| Newts | |
|---|---|
| Smooth newt (Lissotriton vulgaris) | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Subphylum: | Vertebrata |
| Superclass: | Tetrapoda |
| Class: | Amphibia |
| Subclass: | Lissamphibia |
| Order: | Caudata |
| Family: | Salamandridae |
| Subfamily: | Pleurodelinae |
A newt is an aquatic amphibian of the family Salamandridae, although not all aquatic salamanders are considered newts. Newts are classified in the subfamily Pleurodelinae of the family Salamandridae, and are found in North America, Europe and Asia. Newts metamorphose through three distinct developmental life stages: aquatic larva, terrestrial juvenile (called an eft[1]), and adult. Adult newts have lizard-like bodies and may be either fully aquatic, living permanently in the water, or semi-aquatic, living terrestrially but returning to the water each year to breed.
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Like all members of the order Caudata, newts are characterised by a frog-like body with four equal sized limbs and a distinct tail. Aquatic larvae have true teeth on both upper and lower jaws, and external gills.[2] They have the ability to regenerate limbs, eyes, spinal cords, hearts, intestines, and upper and lower jaws. Recently it was discovered that the Japanese fire belly newt can regenerate its eye lens 18 times over a period of 16 years and retain its structural and functional properties. [3] The cells at the site of the injury have the ability to de-differentiate, reproduce rapidly, and differentiate again to create a new limb or organ. One theory is that the de-differentiated cells are related to tumour cells since chemicals which produce tumours in other animals will produce additional limbs in newts.[4]
The main breeding season for newts is between the months of June and July. 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. This distinguishes them from the free-floating eggs of frogs or toads, that are laid in clumps or in strings. Plant leaves are usually folded over and adhered to the eggs to protect them. The tadpoles, which resemble fish fry but are distinguished by their feathery external gills, hatch out in about three weeks. After hatching they eat algae, small invertebrates or other tadpoles.
During the next few months the tadpoles undergo metamorphosis, during which they develop legs, and the gills are absorbed and replaced by air-breathing lungs.[5] Some species, such as the North American newts, also become more brightly coloured during this phase. Once fully metamorphosised they leave the water and live a terrestrial life, when they are known as "efts".[6] 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.[7]
Many newts produce toxins in their skin secretions as a defense 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 Native Americans of the Pacific Northwest used the toxin to poison their enemies.[8] However, the toxins are only dangerous if ingested, and the newts can easily and safely live in the same ponds or streams as frogs and other amphibians, or be safely kept as pets. The only predators of Taricha newts are garter snakes, some having developed a resistance to the poison. Most newts can be safely handled, provided that the toxins they produce are not ingested or allowed to come in contact with mucous membranes, or breaks in the skin.[8] After handling, proper hand-washing techniques should be followed due to the risk from the toxins they produce and bacteria they carry, such as salmonella.[9][10] It is, however, illegal to handle or disturb Great Crested Newts in the UK without a licence.[11] Newts and salamanders are also very good environmental indicators because of their thin, sensitive skin. Most species are highly sensitive to subtle changes in the pH level of streams and lakes they live in. Because their skin is permeable to water they absorb oxygen and other substances they need through their skin. Scientists will study the stability of the amphibian population when studying the water quality of a particular body of water.
About two thirds of all species of the family Salamandridae are commonly called "newts", comprising the following genera:
The term "newt" has traditionally been seen as an exclusively functional term for salamanders living in water, and not a systematic unit. The relationship between the genera has been uncertain, although it has been suggested that they constitute a natural systematic unit and newer molecular analyses tend to support this position.[12][13][14] Newts only appear in one subfamily of salamanders, the Pleurodelinae (of the family Salamandridae),[15] however, Salamandrina and Euproctus, which are sometimes listed as Pleurodelinae, are not newts. Whether these are basal to the subfamily (and thus the sister group of the newt group) or derived, making the newts an evolutionary grade (an "incomplete" systematic unit, where not all branches of the family tree belong to the group) is currently not known.[14][16]
The three common European genera are the crested newts (Triturus spp.), the smooth and palmate newts (Lissotriton spp.) and the banded Newts (Ommatotriton spp.). Other species present in Europe are the Iberian ribbed newt (Plurodeles waltl), which is the largest of the European newts,[17] the pyrenean brook newt (Calotriton sp.); the European brook newt (Euproctus sp.) and the Alpine newt (Mesotriton alpestris).[13][18]
In North America, there are the Eastern newts (Notophthalmus spp.), of which the red-spotted newt (Notophthalmus viridescens) is the most abundant species, but it is limited to the area east of the Rocky Mountains. The three species of coastal or Western newts are the red-bellied newt, the California newt, and the rough-skinned newt, all of which belong to the genus Taricha, which is confined to the area west of the Rockies.
In Southeast Asia and Japan, species commonly encountered in the pet trade include the fire belly newts (Cynops spp.), the paddletail newts (Pachytriton spp.), the crocodile newts (Tylototriton spp.), and the warty newts (Paramesotriton spp.). In the Middle East there are the spotted newts (Neurergus spp.).[19]
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.[20][21] 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 Newts without a licence, and it is also illegal to cause them harm or death, or to disturb their habitat in any way. The IUCN Red List categorises the species as ‘lower risk’[11][22] 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.[23]
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:[24]
The remaining European species are listed as "protected fauna species" under appendix III.[25]
The etymology for this term has gone through a complex twist of old Middle English variations. The oldest form of the name is eft, which is still used for newly metamorphosed specimens, but according to the Oxford English Dictionary it changed for unknown reasons first to euft and then to ewt. For some time it remained as an ewt, but the "n" from the indefinite article an shifted to form a newt. The sexually mature stage was also called an ewte, with similar etymology roots linking an ewte, newt, "euft", and eft: "small lizard-like animal," [26].