Water bears are probably the most indestructible animals on the planet. In the harsh environment of no food and no water, it only needs to shrink itself into a ball and stop its metabolism, and it has a chance to continue to survive for up to 30 years. Using this method, tardigrades can also endure low temperatures close to absolute zero (-273°C), are also good at enduring hypoxia, and can survive in a vacuum environment.
In addition, even if irradiated with radiation equivalent to 1,000 times the lethal dose of humans, the tardigrades are not serious. Some scientists also loaded the low-temperature frozen tardigrades into bullets and shot at the target at a speed of more than 800 meters per second, but the strong impact still failed to kill the tardigrades. There are even many people who suspect that even if a huge meteorite falls, causing the mass extinction of life on Earth, the water bears may survive.
So, do tardigrades really have no Achilles’ heel? Two researchers from Poland have found a “death train” for tardigrades.
How the snail became a fast car
Water bears, also called tardigrades, are not one species, but a phylum of tardigrades that includes thousands of species.
Those gathered under this gate are basically microscopic creatures, and their body lengths are mostly between 0.3 mm and 0.5 mm, and if they exceed 1 mm, they are considered huge. They have 8 feet, and each foot has 4 to 8 toes. They have excellent athletic ability and can sometimes walk two body-length distances in one second. However, due to the small size of the body, the speed is usually only measured in centimeters, so it has no choice but to be crowned as a “tardigrade”.
These small animals that can only be seen clearly with a microscope should be difficult to go to distant places by their own strength. But the fact is that there are traces of water bears in almost every corner of the earth, whether it is more than 6,000 meters in the mountains or more than 4,000 meters in the deep sea. So, what more efficient means of transportation did they use to transport themselves around the world and have the majestic territory they have today?
Many small animals, such as some nematodes or mites, can attach themselves to larger animals and make long journeys — a phenomenon called carry-over. And this time, researchers at Mickiewicz University in Poznan wanted to show that tardigrades, or water bears, behave similarly.
The tardigrades the team used for their experiments came from a species called Milnesium inceptum. The vehicle prepared for it is the forest onion snail. The reason for this choice, scientists say, is because the two species have overlapping natural habitats and similar atmospheric conditions: in places with high humidity, the surface of snails is also wet, which is conducive to water bears Bugs stay active. Of course, there is another point, that is, the snail is larger than the water bear, and there is room for such passengers. In this way, there is reason to expect water bears to get on the snail train.
The researchers prepared three kinds of boxes: box A contained water bears; box B contained water bears and snails; in addition to water bears and snails, box C also added some tardigrades collected from concrete walls. moss. After all, moss is one of the tardigrades’ preferred daily dwellings.
The scientists prepared 30 of each of these three boxes, and each box contained 10 water bears. So, a total of 900 water bears will participate in this experiment, and their initial positions are all within the range of a silicone square. The researchers placed 90 boxes in the rearing room and waited three days.
After 72 hours, they needed to see how many tardigrades had moved and how many remained. It was found that in box A without snails, the tardigrades did not leave the silica gel square; in boxes B and C with snails, some tardigrades left the silica gel square.
Forest onion snail
As a result, scientists believe that the long-distance movement of water bears needs to rely on the help of snails. Although the snail’s movement is known for its slowness, for small tardigrades, attaching to the snail is like riding a high-speed train.
In addition, the researchers also noticed an important thing, that is, many of the tardigrades that moved out of the square have died. The first speculation the scientists put forward was that a living tardigrade could firmly anchor itself to the surface with its feet, making it difficult for the snail to carry it away, while a dead tardigrade was easier to separate from the surface Come, it also creates an opportunity for snail transportation.
Of course, there is another possibility: something in the car killed the passengers.
The secret to killing tardigrades
Scientists suspect that the snail’s mucus could be deadly to some tardigrades.
So they tested some water bears with snail mucus. In the harsh environment of lack of water, tardigrades can turn themselves into a “ball” and stop their metabolism. It is the tardigrades in this state that scientists test.
Specifically, the scientists let the snails crawl through the living environment of the tardigrades, leaving their own mucus; then the snails were invited away, and after 24 hours, they hydrated the “suspended” tardigrades and watched them Will it be “resurrected”? It turned out that only 34 percent of the “balls” that touched the snail’s mucus survived, while the rest died. In contrast, 98 percent of the tardigrades in the control group, which had not been drenched in snail mucus, successfully recovered after the hydration treatment.
Water bears exposed to snail mucus have a higher mortality rate. The main component of snail mucus is water. Scientists suspect that the reason is that the mucus dries too fast: when the snail passes the “suspended” tardigrade, it is hydrating it, but if the mucus dries quickly, it will make the tardigrade too late to do anything about the hydration process and re-dehydration. effective response. At this time, it is difficult for water bears to form a “ball” again with the correct posture, and the high mortality rate can be explained.
However, research has only confirmed that this method can kill the “feigned death” water bears, and it is not a hundred-percent. Even if snail mucus can kill some active tardigrades, as long as one lucky person survives, it will have the opportunity to take the snail train to the next place and expand a new territory for the tardigrade family.