerve in the whale may have helped the family of whales thrive as they evolved into larger forms over the course of millions of years.

Rorqual whales feed by taking large amounts of water into their mouths, using their tongues to strain the life-filled liquid through baleen plates. Krill, small shrimplike planktonic crustaceans, are the main component of baleen whales' diet, along with sardines, herrings and other small marine life. They take in as much as half a million calories in a single mouthful.

In order to capture enough krill, small fish and crustaceans to support their massive bodies, these whales, also called Balaenopteridae, open their jaws until they hang at nearly a 90-degree angle from their bodies. Cetacean biologists have previously identified several other adaptations in the whales that allow the animal to open its mouth to such a degree.

"[R]orquals ... have evolved unique features such as highly flexible jaw joints, a deformable tongue that inverts into a sac to hold the seawater, and grooved ventral blubber — stretching from the mouth to the belly button — that can balloon to several times its original size," Emily DeMarco wrote for Science magazine.

Discovery and analysis of the unusual stretchy nerves in rorqual whales was detailed in the journal Current Biology.

Photo: Gregory "Slobirdr" Smith | Flickr

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