The earth is hot and wet. The sea is full of life. Early squids, eels, and sea worms preyed on smaller animals. However, there was no movement on the ground. The animals have not climbed ashore yet. This is what Earth looked like at the end of the Ordovician Period, about 450 million years ago. Warm waters create perfect conditions for wildlife. But that could soon change. Soon after, the land began to freeze and the ice sheets began to spread.
Springtails are ancient. They first appeared more than 400 million years ago and may share a common ancestor with insects. Since then, however, they have evolved in a different direction than insects. We now know that they were the first animals to develop antifreeze proteins. Image source: Philippe Garcelon/Wikimedia Commons
Water that was previously warm and hospitable to wildlife became cold and uninhabitable. Species after species succumbed. In a short period of time, half of all life was wiped out as part of the second-worst mass extinction in Earth's history.
Life during the Ordovician period looked much different than it does today. The land is barren and lifeless, but the sea is full of life. The squid and sea anemones pictured here are particularly dominant. But springtails are also present at this time. Image source: FritzGeller-Grimm/WikimediaCommons
Springtails: Survivors with antifreeze proteins
However, one of the animals that survived was the springtail. A small insect-like animal has developed a special strategy to combat the cold. Animal cells have begun producing proteins that protect cells from freezing.
Springtails may have been the first animals to produce antifreeze proteins. Scientists previously thought animals didn't start doing this until much later. Research from Aarhus University and Queen's University in Canada shows this.
"We know that antifreeze proteins have developed independently many times in evolutionary history. Fish have them. Insects have them. Some spiders have them. But until we saw these results, we had no idea that they developed so early in the animal world," says Martin Holmstrup.
He is a professor at the Department of Ecological Sciences at Aarhus University and one of the researchers on the new study.
Springtails can be found everywhere—including in your garden
Springtails are small animals, with the largest species only six millimeters long. It has six legs and two tentacles on the front. At first glance they look like insects, but they are not. In fact, it has its own branch on the evolutionary tree.
So far, researchers have discovered more than 9,000 different species of springtails, and they can be found just about everywhere, including in your garden. Springtail worms usually live in the upper layers of soil or in leaf litter, feeding on tiny fungi, bacteria and other microorganisms.
The animal gets its name from its forked tail, which is fastened under its body like the rod of a catapult. The tail is also called a forked tail, and if attacked by an enemy (such as a tiger), the animal can quickly release its tail and jump up to 10 centimeters in the air.
Springtails are beneficial to soil health because they help recycle nutrients into the plants.
Martin Holmstrup raises nearly 20 different species of springtails in the laboratory. Small animals don’t need much space. An entire colony could live in a glass bowl, he said. "We put them in a petri dish with a plaster base, which keeps them moist. As a feed, we give them a little bit of dry yeast. That's basically all they need," he said.
Springtails from Martin's laboratory were used in the experiment. He sent samples from the animals to three colleagues in Canada, who conducted a series of molecular experiments to find out when the animals first produced antifreeze proteins.
Because researchers know the DNA sequence that enables cells to build antifreeze proteins, they can search for the same sequences across species, families and classes. They can also calculate when the mutation that led to the gene's origin occurred: the Ordovician period.
"Calculations show that springtails produced antifreeze proteins long before other animals. This did not happen until a million years later in fish and insects. Although plants and microorganisms, such as bacteria and single-celled algae, may have developed similar mechanisms much earlier," he said.
How to find springtails
Martin Holmstrup and his colleagues in the Department of Ecological Sciences collected the springtails themselves for the laboratory. They gathered in Denmark, Iceland and Greenland.
They are not hard to find and you can even find them in your own garden.
Just follow these steps:
Grab a handful of soil or leaves from the garden and place it in a sieve.
Place the adjustable light over the sieve and place the tray under the sieve.
The heat from the lights causes the springtails to seek out cooler environments. This will cause them to fall through the sieve into the tray, where you'll find them crawling.
Although you can find springtails almost anywhere in the world, the Arctic has more springtails than anywhere else. Only a handful of other land animals can survive the cold of Greenland and Canada, meaning the springtails can feed on bacteria and fungi undisturbed.
"The super-strong antifreeze proteins of springtails allow them to survive in cold areas, where they only have to share their food with a few other worms and insects. And they don't have many natural enemies," says Martin Holmstrup.
In winter, when Arctic temperatures drop, springtails begin producing antifreeze proteins. They are also called "ice-binding proteins" because they can attach to the surface of tiny ice crystals and prevent them from growing. When soil freezes, terrestrial animals come into close contact with ice crystals, so antifreeze proteins play an important role in preventing ice from spreading into the animal's body and killing it.
"Like us and most other animals, springtails cannot survive if their 'blood' freezes. Antifreeze proteins help prevent this," he said.
Springtails come in many shapes and sizes, with more than 9,000 different species. These are just the number of species we found. Researchers estimate there are twice as many springtail species or more. Image credit: Andy Murray/Wikimedia Commons
dry like raisins
However, this special protein isn't the springtails' only ability to survive the Arctic cold, they have another way of survival.
"Because every living thing has water molecules inside its cells, we are very susceptible to freezing temperatures. If water freezes, the cells are destroyed. To prevent this, springtails dry themselves out and enter a kind of hibernation during the winter," explains Martin Holmstrup.
When springtails hibernate, their metabolism slows down so much that scientists can't actually measure it. However, when spring arrives, they absorb water back into their bodies and restart their metabolism.
"You can compare them to grapes being dried into raisins, a process reminiscent of freeze-drying. Over the winter, the springtails shrink and become small, wrinkled critters. Then, when spring arrives, they absorb water and swell to their normal size," he said.
Also found in fish that should have been frozen to death
How certain animal species survive in the coldest regions on Earth has been a mystery for years. It wasn't until the middle of the last century that scientists discovered the antifreeze proteins that enable animals to cope with cold.
For decades, scientists have wondered how Arctic fish are able to swim in waters as cold as -1.8 degrees Celsius. Seawater has a low freezing point due to its salt content. Fish blood, on the other hand, has a freezing point of -1 degrees Celsius, which means they cannot avoid freezing in the water.
"How fish survive in freezing waters has long been a mystery. However, in the late 1960s, American researcher Arthur DeVries was able to isolate proteins found in Arctic fish, which he found to prevent ice from forming in the fish's cells and blood, even if the fish was supercooled throughout its life," explains Martin Holmstrup.
Since then, researchers have discovered antifreeze proteins in many other animals, plants and microorganisms. These antifreeze proteins are now used by industry.
History and applications of antifreeze proteins
Today, many foods are bought and sold as frozen meals. The problem, however, is that frozen food can change if ice crystals start to form. They often reduce the taste and texture of food.
However, this condition can be prevented with special antifreeze proteins, explains Martin Holmstrup:
"The gene encoding the fish antifreeze protein has been copied into industrial yeast cell cultures. This allows the yeast to produce very useful proteins that can then be added to different foods," he said.
One of the foods that is particularly potent for protein is ice cream.
"I know Unilever uses proteins in their ice cream as they help create a really lovely texture. Ice cream can also be thawed and refrozen without turning into hard ice crystals. In the longer term, this effect could be used for cryopreservation of transplanted organs. Other industries such as the aerospace and wind turbine industries are also experimenting with these proteins. They hope these proteins will protect aircraft wings from ice forming and the need to be de-iced."