Content deleted Content added
No edit summary Tag: Reverted |
Kerdooskis (talk | contribs) m →Survival after exposure to outer space: Broke large paragraph. |
||
| (34 intermediate revisions by 25 users not shown) | |||
Line 4:
{{Automatic taxobox
| fossil_range = {{fossil range|Turonian|Recent|earliest=Cambrian}}
| image = SEM image of Milnesium tardigradum in active state - journal.pone.0045682.g001-2 (white background).png
| image_caption = ''[[Milnesium tardigradum]]'', a [[eutardigrade]]
Line 15:
| subdivision = *[[Eutardigrada]]
*[[Heterotardigrada]]
*[[Mesotardigrada]] (
}}
Line 21:
They have been found in diverse regions of Earth's [[biosphere]]{{snd}}mountaintops, the [[deep sea]], [[tropical rainforest]]s, and the [[Antarctic]].<ref name="Bordenstein" /> Tardigrades are among the most resilient animals known,<ref name="WP-20170714">{{cite news|last=Guarino|first=Ben|title=These animals can survive until the end of the Earth, astrophysicists say|url=https://www.washingtonpost.com/news/speaking-of-science/wp/2017/07/14/these-animals-can-survive-until-the-end-of-the-earth-astrophysicists-say/|date=14 July 2017|newspaper=The Washington Post|access-date=14 July 2017}}</ref><ref name="NAT-20170714">{{cite journal|doi=10.1038/s41598-017-05796-x|pmid=28710420|pmc=5511186|title=The Resilience of Life to Astrophysical Events|journal=Scientific Reports|volume=7|issue=1|page=5419|year=2017|last1=Sloan|first1=David |last2=Alves Batista|first2=Rafael|last3=Loeb|first3=Abraham|bibcode=2017NatSR...7.5419S|arxiv=1707.04253}}</ref> with individual species able to survive extreme conditions – such as exposure to extreme temperatures, extreme [[pressures]] (both high and low), air deprivation, [[radiation]], [[dehydration]], and [[starvation]] – that would quickly kill most other known forms of [[life]].<ref>{{cite journal |last1=Orellana|first1=Roberto|last2=Macaya|first2=Constanza|last3=Bravo|first3=Guillermo|last4=Dorochesi|first4=Flavia|last5=Cumsille|first5=Andrés|last6=Valencia|first6=Ricardo|last7=Rojas|first7=Claudia|last8=Seeger|first8=Michael|date=2018-10-30|title=Living at the Frontiers of Life: Extremophiles in Chile and Their Potential for Bioremediation|journal=Frontiers in Microbiology|volume=9|page=2309 |doi=10.3389/fmicb.2018.02309|pmid=30425685|pmc=6218600|issn=1664-302X|doi-access=free}}</ref> Tardigrades have survived exposure to [[outer space]].<ref>{{cite news |url=https://www.newscientist.com/article/dn14690-water-bears-are-first-animal-to-survive-vacuum-of-space.html|title={{'}}Water Bears' are first animal to survive vacuum of space. |magazine=New Scientist|access-date=10 September 2008|archive-url=https://web.archive.org/web/20080910062613/http://space.newscientist.com/article/dn14690-water-bears-are-first-animal-to-survive-vacuum-of-space.html|archive-date=10 September 2008|url-status=live}}</ref><ref>{{cite news|url=https://www.sciencedaily.com/releases/2008/09/080908135906.htm|title='Water Bears' Able To Survive Exposure To Vacuum Of Space|publisher=Science Daily|access-date=10 September 2008|archive-url=https://web.archive.org/web/20080911091656/https://www.sciencedaily.com/releases/2008/09/080908135906.htm|archive-date=11 September 2008|url-status=live}}</ref> There are about 1,300 known species<ref>{{cite web |first1=Peter |last1=Degma |first2=Roberto |last2=Bertolani |first3=Roberto |last3=Guidetti |title=Actual checklist of Tardigrada species (2009–2021, 40th Edition: 19-07-2021) |year=2021 |publisher=Università di Modena e Reggio Emilia
|url=https://iris.unimore.it/retrieve/358743/Actual%20checklist%20of%20Tardigrada%2040th%20Edition%2019-07-21.pdf |access-date=2023-12-10 |doi=10.25431/11380_1178608}}</ref> in the [[phylum]] Tardigrada, a part of the superphylum [[Ecdysozoa]] consisting of animals that grow by [[ecdysis]] (shedding an [[exoskeleton]]) such as [[arthropod]]s and [[nematode]]s. The earliest known true members of the group are known from [[Cretaceous]] (145 to 66 million years ago) amber, found in North America, but are essentially modern forms. Their origin is therefore likely much earlier, as they diverged from their closest relatives in the [[Cambrian]] more than 500 million years ago.
Tardigrades are usually about {{cvt|0.5|mm}} long when fully grown.<ref name="American Scientist">{{cite web|url=https://www.americanscientist.org/article/tardigrades|title=Tardigrades|publisher=American Scientist|access-date=2018-04-13|first=William|last=Miller|date=2017-02-06}}</ref> They are short and plump, with four pairs of legs, each ending in claws (usually four to eight) or suction disks.<ref name="American Scientist"/><ref name="Nelson-CurrentStatus">{{cite journal|title=Current status of Tardigrada: Evolution and Ecology|last=Nelson|first=Diane|journal=Integrative and Comparative Biology |volume=42|issue=3|date=1 July 2002|pages=652–659|doi=10.1093/icb/42.3.652|pmid=21708761|doi-access=free}}</ref> Tardigrades are prevalent in [[moss]]es and [[lichen]]s and feed on plant cells, algae, and small invertebrates. When collected, they may be viewed under a low-power [[microscope]], making them accessible to students and amateur scientists.<ref>{{cite web|url=http://tardigrade.us/how-to-articles/how-to-find-tardigrades/|title=How to Find Tardigrades|last=Shaw|first=Michael W.|publisher=Tardigrade USA|archive-url=https://web.archive.org/web/20140210001506/http://tardigrade.us/how-to-articles/how-to-find-tardigrades/|archive-date=10 February 2014|url-status=dead|access-date=2013-01-14}}</ref>
Line 36:
== Habitat ==
Tardigrades are often found on lichens and mosses
With the exception of 62 known species that live exclusively in freshwater, all non-marine tardigrades are found in terrestrial environments. Because the majority of the marine species belongs to Heterotardigrada, the most ancestral class, it confirms the phylum's marine origin.<ref>{{Cite journal |last=van Straalen |first=Nico M. |date=August 2021 |title=Evolutionary terrestrialization scenarios for soil invertebrates |journal=Pedobiologia |language=en |volume=87-88 |pages=150753 |doi=10.1016/j.pedobi.2021.150753|bibcode=2021Pedob..8750753V |doi-access=free }}</ref>
== Anatomy and morphology ==
Line 68 ⟶ 70:
[[File:Тихоходки, темное поле 280х.webm|thumb|upright=1.0|right|Living tardigrades moving around]]
Most tardigrades are [[phytophagous]] (plant eaters) or [[wikt:bacteriophagous|bacteriophagous]] (bacteria eaters), but some are [[Carnivore|carnivorous]] to the extent that they eat smaller species of tardigrades (for example, ''[[Milnesium tardigradum]]'').<ref>{{cite journal |title=Population dynamics of two species of Tardigrada, ''Macrobiotus hufelandii'' (Schultze) and ''Echiniscus (Echiniscus) testudo'' (Doyere), in roof moss from Swansea |first=Clive I. |last=Morgan |journal=Journal of Animal Ecology |volume=46 |issue=1 |date=1977 |pages=263–79 |doi=10.2307/3960|jstor=3960|bibcode=1977JAnEc..46..263M }}</ref><ref>{{cite web |last=Lindahl |first=K. |date=15 March 2008|title=Tardigrade Facts |url=http://www.iwu.edu/~tardisdp/tardigrade_facts.html}}</ref>
Tardigrades share morphological characteristics with many species that differ largely by class. Biologists have a difficult time finding verification among tardigrade species because of this relationship.{{clarify|date=May 2019}} These animals are most closely related to the early evolution of [[arthropod]]s.<ref name=Brent_Nichols_2005>{{cite thesis |type=PhD |title=Tardigrade Evolution and Ecology |last=Brent Nichols |first=Phillip |publisher=University of South Florida |year=2005 |location=Tampa, FL }}</ref> Tardigrade fossils go as far back as the [[Cretaceous]] period in North America. Tardigrades are considered cosmopolitan and can be located in regions all over the world. The eggs and cysts of tardigrades are so durable that they can be carried great distances on the feet of other animals.<ref name="Nelson-CurrentStatus"/>
Line 81 ⟶ 83:
[[File:Tardigrade (unknown species).jpg|thumb|right|Tardigrade (unknown species, ventral view) imaged using [[scanning_electron_microscope|scanning electron microscopy]]]]
Scientists have reported tardigrades in [[hot spring]]s, in glacial [[cryoconite]] holes, on top of the [[Himalayas]]<ref>{{cite encyclopedia |last=Hogan |first=C. Michael |year=2010 |url=http://www.eoearth.org/article/Extremophile?topic=49540 |title=Extremophile |editor1=E. Monosson |editor2=C. Cleveland. |encyclopedia=Encyclopedia of Earth |publisher=National Council for Science and the Environment. |location=Washington, DC }}</ref><ref>[https://zslpublications.onlinelibrary.wiley.com/doi/abs/10.1111/jzo.12832 A hole in the nematosphere: tardigrades and rotifers dominate the cryoconite hole environment, whereas nematodes are missing]</ref> ({{convert|6,000|m|ft|disp=semicolon|abbr=on}}, above sea level), and in the [[deep sea]] ({{convert|-4000|m|ft|abbr=on|disp=semicolon}}); from the [[polar region]]s to the [[equator]], under layers of solid [[ice]], and in ocean sediments. Many species can be found in milder environments such as lakes, ponds, and [[meadow]]s, while others can be found in stone walls and roofs. Tardigrades are most common in moist environments but can stay active wherever they can retain at least some moisture.
Tardigrades are thought to be able to survive even complete global mass [[extinction event]]s caused by [[Astrophysics|astrophysical events]], such as [[gamma-ray bursts]], or large [[Impact event|meteorite impacts]].<ref name="WP-20170714" /><ref name="NAT-20170714" /> Some of them can withstand extremely cold temperatures down to {{convert|0.01|K|F C|0}} (close to [[absolute zero]]), while others can withstand extremely hot temperatures up to {{convert|420|K|F C|-1}}<ref>{{cite magazine|url=https://www.wired.com/2014/03/absurd-creature-week-water-bear/ |title=Absurd Creature of the Week: The Incredible Critter That's Tough Enough to Survive in Space |magazine=Wired |first=Matt |last=Simon |date=21 March 2014}}</ref><ref>{{Cite book |url=https://www.worldcat.org/oclc/340800193 |title=New Zealand inventory of biodiversity |date=2009–2012 |publisher=Canterbury University Press |others=Dennis P. Gordon |isbn=978-1-877257-72-8 |location=Christchurch, N.Z. |pages=28 |oclc=340800193}}</ref> for several minutes, pressures about six times greater than those found in the deepest ocean trenches, [[ionizing radiation]] at doses hundreds of times higher than the lethal dose for a human, and the vacuum of outer space.<ref name="NYT-20150907">{{cite news |last=Dean |first=Cornelia |title=The Tardigrade: Practically Invisible, Indestructible 'Water Bears' |url=https://www.nytimes.com/2015/09/08/science/the-tardigrade-water-bear.html |date=7 September 2015 |work=[[The New York Times]] |access-date=7 September 2015}}</ref> Tardigrades that live in harsh conditions undergo an annual process of [[cyclomorphosis]], allowing for survival in subzero temperatures.<ref>{{cite journal |title=Cyclomorphosis in Tardigrada: adaptation to environmental constraints |first1=Kenneth Agerlin |last1=Halberg |first2=Dennis |last2=Persson |first3=Hans |last3=Ramløv |first4=Peter |last4=Westh |first5=Reinhardt Møbjerg |last5=Kristensen |first6=Nadja |last6=Møbjerg |date=1 September 2009 |journal=Journal of Experimental Biology |volume=212 |issue=17 |pages=2803–11 |doi=10.1242/jeb.029413 |pmid=19684214|s2cid=23429443 |doi-access= }}</ref>
Line 87 ⟶ 89:
They are not considered [[extremophilic]] because they are not adapted to exploit these conditions, only to endure them. This means that their chances of dying increase the longer they are exposed to the extreme environments,<ref name="Bordenstein" /> whereas true [[extremophile]]s thrive in a physically or [[geochemical]]ly [[extreme environment]] that would harm most other organisms.<ref name="WRD-20140321" /><ref>{{cite journal |doi=10.3390/su2061602 |title=Resistance of Microorganisms to Extreme Environmental Conditions and Its Contribution to Astrobiology |journal=Sustainability |volume=2 |issue=6 |pages=1602–23 |year=2010 |last1=Rampelotto |first1=Pabulo Henrique |bibcode=2010Sust....2.1602R |doi-access=free }}</ref><ref>{{cite journal |doi=10.1038/35059215 |pmid=11234023 |title=Life in extreme environments |journal=Nature |volume=409 |issue=6823 |pages=1092–101 |year=2001 |last1=Rothschild |first1=Lynn J |author-link=Lynn J. Rothschild |last2=Mancinelli |first2=Rocco L |bibcode=2001Natur.409.1092R |s2cid=529873 |url=https://zenodo.org/record/1233097 }}</ref>
Tardigrades are one of the few groups of species that are capable of suspending their metabolism {{xref|(see [[
Their ability to remain desiccated for such long periods of time was thought to be dependent on high levels of the nonreducing disaccharide [[trehalose]],<ref name="hibshman">{{cite journal | last1=Hibshman | first1=Jonathan D. | last2=Clegg | first2=James S. | last3=Goldstein | first3=Bob | title=Mechanisms of Desiccation Tolerance: Themes and Variations in Brine Shrimp, Roundworms, and Tardigrades | journal=Frontiers in Physiology | volume=11 | date=2020-10-23 | page=592016 | issn=1664-042X | pmid=33192606 | pmc=7649794 | doi=10.3389/fphys.2020.592016| doi-access=free }}</ref> which is commonly seen in other organisms that survive desiccation, and tardigrades have [[trehalase]] [[gene]]s.<ref name="kamilari">{{cite journal | last1=Kamilari | first1=Maria | last2=Jørgensen | first2=Aslak | last3=Schiøtt | first3=Morten | last4=Møbjerg | first4=Nadja | title=Comparative transcriptomics suggest unique molecular adaptations within tardigrade lineages | journal=BMC Genomics | volume=20 | issue=1 | date=2019-07-24 | page=607 | issn=1471-2164 | pmid=31340759 | pmc=6652013 | doi=10.1186/s12864-019-5912-x | doi-access=free }}</ref> However, it has been seen that in both tardigrades and [[Bdelloidea|bdelloid rotifers]], there is only a partial capability to synthesize trehalose in quantities that may contribute to desiccation tolerance.<ref name=hibshman/><ref>{{Cite journal|last1=Lapinski|first1=Jens|last2=Tunnacliffe|first2=Alan|date=2003|title=Anhydrobiosis without trehalose in bdelloid rotifers|journal=FEBS Letters|language=en|volume=553|issue=3|pages=387–390|doi=10.1016/S0014-5793(03)01062-7|pmid=14572656|s2cid=1692056 |issn=1873-3468|doi-access=|bibcode=2003FEBSL.553..387L }}</ref>
In response to this finding, more research was done on how these animals survived such extreme conditions. It was found that [[intrinsically disordered proteins]] (IDPs) were highly expressed in response to desiccation in tardigrades. Additionally, three new IDPs were found to be specific to tardigrades and coined [[tardigrade specific proteins]] (TDPs). These TDPs may maintain the structure of membranes by associating with the polar heads of the [[Lipid bilayer|phospholipids bilayers]], avoiding structural damage upon rehydration.<ref>{{cite journal |doi=10.1016/j.molcel.2017.02.018 |pmid=28306513 |pmc=5987194 |title=Tardigrades Use Intrinsically Disordered Proteins to Survive Desiccation |journal=Molecular Cell |volume=65 |issue=6 |pages=975–984.e5 |year=2017 |last1=Boothby |first1=Thomas C |last2=Tapia |first2=Hugo |last3=Brozena |first3=Alexandra H |last4=Piszkiewicz |first4=Samantha |last5=Smith |first5=Austin E |last6=Giovannini |first6=Ilaria |last7=Rebecchi |first7=Lorena |last8=Pielak |first8=Gary J |author-link8=Gary J. Pielak|last9=Koshland
Tardigrades can survive in extreme environments that would kill almost any other animal.<ref name=kamilari/> Extremes at which tardigrades can survive include those of:
Line 102 ⟶ 104:
Research published in 2020 shows that tardigrades are sensitive to high temperatures. Researchers showed it takes 48 hours at {{Cvt|37.1|C|F|abbr=}} to kill half of active tardigrades that have not been acclimated to heat. Acclimation boosted the temperature needed to kill half of active tardigrades to {{Cvt|37.6|C|F|abbr=}}. Tardigrades in the tun state fared a bit better, tolerating higher temperatures. It took heating to {{Cvt|82.7|C|F|abbr=}} to kill half of tun-state tardigrades within one hour. Longer exposure time decreased the temperature needed for lethality, though. For 24 hours of exposure, {{Cvt|63.1|C|F|abbr=}} was enough to kill half of the tun-state tardigrades.<ref>{{cite journal |last1=Neves |first1=Ricardo Cardoso |last2=Hvidepil |first2=Lykke K. B. |last3=Sørensen-Hygum |first3=Thomas L. |last4=Stuart |first4=Robyn M. |last5=Møbjerg |first5=Nadja |title=Thermotolerance experiments on active and desiccated states of Ramazzottius varieornatus emphasize that tardigrades are sensitive to high temperatures |journal=Scientific Reports |date=9 January 2020 |volume=10 |issue=1 |page=94 |doi=10.1038/s41598-019-56965-z |pmid=31919388 |pmc=6952461 |bibcode=2020NatSR..10...94N }}</ref>
In 2021 scientists reported they had cooled down a tardigrade of the species Ramazzottius varieornatus to 10 millikelvin above absolute zero, and put it under extremely low pressure of 0.000006 millibars. After 420 hours, the animal was brought back to life again.<ref>[https://www.sciencealert.com/physicists-claim-they-ve-entangled-a-tardigrade-with-qubits-but-did-they Physicists Claim They've Quantum Entangled a Tardigrade With a Qubit. But Have They?]</ref>
* [[Pressure]] – they can withstand the extremely low pressure of a [[vacuum]] and also very high pressures, more than 1,200 times [[atmospheric pressure]]. Some species can also withstand pressures of 6,000 atmospheres, which is nearly six times the pressure of water in the deepest ocean trench, the [[Mariana Trench]].<ref name="Seki98">{{cite journal |doi=10.1038/27576 |title=Preserving tardigrades under pressure |journal=Nature |volume=395 |issue=6705 |pages=853–54 |year=1998 |last1=Seki |first1=Kunihiro |last2=Toyoshima |first2=Masato |bibcode=1998Natur.395..853S |s2cid=4429569 }}</ref> Tardigrades can survive at altitudes of more than {{convert|19,600|ft|m|abbr=off|sp=us}} and depths of more than {{convert|15,000|ft|m}} below the surface.{{Citation needed|date=June 2023}}▼
▲* [[Pressure]] – they can withstand the extremely low pressure of a [[vacuum]] and also very high pressures, more than 1,200 times [[atmospheric pressure]]. Some species can also withstand pressures of 6,000 atmospheres, which is nearly six times the pressure of water in the deepest ocean trench, the [[Mariana Trench]].<ref name="Seki98">{{cite journal |doi=10.1038/27576 |title=Preserving tardigrades under pressure |journal=Nature |volume=395 |issue=6705 |pages=853–54 |year=1998 |last1=Seki |first1=Kunihiro |last2=Toyoshima |first2=Masato |bibcode=1998Natur.395..853S |s2cid=4429569 }}</ref> Tardigrades can survive at altitudes of more than {{convert|19,600|ft|m|abbr=off|sp=us}} and depths of more than {{convert|15,000|ft|m}} below the surface.<ref>{{
* [[Impact (mechanics)|Impact]]s – tardigrades can survive impacts up to about 900 meters per second, and momentary shock pressures up to about 1.14 [[gigapascal]]s.<ref name="Science-20210518"/>
* [[Dehydration]] – the longest that living tardigrades have been shown to survive in a dry state is nearly 10 years,<ref name="auto" /><ref name="Guidetti, R. & Jönsson, K.I. 2002 181–187" /> although there is one report of leg movement, not generally considered "survival",<ref name="Jönsson, K. Ingemar & R. Bertolani 2001 121–123">{{cite journal |doi=10.1017/S0952836901001169 |title=Facts and fiction about long-term survival in tardigrades |journal=Journal of Zoology |volume=255 |issue=1 |pages=121–23 |year=2001 |last1=Jönsson |first1=K. Ingemar |last2=Bertolani |first2=Roberto |url=http://lup.lub.lu.se/record/147519 }}</ref> in a 120-year-old specimen from dried moss.<ref name="Franceschi, T. 1948 47–49">{{cite journal |last= Franceschi |first=T. |year=1948 |title=Anabiosi nei tardigradi |trans-title=Anabiosis in Tardigrades |language=it |journal=Bollettino dei Musei e Degli Istituti Biologici dell'Università di Genova |volume=22 |pages=47–49 }}</ref> When exposed to extremely low temperatures, their body composition goes from 85% water to only 3%. Because water expands upon freezing, dehydration ensures the tardigrades' tissues are not ruptured by the expansion of freezing ice.<ref>{{citation|first= Michael |last= Kent |year=2000| title= Advanced Biology| publisher=Oxford University Press}}</ref>
Line 111 ⟶ 115:
===Survival after exposure to outer space===
Tardigrades are the first known animal to survive after exposure to outer space.<ref name="NS-20080908" /> In September 2007, dehydrated tardigrades were taken into [[low Earth orbit]] on the [[Foton-M|FOTON-M3]] mission carrying the [[BIOPAN]] astrobiology payload. For 10 days, groups of tardigrades, some of them previously dehydrated, some of them not, were exposed to the [[hard vacuum]] of outer space, or vacuum and solar [[UV]] radiation.<ref name="low-earth-orbit" /><ref name="WRD-20140321" /><ref name="Science-20080908">{{cite web |title=Creature Survives Naked in Space |url=http://www.space.com/5817-creature-survives-naked-space.html |date=8 September 2008 |publisher=[[Space.com]] |access-date=2011-12-22 }}</ref><ref name="MSNBC-20111222">{{cite web |last=Mustain |first=Andrea |title=Weird wildlife: The real land animals of Antarctica |url=http://www.nbcnews.com/id/45766560 |date=22 December 2011 |publisher=[[NBC News]] |access-date=2011-12-22 }}</ref> Back on Earth, more than 68% of the subjects protected from solar UV radiation were reanimated within 30 minutes following rehydration; although subsequent mortality was high, many of these produced viable embryos.<ref name="low-earth-orbit">{{cite journal |doi=10.1016/j.cub.2008.06.048 |pmid=18786368 |title=Tardigrades survive exposure to space in low Earth orbit |journal=Current Biology |volume=18 |issue=17 |pages=R729–R731 |year=2008 |last1=Jönsson |first1=K. Ingemar |last2=Rabbow |first2=Elke |last3=Schill |first3=Ralph O |last4=Harms-Ringdahl |first4=Mats |last5=Rettberg |first5=Petra |s2cid=8566993 |doi-access=free |bibcode=2008CBio...18.R729J }}</ref><ref name="NS-20080908">{{Cite news |last=Courtland |first=Rachel |date=8 September 2008 |url=https://www.newscientist.com/article/dn14690-water-bears-are-first-animal-to-survive-space-vacuum.html |title='Water bears' are first animal to survive space vacuum |work=[[New Scientist]] |access-date=2011-05-22 }}</ref>
In contrast, hydrated samples exposed to the combined effect of vacuum and full solar UV radiation had significantly reduced survival, with only three subjects of ''[[Milnesium tardigradum]]'' surviving.<ref name="low-earth-orbit" /> Also, it was found that the space vacuum did not have a significant effect on egg-laying in either ''R. coronifer'' or ''M. tardigradum''. However, ''M. tardigradum'' exposed to UV radiation had a lower egg laying rate.<ref>{{Cite journal|last1=Jönsson|first1=K. Ingemar|last2=Rabbow|first2=Elke|last3=Schill|first3=Ralph O.|last4=Harms-Ringdahl|first4=Mats|last5=Rettberg|first5=Petra|date= September 2008 |title=Tardigrades survive exposure to space in low Earth orbit|journal=Current Biology|language=en|volume=18|issue=17|pages=R729–R731|doi=10.1016/j.cub.2008.06.048|pmid=18786368|s2cid=8566993|doi-access=free|bibcode=2008CBio...18.R729J }}</ref> In May 2011, Italian scientists sent tardigrades on board the International Space Station along with extremophiles on [[STS-134]], the final flight of {{OV|105}}.<ref>{{cite web |author=NASA Staff |url=http://www.nasa.gov/mission_pages/station/research/experiments/BIOKIS.html |archive-url=https://web.archive.org/web/20110417085459/http://www.nasa.gov/mission_pages/station/research/experiments/BIOKIS.html |url-status=dead |archive-date=17 April 2011 |title=BIOKon In Space (BIOKIS) |date=17 May 2011 |publisher=[[NASA]] |access-date=2011-05-24}}</ref><ref>{{cite web |last=Brennard |first=Emma |title=Tardigrades: Water bears in space |url=https://www.bbc.co.uk/nature/12855775 |date=17 May 2011 |publisher=BBC |access-date=2011-05-24}}</ref><ref>{{cite web|date=17 May 2011|title=Tardigrades: Water bears in space|publisher=BBC Nature|url=https://www.bbc.co.uk/nature/12855775}}</ref> Their conclusion was that microgravity and cosmic radiation "did not significantly affect survival of tardigrades in flight, and stated that tardigrades represent a useful animal for space research."<ref>{{cite book |hdl=2434/239127 |first1=L. |last1=Rebecchi |first2=T. |last2=Altiero |first3=A. M. |last3=Rizzo |first4=M. |last4=Cesari |first5=G. |last5=Montorfano |first6=T. |last6=Marchioro |first7=R. |last7=Bertolani |first8=R. |last8=Guidetti |chapter=Two tardigrade species on board of the STS-134 space flight |page=89 |title=12th International Symposium on Tardigrada |chapter-url=http://www.tardigrada.net/newsletter/images/symposia/12_Booklet.pdf |isbn=978-989-96860-7-6 |year= 2012 }}</ref><ref>{{Cite web|url=https://news.harvard.edu/gazette/story/2019/07/harvard-study-suggests-asteroids-might-play-key-role-in-spreading-life/|title=Harvard study suggests asteroids might play key role in spreading life|last=Reuell|first=Peter|date=2019-07-08|website=Harvard Gazette|language=en-US|access-date=2019-11-30}}</ref>
In recent years, there has also been increased speculation regarding tardigrades' ability to survive on Mars without any life support systems,<ref>Łukasz Kaczmarek. Can Tardigrades Theoretically Survive on Mars? Conference: Early Earth and ExoEarths: origin and evolution of lifeAt: Warszawa, Poland. April 2017. https://www.researchgate.net/publication/319213582_Can_tardigrades_theoretically_survive_on_Mars. Accessed on Oct 16, 2021</ref> but it would still "need stuff to eat" to survive.<ref>{{cite journal |last1=Ledford |first1=Heidi |title=Spacesuits optional for 'water bears' |journal=Nature |date=8 September 2008 |doi=10.1038/news.2008.1087 }}</ref>▼
In November 2011, they were among the organisms to be sent by the U.S.-based [[Planetary Society]] on the Russian [[Fobos-Grunt]] mission's [[Living Interplanetary Flight Experiment]] to [[Phobos (moon)|Phobos]]; however, the launch failed. In August 2019, scientists reported that a [[Tardigrades on the Moon|capsule containing tardigrades]] in a [[cryptobiotic state]] may have survived for a while on the [[Moon]] after the April 2019 crash landing of ''[[Beresheet]]'', a failed Israeli [[lunar lander]], but in May 2021 it was reported that they were unlikely to have survived the impact.<ref name="WRD-20190805">{{cite news|url=https://www.wired.com/story/a-crashed-israeli-lunar-lander-spilled-tardigrades-on-the-moon/|title=A Crashed Israeli Lunar Lander Spilled Tardigrades On The Moon|last=Oberhaus|first=Daniel|date=5 August 2019|magazine=[[wired (magazine)|Wired]]|access-date=6 August 2019}}</ref><ref name="VOX-20190806">{{cite news|url=https://www.vox.com/science-and-health/2019/8/6/20756844/tardigrade-moon-beresheet-arch-mission|title=Tardigrades, the toughest animals on Earth, have crash-landed on the moon – The tardigrade conquest of the solar system has begun|last=Resnick|first=Brian|date=6 August 2019|work=[[Vox (website)|Vox]]|access-date=6 August 2019}}</ref><ref name="Science-20210518">{{cite journal |doi=10.1126/science.abj5282|title=Hardy water bears survive bullet impacts—up to a point|year=2021|last1=O'Callaghan|first1=Jonathan|journal=Science|s2cid=236376996}}</ref>
▲In recent years, there has also been increased speculation regarding tardigrades' ability to survive on Mars without any life support systems,<ref>Łukasz Kaczmarek. Can Tardigrades Theoretically Survive on Mars? Conference: Early Earth and ExoEarths: origin and evolution of lifeAt: Warszawa, Poland. April 2017. https://www.researchgate.net/publication/319213582_Can_tardigrades_theoretically_survive_on_Mars. Accessed on Oct 16, 2021</ref> but it would still "need stuff to eat" to survive.<ref>{{
== Taxonomy ==
Line 129 ⟶ 137:
}}
Scientists have conducted [[Morphology (biology)|morphological]] and molecular studies to understand how tardigrades relate to other lineages of ecdysozoan animals. Two plausible placements have been proposed: tardigrades are either most closely related to [[Arthropoda]] and [[Onychophora]], or to [[nematodes]]. Evidence for the former is a common result of [[Morphology (biology)|morphological studies]]; evidence for the latter is found in genomic analysis.<ref name=":0">{{Cite journal |last1=Yoshida
{{clade
Line 145 ⟶ 153:
The minute sizes of tardigrades and their membranous integuments make their [[fossil]]ization both difficult to detect and highly unusual. The only known fossil specimens are those from mid-[[Cambrian]] deposits in [[Siberia]] ([[Orsten fauna]]) and a few rare specimens from [[Cretaceous]] [[amber]].<ref name="EotI">{{cite book |date=2005 |publisher=Cambridge University Press |isbn=978-0-521-82149-0 |title=Evolution of the Insects |url=https://archive.org/details/evolutioninsects00grim_110 |url-access=limited |first1=David A. |last1=Grimaldi |first2=Michael S. |last2=Engel |pages=[https://archive.org/details/evolutioninsects00grim_110/page/n110 96]–97}}</ref>
The Siberian tardigrade fossils differ from living tardigrades in several ways. They have three pairs of legs rather than four, they have a simplified head morphology, and they have no posterior head appendages, but they share with modern tardigrades their columnar cuticle construction.<ref name=Budd2001>{{cite journal |doi=10.1078/0044-5231-00034 |title=Tardigrades as 'Stem-Group Arthropods': The Evidence from the Cambrian Fauna |journal=Zoologischer Anzeiger |volume=240 |issue=3–4 |pages=265–79 |year=2001 |last1=Budd |first1=Graham E |bibcode=2001ZooAn.240..265B | url=https://www.researchgate.net/publication/223465290}}</ref> Scientists think they represent a stem group of living tardigrades.<ref name="EotI" />
In October 2021, a new species, ''[[Paradoryphoribius|Paradoryphoribius chronocaribbeus]]'', was discovered as a fossil in amber that was dated to be 16 million years old.<ref name="LS-20211005">{{cite news |last=Lanese |first=Nicoletta |title=Tardigrade trapped in amber is a never-before-seen species |url=https://www.livescience.com/new-tardigrade-species-found-in-amber |date=5 October 2021 |work=[[Live Science]] |accessdate=6 October 2021 }}</ref>
== Evolutionary history ==
[[File:20210000 Luolishaniids Luolishaniidae Luolishaniida.png|thumb|Schematic reconstruction of four [[Luolishaniidae|luolishaniids]], possibly the closest known fossil relatives of modern tardigrades
[[File:OrstenTardigrade.jpg|thumb|Reconstruction of the unnamed "[[Orsten]]" tardigrade, from the Cambrian Kuonamka Formation]]
[[File:Fossil_Tardigrade_Dominican_Amber.png|thumb|Reconstruction of ''[[Paradoryphoribius]]'', a miocene tardigrade]]
There are multiple lines of evidence that tardigrades are secondarily miniaturized from a larger ancestor,<ref>{{cite journal|doi = 10.1016/j.asd.2018.11.006|pmid = 30447338|title = Miniaturization of tardigrades (water bears): Morphological and genomic perspectives|journal = Arthropod Structure & Development|volume = 48|pages = 12–19|year = 2018|last1 = Gross|first1 = Vladimir|last2 = Treffkorn|first2 = Sandra|last3 = Reichelt|first3 = Julian|last4 = Epple|first4 = Lisa|last5 = Lüter|first5 = Carsten|last6 = Mayer|first6 = Georg| s2cid=53669741 |doi-access = }}</ref> probably a [[lobopodian]] and perhaps resembling ''[[Aysheaia]]'', which many analyses place close to the divergence of the tardigrade lineage.<ref name="ArtRels">{{cite book|date=2001|publisher=Chapman & Hall|isbn=978-0-412-75420-3|title=Arthropod Relationships|first1=Richard A. |last1=Fortey |author-link = Richard Fortey|first2=Richard H. |last2=Thomas|page=383}}</ref><ref name=Smith2014>{{Cite journal | doi=10.1038/nature13576 | pmid=25132546| title=Hallucigenia's onychophoran-like claws and the case for Tactopoda| journal=Nature| volume=514| issue=7522| pages=363–66| year=2014| last1=Smith| first1=Martin R.| last2=Ortega-Hernández| first2=Javier| bibcode=2014Natur.514..363S| s2cid=205239797| url=http://dro.dur.ac.uk/19108/1/19108.pdf}}</ref> An alternative hypothesis derives [[tactopoda]] from a clade encompassing dinocaridids and ''[[Opabinia]]''.<ref name="Budd1996">{{cite journal|last1=Budd|first1=Graham E|year=1996|title=The morphology of Opabinia regalis and the reconstruction of the arthropod stem-group|journal=Lethaia|volume=29|issue=1|pages=1–14|doi=10.1111/j.1502-3931.1996.tb01831.x|bibcode=1996Letha..29....1B }}</ref> A 2023 analysis concluded, on the basis of numerous morphological similarities, that [[Luolishaniidae|luolishaniids]], a group of Cambrian lobopodians, might be the closest known relatives of Tardigrada.<ref name="Kihm2023">{{cite journal |doi=10.1073/pnas.2211251120 |title=Cambrian lobopodians shed light on the origin of the tardigrade body plan |year=2023 |last1=Kihm |first1=Ji-Hoon |last2=Smith |first2=Frank W. |last3=Kim |first3=Sanghee |last4=Rho |first4=Hyun Soo |last5=Zhang |first5=Xingliang |last6=Liu |first6=Jianni |last7=Park |first7=Tae-Yoon S. |journal=Proceedings of the National Academy of Sciences |volume=120 |issue=28 |pages=e2211251120 |pmid=37399417 |pmc=10334802 |bibcode=2023PNAS..12011251K |doi-access=free }}</ref>
The oldest remains of modern tardigrades are those of ''[[Milnesium swolenskyi]],'' belonging to the living genus ''[[Milnesium]]'' known from a [[Late Cretaceous]] ([[Turonian]]) aged specimen of [[New Jersey amber]], around 90 million years old. Another fossil, ''[[Beorn (tardigrade)|Beorn leggi]]'', is known from a Late [[Campanian]] (~72 million years old) specimen of Canadian amber<ref>{{cite journal |doi=10.1155/1964/48418 |first=Kenneth W. |last=Cooper|title=The first fossil tardigrade: ''Beorn leggi'', from Cretaceous Amber |journal=Psyche: A Journal of Entomology |date=1964 |volume=71 |issue=2 |pages=41–48|doi-access=free }}</ref> and has been placed in its own family ([[Beornidae]]), but was subsequently suggested as belonging to [[Hypsibiidae]]. An indeterminate heterotardigrade was also noted from the same deposit.<ref>{{Citation|last1=Guidetti|first1=Roberto|title=Paleontology and Molecular Dating|date=2018|url=http://link.springer.com/10.1007/978-3-319-95702-9_5|work=Water Bears: The Biology of Tardigrades|volume=2|pages=131–143|editor-last=Schill|editor-first=Ralph O.|place=Cham|publisher=Springer International Publishing|language=en|doi=10.1007/978-3-319-95702-9_5|isbn=978-3-319-95701-2|access-date=2020-11-24|last2=Bertolani|first2=Roberto|series=Zoological Monographs }}</ref>
Line 162 ⟶ 168:
== Genomes and genome sequencing ==
Tardigrade [[genome]]s vary in size, from about 75 to 800 mega[[base pair]]s of DNA.<ref>{{cite web|url=http://www.genomesize.com/search.php?search=type&value=Tardigrades&display=100|title=Genome Size of Tardigrades}}</ref> ''[[Hypsibius exemplaris]]'' (formerly ''Hypsibius dujardini'') has a compact genome of 100 megabase pairs<ref
The genome of ''Ramazzottius varieornatus'', one of the most stress-tolerant species of tardigrades, was sequenced by a team of researchers from the [[University of Tokyo]] in 2015. While previous research had claimed that around one-sixth of the genome had been acquired from other organisms,<ref>Fiona Macdonald (7 December 2015). "[https://www.sciencealert.com/new-research-casts-doubt-on-the-claim-that-tardigrades-get-one-sixth-of-dna-from-other-species New Research Casts Doubt on The Claim That Tardigrades Get 1/6 of DNA From Other Species]". ''ScienceAlert''.</ref> it is now known that less than 1.2% of its genes were the result of [[horizontal gene transfer]]. They also found evidence of a loss of gene pathways that are known to promote damage due to stress. This study also found a high expression of novel tardigrade-unique proteins, including [[Dsup|Damage suppressor (Dsup)]],<ref name="NYT-20240412">{{cite news |last=Zimmer |first=Carl |title=What Makes Tiny Tardigrades Nearly Radiation Proof - New research finds that the microscopic "water bears" are remarkably good at repairing their DNA after a huge blast of radiation. |url=https://www.nytimes.com/2024/04/12/science/tardigrades-moss-piglets.html |date=12 April 2024 |work=[[The New York Times]] |url-status=live |archiveurl=https://archive.today/20240412184502/https://www.nytimes.com/2024/04/12/science/tardigrades-moss-piglets.html |archivedate=12 April 2024 |accessdate=13 April 2024 }}</ref> which was shown to protect against DNA damage from [[X-ray]] radiation. The same team applied the Dsup protein to human cultured cells and found that it suppressed X-ray damage to the human cells by around 40%.<ref name="Hashimoto et al. 2015"/> While the exact mechanism of DNA protection is largely unknown, the results from an August 2020 study suggest that strong electrostatic attractions along with high protein flexibility help form a molecular aggregate, which allows Dsup to shield DNA.<ref>{{Cite journal|last1=Mínguez-Toral|first1=Marina|last2=Cuevas-Zuviría|first2=Bruno|last3=Garrido-Arandia|first3=María|last4=Pacios|first4=Luis F.|date= December 2020|title=A computational structural study on the DNA-protecting role of the tardigrade-unique Dsup protein|url= |journal=Scientific Reports|language=en|volume=10|issue=1|pages=13424|doi=10.1038/s41598-020-70431-1|issn=2045-2322|pmc=7414916|pmid=32770133|bibcode=2020NatSR..1013424M}}</ref>
The [[Dsup]] proteins of tardigrades ''Ramazzottius varieornatus'' and ''[[Hypsibius exemplaris]]'' promote survival by binding to [[nucleosome]]s and protecting [[chromosome|chromosomal]] [[DNA]] from [[hydroxyl radical]]s.<ref>{{Cite journal |last1=Chavez
== Ecological importance ==
Many organisms that live in aquatic environments feed on species such as nematodes, tardigrades, bacteria, algae, mites, and [[collembolan]]s.<ref>{{Cite journal |last=Kinchin |first=IM |date=1987 |title=The moss fauna 1; Tardigrades. |journal=Journal of Biological Education |volume=21 |issue=4 |pages=288–90|doi=10.1080/00219266.1987.9654916 }}</ref> Tardigrades work as [[pioneer species]] by inhabiting new developing environments. This movement attracts other invertebrates to populate that space, while also attracting predators.<ref name=Brent_Nichols_2005/>
== In popular culture ==
Line 214 ⟶ 220:
[[Category:Thermophiles]]
[[Category:Xerophiles]]
| |||