Tardigrades are a group of tiny, eight-legged animals commonly called water bears or moss piglets. There are around 1300 known species of tardigrades. They are known to be extremely resilient and can even live in adverse conditions such as extreme temperatures and pressure. However, they are not immortal (Jönsson et al., 2019).
Domain: Eukarya Kingdom: Animalia Subkingdom: Eumetazoa Superphylum: Ecdysozoa Phylum: Tardigrada
Interesting Facts About Tardigrades
Tardigrades were first described by a German zoologist called Goeze in 1773 who called them kleiner wasserbär (little water bear).
Four years later, in 1777, an Italian scientist named Spallanzani called them Tardigrada.
They are invertebrates and generally live in moist environments. They can be found everywhere on Earth, even in the polar regions. In fact, you can find tardigrades near your home/school and observe them with a home-made microscope. Perhaps you can consider keeping one or two of them as a pet? (Roszkowska et al., 2021)
They were thought to be more closely related to insects but scientists now consider them to be closer to worms.
The adults usually grow up to 0.5 mm long. The largest tardigrade recorded was around 1.5 mm long. The smallest was found to be less than a tenth of a millimeter long.
Newly hatched babies may be smaller than 0.05 mm long (super tiny).
They are one of the most stress-tolerant animals on Earth.
They can easily survive in extreme conditions such as freezing, dehydration, high radiation, high pressure, lack of oxygen, salty environments, vacuum, exposure to toxic chemicals or extreme pH and high temperatures.
Scientists think that tardigrades can survive even catastrophic events that would generally be deadly to life (Sloan et al., 2017).
In an interesting experiment, they were also able to survive the harsh cosmic radiation and micro-gravity of lower Earth orbit in space (Jönsson et al., 2008).
They were even able to survive, to a certain extent, when fired like a bullet from a gun.
However, when these animals crash landed on to the surface of the moon aboard the Israeli lunar lander Beresheet, they probably did not survive, but we don’t know for sure (O'Callaghan, 2021).
Tardigrades use a technique called cryptobiosis to withstand extreme conditions.
During cryptobiosis, these animals enter into a state of extreme inactivity, essentially suspending all physiological processes.
In this state, water is replaced by special proteins called intrinsically disordered proteins which helps them to survive dehydration (Boothby et al., 2017).
One of the cryptobiotic states is the tun-state where these animals withdraw their legs and shrink their bodies, similar to a tortoise hiding in their shell.
They can stay in this state for decades and then be resurrected (Tsujimoto et al., 2015).
Recent research also indicates that some species of tardigrades use fluorescence to protect themselves from harmful UV radiation (Suma et al., 2020).
Some reports have indicated that tardigrades show tolerance to extreme conditions even in their active state (Møbjerg and Neves, 2020).
The lifespan of tardigrades ranges from 3 to 30 months.
They usually feed on microscopic organisms like algae and fungi.
Some species exhibit cannibalistic behaviour by eating other tardigrades.
Tardigrades are very successful animals. They have been around for about 600 million years (even before some species of dinosaurs). This means that they survived at least one or more catastrophic events like an ice-age (Goldstein and Blaxter, 2002).
In 2015, the genome of one of the species was fully sequenced. Interestingly, scientists found that 17.5% of the genes in this species was acquired from non-animal life such as bacteria, plants and fungi during the course of evolution (Boothby et al., 2015).
Real photograph of a species of Tardigrade found in Antarctica. Credit: Tsujimoto et al., 2016.
Light microscope photograph of a terrestrial Tardigrade showing the different metabolic states. The hydrated active state is preferred when environmental conditions are favourable. On the contrary, when environmental conditions are stressful, the Tun state, which is a metabolically inactive state, is preferred. Credit: Møjberg and Neves, 2021.
How do Tardigrades Reproduce?
Tardigrades reproduce both asexually and sexually, depending on the species. During sexual reproduction, female tardigrades lay eggs which are then fertilised by the males. During asexual reproduction, the eggs laid by females develop into adults without fertilisation.
So those were some interesting facts about tardigrades. Do you know some facts about them that I missed? Let us know in the comments section below.e were some interesting facts about tardigrades. Do you know some facts about them that I missed? Let us know in the comments section below.
References
K. Jönsson, I. Holm and H. Tassidis, Cell Biology of the Tardigrades: Current Knowledge and Perspectives. Results and Problems in Cell Differentiation. 231-249 (2019). 10.1007/978-3-030-23459-1_10. context
M. Roszkowska et al., Tips and tricks how to culture water bears: simple protocols for culturing eutardigrades (Tardigrada) under laboratory conditions. The European Zoological Journal. 88, 449-465 (2021). 10.1080/24750263.2021.1881631. context
D. Sloan, R. Alves Batista and A. Loeb, The Resilience of Life to Astrophysical Events. Scientific Reports. 7, (2017). 10.1038/s41598-017-05796-x. context
K. Jönsson et al., Tardigrades survive exposure to space in low Earth orbit. Current Biology. 18, R729-R731 (2008). 10.1016/j.cub.2008.06.048. context
J. O'Callaghan, Hardy water bears survive bullet impacts—up to a point. Science. (2021). 10.1126/science.abj5282. context
T. Boothby et al., Tardigrades Use Intrinsically Disordered Proteins to Survive Desiccation. Molecular Cell. 65, 975-984.e5 (2017). 10.1016/j.molcel.2017.02.018. context
M. Tsujimoto, S. Imura and H. Kanda, Recovery and reproduction of an Antarctic tardigrade retrieved from a moss sample frozen for over 30 years. Cryobiology. 72, 78-81 (2015). 10.1016/j.cryobiol.2015.12.003. context
H. Suma, S. Prakash and S. Eswarappa, Naturally occurring fluorescence protects the eutardigradeParamacrobiotussp. from ultraviolet radiation. Biology Letters. 16, 20200391 (2020). 10.1098/rsbl.2020.0391. context
N. Møbjerg and R. Neves, New insights into survival strategies of tardigrades. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology. 254, 110890 (2020). 10.1016/j.cbpa.2020.110890. context
T. Boothby et al., Evidence for extensive horizontal gene transfer from the draft genome of a tardigrade. Proceedings of the National Academy of Sciences. 112, 15976-15981 (2015). 10.1073/pnas.1510461112. context
