Tardigrades – The Toughest Animals on The Planet

Tardigrades, a phylum of eight-legged, segmented micro-invertebrate animals with an average body size of 0.5mm (0.020 inch)—the toughest animal known to science—are also known as water bears or moss piglets. When Johann August Ephraim Goeze, a German zoologist, first described them in 1773, he gave them the moniker “little water bears” because they resembled adorable mini-nature bears.

They have been discovered in many different biospheres on Earth, including the Antarctic, deep water, tropical rainforests, and mountaintops. Individual species of tardigrades may endure extreme conditions that would swiftly kill the majority of other species of animals, including exposure to extreme temperatures, extreme pressures, air deprivation, radiation, dehydration, and malnutrition. Even in space, tardigrades have managed to survive. The phylum Tardigrada, a subclass of the superphylum Ecdysozoa, which includes organisms that undergo ecdysis, has nearly 1,400 species that are now recognized.

Tardigrades are common in mosses and lichens and eat small invertebrates, algae, and plant cells for food. They can be seen with a low-power microscope after collection, making them available to students and amateur researchers.

Description:

The largest adult tardigrades may reach a body length of 1.5 mm (0.059 inch); the smallest are below 0.1 mm (0.0039 inch). Newly hatched tardigrades may be smaller than 0.05 mm (0.0020 in). The creatures have barrel-shaped bodies with four pairs of stubby legs. Each foot has 4 to 8 claws, which help them cling to plant matter, and a specialized mouthpart called a buccopharyngeal apparatus, which allows them to suck nutrients from plants and microorganisms. Many species possess a pair of pigment-cup eyes without lenses, which suggests that they can’t form images. That means their response to light “might be more directional or intensity-based than image- or space-based.”

Habitat:

The tiny aquatic creature tardigrades can frequently be found in lichens and mosses and in a variety of other settings, such as soil, leaf litter, and marine or freshwater sediments, in almost every habit on Earth, where there may be up to 25,000 animals per liter. Tardigrades are common in mosses and lichens and eat small invertebrates, algae, and plant cells for food. They can be seen with a low-power microscope after collection, making them available to students and amateur researchers.

Mating and Reproduction:

Both males and females are typically present, even though females are frequently larger and more prevalent. However, some species are parthenogenic. Because they are oviparous, tardigrades typically undergo external fertilization. The eggs are laid inside the female’s shed cuticle and are later coated with sperm during mating, which takes place during the moult. In a few species, mating takes place before the female has completely shed her cuticle, a process known as internal fertilization. Prior to mating, tardigrades frequently court. According to the study, courtship is the first stage of mating, and up to nine males may congregate around a female to mate. When eggs are dehydrated, the time it takes to hatch can increase to 90 days.

Ecology:

The majority of tardigrades feed on bacteria or plants; however, some are carnivorous to the point where they also consume other tardigrade species. This link makes it difficult for biologists to discover confirmation among tardigrade species. These creatures are most closely related to early arthropod evolution. There are tardigrades all throughout the world, and they are regarded as cosmopolitan creatures.

Tardigrades can live for three to four months in some species and up to two years in others, not including the 30 to 40 years they spend in dormant states.

Exposure to extreme environments:

 Extremophile animals known as tardigrades have been discovered in hot springs, on top of the Himalayas (6,000 m; 20,000 ft. above sea level), in the deep sea (4,000 m; 13,000 ft.), and in sediments from the ocean floor. They have also been discovered from the poles to the equator and under solid ice layers. While certain species can be found on stone walls and rooftops, others can be found in softer habitats like lakes, ponds, and meadows.

It is believed that tardigrades can endure even full global mass extinctions brought on by astronomical occurrences like gamma-ray bursts or significant meteorite impacts. They can withstand pressures roughly six times greater than those found in the deepest ocean trenches, ionising radiation at doses hundreds of times greater than the lethal dose for a human, and the vacuum of space for several minutes. Some of them can withstand extremely cold temperatures as low as 0.01 K (460 °F; 273 °C), which is close to absolute zero, while others can withstand extremely hot temperatures as high as 420 K (300 °F; 150 °C). Many tardigrade species may endure being severely dehydrated for five to ten years, or even longer in certain circumstances.

Exposure to outer space:

Tardigrades are the first known animal to survive after exposure to outer space.

• The European Science Agency released dehydrated tardigrades into low Earth orbit in September 2007. For ten days, they were exposed in groups to the harsh vacuum of space and solar UV radiation. After rehydrating within 30 minutes, more than 68% of the subjects shielded from solar UV rays who were brought to Earth were revived.
• On the Space Shuttle Endeavour’s final trip in May 2011, Italian researchers delivered tardigrades to the International Space Station. It was found that cosmic radiation and microgravity did not significantly influence tardigrade survival in flight, implying that tardigrades are a viable species for space research.
• A container with an Israeli lunar lander inside crashed on the moon in August 2019.
• In recent years, there has also been increased speculation regarding tardigrades’ ability to survive on Mars without any life support systems.

Survival tricks in extreme environmental conditions:

• Special protein: Scientists recently made another discovery—a protein that is unique to tardigrades—that explains how these microbes are so resilient.

One gene produces the protein Dsup (damage suppressor). There are two components to the protein. The DNA is held to the cell nucleus by one component and shielded from radiation by the other component, which also creates a hazy shape around the DNA. DNA must always be protected because it holds an organism’s entire genetic code. When their wet, mossy environment dries out, tardigrades may come into contact with radiation. If they do, they will go into dehydration-induced cryptobiosis as a defense mechanism.

In the future, this protein could be used to protect human cells from radiation, as it has the potential to reduce radiation damage in human cells by up to 40%. These biotechnological innovations will, however, take some time. It will be a while before we see superhumans walking around with tardigrade characteristics.

• Cryptobiosis: Another amazing survival trick is cryptobiosis, a state of inactivity triggered by a dry environment. The micro-animals squeeze all the water out of their bodies, retract their heads and limbs, roll up into a little ball, and become dormant. When conditions improve, they unfurl themselves and go about their business.

Resources:

• https://medium.com/mind-cafe/three-subtle-life-lessons-from-the-bizarre-and-invincible-tardigrade-d00f8e97d0a6
• https://serc.carleton.edu/microbelife/topics/tardigrade/index.html
• https://www.newscientist.com/article/2252583-secret-to-tardigrades-toughness-revealed-by-supercomputer-simulation/
• https://soil.evs.buffalo.edu/index.php/File:Tardigrade_boy.JPG
• https://www.nationalgeographic.com/animals/invertebrates/facts/tardigrades-water-bears#:~:text=What%20is%20a%20tardigrade%3F,of%20tardigrades%20are%20found%20worldwide.
• https://tumblr.amnh.org/post/132884503459/tardigradesmicroscopic-eight-legged-animals-that
• https://en.wikipedia.org/wiki/Tardigrade#:~:text=Tardigrades%20(%2F%CB%88t%C9%91%CB%90rd,%22little%20water%20bear%22).
• https://www.americanscientist.org/article/tardigrades
• https://en.wikipedia.org/wiki/Tardigrade_specific_proteins#:~:text=Tardigrade%20specific%20proteins%20are%20a,to%20move%20through%20different%20structures.
• https://sqonline.ucsd.edu/2018/05/tardigrades-testing-the-limits-of-space-travel/
• https://www.science.org/content/article/hardy-water-bears-survive-bullet-impacts-point
• https://www.livescience.com/tardigrades-cant-see-color.html
• https://www.vox.com/science-and-health/2018/2/8/16991280/tardigrade-facts-waterbear-explained

Glossary:

• Air deprivation– (Hypoxia) is a condition in which the body or a region of the body is deprived of adequate oxygen supply at the tissue level
• Arthropods– Arthropods are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages.
• Astronomical occurrences– Typically refers to anything that occurs in the universe that is outside of the earth’s atmosphere and has an effect on it.
• Bacteriophagous – bacteria eaters
• Carnivorous– of an animal feeding on other animals.
• Cryptobiosis– a state of extreme inactivity in response to adverse environmental conditions. In the cryptobiotic state, all metabolic procedures stop, preventing reproduction, development, and repair.
• DNA
• Dsup– Damage suppressor
• Ecdysis – the process of shedding the old skin
• Extremophiles– An extremophile is an organism that is able to live in extreme environments
• Genome: The genome is the entire set of DNA instructions found in a cell.
• Invertebrates– a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a backbone or spine), derived from the notochord.
• Paraphyletic– (of a group of organisms) descended from a common evolutionary ancestor or ancestral group, but not including all the descendant groups.
• Mass extinction– A mass extinction event is when species vanish much faster than they are replaced.
• Moulting– The process of moulting is the casting off of an outer layer to reveal a new one
• Phylum – a principal taxonomic category that ranks above class and below kingdom, equivalent to the division in botany.
• Species– a group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding.
• Subphylum– a subphylumis a taxonomic rank below the rank of phylum.
• Parthenogenesis – is a natural form of asexual reproduction in which growth and development of embryos occur in a gamete (egg or sperm) without combining with another gamete.
• Phytophagous– Plant eaters
• Radiation-Energy that comes from a source and travels through space at the speed of light
• Superhuman– The term superhuman refers to humans or human-like beings with enhanced qualities and abilities that exceed those naturally found in humans.
• Tropical rainforests– Rainforests that occur in areas of tropical rainforest climate in which there is no dry season

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