Alpine newt

The alpine newt 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 larvae grow up to in around three months before metamorphosing into terrestrial juvenile efts, 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, pollution and the introduction of fish such as trout into breeding sites. Where it has been introduced, the alpine newt can potentially transmit diseases to native amphibians, and it is being eradicated in New Zealand.

Taxonomy

Nomenclature

The alpine newt was first described in 1768 by Austrian zoologist Laurenti, as Triton alpestris, from the Ötscher mountain in the Austrian Alps. He used that name for a female and described the male and the larva as different species. Later, the alpine newt was placed in the genus Triturus along with most other European newts. When genetic evidence showed that Triturus as then defined contained several unrelated lineages, García-París and colleagues in 2004 split off the alpine newt as the monotypic genus Mesotriton, which had been erected as a subgenus by Bolkay in 1928.
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. The taxonomic issue was finally clarified by designation of a larva of the fire salamander 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.

Subspecies

Four subspecies were recognised for the alpine newt by Roček and colleagues, followed by later authors, while some previously described subspecies were not retained. The four subspecies correspond only in part to the five major lineages identified within the species : The western populations of the nominate subspecies I. a. alpestris, together with the Cantabrian I. a. cyreni and the Apennine I. a. apuana form one group, while the eastern populations of I. a. alpestris are genetically closer to the Greek I. a. veluchiensis. Differences in body shape and colour between the subspecies are not consistent.
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.

Evolution

Alpine newt populations have separated since the Early Miocene, around 20 million years ago, according to a molecular clock estimate by Recuero and colleagues. Known fossil remains are much more recent: they were found in the Pliocene of Slovakia and the Pleistocene of Northern Italy. An older, Miocene fossil from Germany, Ichthyosaura randeckensis, may be the sister species of the alpine newt.
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. These ancient genetic differences suggest that the alpine newt may be a 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" population. The Quaternary glaciation probably led to cycles of retreat into refugia, expansion and range shifts.

Description

The alpine newt is medium-sized and stocky. It reaches length in total, females measuring roughly longer than males, and a body weight of 1.4–6.4 g. The tail is compressed sideways and is half as long or slightly shorter than the rest of the body. During their life in water, both sexes develop a tail fin, and males a low, smooth-edged crest on their back. The cloaca of males swells during breeding season. The skin is smooth during the breeding season and granular outside it, and is velvety during the animal's land phase.
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 efts, 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, 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.

Distribution

The alpine newt is native to continental Europe. It is relatively common over a large, more or less continuous range from northwestern France to the Carpathians in Romania, and from southern Denmark in the north to the Alps and France just north of the Mediterranean in the south, but absent from the Pannonian basin. Isolated areas of distribution in Spain, Italy and Greece correspond to distinct subspecies. Alpine newts have been deliberately introduced to parts of continental Europe, including within the boundaries of cities such as Bremen and Berlin. Other introductions have occurred to Great Britain, mainly England but also Scotland, and Coromandel Peninsula in New Zealand. A thriving introduced population was discovered in 2014 in the Catalonian Pre-Pyrenees, likely established from released captive individuals; this population was found to be a carrier of ranavirus.
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.

Habitats

Forests, including both deciduous and coniferous forests, are the main land habitat. Less common are forest edges, brownfield land, or gardens. Populations can be found above tree line in the high mountains, where they prefer south-exposed slopes. The newts use logs, stones, leaf litter, burrows, construction waste or similar structures as hiding places.
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 non-permanent, 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 beavers 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.