To feed, fin whales open their mouths wide open to entrap their prey and plenty of water, then filter it all through baleen plates. The fin whale, which is found in deep offshore waters around the planet, can open its mouth so wide that you could stick a school bus inside, said University of British Columbia researcher Margo Lillie.
So how do whale jaws stretch that much?
It has to do with their nerves. Unlike the nerves in most other species, rorqual whales (including the fin whale) are capable of stretching to double their size and shortening without sustaining damage—and we finally know how, thanks to findings published today in Current Biology.
These nerves have a double-waviness that lets them expand, said the same UBC scientists who observed the capability two years ago in the Ventral Groove Blubber (VGB) nerves of fin whales. This expansion is necessary for whales to open their jaws and take in an incredible amount of water, sometimes more than the volume of the whale itself.
In other species, like humans, more than a bit of nerve stretching can cause lethal damage. But when Lillie put the fin whale nerves under a microscope, they didn't look like other nerve cells: they expanded, contracted, and were abnormally wavy on two levels.
"I saw what looked like hairpin turns, and I said, 'Well this doesn't make sense,'" Lillie told Motherboard in a phone interview. "It shouldn't be able to make those really tight turns. How do you build a nerve, something that cannot stretch, to get longer and shorter?"
All nerves have some level of waviness—but while my nerves would look like a gently sloping, mostly straight line, Lillie said whale nerves look more like "meandering rivers."
The surprise in this discovery was that it's not only the outer nerve walls that curve and fold (as shown in the navy walls of the winding islands in the illustration, which is actually a 3D scan of a fin whale nerve), letting the nerve stretch when it needs to, but also the nerve core (represented in light blue). It is this core that leads to nerve damage when overexerted in other species.
Lillie and her colleagues collected some whale nerves, stretched them to see how far they would extend, and looked at their structure with micro-CT scan. They found that different nerves could extend to different amounts, and instead of the normal one layer, the VGB had a double layer of waviness that let them expand into a straight line or contract like tightly-twisted coil.
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