Most animals, especially vertebrates, have nerves without much give. In humans, a stretched nerve can cause serious injury or even paralysis. But it turns out that the massive whales in the rorqual group have something much more useful than nerves of steel: They have nerves of elastic.
In a study published Monday in Current Biology, University of British Columbia researchers report that these 40- to 80-ton sea-dwellers (which include blue whales, the largest living animals on Earth) have uniquely stretchy nerves in their tongues that work like bungee cords. And without these unusual nerves, the whales probably couldn't grow as big as they do. It's probably an adaptation they evolved to sustain their gluttonous feeding habits.
The nerve is so weird that the research team actually found its significance by accident. According to lead author A. Wayne Vogl, a member of the lab picked it up and stretched it, saying something like, "Wow, look at this." They assumed it was a blood vessel, because blood vessels are much stretchier than most nerves, but soon realized they were mistaken.
And that's how cool science happens, folks: playing around with stretchy whale guts in the lab.
"This discovery was totally unexpected and unlike other nerve structures we've seen in vertebrates, which are of a more fixed length," Vogl said in a statement. The nerve can stretch to nearly twice its original length. The actual nerve fibers don't stretch. They're very long, and they're folded up inside a stretchy outer layer. When the outer layer stretches out, the nerve fibers unfurl themselves.
That's important when the whales eat: Rorqual whales open their mouths wide and lunge forward at high speeds, creating enough water pressure to fill their mouths with an incredible amount of water. Sometimes a rorqual can bring in more water in a single gulp than the original volume of the actual whale. Then they slowly push the water through the baleen hairs they have in place of teeth, using them like a giant fishing net to keep fish and krill inside.
This feeding method allows them to sustain incredible sizes, because they can get massive mouthfuls of prey pretty efficiently. But without a super-flexible tongue it might not be possible. Researchers already knew that these whales have adaptations in the tongue, jaw and mouth blubber that make the great gulps possible, but now they know that nerves in those tissues had to change, as well.
"This discovery underscores how little we know about even the basic anatomy of the largest animals alive in the oceans today," former UBC postdoctoral researcher Nick Pyenson, currently at the Smithsonian's National Museum of Natural History, said in a statement. "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."
The researchers will continue studying the mechanism of the unusual nerve cord and hope to learn whether other invertebrates with stretchy anatomy have developed something similar.
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