Facts About Tardigrade (Water Bears): What Makes Them So Special?

You may have heard of water bears and wondered if they’re really as amazing as people make them out to be.

As someone who has personally worked with Tardigrades in the lab, I can confirm that, not only are they fascinating, they’re adorable too.

And, in this article, I’m going to show you what sets them apart from the rest of the animal kingdom.

What is a Tardigrade?

The name Tardigrade literally means “slow steppers.” But they’re most commonly known as water bears due to their walking gait resembling that of a bear.

They have eight legs, three pairs for walking and one pair for grasping, each ending in claws. So far, more than 1,150 species of Tardigrade have been discovered, and counting.

Tardigrade Lifespan

A Tardigrade’s lifespan varies from species to species. In terms of their natural lifespan, some live a few months, while others can live for up to 2 years.

But they can also go into a dormant state which stretches their lifespan even further. In this state, they can go more than 30 years without any food or water.

How Big is a Tardigrade?

Tardigrades are really tiny and are best viewed through a microscope. Most species are in the range of 0.3 to 0.5 mm (or 0.012 to 0.02 inches). Having said that, the largest species of water bear, Echiniscoides sigismundi, can reach a length of 1.2 mm (or 0.047 inches).

Habitat: how to find a Tardigrade?

Tardigrades can be found pretty much anywhere that there is water, marine or fresh. They have even been recorded in Antarctic ice, as well as in the deepest sediments of the ocean floor, and way up on the peaks of the Himalayas 6,000 m (or 20,000 ft) above sea level.

But you don’t need to go to such extremes to see one. They are most commonly found on mosses and lichens. In fact, one common nickname for Tardigrades is “moss piglets.”

The easiest way to find a Tardigrade is by looking at damp moss under a microscope. No science background is needed as cheap USB microscopes are readily available to anyone. Simply plug it into your computer and you might see a Tardigrade for yourself.

If you don’t have any luck finding one that way, kick sampling is also good. If you kick up the sediments in any freshwater or marine environment and collect some of the water, you have a good chance of finding a Tardigrade. There can sometimes be up to 25,000 of them per litre.

What Does a Tardigrade Eat?

Tardigrades have incredibly sharp, knife-like teeth that they use to pierce individual cells and suck out the insides.

Their exact diet varies depending on the species. Most are phytophagous, meaning they feed on the cells from algae, moss, and lichens, or bacteriophagous, meaning they feed on bacteria cells.

There are some predatory species, though. These will feed on smaller animals that they find in the water, such as nematode worms. Some are even cannibalistic and will munch on other water bears.

What Can Kill a Tardigrade?

As it turns out, Tardigrades are really hard to kill.

They can cope with extreme temperatures. In one experiment, water bears survived at 151ºC (or 304ºF) for a few minutes. They have also been frozen to -200ºC (or -328ºF) and were able to survive for a few days.

They can even survive a few minutes at -272ºC which is just one degree above absolute zero, the lowest temperature possible. A bit worse than your average sweater weather, right?

They can withstand extreme pressures. The majority are capable of surviving 1,200 times the normal atmospheric pressure, which is impressive enough on its own.

But some species can survive at 6,000 times atmospheric pressure, which is six times the pressure at the very deepest part of the ocean floor, the Mariana Trench.

When exposed to extreme levels of radiation, water bears are relatively unaffected. It would take 5,000 Gy of gamma rays to kill a Tardigrade. To put that in perspective, the lethal dose for humans is just 5 to 10 Gy. What’s more, Tardigrades can withstand their lethal dose for several days before they finally die off.

In 2007, dehydrated Tardigrades were taken into orbit for 10 days on the FOTON-M3 mission.

During that time, they were exposed to the vacuum of outer space and solar UV radiation. Once they were returned to Earth, the Tardigrades were rehydrated and two thirds of them were successfully revived and able to reproduce.

So, what can kill them? Given their small size, they are easy prey for many aquatic predators. Plus, when they’re not in a dormant or dehydrated state, their life cycle is quite short. So, despite all the crazy things they’re able to live through, it’s the simple everyday things that can kill them. It’s a case of letting nature taking its course.

10 Mind Boggling Facts About Water Bears

1. They have been around for at least 530 million years.

Tardigrades start to appear in fossils from the Cambrian, a period that ranges from 541 million years ago to 485 million years ago. It is the point at which life really started to diversify.

This means that Tardigrades have survived a whopping five mass extinctions, including the one that wiped out the dinosaurs.

2. They are born with a full set of adult cells.

Almost all living things on Earth grow by increasing the number of their cells using cell division. But not Tardigrades. They are born with up to 40,000 cells, depending on the species, and maintain this same number of cells throughout their life. So, instead, they grow by simply expanding the size of these cells.

3. They are capable of reproducing by themselves.

While Tardigrades are able to reproduce in the normal manner, they can also reproduce asexually, creating perfect clones of themselves. As a result, a single Tardigrade is able to establish a new colony and populate less habitable environments.

They even act as pioneers in these developing environments, bringing other species with them that are attracted by the prospect of an easy meal.

4. They can lose 99% of the water content in their bodies and live in a suspended state.

A Tardigrade’s dehydrated form is known as a tun and it can live in this state for several years before being rehydrated. It does this by producing a special protein, called TDP, which replaces water. This allows the water bear’s cells to keep their shape and not become damaged.

While in this tun state, Tardigrades can be carried on the wind or on the feet of other animals to a new environment. It’s amazing how far this can take them. Once they reach a more hospitable environment, they can revert to their natural form and start a new colony.

5. Being submerged in harmful chemicals does little to harm them.

Alcohol is very damaging to cells and can completely disrupt their structure in less than a minute. And yet, Tardigrades can survive being immersed in alcohol for an entire day.

As if that wasn’t impressive enough, there are examples of Tardigrades surviving carbolic acid exposure, as well as exposure to hydrogen sulphide, which is both highly flammable and highly corrosive.

6. They are able to repair their DNA when it is damaged by radiation.

After extreme radiation exposure, Tardigrades can repair their DNA in just a few days. This is part of the reason why they are able to withstand such high radiation levels where other animals would be killed by it. Another important factor is the fact that their DNA is so unique.

7. They contain DNA from non-animal organisms.

Despite how long it’s been since they were first discovered, the Tardigrade’s genome was only just sequenced in 2015. Surprisingly, it turns out that around 17.5% of their genes comes from non-animal life, such as plants, bacteria, and viruses.

This means that Tardigrades don’t just get their genetic material in the usual manner from parent to offspring, but by other means as well.

8. Their genes could be used to preserve food in the future.

Scientists have already confirmed that that the Tardigrade genes for producing TDPs can be used to protect yeast and bacteria from dehydration. They now think that the same idea could be applied to crops to make sure that they can survive droughts.

This method could even help produce medication that doesn’t need to be refrigerated. As you can imagine, this would be a really useful development, especially in poorer countries where hospitals don’t always have the equipment that they need.

9. There are possibly Tardigrades on the moon.

The Israeli lunar lander, Beresheet, was launched in April 2019. They had on board, among other things, an entire colony of Tardigrades. Unfortunately, the lander crashed onto the Moon’s surface, which brought the mission to an unexpected halt. But, given their near indestructible nature, it is highly likely that the Tardigrades survived the impact and are still there in a dehydrated state.

10. They may have originally come from space.

Because they are so widespread and able to tolerate so many different environments, including the vacuum of space, some think that this may be where they originated.

The most popular theory is that Tardigrades were first brought to Earth on meteors or comets, which isn’t as out there as it may sound. There’s even a name for the process: panspermia.

Final Thoughts

Tardigrades are hardy little creatures. More so than the cockroaches we often refer to as indestructible. Having proven themselves against the harshest conditions the planet has to offer, it makes me wonder where water bears will be millions of years from now.

What do you think? Could water bears be the last ones standing when life on Earth begins to reach its end? I’d say they’re a strong contender.

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