A group of marine biologists from the University of British Columbia, Stanford University, and the Smithsonian Institution’s National Museum of Natural History, has discovered that nerves in the mouth and tongue of rorqual whales can more than double their length with no trouble at all.
The sei whale (Balaenoptera borealis) is the fourth-largest rorqual after the blue whale, the fin whale and the humpback whale. Sei whale mother and calf as seen from the air. Image credit: Christin Khan / NOAA / NEFSC.
Rorqual whales (Balaenopteridae) are among the largest vertebrates that have ever lived, weighing in at an impressive 40 to 80 tons, and include the blue whale (Balaenoptera musculus) and the fin whale (Balaenoptera physalus).
To eat, rorquals open their mouths and lunge while their tongues invert and their mouths fill like giant water balloons full of floating prey. Those prey are concentrated by slowly expelling the water through baleen plates. The volume of water brought in with a single gulp can exceed the volume of the whale itself.
A new study, published online in the journal Current Biology, shows that nerves in the floor of the oral cavity of rorqual whales are highly extensible.
“These large nerves actually stretch and recoil like bungee cords,” said study lead author Dr Wayne Vogl of the University of British Columbia.
“This discovery was totally unexpected and unlike other nerve structures we’ve seen in vertebrates, which are of a more fixed length.”
In humans, stretching nerves usually damages them. In the rorquals, the nerve cells are packaged inside a central core in such a way that the individual nerve fibers are never really stretched, they simply unfold.
The scientists hadn’t expected this at all. They made the discovery after they picked up a dull white cord-like structure and stretched it in a lab. It looked like a blood vessel, which ought to be stretchy. But they realized upon closer inspection that it was a nerve – one unlike any they’d ever seen before.
“The rorquals’ bulk feeding mechanism required major changes in anatomy of the tongue and mouth blubber to allow large deformation, and now we recognize that it also required major modifications in the nerves in these tissues so they could also withstand the deformation,” Dr Vogl said.
The scientists don’t know yet whether anything similar will turn up in other animals – the ballooning throats of frogs, for example, or the long and fast tongues of chameleons.
They plan to keep studying the whales’ nerves in greater detail, in hopes of understanding better how the nerve core is folded in such a way to allow its rapid unpacking and re-packing as the entire structure is stretched and then relaxed again.
“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,” said co-author Dr Robert Shadwick of the University of British Columbia.
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A. Wayne Vogl et al. 2015. Stretchy nerves are an essential component of the extreme feeding mechanism of rorqual whales. Current Biology, vol. 25, no. 9, pR360–R361; doi: 10.1016/j.cub.2015.03.007
