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{{Short description|Salamander in the subfamily Pleurodelinae}}
{{About|the animal}}
{{Redirect|Eft||EFT (disambiguation){{!}}EFT}}
{{pp-move}}
{{Automatic taxobox
| name = Newt
| fossil_range = {{Geological range|Late Cretaceous|Recent|ref=<ref name="ZhangPapenfuss2008">{{cite journal|last1=Zhang|first1=Peng|last2=Papenfuss|first2=Theodore J.|last3=Wake|first3=Marvalee H.|last4=Qu|first4=Lianghu|last5=Wake|first5=David B.|title=Phylogeny and biogeography of the family Salamandridae (Amphibia: Caudata) inferred from complete mitochondrial genomes|journal=Molecular Phylogenetics and Evolution|volume=49|issue=2|year=2008|pages=586–597|issn=1055-7903|doi=10.1016/j.ympev.2008.08.020|url=https://bsp.berkeley.edu/labs/mwake/papers/206.pdf|pmid=18801447|access-date=2016-08-29|archive-url=https://web.archive.org/web/20170202004738/https://bsp.berkeley.edu/labs/mwake/papers/206.pdf|archive-date=2017-02-02|url-status=dead}}</ref>
}}
| image = Uhandre goimenditarra.jpg
| image_caption = [[Alpine newt]]
| taxon = Pleurodelinae
| subdivision_ranks = Genera
| subdivision = 14–17 [[extant taxon|extant]] and six [[fossil]] genera, see text
}}

A '''newt''' is a [[salamander]] in the [[subfamily]] '''Pleurodelinae'''. The terrestrial juvenile phase is called an '''eft'''. Unlike other members of the family [[Salamandridae]], newts are [[semiaquatic]], alternating between aquatic and terrestrial habitats. Not all aquatic salamanders are considered newts, however. More than 100 known species of newts are found in North America, Europe, North Africa and Asia. Newts [[metamorphose]] through three distinct developmental life stages: aquatic [[larva]], terrestrial juvenile (eft), and adult. Adult newts have [[lizard]]-like bodies and return to the water every year to breed, otherwise living in humid, cover-rich land habitats.

Newts are threatened by [[habitat loss]], [[habitat fragmentation|fragmentation]] and [[pollution]]. Several species are endangered, and at least one species, the [[Yunnan lake newt]], has been considered [[extinct]] since 1979.

==Etymology==
[[File:Pleurodeles waltl BUD.jpg|thumb|left|alt=Two grey newts, taken from the front, under water, presumably in an aquarium|''[[Pleurodeles]]'', including the [[Iberian ribbed newt]], is the type genus of subfamily Pleurodelinae.]]

The [[Old English]] name of the animal was {{lang|ang|efte}}, {{lang|ang|efeta}} (of unknown origin), resulting in [[Middle English]] {{lang|enm|eft}};
this word was transformed irregularly into {{lang|enm|euft}}, {{lang|enm|evete}}, or {{lang|enm|ewt(e)}}. The initial "n" was added from the indefinite article "an" by [[English articles#Juncture loss|provection (juncture loss)]] ("an eft" → "a n'eft" → ...) by the early 15th century.<ref>[[Oxford English Dictionary]]; {{cite web |url=http://www.etymonline.com/index.php?term=eft |title=Online etymological dictionary |last=Anon |publisher=Douglas Harper |access-date=9 October 2013}}</ref> The form "newt" appears to have arisen as a dialectal variant of ''eft'' in [[Staffordshire]], but entered Standard English by the Early Modern period (used by Shakespeare in ''[[Macbeth]]'' iv.1).<ref>The Gentleman's Magazine, and Historical Chronicle, Volume 47 (1777), [https://books.google.com/books?id=9ntIAAAAYAAJ&pg=PA321 p. 321].</ref> The regular form ''eft'', now only used for newly metamorphosed specimens, survived alongside ''newt'', especially in composition, the larva being called "water-eft" and the mature form "land-eft" well into the 18th century, but the simplex "eft" as equivalent to "water-eft" has been in use since at least the 17th century.<ref>[[John Wilkins]], ''An Essay Towards a Real Character, and a Philosophical Language'' (1668), [https://books.google.com/books?id=Q85TAAAAcAAJ&pg=PA161 p. 161]. Gilbert White, ''The Natural History and Antiquities of Selborne, in the County of Southampton'' (1789) [https://archive.org/details/naturalhistorya04whitgoog/page/n68 p. 50]: "the water-eft, or newt, is only the larva of the land-eft, as tadpoles are of frogs". Archibald Constable, ''Constable's miscellany of original and selected publications in the various departments of literature, science, & the arts'', Volume 45 (1829), [https://books.google.com/books?id=vWdVAAAAYAAJ&pg=PA63 p. 63]: "the ''salamandra aquatica'' of Hay, (the water-newt, or eft)".</ref>

Dialectal English and Scots also has the word ''[[:wikt:ask#English|ask]]'' (also ''awsk'', ''esk'' in Scots<ref>
John Jamieson, ''An etmological dictionary of the Scottish language'' (1818).</ref>) used for both newts and [[Lacertidae|wall lizards]], from Old English ''[[:wikt:aþexe|āþexe]]'', from [[Proto-Germanic]] ''[[:wikt:Appendix:Proto-Germanic/agiþahsijǭ|*agiþahsijǭ]]'', literally "lizard-badger" or "distaff-like lizard" (compare German ''[[:wikt:Eidechse#German|Eidechse]]'' and ''[[:wikt:Echse#German|Echse]]'', both "lizard;" ''*agi-'' is ultimately cognate with Greek {{lang|el|ὄφις}} "snake," from [[Proto-Indo-European language|Proto-Indo-European]] ''[[:wikt:Appendix:Proto-Indo-European/h₁ógʷʰis|*h₁ogʷʰis]]''<ref>Wolfgang Pfeifer (ed.), ''Etymologisches Wörterbuch des Deutschen''. Deutscher Taschenbuch Verlag, Munich 1997 (revised edition of Akademie Verlag, Munich 1989 and 1993), p. 265, s.v. [http://www.dwds.de/?qu=Eidechse Eidechse]. Pfeifer gives the second element as germ. ''*þahsjō(n)'', relating it to [[Middle High German]] ''dehse'' "distaff", so that both animals (lizard and badger) were parallelized due to their common, spindle-shaped bodies.</ref>). Latin had the name ''stellio'' for a type of spotted newt, now used for species of the genus ''[[Stellagama]]''. Ancient Greek had the name {{lang|grc|κορδύλος}}, presumably for the water newt (immature newt, eft).<ref>Henry George Liddell, Robert Scott, [https://www.perseus.tufts.edu/hopper/morph?l=kordu%2Flos&la=greek&can=kordu%2Flos0#lexicon A Greek-English Lexicon].</ref> German has {{lang|de|Molch}}, from [[Middle High German]] ''mol'', ''[[:wikt:olm]]'', like the English term of unknown etymology.

Newts are also known as ''Tritones'' (viz., named for the mythological [[Triton (mythology)|Triton]]) in historical literature, and "triton" remains in use as common name in some Romance languages, such as Spanish and Romanian, but as well as in Greek, Russian, and Bulgarian. The systematic name ''Tritones'' was introduced alongside Pleurodelinae by [[Johann Jakob von Tschudi|Tschudi]] in 1838, based on the type genus named ''Triton'' by [[Josephus Nicolaus Laurenti|Laurenti]] in 1768. Laurenti's ''Triton'' was renamed to ''[[Triturus]]'' ("Triton-tail") by [[Constantine Samuel Rafinesque|Rafinesque]] in 1815.<ref>Alain Dubois and Roger Bour, ''[http://www.iucn-tftsg.org/wp-content/uploads/file/Articles/Dubois_and_Bour_2010a.pdf The nomenclatural status of the nomina of amphibians and reptiles created by Garsault (1764), with a parsimonious solution to an old nomenclatural problem regarding the genus Bufo (Amphibia, Anura), comments on the taxonomy of this genus, and comments on some nomina created by Laurenti (1768)] {{Webarchive|url=https://web.archive.org/web/20140109164225/http://www.iucn-tftsg.org/wp-content/uploads/file/Articles/Dubois_and_Bour_2010a.pdf |date=2014-01-09 }}'', Zootaxa 2447 (2010), 1–52.</ref> Tschudi's Pleurodelinae is based on the type genus ''[[Pleurodeles]]'' (ribbed newt) named by [[Karl Michahelles|Michahelles]] in 1830 (the name meaning "having prominent ribs," formed from {{lang|el|πλευρά}} "ribs" and {{lang|el|δῆλος}} "conspicuous").
Collective nouns for newts are flotilla and armada.

==Distribution and habitats==
[[File:BennyTrapp Calotriton asper Pyrenäen Spanien.jpg|thumb|right|upright=1.5|alt=A brown newt under water, on gravel|The [[Pyrenean brook salamander|Pyrenean brook newt]] lives in small streams in the [[Pyrenees]] mountains.]]

Newts are found in North America, Europe, North Africa and Asia. The [[Taricha|Pacific newts]] (''Taricha'') and the [[Notophthalmus|Eastern newts]] (''Notophthalmus'') with together seven species are the only representatives in North America, while most diversity is found in the Old World: In Europe and the Middle East, the group's likely origin, eight genera with roughly 30 species are found, with the [[Pleurodeles|ribbed newts]] (''Pleurodeles'') extending to northernmost Africa. Eastern Asia, from Eastern India over Indochina to Japan, is home to five genera with more than 40 species.{{citation needed|date=September 2016}}

Newts are [[semiaquatic]], spending part of the year in the water for reproduction and the rest of the year on land. While most species prefer stagnant water bodies such as ponds, ditches, or flooded meadows for reproduction, some species such as the [[Danube crested newt]] can also occur in slow-flowing rivers. The [[Calotriton|European brook newts]] (''Calotriton'') and [[Euproctus|European mountain newts]] (''Euproctus'') have even adapted to life in cold, oxygen-rich mountain streams. During their terrestrial phase, newts live in humid habitats with abundant cover such as logs, rocks, or earth holes.{{citation needed|date=September 2016}}

{{multiple image
| align = left
| direction = horizontal
| total_width = 400
| image1 = Eastern red-spotted newt.jpg
| alt1 = Strikingly red eft on a rocky underground
| width1 = 2048
| height1 = 1365
| image2 = Redspotted newt.jpg
| alt2 = Green newt with red spots under water
| width2 = 2925
| height2 = 1890
| footer = The [[eastern newt]] as terrestrial ''eft'' (left) and as an adult during aquatic breeding season (right)
}}

==Characteristics==
Newts share many of the characteristics of their salamander kin, [[Caudata]], including semipermeable glandular skin, four equal-sized limbs, and a distinct tail. The newt's skin, however, is not as smooth as that of other salamanders.<ref name="Collins99">{{cite book | last1=Collins | first1=J. T. | last2=Conant | first2=R. | last3=Stebbins | first3=R. C. | last4=Peterson | first4=R. T. | title=Peterson First Guide to Reptiles and Amphibians | publisher=Houghton Mifflin Harcourt | year=1999 | isbn=978-0-395-97195-6 | url=https://books.google.com/books?id=epHJE6NL3j8C&q=peterson+reptiles+and+amphibians}}</ref> The [[cell (biology)|cell]]s at the site of an injury have the ability to un[[Cellular differentiation|differentiate]], reproduce rapidly, and differentiate again to create a new limb or organ. One hypothesis is that the undifferentiated cells are related to [[tumor]] cells, since chemicals that produce tumors in other animals will produce additional limbs in newts.<ref>{{cite web|url=http://www.bioscience.utah.edu/mb/mbFaculty/odelberg/odelberg.html|title=Shannon Odelberg|website=Molecular Biology Program - Bioscience Graduate Studies|publisher=University of Utah|archive-url=https://web.archive.org/web/20060902234319/http://www.bioscience.utah.edu/mb/mbFaculty/odelberg/odelberg.html|archive-date=2006-09-02}}</ref>

==Development==
The main breeding season for newts (in the Northern Hemisphere) is in June and July. A single newt female can produce hundreds of eggs. For instance, the warty newt can produce 200–300 eggs (Bradford 2017). After courtship rituals of varying complexity, which take place in ponds or slow-moving streams, the male newt transfers a [[spermatophore]], which is taken up by the female. Fertilized eggs are laid singly and are usually attached to aquatic plants.{{Citation needed|date=March 2012}} This distinguishes them from the free-floating eggs of [[frog]]s or [[toad]]s, which are laid in clumps or in strings. Plant leaves are usually folded over and attached to the eggs to protect them. The [[larvae]], which resemble fish [[Spawn (biology)#Fry|fry]] but are distinguished by their feathery external gills, hatch out in about three weeks. After hatching, they eat algae, small invertebrates, or other amphibian larvae.{{Citation needed|date=March 2012}}

During the subsequent few months, the larvae undergo [[Metamorphosis (biology)|metamorphosis]], during which they develop legs, and the gills are absorbed and replaced by air-breathing lungs.<ref>{{cite web|url=http://www.scienceclarified.com/Al-As/Amphibians.html |title=Amphibians - body, used, water, process, Earth, life, characteristics, form, animals, oxygen, air, plant, change, History, Characteristics, Life cycle, Three major groupings |publisher=Scienceclarified.com |date=2009-10-13 |access-date=2013-06-06}}</ref> Some species, such as the North American newts, also become more brightly colored during this phase. Once fully metamorphosed, they leave the water and live a terrestrial life, when they are known as "efts."<ref>{{cite web |url=http://lnr.cambridge.gov.uk/news/article.asp?ItemID=285 |title=Cambridge City Council: Local Nature Reserves |publisher=Lnr.cambridge.gov.uk |date=2005-07-25 |access-date=2013-06-06 |url-status=dead |archive-url=https://web.archive.org/web/20130723214517/http://lnr.cambridge.gov.uk/news/article.asp?ItemID=285 |archive-date=2013-07-23 }}</ref><ref>{{cite journal|title= Newts|date= Jan 2005|doi=10.1016/j.cub.2004.12.049 |volume=15 |issue= 2|journal=Current Biology |pages=R42–R44 |pmid=15668151|last1= Brockes|first1= J|last2= Kumar|first2= A|doi-access= free|bibcode= 2005CBio...15..R42B}}</ref> Only when the eft reaches adulthood will the North American species return to live in water, rarely venturing back onto the land. Conversely, most European species live their adult lives on land and only visit water to breed.<ref name="autogenerated1970">{{cite web|url=http://www.bbc.co.uk/nature/wildfacts/factfiles/478.shtml |title=BBC Nature - Great crested newt videos, news and facts |publisher=Bbc.co.uk |access-date=2013-06-06}}</ref>

{{Multiple image
|header=Development in the [[northern crested newt]] (''Triturus cristatus'')
|total_width=800
|align=center
|image1=OpenedLeafwithEggOfTriturusCristatus.JPG
 |caption1=Embryo in jelly capsule
 |alt1=A transparent egg with a white embryo on the leaf of an aquatic plant
 |width1=2288
 |height1=1712
|image2=TriturusCristatusYoungLarva.JPG
 |caption2=Young larva
 |alt2=A newt larva with gills and forelimbs, but no hindlimbs developed
 |width2=2272
 |height2=1704
|image3=TriturusCristatusLarvaAlmostGrown.jpg
 |caption3=Larva shortly before metamorphosis
 |alt3=A dark-coloured larva with all limbs developed but gills still apparent
 |width3=2272
 |height3=1704
|image4=Noerdlicher-Kammmolch-triturus-cristatus.jpg
 |caption4=Terrestrial juvenile
 |alt4=A small, black newt without gills or crest on moss
 |width4=3744
 |height4=2262
|footer= Newts lay their eggs on structures such as plants or stones under water. The larvae first develop fore- and later hindlimbs, and are strictly carnivorous. After metamorphosis, juveniles known as ''efts'' emerge from the water and live a terrestrial lifestyle.
|footer_align=center
}}

==Toxicity==
[[File:Taricha torosa, Napa County, CA.jpg|thumb|The [[Taricha|Pacific newts]] (''Taricha''), including the [[California newt]], are known for their toxicity.]]

Many newts produce [[toxin]]s in their skin secretions as a defence mechanism against predators. ''Taricha'' newts of western North America are particularly toxic. The [[rough-skinned newt]] ''Taricha granulosa'' of the [[Pacific Northwest]] produces more than enough [[tetrodotoxin]] to kill an adult human, and some [[Indigenous peoples of the Americas|Native American]]s of the Pacific Northwest used the toxin to poison their enemies.<ref name="caudata"/> However, the toxins are only dangerous if ingested or otherwise enter the body; for example, through a wound. Newts can safely live in the same ponds or streams as frogs and other amphibians or be kept as pets. The only predators of ''Taricha'' newts are [[garter snakes]], some having developed a resistance to the toxin. Most newts can be safely handled, provided the toxins they produce are not ingested or allowed to come in contact with [[mucous membrane]]s or breaks in the skin.<ref name="caudata">{{cite web|url=http://www.caudata.org/cc/articles/toxin2.shtml |title=Caudata Culture Articles - Newt Toxins |publisher=Caudata.org |access-date=2013-06-06}}</ref>

==Systematics==
Newts form one of three [[subfamily|subfamilies]] in the family [[Salamandridae]], aside [[Salamandrinae]] and [[Salamandrininae]].<ref name=PyronWiens2011>{{cite journal |url=http://home.gwu.edu/~rpyron/publications/Pyron_Wiens_2011.pdf |title=A large-scale phylogeny of Amphibia including over 2800 species, and a revised classification of advanced frogs, salamanders, and caecilians |pmid= 21723399|year=2011|last1=Pyron|first1=R.A.|last2=Weins |first2=J.J. |volume=61 |issue= 2|pages=543–853 |doi= 10.1016/j.ympev.2011.06.012|journal=Molecular Phylogenetics and Evolution}}</ref> They comprise most [[extant taxon|extant]] species in the family, roughly 100, which are classified in sixteen genera:<ref name="amphibian-species-world">{{cite web |last1=Frost |first1=D.R. |title=Pleurodelinae. Amphibian Species of the World: an Online Reference. Version 6.0 |year=2016 |publisher=American Museum of Natural History |location=New York |url=http://research.amnh.org/vz/herpetology/amphibia/Amphibia/Caudata/Salamandridae/Pleurodelinae |access-date=2019-10-11}}</ref>
{{div col|colwidth=20em}}
* ''[[Calotriton]]''
* ''[[Cynops]]'' (incl. ''Hypselotriton'')
* ''[[Echinotriton]]''
* ''[[Euproctus]]''
* ''[[Ichthyosaura]]''
* ''[[Laotriton]]''
* ''[[Lissotriton]]''
* ''[[Neurergus]]''
* ''[[Notophthalmus]]''
* ''[[Ommatotriton]]''
* ''[[Pachytriton]]''
* ''[[Paramesotriton]]''
* ''[[Pleurodeles]]''
* ''[[Taricha]]''
* ''[[Triturus]]''
* ''[[Tylototriton]]'' (incl. ''Liangshantriton'')
{{Div col end}}

''Hypselotriton'' and ''Liangshantriton'' are regarded as separate genera by some authors, but this is not unanimous.<ref name="amphibian-species-world"/>

The term "newt" has traditionally been seen as an exclusively functional term for salamanders living in water, and not a [[clade]]. [[Phylogenetic]] analyses have however shown that species in the Salamandridae traditionally called newts do form a [[monophyletic group]].<ref name="ZhangPapenfuss2008"/><ref name=PyronWiens2011/><ref name="amphibian-species-world"/> Other, more distantly related salamander families also contain fully or in part aquatic species, such as the [[mole salamanders]], the [[Proteidae]], or the [[Sirenidae]].

Classification of all genera of the Pleurodelinae subfamily after Pyron and Weins,<ref name=PyronWiens2011/> revised by Mikko Haaramo.
{{Clade
  |1={{Clade
    |label1='''[[Pleurodelinae]]'''
    |1={{Clade
      |label1=Pleurodelini
      |1={{Clade
        |1=''[[Pleurodeles]]'' [[File:Erpétologie générale, ou, Histoire naturelle complète des reptiles (Pleurodeles waltl).jpg|70 px]]
        |2={{Clade
          |1=''[[Echinotriton]]''
          |2=''[[Tylototriton]]'' [[File:T.anguliceps (cropped).jpg|70 px]]}} }}
      |label2=Molgini
      |2={{Clade
        |label1=Tarichina
        |1={{Clade
          |1=''[[Notophthalmus]]'' [[File:North American herpetology (Notophthalmus viridescens).jpg|70 px]]
          |2=''[[Taricha]]'' [[File:Taricha torosa (white background).jpg|70 px]]}}
        |label2=Molgina
        |2={{Clade
          |1=''[[Lissotriton]]'' [[File:Lissotriton vulgaris (white background).jpg|70 px]]
          |2={{Clade
            |1={{Clade
              |1={{Clade
                |1=''[[Neurergus]]''
                |2=''[[Ommatotriton]]'' }}
              |2={{Clade
                |1=''[[Calotriton]]''
                |2=''[[Triturus]]'' [[File:Triturus cristatus (white background).jpg|70 px]]}} }}
            |2={{Clade
              |1=''[[Euproctus]]''
              |2={{Clade
                |1=''[[Ichthyosaura alpestris|Ichthyosaura]]''
                |label2=Cynopita
                |2={{Clade
                  |1=''[[Laotriton laoensis|Laotriton]]''
                  |2={{Clade
                    |1=''[[Pachytriton]]''
                    |2={{Clade
                      |1=''[[Cynops]]'' [[File:Hypselotriton wolterstorffi ♂.jpg|70 px]]
                      |2=''[[Paramesotriton]]'' }} }} }} }} }} }} }} }} }} }} }}
===Phylogenetics===
Phylogenetic analyses estimated the origin of the newt subfamily in the [[Late Cretaceous]] to [[Eocene]].<ref name="ZhangPapenfuss2008"/> Several [[Prehistoric amphibian|fossil salamanders]] have also been referred to the Pleurodelinae, including:<ref name="BeattyMarjanović2015">{{cite journal|last1=Marjanović|first1=David|last2=Witzmann|first2=Florian|title=An Extremely Peramorphic Newt (Urodela: Salamandridae: Pleurodelini) from the Latest Oligocene of Germany, and a New Phylogenetic Analysis of Extant and Extinct Salamandrids|journal=PLOS ONE|volume=10|issue=9|year=2015|pages=e0137068|issn=1932-6203|doi=10.1371/journal.pone.0137068|pmid=26421432|pmc=4589347|bibcode=2015PLoSO..1037068M|doi-access=free}} {{open access}}</ref>

{{div col|colwidth=20em}}
* ''[[Archaeotriton]]''
* ''[[Brachycormus]]''
* ''[[Carpathotriton]]''
* ''[[Chelotriton]]''
* ''[[Koalliella]]''
* ''[[Palaeopleurodeles]]''
{{Div col end}}

==Anatomy and physiology==
===Circulation===
The heart of newts, like that of most amphibians, consists of two atria and one ventricle.<ref name="Miya">(Miyachi, Y. 2011. The Unusual Circulation of the Newt Heart after Ventricular Injury and Its Implications for Regeneration. Anatomy Research International:1-7).</ref> Blood flows from the anterior and posterior caval veins into the right atrium; blood that entered the heart from the left atrium is then expelled out of the ventricle. Newts do not have a [[coronary artery]] on the ventricle, due to circulation that is found in the [[conus arteriosus]]. Newts contain a special circulatory adaptation that allows them to survive [[ventricular penetration]]: when a newt's ventricle is punctured, the heart will divert the blood directly into an ascending aorta via a duct located between the ventricle and the conus arteriosus. Newts begin to regenerate the ventricle by a thickening of the [[epicardial]] layer that protrudes to allow the new vessels to form, and conclude with a regeneration of the entire [[myocardial wall]].<ref name="Miya" />

In early stages of development in amphibians, ventilator gas transport and hemoglobin gas transport are independent mechanisms and not yet coupled as they are in adulthood.<ref name="Pes">(Pelster, B. 1999. Environmental Influences on the Development of the Cardiac System in Fish and Amphibians. Comparative Biochemistry and Physiology Part A 124:407-412)</ref> In juvenile amphibians, there is no cardiovascular response in conditions of hypoxia.<ref name="Pes" /> When newts are induced into anemia, they are able to respire without the need of blood cells.<ref name="Cas">(Casale. G.P, Khairallah. E. A., Grasso. J. A. 1980. An Analysis of Hemoglobin Synthesis in Erythropoietic Cells. Developmental Biology 80:107-119. )</ref> In ''T. carnifex'', around two weeks after anemia is induced, the newts produced a mass of cells that helps to revitalize the already circulating red blood cell mass.<ref name="Cas" />

===Respiration===
Adult crested newts (''Triturus cristus'') were found to breathe mainly via the skin but also through the lungs and the [[buccal cavity]]. Lung breathing is mainly used when there is a lack of oxygen in the water, or at high activity such as during courtship, breeding, or feeding.<ref name= Eddy>(Eddy, F. B., P. McDonald. 1978. Aquatic respiration of The Crested Newt Triturus Cristatus. Comparative Biochemical Physiology. 59: 85–88)</ref>

A form of [[compensatory respiration]] is the ability to release stored [[erythrocytes]] when needed, for example under [[Hypoxia (environmental)|hypoxia]].<ref name= Frang>(Giuliano Frangioni, Mario Santoni, Stefano Bianchi, Marco Franchi, Giancarlo Fuzzi, Stefano
Marcaccini, Carlo Varlani, Gianfranco Borgioli. 2006. Function of the Hepatic Melanogenesis in the Newt, Triturus Carnifex. Journal of Experimental Zoology. 303A:123-131.)</ref><ref name="Frang3">(Frangioni, G., G. Borgioli. 1996. Variations in blood pressure of newts according to their
respiratory conditions. Italian Journal of Zoology. 63:3, 201–206).</ref> Spleen size can increase as the temperature declines for adults – in larvae, there is no dramatic change in spleen size.<ref name= Borg>(Frangioni, G., G Borgioli. 1997. Blood and splenic respiratory compensation in larval newts. Italian Journal of Zoology. 64:3, 221–226)</ref> During hibernation, an increase in liver pigment cells allows for storage of oxygen, as well as other important ions and free radicals.<ref name= Barni>(Barni et al. 1999)</ref>

===Osmoregulation===
In experiments, dehydrated [[eastern newt]]s were prone to a loss of motor control: After only 22% water weight loss, newts in the aquatic phase lost their ability to remain upright and mobile. However, after adaptation to a terrestrial phase, they could lose 30% before a loss of motor control was recorded. Newts in the terrestrial phase were found to dehydrate much quicker than newts in the aquatic phase, but conversely, during rehydration, dehydrated terrestrial animals will go through water gain 5x faster than dehydrated newts that are in the aquatic phase.<ref name="Walt">P. Walters, L. Greenwald. 1977. Physiological adaptations of aquatic newts (Notophtalmus viridescens) to a terrestrial environment. Physiological Zoology. 50(2): 88–98.</ref>

In the Italian crested newt, it was shown that during winter months, [[prolactin]] is released into the circulatory system, which drives the newts into the aquatic environment and reduces the active transport of sodium ions.<ref name="Lodi81">Lodi, G., Biciotti, M., and Viotto, B. 1981. Cutaneous Osmoregulation in Triturus cristatus carnifex (Laur.) (Urodela). General and Comparative Endocrinology 46: 452–457.</ref> In contrast to prolactin, which decreases osmotic permeability, [[vasotocin]] increases the permeability and is secreted during the summer months.<ref name="Bplus">Brown, M., Brown, S., Bisceglio, I., and Lemke, S. 1983. Breeding Condition, Temperature, and the Regulation of Salt and Water by Pituitary Hormones in the Red-Spotted Newt, Notophthalmus viridescens. General and Comparative Endocrinology 51, 292–302.</ref> Arginine vasotocin not only increases cutaneous water permeability, but promotes increased cutaneous blood flow.<ref name="Uch">Minoru Uchiyama, Norifumi Konno, Hormonal regulation of ion and water transport in anuran amphibians, General and Comparative Endocrinology, Volume 147, Issue 1, 15 May 2006, Pages 54–61, {{ISSN|0016-6480}}</ref>

===Thermoregulation===
Thermoregulation, in combination with seasonal [[acclimation]], describes the major mechanisms of how newts, as [[ectotherms]] cope with the changing temperatures existing in their environments. This regulation is most often achieved through behavioral thermoregulation.<ref name="Hada">(M. Hadamova, L. Gvozdik. 2011. Seasonal acclimation of preferred body temperatures improves the opportunity for thermoregulation in newts. Physiological and Biochemical Zoology. 84(2):166-174. )</ref> They are [[thermoconformers]], which means they will acclimate to their surrounding environmental temperatures.<ref name="Hada" /> When there is a large range of environmental temperatures, newts are insensitive to a [[thermal gradient profile]].<ref name="Marik">(V. Marek, L. Gvozdik. 2012. The insensitivity of thermal preferences to various thermal gradient profiles in newts. Journal of Ethology. 30(1): 35–41)</ref>

To escape predators, newt larvae have been found to shift their [[microhabitat]] to a temperature range that exists outside the predator's preferred temperature range.<ref name="Smaug">(R. Smolinsky, L. Gvozdik. 2009. The ontogenetic shift in thermoregulatory behavior of newt larvae: testing the "enemy-free temperature" hypothesis. Journal of Zoology. 279(2): 180–186. doi: 10.1111/j.1469-7998.2009.00603.x)</ref> Larvae that are in the metamorphosizing stage tend to prefer warmer temperatures than those in the stage following metamorphosis.<ref name="Smaug" /> Therefore, the larvae in this stage will undergo a much more precise thermoregulation process than those in the intermediate stage.<ref name="Smaug" />

Reproductive females of the Italian crested newt were shown to regulate their body temperature more precisely and prefer higher temperatures than non-reproductive females and males.<ref name="Dik">(L. Gvozdik. 1995. Does reproduction influence temperature preference in newts. Canadian Journal of Zoology. 83(8): 1038–1044. doi: 10.1139/z05-096)</ref>

===Spermatogenesis===
The newt is regarded as an ideal [[vertebrate]] model for investigating the mechanism(s) controlling the transition from [[mitosis]] to [[meiosis]] during [[spermatogenesis]].<ref name = Yazawa2000>Yazawa T, Yamamoto T, Nakayama Y, Hamada S, Abé S. Conversion from mitosis to meiosis: morphology and expression of proliferating cell nuclear antigen (PCNA) and Dmc1 during newt spermatogenesis. Dev Growth Differ. 2000 Dec;42(6):603-11. doi: 10.1046/j.1440-169x.2000.00544.x. PMID 11142682</ref> In the male newt ''[[Japanese fire-bellied newt|Cynopa pyrrhogaster]]'', this transition was shown to involve expression of [[Proliferating cell nuclear antigen|PCNA]], a [[DNA polymerase delta]] auxiliary protein involved in [[DNA replication]] and [[DNA repair]], as well as [[DMC1 (gene)|DMC1]] protein, a marker for [[genetic recombination]] activity.<ref name = Yazawa2000/>

===Susceptibility to pollution===
Larvae, with their great number of lamellae in their gills,<ref name= Brun>(Brunelli, E., E. Sperone, M. Maisano, and S. Tripepi. 2009. Morphology and ultrastructure of the gills in two Urodela species: Salamandrina terdigitata and Triturus carnifex. Italian Journal of Zoology. 76(2): 158–164)</ref> are more susceptible to pollutants than adults. [[Cadmium]], a heavy metal released into the environment from industrial and consumer waste, has been shown to be detrimental to the [[Italian crested newt]] even at concentrations below Italian and European thresholds, by disrupting the activity of the [[adrenal gland]].<ref name="Gay">(Gay, F., V. Laforgia, I. Caputo, C. Esposito, M. Lepretti, and A. Capaldo, "Chronic Exposure to Cadmium Disrupts the Adrenal Gland Activity of the Newt Triturus carnifex(Amphibia, Urodela)," BioMed Research International.)</ref> In experiments allowing Italian crested newts to be exposed to [[nonylphenol]], an [[endocrine disruptor]] common in leakage from sewers, there was a decrease in [[corticosterone]] and [[aldosterone]], hormones produced by the [[adrenal gland]] and important for stress response.<ref name="Cap">(A. Capaldo, F. Gay, S. Valiante, M. DeFalco, R. Sciarrillo, M. Maddaloni, V. Laforgia. 2012. Endocrine-disrupting effects of nonylphenol in the newt, Triturus carnifex (Amphibia, Urodela). Comparative Biochemistry and Physiology. 155(2): 352–358. doi: 10.1016/j.cbpc.2011.10.004)</ref> 

==Conservation status==
[[File:Cynops_wolterstorffi.JPG|thumb|left|alt=Panel of drawings of a red-black newt|The [[Yunnan lake newt]] is considered extinct.]]

Although some species, such as the [[rough-skinned newt]] (''Taricha granulosa'') and [[Eastern newt]] (''Notophthalmus viridescens)'' in North America or the [[smooth newt]] (''Lissotriton vulgaris'') in Europe, are still relatively common, populations of newts throughout their distribution range suffer from [[habitat loss]], [[habitat fragmentation|fragmentation]], and [[pollution]]. This affects especially the aquatic breeding sites they depend on, but also their land habitats.{{citation needed|date=September 2016}} Several species, such as the [[Edough ribbed newt]] (''Pleurodeles poireti''), [[Kaiser's spotted newt]] (''Neurergus kaiseri''), or the [[Montseny brook newt]] (''Calotriton arnoldi'') are considered threatened by the [[International Union for Conservation of Nature|IUCN]], and the [[Yunnan lake newt]] is an example of a newt species that has gone extinct recently.<ref name=IUCN>{{Cite iucn | author = Yang Datong | author2 = Michael Wai Neng Lau | title = Hypselotriton wolterstorffi | volume = 2004 | page = e.T59445A11942589 | date = 2004 | doi = 10.2305/IUCN.UK.2004.RLTS.T59445A11942589.en }}</ref>

Some newt populations in Europe have decreased because of pollution or destruction of their breeding sites and terrestrial habitats, and countries such as the UK have taken steps to halt their declines.<ref>{{cite web|url=http://fresc.usgs.gov/research/StudyDetail.asp?Study_ID=239 |title=USGS Amphibian Research Monitoring Initiative (Pacific Northwest Region) |publisher=Fresc.usgs.gov |date=2013-01-30 |access-date=2013-06-06}}</ref><ref>[http://www.ukbap.org.uk/UKPlans.aspx?ID=619 UK Biodiversity Action Plan] {{webarchive |url=https://web.archive.org/web/20071024112706/http://www.ukbap.org.uk/UKPlans.aspx?ID=619 |date=October 24, 2007 }}</ref> In the UK, they are protected under the [[Wildlife and Countryside Act 1981]] and the Habitat Regulations Act 1994. It is illegal to catch, possess, or handle [[Great Crested Newt|great crested newts]] without a licence, or to cause them harm or death, or to disturb their habitat in any way. The [[IUCN Red List]] categorises the species as ‘lower risk’<ref name="autogenerated1970"/><ref name="bbc.co.uk Factfile 479">{{cite web|url=http://www.bbc.co.uk/nature/wildfacts/factfiles/479.shtml |title=Science & Nature - Wildfacts - Smooth newt, common newt |publisher=BBC |date=2012-04-27 |access-date=2013-06-06}}</ref>
Although the other UK species, the [[smooth newt]] and [[palmate newt]] are not listed, the sale of either species is prohibited under the Wildlife and Countryside Act, 1981.<ref>{{cite web |url=http://www.arkive.org/species/ARK/amphibians/Triturus_vulgaris/more_info.html |title=Smooth newt videos, photos and facts - Triturus vulgaris |publisher=ARKive |access-date=2013-06-06 |archive-url=https://web.archive.org/web/20081201105832/http://www.arkive.org/species/ARK/amphibians/Triturus_vulgaris/more_info.html |archive-date=2008-12-01 |url-status=dead }}</ref>

In Europe, nine newts are listed as "strictly protected fauna species" under appendix II of the [[Convention on the Conservation of European Wildlife and Natural Habitats]]:<ref>{{cite web|url=http://conventions.coe.int/Treaty/FR/Treaties/Word/104-2.doc |title=Annexe II: Strictly protected fauna species |access-date=2013-06-06}}</ref>

{{div col|colwidth=15em}}
*''[[Calotriton asper]]''
*''[[Euproctus montanus]]''
*''[[Euproctus platycephalus]]''
*''[[Lissotriton italicus]]''
*''[[Lissotriton montandoni]]''
*''[[Triturus carnifex]]''
*''[[Triturus cristatus]]''
*''[[Triturus dobrogicus]]''
*''[[Triturus karelinii]]''
{{Div col end}}

The remaining European species are listed as "protected fauna species" under appendix III.<ref>{{cite web|url=http://conventions.coe.int/Treaty/FR/Treaties/Word/104-3.doc |title=Annexe III: Protected fauna species |access-date=2013-06-06}}</ref>

==As bioindicators==
Newts, as with salamanders in general and other amphibians, serve as [[bioindicators]] because of their thin, sensitive skin and evidence of their presence (or absence) can serve as an indicator of the health of the environment. Most species are highly sensitive to subtle changes in the [[pH]] level of the streams and lakes where they live. Because their skin is permeable to water, they absorb oxygen and other substances they need through their skin. Scientists study the stability of the amphibian population when studying the water quality of a particular body of water.{{Citation needed|date=March 2012}}

==As pets==
[[Chinese warty newt]]s, [[Chinese fire belly newt]]s, [[eastern newt]]s, [[Pachytriton|paddletail newt]]s, [[Japanese fire belly newt]]s, [[Chuxiong fire-bellied newt]]s, ''[[Triturus]]'' species, [[emperor newt]]s, [[Spanish ribbed newt]]s ([[leucistic]] genes exist), and [[red-tailed knobby newt]]s are some commonly seen newts in the pet trade. Some newts rarely seen in the pet trade are [[rough-skinned newt]]s, [[Kaiser's spotted newt]]s, [[Ommatotriton|banded newt]]s and [[yellow-spotted newt]]s.{{original research inline|date=November 2019}}

==References==
{{Reflist|30em}}

==External links==
{{wiktionary|newt}}
{{wiktionary|newt|eft}}
*{{Wikispecies-inline|Pleurodelinae}}

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[[Category:Newts|*]]
[[Category:Extant Late Cretaceous first appearances]]