Natures wonders: how sea otters keep warm (Introduction)

by David Turell , Thursday, July 08, 2021, 23:04 (1019 days ago) @ David Turell

All that fur and no blubber to insulate them:

https://www.sciencenews.org/article/sea-otter-warmth-mitochondria-muscle-metabolism-bio...

"Sea otters’ secret to staying warm isn’t in thick stores of blubber. It’s in their muscles.

"Leaks in the energy-generating parts of muscle cells help otters maintain a resting metabolism three times as fast as predicted for a creature their size, researchers report in the July 9 Science. The find shows how otters meet the challenge of staying warm at sea — and could apply to other marine mammals, too.

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"Sea otters are lean and compact, the smallest mammals in the ocean, bobbing like furry barrels on waves. And the insulating properties of sea otters’ fur — the densest on the planet — can’t fully protect them from losing too much heat. Water transfers heat 23 times as efficiently as air, and small bodies with less surface area lose heat faster, even when covered in fluff.

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"Leaks in mitochondria — the energy-generating part of cells — generate extra heat and cause sea otters’ extreme metabolism, the researchers found. Metabolism describes how food gets converted into energy in cells. Mitochondria pump protons across their inner membrane to store energy that can be used to power the cell. But if those protons leak back over the membrane before being used for work, that energy is lost as heat. Because these proton leaks increase the amount of energy lost as heat, otters need to eat more food to make up for that lost energy, revving up their metabolism.

"Other mammals — including extremely small mice with high metabolisms — can also generate heat this way. But sea otters are much better at it: These proton leaks account for about 40 percent of otters’ muscle cells’ total respiratory capacity, higher than any known mammal. Producing heat this way helps the animals stay comfortable in 0° C Pacific waters. “That message is loud and clear, and just brilliant,” Williams says.

"Sea otters’ high leak capacity “is not necessarily what they’re running all the time,” Wright says, but probably can be activated when otters need to generate more warmth. Scientists don’t yet know how otters’ cells turn this process on and off.

"Baby otters don’t yet have the muscle mass to stay warm through these leaks, but their muscle cells generate heat at adult rates, the researchers found, showing that proton leak begins early. Finding similar leak capacities in wild and captive otters of different ages suggests that these leaks are the “driving force” behind otters’ metabolism, Wright says.

"It’s not yet clear if otters inherit this trait or develop it with exposure to cold water. “We don’t know if this is inherent,” Wright says, “or if this is something that quickly comes on after birth as a means of generating heat on demand.'” (my bold)

Comment: How did otters develop this? Hypothermia kills quickly. Two possibilities: otters developed in warm seas and changed/adapted as seas cooled. Or God designed them that way .