Meet the ice worm, which lives in glaciers—a scientific 'paradox'

Glacier ice worms thrive at freezing temperatures and exhibit other mysterious traits that make them an urgent subject of research—since their habitat is disappearing.

Published 24 Aug 2021, 17:57 BST
Glacier ice worms cover the surface of the Paradise Glacier on the south side of Mount ...
Glacier ice worms cover the surface of the Paradise Glacier on the south side of Mount Rainier, Washington. These animals thrive at the freezing point of water, a scientific “paradox.”
Photograph by Scott Hotaling

At first glance, a glacier looks like a rather lifeless thing—a barren chunk of ice. But there’s much more than meets the eye: Glaciers are home to a host of tiny organisms that make up a flourishing frigid ecosystem.

Most prominent among these in western North America are ice worms. Measuring about a half-inch in length and thin as threads of dental floss, ice worms (Mesenchytraeus solifugus) dot glaciers throughout the Pacific Northwest, British Columbia, and Alaska. Vast numbers of the tiny black worms emerge on summer afternoons and evenings to feed on algae, microbes, and other detritus on the surface. Then they burrow back into the ice at dawn—and during the winter, disappear into the frozen depths.

These distant relatives of earthworms survive in layers of ice-cold water within the snow and ice, thriving at water’s freezing point. This would be impossible for most creatures, especially cold-blooded ones without any insulation, like worms. So how do ice worms do it? Scientists have discovered some of the worms’ tricks, noting that understanding these biological oddballs is surprisingly relevant—and urgent.

Learning more about how these animals tolerate extremes can help us understand the limits of life on Earth and beyond, says Daniel Shain, a Rutgers University researcher who has studied the animals for 25 years.

But as glaciers are vanishing, so are ice worms. “We want to find out as much about the worms as we can before they disappear,” says Shirley Lang, a biologist at Haverford College in Pennsylvania. “And I have little doubt they will disappear one day,” if glaciers continue to melt at their current rate.

Worm mysteries

The laws of biology dictate that as temperatures dive, bodily reactions slow and energy levels drop. While warm-blooded animals must burn energy to keep a relatively constant temperature, cold-blooded creatures become sluggish and even go dormant when it gets too cold. But not ice worms.

“Their energy levels go up as they get colder,” Shain says. “And this is a paradox.”

Research by Shain and Lang, who completed her doctorate in Shain’s lab, helps explain why in a series of papers published in recent years. It all relates to a special molecule known as ATP, short for adenosine triphosphate. ATP serves as the currency of energy in cells, and it powers most reactions in the body. It’s made using a complex enzyme, called ATP synthase, which is virtually identical in all known organisms. The molecule is close to 100 percent efficient in its work—unheard of for any invention outside the natural world. Biochemists view it with awe. “It’s an extraordinary machine,” Shain says.

But ice worms have an added tweak in their machinery, an extra bit in the DNA that creates ATP synthase. The alteration appears to help speed up the production of ATP. “It’s like a turbo,” Shain says.

It’s hard to explain the evolution, Shain says, but it’s possible the worms stole a chunk of genetic material that’s been seen in high-altitude fungi. If so, this genetic theft is particularly unusual because stolen DNA doesn’t normally get incorporated into the mitochondria, where ATP is made.

Besides the genetic addition, the worms also have an altered cellular “thermostat” that allows ATP production to proceed when it’s cold. The two changes combined mean that ice worms have much higher cellular concentrations of ATP than most creatures, which helps explain how they maintain their energy levels in the freezing cold.

Lang plans to explore another theory for their high energy levels. The worms are chock-full of melanin, the same pigment that helps shield human skin from UV radiation. But in ice worms, melanin is found throughout the body: in the brain, the gut, the muscles. Some research suggests that melanin may be able to harvest energy from solar radiation in some situations, and Lang suspects this might be happening in ice worms. She hopes to test this idea.

The animals live only in coastal glaciers, and are found nowhere else in the world, though another similar species has been found in Tibet. Almost nothing is known about it. While ice worms thrive at 32 degrees Fahrenheit, they cannot tolerate temperatures much below this frigid sweet spot.

Predator and prey

Besides their incredible energetics, ice worms are also part of an ecosystem that we know very little about. They exist alongside rotifers, tardigrades, algae, fungi, and other microscopic creatures, explains Scott Hotaling, a biologist at Washington State University. They also provide food for birds.

Hotaling and his colleagues have observed at least five species of birds eating ice worms. The invertebrates are a vital food source in places like Mount Rainier, where rosy finches snarf them up in large quantities and feed them to their young, Hotaling says.

Birds may also help explain how these small animals are able to disperse from glacier to glacier. The animals are genetically different in disparate locations, with the animals in Alaska likely comprising a different species than many of the worms in the Pacific Northwest, Shain says.

Hotaling’s work suggests that live worms could be transported by sticking to birds’ plumage or feet, or perhaps some survive passage through a bird’s gut. One population of ice worms on Vancouver Island, for example, shows a close relationship to a population in southern Alaska—suggesting one or several may have been carried there by a bird in the recent past.

But time is running out to unravel the ice worm’s mysteries. Some of the glaciers in which they were formerly found, such as the Lyall and Lewis glaciers in Washington’s North Cascades, have disappeared. Others are shrinking. The Nisqually Glacier, on the south side of Mount Rainier, home to ice worms, has retreated by an average of three feet every 10 days between 2003 and 2015.

Joanna Kelley, an evolutionary geneticist, and Hotaling are working to sequence the worm’s genome, which has proved difficult. That’s partially because they’re so full of melanin, which clings to DNA and interferes with genome sequencing technology.

They hope to uncover their other secrets before it’s too late. “I feel like I need to rush to study these animals,” Hotaling says.

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