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The alpine newt ( Mesotriton alpestris) is a species of newt native to continental Europe and introduced to Great Britain and New Zealand. Adults measure and are usually dark grey to blue on the back and sides, with an orange belly and throat. Males are more conspicuously coloured than the drab females, especially during breeding season.
The alpine newt occurs at high altitude as well as in the lowlands. Living mainly in forested land habitats for most of the year, the adults migrate to puddles, ponds, lakes or similar water bodies for breeding. Males court females with a ritualised display and deposit a spermatophore. After fertilisation, females usually fold their eggs into leaves of water plants. The aquatic grow up to in around three months before metamorphosis into terrestrial juvenile , which mature into adults at around three years. In the southern range, the newts sometimes do not metamorphose but keep their gills and stay aquatic as paedomorphic adults. Larvae and adults feed mainly on diverse invertebrates and themselves fall prey to dragonfly larvae, large beetles, fish, snakes, birds or mammals.
Populations of the alpine newt started to diverge around 20 million years ago. At least four subspecies are distinguished, and some argue there are several distinct, cryptic species. Although still relatively common and classified as Least Concern on the IUCN Red List, alpine newt populations are decreasing and have locally gone extinct. The main threats are habitat destruction, water pollution and the introduction of fish such as trout into breeding sites. Where it has been introduced, the alpine newt can potentially disease vector to native amphibians, and it is being eradicated in New Zealand.
However, the name Ichthyosaura had been introduced in 1801 by Sonnini de Manoncourt and Latreille for " Proteus tritonius", the larva of the alpine newt. It would therefore have priority over Mesotriton. "Ichthyosaura", Greek for "fish lizard", refers to a nymph-like creature in classical mythology. The name Mesotriton alpestris, which was revalidated in 2004 and has since been increasingly used, would therefore no longer be valid, as it had only been coined in 1928. However, the validity of the name Ichthyosaura alpestris was not recognized by all authors, and Mesotriton alpestris continued to be used.see for example: Rote Liste der Lurche in Nordrhein-Westfalen, Stand September 2011 ( PDF online). The taxonomic issue was finally clarified by designation of a larva of the fire salamander ( Salamandra salamandra) collected at the type locality of Proteus tritonius, the type species of Ichthyosaura, as the neotype of Proteus tritonius, rendering Ichthyosaura a synonym of Salamandra and thus Mesotriton the oldest available genus name for the alpine newt.Thomas Mutz & Wolfgang Böhme: Ichthyosaura as a generic nomen for the Alpine Newt (Caudata: Salamandridae): a doubtful case of literarian archeology. In: Salamandra 61(2025). Deutsche Gesellschaft für Herpetologie und Terrarienkunde, , S. 41–52. ( Aufsatz online).
Several authors argued that the ancient lineages of the alpine newt might represent cryptic species. Four species were therefore distinguished by Raffaëlli in 2018, but Frost considers this premature.
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| Northwestern France to northern Carpathians in Romania, southern Denmark in to Alps and France just north of the Mediterranean |
| Balkan peninsula north of Greece to Bulgaria and southern Carpathians in Romania |
| Extreme southeastern France, Apennines to Lazio in central Italy, isolated populations in Calabria |
| Spain: Cantabrian mountains and Sierra de Guadarrama (introduced) |
| Greece: mainland and northern Peloponnese |
Molecular phylogenetic analyses showed that alpine newts split into a western and an eastern group. Each of these again contains two major lineages, which in part correspond to described subspecies (see section Distribution and subspecies above). These ancient genetic differences suggest that the alpine newt may be a species complex of several distinct species. Higher temperatures during the Miocene or sea level oscillations may have separated early populations, leading to allopatric speciation, although admixture and introgression between lineages probably took place. Populations from Vlasina Lake in Serbia have mitochondrial DNA that is distinct from and more ancient than that of all other populations; it may have been inherited from a now extinct "ghost lineage" population. The Quaternary glaciation probably led to cycles of retreat into refugia, expansion and range shifts.
The characteristic dark grey to bright blue of the back and sides is strongest during breeding season. This base colour may vary to greenish and is more drab and mottled in females. The belly and throat are orange and only occasionally have dark spots. Males have a white band with black spots and a light blue flash running along the flanks from the cheeks to the tail. During breeding season, their crest is white with regular dark spots. Juvenile , just after metamorphosis, resemble adult terrestrial females, but sometimes have a red or yellow line on the back. Very rarely, leucistic individuals have been observed.
While these traits apply to the widespread nominate subspecies, I. a. alpestris, the other subspecies differ slightly. I. a. apuana often has dark spots on the throat and sometimes on the belly. I. a. cyreni has a slightly rounder and larger skull than the nominate subspecies but is otherwise very similar. In I. a. veluchiensis, females have a more greenish colour, spots on the belly, sparse dark spots on the lower tail edge, and a narrower snout, but these differences between subspecies are not consistent.
Larvae are 7–11 mm long after hatching and grow to just before metamorphosis. They initially have only two small filaments (balancers), between the eyes and gills on each side of the head, which later disappear as the forelegs and then the hindlegs develop. The larvae are light brown to yellow and initially have dark longitudinal stripes, which later dissolve into a dark pigmentation that is stronger towards the tail. The tail is pointed and sometimes ends in a short filament. Alpine newt larvae are more robust and have wider heads than those of the smooth newt and palmate newt.
The alpine newt can occur at high elevation and has been found up to above sea level in the Alps. It also occurs in the lowlands down to sea level. Towards the south of its range, most populations are found above .
Aquatic breeding sites close to adequate land habitat are critical. While small, cool water bodies in forested areas are preferred, alpine newts tolerate a wide range of permanent or vernal pool, natural or human-made water bodies. These can range from shallow puddles over small ponds to larger, fish-free lakes or reservoirs and quiet parts of streams. Damming by Eurasian beaver creates suitable breeding sites. Overall, the alpine newt is tolerant regarding chemical parameters such as pH, water hardness and eutrophication. Other European newts such as the crested, smooth, palmate or Carpathian newt often use the same breeding sites, but are less common at higher elevation.
Alpine newts tend to stay close to their breeding sites and only a small proportion, mainly juvenile efts, disperse to new habitats. A dispersal distance of has been observed, but such large distances are uncommon. Over short distances, the newts use mainly their sense of smell for navigation, while over long distances, orientation by the night sky, and potentially through magnetoreception are more important.
Breeding behaviour occurs mainly in the morning and at dawn. Males perform a courtship display. The male first places himself in front of the female remains static for a while, then fans his tail to stimulate the female and wave pheromones towards her. After leaning in and touching her snout, he creeps away, followed by the female. When she touches the base of his tail with her snout, he releases a sperm packet (spermatophore) and blocks the female's path so she picks it up with her cloaca. Several rounds of spermatophore deposition may follow. Males frequently interfere with displays of rivals. Experiments suggest that it is mainly male pheromones that trigger mating behaviour in females, while colour and other visual cues are less relevant. In a breeding season, a male can produce more than 48 spermatophores, and offspring from one female usually have several fathers.
Females wrap their eggs in leaves of water plants for protection, preferring leaves closer to the surface where temperatures are higher. Where no plants are available, they may also use leaf litter, dead wood or stones for egg deposition. They can lay 70–390 eggs in a season, which are light grey-brown and 1.5–1.7 mm in diameter (2.5–3 mm including the jelly capsule). Incubation time is longer under cold conditions, but larvae typically hatch after two to four weeks. The larvae are benthic, staying in general close to the bottom of the water body. Metamorphosis occurs after around three months, again depending on temperature, but some larvae overwinter and metamorphose only in the next year.
of adult alpine newts are snakes such as the grass snake, fish such as trout, birds such as or , and mammals such as hedgehogs, or . Under water, large diving beetles ( Dytiscus) can prey on newts, while small efts on land may be predated by ground beetles ( Carabus). For eggs and larvae, diving beetles, fish, dragonfly larvae, and other newts are the main enemies.Predator pressure can affect the phenotype of developing alpine newts. In an experiment, alpine newt larvae raised in the presence of caged dragonfly larvae took longer to emerge from the larval stage, growing slower and emerging later in the season than newt larvae that did not experience predator presence. They also exhibited traits such as darker coloration, larger body size, a proportionally larger head and tail, and more wary behavior than their predator-free counterparts.
Threatened adult newts often take on a defensive position, where they expose the aposematism of their belly by bending backwards or raising their tail and secrete a milky substance. Only trace amounts of the poison tetrodotoxin, abundant in the North American Pacific newts ( Taricha), have been found in the alpine newt. They also sometimes produce sounds, whose function is unknown. When adult newts are in the presence of a predator, they tend to flee a majority of the time. However, the decision of whether or not to flee can depend on the newt's sex and temperature. In an experiment, female newts fled more often and at a greater speed over a greater range of temperatures than males, who tended to flee at a slower speed and remained immobile while secreting tetrodotoxin when the temperature was outside of the normal range.
Parasites include , leeches, the ciliate Balantidium elongatum, and potentially toadflies. A ranavirus transmitted to alpine newts from in Spain caused bleeding and necrosis. The chytridiomycosis-causing fungus Batrachochytrium dendrobatidis has been found in wild populations, and the emerging B. salamandrivorans was lethal for alpine newts in laboratory experiments.
Threats are similar to those affecting other newts and include mainly destruction and water pollution of aquatic habitats. European beaver, previously widespread in Europe, were probably important in maintaining breeding sites. Introduction of fish, especially salmonids such as trout, and potentially crayfish is a significant threat that can eradicate populations from a breeding site. In the Montenegro karst region, populations have declined as ponds created for cattle and human use were abandoned over the last decades. Lack of adequate, undisturbed land habitat (see section Habitats above) and dispersal corridors around and between breeding sites, is another problem.
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