Key to ‘ lunge feeding’ found
Sensory organ in chin coordinates mammals’ gulping motion
It’s described as the largest biomechanical event on Earth. Bus- sized whales lunge, their mouths inflating like parachutes to engulf more water than the weight of their own bodies.
Within seconds the whales filter out millions of krill and small fish, then swim away, their hyper- expandable throat pleats all neatly folded back into place.
Biologists have puzzled over the spectacle for decades, but a team of Canadian and U. S. scientists has now discovered a sensory organ on the tip of the whales’ chin that appears to orchestrate the remarkable feeding behaviour.
They uncovered the grapefruitsized organ, described in the journal Nature Wednesday, in the jaws of whales killed in Iceland and hauled them back to Vancouver for close inspection.
When they sawed open the lower chin they saw the “strange gel- like organ” which had grape- sized polyps inside, says co- author Jeremy Goldbogen, who worked on the University of British Columbia project for his graduate studies. He is now at the Cascadia Research Collective in Washington state.
“We had never seen anything like it before,” says Goldbogen, who likens the whales to “mammals from space” because of all their special adaptations for feeding and living underwater.
He and his colleagues — Nicholas Pyenson, now at the Smithsonian Institution in Washington, D. C., and their professor Robert Shadwick of UBC — were studying the socalled lunge feeding behaviour seen only in rorqual whales. These include fin, humpback and blue whales, which are the largest mammals ever, reaching more than 150 tonnes and 30 metres from nose to tail.
The whales have three jaw joints, one at the centre of the lower chin, which enable them to open their jaws to 90 degrees and quickly rotate and manoeuvre them to engulf fish and krill in front of them.
“They’re incredibly agile in terms of their mouth mechanics,” says Goldbogen.
To see if there was something special in their anatomy, the biologists headed to Iceland to salvage whale parts that would otherwise have ended up as fertilizer as part of the country’s commercial whaling operations.
The scientists sawed open the giant chins and found the strange organ, which puzzled everyone they consulted.
Then they recruited the help of technicians at Fpinnovations, who operate an X- ray computed tomography machine big enough to accommodate the massive whale specimens.
“A whale chin is pretty hefty,” says Goldbogen, explaining how they can weigh a tonne.
The machine, normally used to scan logs for forestry research, provided a threedimensional map of the internal structure of the whale’s chin tissues.
“The odd arrangement of tissues didn’t make much sense to us at first, but then we realized that this organ was perfectly placed, anatomically, to coordinate a lunge because that soft structure [ the sensory organ] is pinched by the tips of the jaws, and deforms through the course of a lunge,” Pyenson said in a statement issued with the study.
The teams says the sensory organ, and its role in coordinating successful lunging, likely played a “fundamental role” in enabling whales to evolve to their huge size. Shadwick says it’s likely responsible for rorquals claiming the status as largest animals on Earth.
Pyenson says the “supreme irony” is that after decades of whaling “where scientists had the opportunity to observe hundreds of thousands of whale carcasses, we are still only beginning to understand the anatomy of the largest ocean predators of all time.”