December 14, 2021 | David F. Coppedge

Leaky Mitochondria Keep Sea Otters Warm

Darwin-free research on sea otters
might have benefits for humans.


Wouldn’t it be nice to eat more without gaining weight? Sea otters may have a secret.

Sea otters rank among the cutest of mammals. Who doesn’t love watching them float on their backs cracking oysters or sea urchins with rocks and then devouring their tasty sushi with big grins on their furry whiskered faces? A good place to watch them is at the Monterey Bay Aquarium, which functions as a research institute as well as a popular California tourist attraction.

Sea otter mom and pup. Credit: Randy Davis, Creative Commons.

There’s more design going on in a sea otter’s body than meets the eye. A team of researchers, writing at The Scientist, wanted to know how those unbearably cute critters keep warm in the cold waters of the bay. Knowing thermodynamics, the scientists realized that small animals face two problems: (1) smaller bodies lose heat faster, and (2) water conducts heat away from the body much faster than air. Most marine mammals like whales and seals insulate themselves with thick layers of blubber, but sea otters do not. How do they manage the cold?

Sea otters have two strategies to stay warm and cozy. One is a specialized type of fur:

Amazing FactsSea otters are the smallest of the marine mammals, and do not have this thick layer of blubber. Instead, they are insulated by the densest fur of any mammal, with as many as a million hairs per square inch. This fur, however, is high maintenance, requiring regular grooming. About 10 percent of a sea otter’s daily activity involves maintaining the insulating layer of air trapped in their fur.

To avoid overdosing on cuteness, don’t watch the embedded video of a sea otter grooming and looking oh-so-happy doing it. Hey, work doesn’t have to be a chore if it feels good.



Otter Thermodynamics

The other strategy involves “leaky” mitochondria. Those are the organelles in cells that produce energy from our food. As the title of the article says, “Sea Otters Demonstrate that There Is More to Muscle than Just Movement—It Can Also Bring the Heat.” They explain,

The process of converting nutrients into ATP is similar to how a dam turns stored water into electricity. As water flows out from the dam, it makes electricity by spinning blades connected to a generator—similar to wind turning the blades on a windmill. If the dam is leaky, some water—or stored energy—is lost and cannot be used to make electricity.

Similarly, leaky mitochondria are less efficient at making ATP from nutrients. Although the leaked energy in the mitochondria cannot be used to do work, it generates heat to warm the sea otter’s body.

Those spinning blades, our readers will know, come from the exquisite molecular machine called ATP synthase (see video at CMI). The proton motive force from upstream machines causes this rotary engine to spin at 6,000 RPM, generating three ATP molecules per revolution. ATP is the universal “energy currency” for most cellular processes.

ATP synthase, however, is too good. Unlike any man-made machine, it is nearly 100% efficient – all the incoming energy from protons is used to make product, adenosine triphosphate (ATP). The sea otter’s machines in its muscles, though, have a trick:

We discovered the mitochondria in sea otter muscles could be very leaky, allowing otters to turn up the heat in their muscles without physical activity or shivering. It turns out that sea otter muscle is good at being inefficient. The energy “lost” as heat while turning nutrients into movement allows them to survive the cold.

Good News for Humans

Could this strategy be used for humans? If so, we could eat more without gaining weight, and use the excess calories to stay warm in cold weather. The researchers see possibilities there.

This has important implications for human health. If scientists discover ways to safely and reversibly increase skeletal muscle metabolism at rest, doctors could possibly use this as a tool to reduce climbing rates of obesity by increasing the amount of calories a patient can burn.

The authors note that cancer patients might benefit from the reverse process: conserving energy from their food. Even astronauts might be able to survive long trips by eating less. Thank you, sea otters!

Thank you, Darwin-free science.


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