Weddell seal chews breathing hole in the ice « Why Evolution Is True


As I mentioned earlier, I’m preparing a set of talks for an upcoming voyage to Antarctica on which I’m a guest lecturer. One of them, which I posted on before, is about the science done by the Scott Expedition to the South Pole. It turns out that at least two of the group’s aims had something to do with evolution, and I’ll discuss those as well as dilate in general about the science that went on side by side with the exploration.

While these lectures are challenging, as I’m not an expert on polar biology, they’re also enormously fun, as I’m learning a ton about stuff that I’d never know otherwise. The second one is on the adaptations of animals to the extreme Antarctic environment (cold, windy, dry, and extremely variable in light regime over the year). I’m taking a few examples to show how these adaptations operate and how they evolved. One, of course, is the famous “antifreeze” proteins of fish that live at -1.9° C.

But this post is about the Weddell Seal (Leptonychotes weddellii), probably the most well-studied mammal in the Antarctic, for it lives close to the polar stations. It’s also the only pinniped in the region that lives under permanent ice. It can stay underwater for an hour and dive up to 2,000 feet (!!) to hunt for fish, crustaceans, and cephalopods. It spends most of its time in the water.

But it’s a mammal, and so it needs to surface for air—and find land to breed on.  How does it do this under permanent ice?

It does it by finding “tide cracks” in the ice, but also by chewing “breathing holes” that it uses repeatedly. They gnaw these holes with special dentition having huge incisors and canines (arrows). This picture, taken from a Research Gate post on tooth wear as a cause of mortality in the species, is captioned “Skull of a Weddell seal showing incisor and canine teeth (arrows) worn to pulp cavity and two abscesses in bone of palate (right canine removed for age determination). Photograph by B. M. Dukes.”

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A few notes from TravelWild:

This chewing wears down their teeth and, by 20 years of age, the Weddell seal may no longer have viable teeth and, unable to hunt or maintain its breathing hole, may die.

The Weddell seal’s hole is its lifeline: critical for both diving for food and resurfacing for air. When on ice, the seal rarely travels beyond three meters from its hole. Since there are no polar bears in Antarctica, these seals do not use their breathing holes to escape from terrestrial predators such as those found in the Arctic.

But enough background: look at this seal chew! It’s more like scraping than chewing, but I find it mesmerizing. I’ve never seen an animal do anything like this. (Now if evolution produced perfect adaptations, it would give this seal permanently growing teeth, like rodents!)

And here’s a general video on the biology of this species (another nice video, from the BBC, is here):





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