Smooth newt

The smooth newt, European newt, northern smooth newt or common newt (Lissotriton vulgaris) is a species of newt. It is widespread in Europe and parts of Asia, and has also been introduced to Australia. Individuals are brown with a spotted underside that ranges in colour from orange to white. They reach an average length of 8–11 cm (3.1–4.3 in), with males being larger than females. The newts' skins are dry and velvety when they are living on land, but become smooth when they migrate into the water to breed. Males develop a more vivid colour pattern and a conspicuous skin seam (crest) on their back during the breeding season.

The smooth newt was originally described by Carl Linnaeus as a lizard, and was then given different genus names before being classified as a member of Lissotriton. There are currently three accepted subspecies of smooth newt. Formerly, there were also four subspecies—all with more restricted ranges that are now classified as separate species, because they have been found to be distinct genetically as well as in appearance: the Caucasian smooth newt, the Greek smooth newt, Kosswig's smooth newt and Schmidtler's smooth newt. Together with these four species and the Carpathian newt, the smooth newt forms what is known as a species complex: some of the species hybridise with each other.

For most of the year, smooth newts live on land, are mostly nocturnal, and hide during the day. They can adapt to a wide range of natural or semi-natural habitats, from forests at field edges to parks and gardens. Their diet consists mainly of invertebrates such as insects and earthworms and they are mainly preyed upon by fish, birds and snakes. Between spring and summer, they breed in ponds or similar bodies of water. Males court females with a ritualised underwater display. Females lay their eggs on water plants, and larvae hatch after 10 to 20 days. The larvae develop for around three months before metamorphosing into terrestrial juveniles, at which point they become known as efts. They reach maturity after two to three years, and the adults live for up to 14 years.

The smooth newt is abundant over much of its range and is classified as a species of least concern by the International Union for Conservation of Nature (IUCN). However, it has been negatively affected by habitat destruction and fragmentation, as well as the introduction of new species of fish. Like other European amphibians, the smooth newt has now been listed as a protected species by the Berne Convention.

Swedish naturalist Carl Linnaeus described the smooth newt in 1758 as Lacerta vulgaris, placing it in the same genus as the green lizards.^[4]:370 It was later re-described under several different species and genus names, including Triton, Molge, Salamandra and Lissotriton, with in total 48 species synonyms published.^[3] Most recently, it was included in the genus Triturus, along with most European newts.^[5]:221 This genus was found to be polyphyletic, containing several unrelated lineages,^[6][7][8] and the small-bodied newts, including the smooth newt, were therefore split off as separate genus in 2004 by García-París and colleagues.^[9]:233 They used the name Lissotriton, introduced by the English zoologist Thomas Bell in 1839 with the smooth newt as type species^[10]:132 but then considered a synonym of Triturus.^[3] "Lissotriton" is a combination of the Greekλισσός (lissós), meaning "smooth", and the name of Triton, an ancient Greek god of the sea, while the species epithetvulgaris means "common" in Latin.^[11]:17

Three subspecies are accepted by Pabijan, Wielstra and colleagues: L. v. vulgaris, L. v. ampelensis and L. v. meridionalis.^[2][12] These authors, followed by Amphibian Species of the World,^[3] recognise four former subspecies from southern Europe and west Asia as separate species, as they are morphologically and genetically distinct: the Greek smooth newt (L. graecus), Kosswig's smooth newt (L. kosswigi), the Caucasian smooth newt (L. lantzi) and Schmidtler's smooth newt (L. schmidtleri). The five smooth newt species and the Carpathian newt (L. montadoni), which is their sister species, have collectively been referred to as the "smooth newt species complex".^[12]

To distinguish the smooth newt from its close relatives, the English name "northern smooth newt" has been suggested.^[12] Other common names that have been used in the literature include: common newt, great water-newt, common water-newt, warty eft, water eft, common smooth newt, small newt, small eft, small evet, and brown eft.^[3]

Molecular phylogenetic analyses have shown that the smooth newt is distinct from its four close relatives – the Caucasian, Greek, Kosswig's, and Schmidtler's smooth newt – which were formerly considered to be subspecies (see section Taxonomy above). The relationships within this species complex remain unclear. Within the smooth newt itself, genetic groups do not entirely correspond to the currently accepted subspecies (ampelensis, meridionalis, vulgaris), which were described based on morphology.^[2] It is estimated that the five smooth newt species collectively were estimated to have diverged from the Carpathian newt around four to six million years ago.^[13][14]

遺伝子解析により、イモリと近縁種の間で遺伝子流動が継続していることも明らかになっている。カルパチアイモリは外見上明らかに異なるが、両種間の交雑は頻繁に起こる。 ^{[ 11 ] : 26}イモリのミトコンドリアDNAがカルパチアイモリ集団に浸透し、完全に置き換えたことが示されている。 ^{[ 15 ]}イモリからギリシャイモリへの部分的な浸透も起こっている。^{[ 2 ]}これらのパターンは、最終氷期最盛期後の種の分布域の拡大と二次接触によるものと考えられ、これらの種は主に南ヨーロッパと東ヨーロッパの避難地で生き延びたと考えられる。 ^{[ 15 ] [ 14 ] [ 16 ]}パルマテイモリ（Lissotriton helveticus ）は、同じ生息地に生息することが多いが、イモリと交雑することはほとんどない。^{[ 11 ] : 25}アルプスイモリ（Ichthyosaura alpestris）やキタイモリ（Triturus cristatus ）といったさらに遠縁の種との人工交配も、実験室実験で成功した。^{[ 11 ] : 29}

The smooth newt is primarily a lowland species, though it can occasionally be found at elevations above 1,000 m (3,300 ft).^[11]:78–80 This species has a wide habitat breadth, as it is able to thrive in a variety of terrestrial and aquatic environments. On land, it inhabits wooded areas (dense coniferous woods are avoided), as well as more open areas such as damp meadows, field edges, parks, and gardens. It can also tolerate human disturbance and urban environments and will hide under structures such as logs or stones or in small mammal burrows.^{[11]:120–134[19][5]:238} Smooth newts may also climb vegetation, although the exact function of this behaviour is currently unknown.^[23]

Freshwater breeding sites are usually exposed to the sun, free from fish, and filled with stagnant water for at least three months of the year. They are typically close to similar bodies of water and have shallow areas with an abundance of water plants. These sites can range in size from small puddles to larger ponds or shallow parts of lakes. Water quality is less important, with pH values ranging from 4 (more acidic) to 9.6 (more alkaline) being tolerated. In Germany, smooth newts have even been found in slightly brackish water.^{[11]:121–129} They often share breeding sites with other amphibians, including other newts. In northern France, for example, there are ponds with five newt species: smooth, palmate, alpine, northern crested and marbled (T. marmoratus) newt – have been described.^{[11]:151–152}

Smooth newts live on land for most of the year and are mainly nocturnal. They also usually hibernate on land, often in groups of several individuals in winter shelters, such as under logs or in burrows, but they can be active during mild weather.^[24] The efts turn into mature adults at two to three years of age, and newts can live for 6–14 years in the wild.^[5]:238 The newts recognise familiar territory using smell and visual cues, but they are unable to orient themselves in experiments when they were transported far away from the home range.^[25]

Reproduction

Migration to the breeding sites can begin as early as February, but in the northernmost parts of the range and at higher altitudes, it may not start before summer. After entering the water, it takes a few weeks for the breeding characters, especially the male's crest, to develop.^[5]:238

The mating process involves an elaborate courtship display: the male swims in front of the female and sniffs her cloaca in an attempt to attract her. He then vibrates his tail against his body, sometimes violently lashing it, thereby fanning pheromones towards her. In the final phase, he moves away from her, his tail quivering. If she is still interested, she will follow him, touching his cloaca with her snout, whereupon he deposits a packet of sperm (a spermatophore). He then guides her over the spermatophore, enabling her to pick it up with her cloaca. Males often try to lead females away from competitors that are displaying.^{[5]:238–240}

Eggs are fertilised internally and the offspring of one female usually have multiple fathers. Females tend to mate preferentially with unrelated males, probably to avoid inbreeding depression.^[26]

Females lay 100–500 eggs, which they usually fold into the leaves of aquatic plants. The eggs are 1.3–1.7 mm (0.051–0.067 in) in diameter (2.7–4 mm (0.11–0.16 in) with jelly capsule) and light brown to greenish or grey in colour. Depending on temperature, larvae typically hatch after 10–20 days, and metamorphose into terrestrial efts after around three months.^{[5]:238–240}

Paedomorphism, where adults remain aquatic and retain their gills and skin seams, or only partially resorb them, occurs regularly, but only in a small proportion of individuals. This trait does not appear to be genetically determined, but is favoured by cold water, low population density and abundant aquatic prey. Wild paedomorphic individuals often metamorphosed when they were transferred into an aquarium.^{[11]:192–193}

Diet, predators and parasites

イモリ類（幼生を含む）は、ミミズ、カタツムリ、ナメクジ、二枚貝、クモ、ダニ、トビムシ、昆虫、昆虫の幼虫、小型プランクトンなど、多様な無脊椎動物を主に捕食する非選択的な肉食動物である。^{[ 27 ]}共食いも起こり、主に同種の卵を捕食する。イモリ類は、水鳥、アナグマ、ヘビ、オオトカゲ、カエルなどの様々な捕食動物に捕食されるが、キタイモリなどの大型のイモリも捕食される。^{[ 5 ]： 238}

様々な病原体や寄生虫がイモリに感染することが分かっており、その中にはラナウイルス^{[ 28 ]}、ピコルナウイルス^{[ 29 ]}、様々な原生動物^{[ 11 ] : 164、} 吸虫[ ^{30 ] [ 11 ] : 164（}そのうちParastrigea robustaはドイツで個体群の局所的な減少を引き起こしていることが分かっている）^{[ 31 ]}、そして少なくとも31種の蠕虫^{[ 32 ]}が含まれる。

The smooth newt is common over much of its range.^[1][5]:237 In 2008, the IUCN, assessed its threat status as Least Concern and found no general decline in populations.^[1] However, this assessment included subspecies that are now recognised as separate species (see section Taxonomy above) and it therefore needs updating.^[12] Despite the overall low level of concern, the smooth newt is now listed on some national red lists, e.g. in Switzerland, the Czech Republic, and the Netherlands.^[11]:196 Like all amphibians, it is also listed as protected species in the Berne Convention (Appendix III).^[33] Disturbance, capture, killing and trade are prohibited in Ireland under the Wildlife Act 1976,^[34] and trade in the UK under the Wildlife and Countryside Act 1981.^[35]

The threats facing smooth newts are similar to those affecting other amphibians. These include the loss of breeding ponds due to destruction or the introduction of fish, as well as the fragmentation of population caused by roads.^{[11]:196–197} Secondary habitats can help sustain the species, e.g. former gravel pits or quarries left open.^{[11]:204–205} The value of artificial water bodies as habitat can be improved when nearby hiding structures like stones or wood are added on land.^[36] Garden ponds are readily colonised if they are sun-exposed, have abundant water plants, no fish, and nearby hiding structures.^{[11]:206–218} Artificial hibernation sites ("newt hotels") were readily used in a study in Norway, especially by juveniles.^[37]

To mark and track individuals and monitor populations, researchers have often amputated phalanges of fingers and toes but these grow back quickly. A safer and less harmful approach is to record the unique patterns on the underside of the animals' bellies through photography.^{[11]:223–224} Researchers have also developed genetic methods based on microsatellite distribution to assess patterns of genetic diversity.^[38]

Smooth newts can be kept in captivity, but they must come from a legal source in accordance with the relevant legislation due to their protected status (see above). They require both a land and water phase, and hibernate for two to three months at 5–10 °C (41–50 °F).^{[11]:210–215} Juveniles remain terrestrial and will only return to water at maturity. In captivity, individuals have been known to live to ages of 4–8, and exceptionally up to 20 years.^[5]:240