It takes a lot of krill to keep a blue whale satisfied. These 150-metric-ton cetaceans get their fill by swallowing huge quantities of prey and water in a lightning-quick maneuver as they swim. Now researchers say they have discovered a new organ that helps coordinate this big gulp: a fluid-filled sack in the chin that may sense the changing position of the jaw.
Researchers have long suspected there must be a sensory structure guiding this so-called lunge feeding, "but no one has, at least until now, been able to demonstrate anything that could do the job," says Alexander Werth, a functional morphologist at Hampden-Sydney College in Virginia who was not involved in the study. "It's as close to a slam-dunk case as you could ask for.”
Blue whales and other so-called rorqual whales are lunge feeders. As they dive, they ram into patches of krill, opening their mouths wide and wrapping their jaws around prey-laden water, a move that nearly stops them short. The whales then close their mouths and push water through baleen, hard plates that filter out the food. They then speed up for another feeding bout. The whales can take in more than their body weight in each gulp.
To better understand how the jaws could coordinate this maneuver, paleontologist Nicholas Pyenson of the Smithsonian National Museum of Natural History in Washington, D.C., and his colleagues collected whale jaw tissue at an onshore whaling station in Iceland where captured whales were brought in for processing. There, they had unique access to tools and help cutting up fin whale carcasses. As Science reported in January, the chin tissue that connects the two sides of the jaws contains a fluid-filled cavity about the size of a whoopee cushion.
After analyzing magnetic resonance images and computed tomography scans of the cavity, Pyenson came to believe it's an organ that might help with the rotation of the jaws that occurs during gulping and enables the mouth open extra wide. It likely changes shape as the jaws move, he explains. The organ has lots of blood vessels, as well as nerves that seem to come from what was a tooth socket earlier in whale evolution, he notes. Inside are microscopic, fingerlike structures that look like the nerve endings in our skin that sense movement. He and colleagues publish the details of their research online today in Nature.
"To identify such a new sensory structure in a vertebrate is quite remarkable," says Douglas Altshuler, an integrative biologist at the University of British Columbia, Vancouver, who was not involved with the study.
Werth hopes the researchers will study the organ and its nerve connections in greater detail and that they will look for this structure in related whales. The best way to show this organ works as suggested would be to test its function in a live whale, notes Casey Holliday, an integrative biologist at the University of Missouri, Columbia, who was not connected to the study. But for whales, "that's out of the realm of possibility."