A plug protects whales from being swallowed

Rorquals have to withstand enormous stress when eating. (Image: ANDREYGUDKOV/iStock)

They mouth more than anyone else: A study now sheds light on how rorquals prevent water from penetrating their airways when they catch their prey. Researchers have discovered a fleshy plug in the marine mammals that seals the airways against the enormous water pressure during feeding. It then moves up to swallow, closing the upper airways but opening the way to the pharynx. This is how the food gets into the esophagus while the larynx closes to protect the lower airway, the research shows.

Humpback whale, fin whale… and the largest animal of all time – the blue whale: The gigantic dimensions of the representatives of the rorquals (Balaenopteridae) are based on an extremely effective diet. The sea giants swim at high speed in swarms of small prey, open their mouths and suck the food along with a huge amount of water into their flexible throat pouch. They then press the contents with their tongues through the baleen, which, like a sieve, filters the food out of the water flowing outwards. Then the whales can swallow the catch.

How do you keep your throat shut?

It was already obvious that marine mammals would have to have mechanisms for this system that fish do not need, because whales are known to breathe air. Like all mammals, they have to ensure that nothing gets into the respiratory tract when they eat, since the entrances to the esophagus and trachea are located together in the back of the pharynx. This poses a particular challenge for whales, because the tissues are exposed to enormous pressure loads from the enormous amounts of water that rapidly flow into their mouths. How the sea giants solve the problem was previously unclear.

In order to close this knowledge gap, the researchers led by Kelsey Gil from the University of British Columbia in Vancouver have now carried out anatomical studies on fin whales. “It’s impossible to study this in living whales, so we relied on tissues from deceased whales and used what’s known as functional morphology to assess the relationship between structures and their functions,” Gil explains. So the team took another close look at the anatomy of the whale’s jaws. They also manipulated various elements and recorded the orientations of the muscle fibers in order to trace the movement sequences during the animals’ lifetime.

Plug structure discovered

The most surprising finding was a previously unknown structure in the transition area between the mouth and pharynx of the whales: “We call this structure the ‘oral plug’ because our results show that this element blocks the channel between the mouth and pharynx . This means it protects the airway when a whale lunges at its prey. This structure is probably present in all rorquals,” says Gil. According to the research, the plug consists of muscle and fat tissue and belongs to the soft palate area of ​​the rorquals. Its shape is reminiscent of a giant uvula.

According to the research results, the plug normally continuously seals the whale’s throat. This prevents the prey, which is still mixed with water, from being pressed into the esophagus when it is feeding. The results show that the plug only releases this path when swallowing. To do this, he moves backwards and upwards. It then blocks access to the upper airways, at the ends of which are the sealable nostrils of the whales, but opens the way for food. Similar to ours, the larynx then takes over the closing function to seal off the lower airways, according to the researchers’ analyses.

As they explain, a structure like this oral plug is not known from any other animal. “This element is probably a protective structure that only occurs in rorquals and was created specifically for sucking in the gigantic amounts of water and prey,” says Gil. Finally, the scientist emphasizes that these results make it clear once again that there is still a lot that we do not know about whales. Apparently, this also applies to the pharynx of the giants: the team now wants to continue to devote itself to its investigation.

Source: University of British Columbia, professional article: Current Biology, doi: 10.1016/j.cub.2021.12.040

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