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Giant Whales Have Super-Stretchy Nerves

“Hey, look at this,” said Bob Shadwick. He and his team were working on the dissected remains of a fin whale, the second largest animal on the planet, when they noticed a white cord-like structure lying against a slab of muscle. Shadwick picked it up and jokingly stretched it. “It was like a bungee cord,” recalls A. Wayne Vogl who was part of the group. It extended to more than twice its original length before recoiling back.

The team initially thought it was a blood vessel, but they soon realised that it wasn’t hollow. They looked closer and noticed that it had a yellowish central core, surrounded by a thick white coating. “It was then that we realized it must be a nerve, unlike anything we had seen before,” says Vogl.

On one hand, that made no sense. In mammals, nerves have a little slack in them but if you extend them by 10 percent, they’ll stop carrying electrical signals properly. Extend them by 30 percent and they’ll snap. Stretch injuries are the most common type of nerve injuries in people, and can lead to shooting pains, loss of sensation, and paralysis. Simply put: nerves don’t stretch.

On the other hand, the fin whale’s stretchy nerve made perfect sense. This is an animal whose entire existence is built upon extreme feats of stretchiness.

A fin whale nerve being stretched. Credit: Vogt et al, 2015.
A fin whale nerve being stretched. Credit: Vogt et al, 2015.

The giant rorqual whales—fins, blues, humpbacks, minkes, and their kin—feed on tiny crustaceans called krill, which they swallow by the millions using a unique technique called lunge-feeding. A rorqual will accelerate towards a swarm of krill at high speed and suddenly open its gargantuan mouth to a right angle. The two bones of the lower jaw swing outwards, widening the mouth; the tongue inverts, creating even more room. The whole mouth balloons outwards, increasing in circumference by around 162 percent and engulfing an astonishing amount of krill and water. A blue whale can swallow around half a million calories in a single mouthful.

Long pleats in the whale’s mouth allow it to expand without tearing skin or muscle. But what about nerves? Large nerves course through the lower jaw, connecting to the tongue and blubber. Those have to stretch and, as Vogl and Shadwick showed, they do.

How?

The strategy, Vogt writes, is “simple yet elegant”. Each nerve contains bundles of fibres, called fascicles, which sit at its core and are highly folded. The fascicles are surrounded by a thick wall made of two proteins: sturdy collage and stretchy elastin. When a whale lunges, the fascicles and collagen fibres unfold, while the elastin fibres stretch. Once the collagen fibres unfold fully, they become taut, stopping the nerve from stretching any further (and potentially breaking). As the whale closes its mouth after a lunge, the elastin fibres pull the nerve back into its original shape.

And that’s it. The nerve fibres themselves don’t actually stretch. It’s more that they unfold. But that still makes them special. Other nerves that reside in the neck and ribcage of a fin whale don’t have this property, and are barely more extensible than those in your face. Those in the whale’s face, by becoming stretchier, allowed it to evolve its extraordinary style of feeding and its record-breaking size. Without stretchy nerves, fin and blue whales would never have become the giants that they are.

This unexpected discovery highlights how little we know about the giant whales, which have captivated our imaginations for millennia. Just a few years ago, the same team behind this new study discovered that rorquals have a volleyball-sized sense organ at the tips of their lower jaws—and no one had ever seen it before. There are undoubtedly surprises still to come. “One of the big mysteries yet to solve is how these animals actually swallow the food they concentrate after a lunge,” says Vogl. “We still don’t know this.”

More on rorqual whales:

4 thoughts on “Giant Whales Have Super-Stretchy Nerves

  1. So the rorquals basically have telephone cords for facial nerves. I wonder if their nerves ever get a “tangling” related injury?

  2. So, the nerves themselves are pleated as well? Pleats are a series of folds, thus the nerves could be considered pleated? Which of course makes sense, the whales didn’t have to evolve a “novel” structure to replace existing nerves it had to evolve a way to store the extra length of the nerve to allow the “stretch” Very cool.

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