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''Triturus'' is a genus of newts comprising the crested and the marbled newts, which are found from Great Britain through most of continental Europe to westernmost Siberia, Anatolia, and the Caspian Sea region. Their English names refer to their appearance: marbled newts have a green–black colour pattern, while the males of crested newts, which are dark brown with a yellow or orange underside, develop a conspicuous jagged seam on their back and tail during their breeding phase. Crested and marbled newts live and breed in vegetation-rich ponds or similar aquatic habitats for two to six months and usually spend the rest of the year in shady, protection-rich land habitats close to their breeding sites. Males court females with a ritualised
display Display may refer to: Technology * Display device, output device for presenting information, including: ** Cathode ray tube, video display that provides a quality picture, but can be very heavy and deep ** Electronic visual display, output devi ...
, ending in the deposition of a spermatophore that is picked up by the female. After fertilisation, a female lays 200–400 eggs, folding them individually into leaves of water plants. Larvae develop over two to four months before metamorphosing into land-dwelling juveniles. Historically, most European newts were included in the genus, but
taxonomists In biology, taxonomy () is the scientific study of naming, defining ( circumscribing) and classifying groups of biological organisms based on shared characteristics. Organisms are grouped into taxa (singular: taxon) and these groups are given ...
have split off the alpine newts (''Ichthyosaura''), the small-bodied newts (''Lissotriton'') and the banded newts (''Ommatotriton'') as separate genera. The closest relatives of ''Triturus'' are the European brook newts (''Calotriton''). Two species of marbled newts and seven species of crested newts are accepted, of which the
Anatolian crested newt The Anatolian crested newt (''Triturus anatolicus'') is a newt species endemic to northern Anatolia in Turkey. Before its description in 2016, it was first considered to belong to the southern crested newt (''Triturus karelinii'') and then the ...
was only described in 2016. Their ranges are largely contiguous but where they do overlap, hybridisation may take place. Although not immediately threatened, crested and marbled newts suffer from population declines, caused mainly by habitat loss and
fragmentation Fragmentation or fragmented may refer to: Computers * Fragmentation (computing), a phenomenon of computer storage * File system fragmentation, the tendency of a file system to lay out the contents of files non-continuously * Fragmented distributi ...
. Both their aquatic breeding sites and the cover-rich, natural landscapes upon which they depend during their terrestrial phase are affected. All species are legally protected in Europe, and some of their habitats have been designated as special reserves.


Taxonomy

The genus name ''Triturus'' was introduced in 1815 by the polymath
Constantine Samuel Rafinesque Constantine Samuel Rafinesque-Schmaltz (; October 22, 1783September 18, 1840) was a French 19th-century polymath born near Constantinople in the Ottoman Empire and self-educated in France. He traveled as a young man in the United States, ultimat ...
, with the
northern crested newt The northern crested newt, great crested newt or warty newt (''Triturus cristatus'') is a newt species native to Great Britain, northern and central continental Europe and parts of Western Siberia. It is a large newt, with females growing up to ...
(''Triturus cristatus'') as type species. That species was originally described as ''Triton cristatus'' by Josephus Nicolaus Laurenti in 1768, but Linnaeus had already used the name ''Triton'' for a genus of sea snails ten years before, making a new genus name for the newts necessary. ''Triturus'' included most European newt species until the end of the 20th century, but was substantially revised after it was shown to be polyphyletic. Three separate genera now accommodate former members of the genus: the small-bodied newts (''Lissotriton''), the banded newts (''Ommatotriton''), and the alpine newt (''Ichthyosaura''). The monophyly of the genus ''Triturus'' in the strict sense is supported by molecular data and
synapomorphies In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...
such as a genetic defect causing 50% embryo mortality (see below, '' Egg deposition and development''). As of 2020, the genus contains seven species of crested newts and two species of marbled newts. Both groups were long considered as single species, ''Triturus cristatus'' and ''T. marmoratus'', respectively. Substantial genetic differences between
subspecies In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (morphology), but that can successfully interbreed. Not all species ...
were, however, noted and eventually led to their recognition as full species, with the crested newts often collectively referred to as "''T. cristatus'' superspecies". The Balkan and the Anatolian crested newt, the most recent species formally described (2013 and 2016, respectively), were only recognised through
genetic data In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding gene ...
; together with the Southern crested newt, they form a cryptic species complex with no morphological differences known.


Description


Common characteristics

''Triturus'' is a genus of rather large-bodied newts. They typically have a total length of between , with some crested newts of up to described. Size depends on sex and the environment: females are slightly larger and have a proportionally longer tail than males in most species, and the Italian crested newt seems to be larger in colder parts of its range. Crested newts are dark brown, with black spots on the sides, and white stippling in some species. Their belly is yellow to orange with black blotches, forming a pattern characteristic for individuals. Females and juveniles of some species have a yellow line running down their back and tail. During breeding phase, crested newts change in appearance, most markedly the males. These develop a skin seam running along their back and tail; this crest is the namesake feature of the crested newts and can be up to 1.5 cm high and very jagged in the northern crested newt. Another feature of males at breeding time is a silvery-white band along the sides of the tail. Marbled newts owe their name to their green–black, marbled colour pattern. In females, an orange-red line runs down back and tail. The crest of male marbled newts is smaller and fleshier than that of the crested newts and not indented, but marbled newt males also have a whitish tail band at breeding time.


Species identification

Apart from the obvious colour differences between crested and marbled newts, species in the genus also have different body forms. They range from stocky with sturdy limbs in the Anatolian, Balkan and the southern crested newt as well as the marbled newts, to very slender with short legs in the Danube crested newt. These types were first noted by herpetologist
Willy Wolterstorff Willy Georg Wolterstorff (16 June 1864 in Calbe – 21 January 1943 in Magdeburg) was a German paleontologist and herpetologist. As a child he lost his hearing due to disease, thus finding it necessary to lip-reading, lip-read from an early ag ...
, who used the ratio of forelimb length to distance between fore- and hindlimbs to distinguish subspecies of the crested newt (now full species); this index however sometimes leads to misidentifications. The number of
rib In vertebrate anatomy, ribs ( la, costae) are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the ches ...
-bearing vertebrae in the skeleton was shown to be a better species indicator. It ranges from 12 in the marbled newts to 16–17 in the Danube crested newt and is usually observed through radiography on dead or sedated specimens. The two marbled newts are readily distinguished by size and colouration. In contrast, separating crested newt species based on appearance is not straightforward, but most can be determined by a combination of body form, coloration, and male crest shape. The Anatolian, Balkan, and southern crested newt however are cryptic, morphologically indistinguishable species. ''Triturus'' newts occupy distinct geographical regions (see ''
Distribution Distribution may refer to: Mathematics *Distribution (mathematics), generalized functions used to formulate solutions of partial differential equations * Probability distribution, the probability of a particular value or value range of a vari ...
''), but
hybrid Hybrid may refer to: Science * Hybrid (biology), an offspring resulting from cross-breeding ** Hybrid grape, grape varieties produced by cross-breeding two ''Vitis'' species ** Hybridity, the property of a hybrid plant which is a union of two dif ...
forms occur at range borders between some species and have intermediate characteristics (see '' Hybridisation and introgression''). Based on the books of Griffiths (1996) and Jehle ''et al.'' (2011), with additions from articles on recently recognised species. NRBV = number of rib-bearing vertebrae, values from Wielstra & Arntzen (2011). ''Triturus anatolicus'', ''T. ivanbureschi'' and ''T. karelinii'' are
cryptic species In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...
and have only been separated through genetic analysis.


Lifecycle and behaviour

Like other newts, ''Triturus'' species develop in the water as larvae, and return to it each year for breeding. Adults spend one half to three quarters of the year on land, depending on the species, and thus depend on both suitable aquatic breeding sites and terrestrial habitats. After larval development in the first year, juveniles pass another year or two before reaching maturity; in the north and at higher elevations, this can take longer. The larval and juvenile stages are the riskiest for the newts, while survival is higher in adults. Once the risky stages passed, adult newts usually attain an age of seven to nine years, although individuals of the northern crested newts have reached 17 years in the wild.


Aquatic phase

The aquatic habitats preferred by the newts are stagnant, mid- to large-sized, unshaded water bodies with abundant underwater vegetation but without fish, which prey on larvae. Typical examples are larger ponds, which need not be of natural origin; indeed, most ponds inhabited by the northern crested newt in the UK are human-made. Examples of other suitable secondary habitats are ditches, channels, gravel pit lakes, garden ponds, or (in the Italian crested newt) rice paddies. The Danube crested newt is more adapted to flowing water and often breeds in river margins,
oxbow lake An oxbow lake is a U-shaped lake or pool that forms when a wide meander of a river is cut off, creating a free-standing body of water. In South Texas, oxbows left by the Rio Grande are called '' resacas''. In Australia, oxbow lakes are call ...
s or flooded marshland, where it frequently co-occurs with fish. Other newts that can be found in
syntopy In biology, two related species or populations are considered sympatric when they exist in the same geographic area and thus frequently encounter one another. An initially interbreeding population that splits into two or more distinct species sh ...
with ''Triturus'' species include the smooth, the
palmate The following is a list of terms which are used to describe leaf morphology in the description and taxonomy of plants. Leaves may be simple (a single leaf blade or lamina) or compound (with several leaflets). The edge of the leaf may be regular o ...
, the
Carpathian The Carpathian Mountains or Carpathians () are a range of mountains forming an arc across Central Europe. Roughly long, it is the third-longest European mountain range after the Urals at and the Scandinavian Mountains at . The range stretches ...
, and the alpine newt. Adult newts begin moving to their breeding sites in spring when temperatures stay above . This usually occurs in March for most species, but can be much earlier in the southern parts of the distribution range. Southern marbled newts mainly breed from January to early March and may already enter ponds in autumn. The time adults spend in water differs among species and correlates with body shape: while it is only about three months in the marbled newts, it is six months in the Danube crested newt, whose slender body is best adapted to swimming. ''Triturus'' newts in their aquatic phase are mostly nocturnal and, compared to the smaller newts of ''Lissotriton'' and ''Ichthyosaura'', usually prefer the deeper parts of a water body, where they hide under vegetation. As with other newts, they occasionally have to move to the surface to breathe air. The aquatic phase serves not only for reproduction, but also offers the animals more abundant prey, and immature crested newts frequently return to the water in spring even if they do not breed.


Terrestrial phase

During their terrestrial phase, crested and marbled newts depend on a landscape that offers cover, invertebrate prey and humidity. The precise requirements of most species are still poorly known, as the newts are much more difficult to detect and observe on land. Deciduous woodlands or groves are in general preferred, but conifer woods are also accepted, especially in the far northern and southern ranges. The southern marbled newt is typically found in Mediterranean oak forests. In the absence of forests, other cover-rich habitats, as for example
hedgerows A hedge or hedgerow is a line of closely spaced shrubs and sometimes trees, planted and trained to form a barrier or to mark the boundary of an area, such as between neighbouring properties. Hedges that are used to separate a road from adjoini ...
,
scrub Scrub(s) may refer to: * Scrub, low shrub and grass characteristic of scrubland * Scrubs (clothing), worn by medical staff * ''Scrubs'' (TV series), an American television program * Scrubs (occupation), also called "scrub tech," "scrub nurse," ...
, swampy meadows, or quarries, can be inhabited. Within such habitats, the newts use hiding places such as logs, bark, planks, stone walls, or small mammal burrows; several individuals may occupy such refuges at the same time. Since the newts in general stay very close to their aquatic breeding sites, the quality of the surrounding terrestrial habitat largely determines whether an otherwise suitable water body will be colonised. Juveniles often disperse to new breeding sites, while the adults in general move back to the same breeding sites each year. The newts do not migrate very far: they may cover around in one night and rarely disperse much farther than . For orientation, the newts likely use a combination of cues including odour and the calls of other amphibians, and orientation by the night sky has been demonstrated in the marbled newt. Activity is highest on wet nights; the newts usually stay hidden during daytime. There is often an increase in activity in late summer and autumn, when the newts likely move closer to their breeding sites. Over most of their range, they
hibernate Hibernation is a state of minimal activity and metabolic depression undergone by some animal species. Hibernation is a seasonal heterothermy characterized by low body-temperature, slow breathing and heart-rate, and low metabolic rate. It most ...
in winter, using mainly subterranean hiding places, where many individuals will often congregate. In their southern range, they may instead sometimes
aestivate Aestivation ( la, aestas (summer); also spelled estivation in American English) is a state of animal dormancy, similar to hibernation, although taking place in the summer rather than the winter. Aestivation is characterized by inactivity and a ...
during the dry months of summer.


Diet and predators

Like other newts, ''Triturus'' species are carnivorous and feed mainly on invertebrates. During the land phase, prey include earthworms and other annelids, different insects, woodlice, and
snails and slugs The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. Ther ...
. During the breeding season, they prey on various aquatic invertebrates, and also tadpoles of other amphibians such as the
common frog The common frog or grass frog (''Rana temporaria''), also known as the European common frog, European common brown frog, European grass frog, European Holarctic true frog, European pond frog or European brown frog, is a semi-aquatic amphibian o ...
or common toad, and smaller newts. Larvae, depending on their size, eat small invertebrates and tadpoles, and also smaller larvae of their own species. The larvae are themselves eaten by various animals such as carnivorous invertebrates and water birds, and are especially vulnerable to predatory fish. Adults generally avoid predators through their hidden lifestyle but are sometimes eaten by herons and other birds, snakes such as the grass snake, and mammals such as shrews, badgers and hedgehogs. They secrete the poison tetrodotoxin from their skin, albeit much less than for example the North American Pacific newts (''Taricha''). The bright yellow or orange underside of crested newts is a warning coloration which can be presented in case of perceived danger. In such a posture, the newts typically roll up and secrete a milky substance.


Reproduction


Courtship

A complex courting ritual performed underwater characterises the crested and marbled newts. Males are territorial and use leks, or courtship arenas, small patches of clear ground where they display and attract females. When they encounter other males, they use the same postures as described below for courting to impress their counterpart. Occasionally, they even bite each other; marbled newts seem more aggressive than crested newts. Males also frequently disturb the courting of other males and try to guide the female away from their rival. Pheromones are used to attract females, and once a male has found one he will pursue her and position himself in front of her. After this first ''orientation'' phase, courtship proceeds with ''display'' and ''spermatophore transfer''. Courtship display serves to emphasise the male's body and crest size and to waft pheromones towards the female. A position characteristic for the large ''Triturus'' species is the "cat buckle", where the male's body is kinked and often rests only on the forelegs ("hand stand"). He will also lean towards the female ("lean-in"), rock his body, and flap his tail towards her, sometimes lashing it violently ("whiplash"). If the female shows interest, the ritual enters the third phase, where the male creeps away from her, his tail quivering. When the female touches his tail with her snout, he deposits a packet of sperm (a spermatophore) on the ground. The ritual ends with the male guiding the female over the spermatophore, which she then takes up with her
cloaca In animal anatomy, a cloaca ( ), plural cloacae ( or ), is the posterior orifice that serves as the only opening for the digestive, reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles and birds, a ...
. In the southern marbled newt, courtship is somewhat different from the larger species in that it does not seem to involve male "cat buckles" and "whiplashes", but instead slower tail fanning and undulating of the tail tip (presumably to mimic a prey animal and lure the female).


Egg deposition and development

Females usually engage with several males over a breeding season. The eggs are fertilised internally in the oviduct. The female deposits them individually on leaves of aquatic plants, such as water cress or floating sweetgrass, usually close to the surface, and, using her hindlegs, folds the leaf around the eggs as protection from predators and radiation. In the absence of suitable plants, the eggs may also be deposited on leaf litter, stones, or even plastic bags. In the northern crested newt, a female takes around five minutes for the deposition of one egg. Crested newt females usually lay around 200 eggs per season, while the marbled newt (''T. marmoratus'') can lay up to 400. ''Triturus'' embryos are usually light-coloured, 1.8–2 mm in diameter with a 6 mm jelly capsule, which distinguishes them from eggs of other co-existing newt species that are smaller and darker-coloured. A genetic particularity in the genus causes 50% of the embryos to die: their development is arrested when they do not possess two different variants of chromosome 1 (i.e., when they are homozygous for that chromosome). Larvae hatch after two to five weeks, depending largely on temperature. In the first days after hatching, they live on their remaining embryonic yolk supply and are not able to swim, but attach to plants or the egg capsule with two balancers, adhesive organs on their head. After this period, they begin to ingest small invertebrates, and actively forage about ten days after hatching. As in all salamanders and newts, forelimbs—already present as stumps at hatching—develop first, followed later by the back legs. Unlike smaller newts, ''Triturus'' larvae are mostly nektonic, swimming freely in the water column. Just before the transition to land, the larvae resorb their external gills; they can at this stage reach a size of in the larger species.
Metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some inse ...
takes place two to four months after hatching, but the duration of all stages of larval development varies with temperature. Survival of larvae from hatching to metamorphosis has been estimated at a mean of roughly 4% for the northern crested newt, which is comparable to other newts. In unfavourable conditions, larvae may delay their development and overwinter in water, although this seems to be less common than in the small-bodied newts. Paedomophic adults, retaining their gills and staying aquatic, have occasionally been observed in several crested newt species.


Distribution

Crested and marbled newts are found in Eurasia, from Great Britain and the Iberian Peninsula in the west to
West Siberia Western Siberia or West Siberia (russian: Западная Сибирь, Zapadnaya Sibir'; kk, Батыс Сібір) is a part of the larger region of Siberia that is mostly located in the Russian Federation. It lies between the Ural region an ...
and the southern Caspian Sea region in the east, and reach north to central
Fennoscandia __NOTOC__ Fennoscandia (Finnish language, Finnish, Swedish language, Swedish and no, Fennoskandia, nocat=1; russian: Фенноскандия, Fennoskandiya) or the Fennoscandian Peninsula is the geographical peninsula in Europe, which includes ...
. Overall, the species have contiguous, parapatric ranges; only the northern crested newt and the marbled newt occur
sympatrically In biology, two related species or populations are considered sympatric when they exist in the same geographic area and thus frequently encounter one another. An initially interbreeding population that splits into two or more distinct species s ...
in western France, and the southern crested newt has a disjunct,
allopatric Allopatric speciation () – also referred to as geographic speciation, vicariant speciation, or its earlier name the dumbbell model – is a mode of speciation that occurs when biological populations become geographically isolated from ...
distribution in Crimea, the Caucasus, and south of the Caspian Sea. The northern crested newt is the most widespread species, while the others are confined to smaller regions, e.g. the southwestern Iberian Peninsula in the southern marbled newt, and the Danube basin and some of its tributaries in the Danube crested newt. The Italian crested newt (''T. carnifex'') has been introduced outside its native range in some European countries and the Azores. In the northern Balkans, four species of crested newt occur in close vicinity, and may sometimes even co-exist. ''Triturus'' species usually live at low elevation; the Danube crested newt for example is confined to lowlands up to above sea level. However, they do occur at higher altitudes towards the south of their range: the Italian crested newt is found up to in the
Apennine Mountains The Apennines or Apennine Mountains (; grc-gre, links=no, Ἀπέννινα ὄρη or Ἀπέννινον ὄρος; la, Appenninus or  – a singular with plural meaning;''Apenninus'' (Greek or ) has the form of an adjective, which wou ...
, the southern crested newt up to in the southern Caucasus, and the marbled newt up to around in central Spain.


Evolution

The closest relatives of the crested and marbled newts are the European brook newts (''Calotriton''). Phylogenomic analyses resolved the relationships within the genus ''Triturus'': The crested and the marbled newts are
sister groups In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...
, and within the crested newts, the Balkan–Asian group with ''T. anatolicus'', ''T. karelinii'' and ''T. ivanbureschi'' is sister to the remaining species. The northern (''T. cristatus'') and the Danube crested newt (''T. dobrogicus''), as well as the Italian (''T. carnifex'') and the Macedonian crested newt (''T. macedonicus''), respectively, are sister species. These relationships suggest evolution from a stocky build and mainly terrestrial lifestyle, as today found in the marbled newts, to a slender body and a more aquatic lifestyle, as in the Danube crested newt. A 24-million-year-old fossil belonging to ''Triturus'', perhaps a marbled newt, shows that the genus already existed at that time. A molecular clock study based on this and other fossils places the divergence between ''Triturus'' from ''Calotriton'' at around 39 mya in the Eocene, with an uncertainty range of 47 to 34 mya. Based on this estimation, authors have investigated diversification within the genus and related it to
paleogeography Palaeogeography (or paleogeography) is the study of historical geography, generally physical landscapes. Palaeogeography can also include the study of human or cultural environments. When the focus is specifically on landforms, the term pale ...
: The crested and marbled newts split between 30 and 24 mya, and the two species of marbled newts have been separated for 4.7–6.8 million years. The crested newts are believed to have originated in the Balkans and radiated in a brief time interval between 11.5 and 8 mya: First, the Balkan–Asian group (the Anatolian, Balkan and southern crested newt) branched off from the other crested newts, probably in a
vicariance Allopatric speciation () – also referred to as geographic speciation, vicariant speciation, or its earlier name the dumbbell model – is a mode of speciation that occurs when biological populations become geographically isolated from ...
event caused by the separation of the Balkan and Anatolian land masses. The origin of current-day species is not fully understood so far, but one hypothesis suggests that ecological differences, notably in the adaptation to an aquatic lifestyle, may have evolved between populations and led to parapatric speciation. Alternatively, the complex geological history of the Balkan peninsula may have further separated populations there, with subsequent allopatric speciation and the spread of species into their current ranges.


Glacial refugia and recolonisation

At the onset of the Quaternary glacial cycles, around 2.6 mya, the extant ''Triturus'' species had already emerged. They were thus affected by the cycles of expansion and retreat of cold, inhospitable regions, which shaped their distribution. A study using environmental niche modelling and phylogeography showed that during the
Last Glacial Maximum The Last Glacial Maximum (LGM), also referred to as the Late Glacial Maximum, was the most recent time during the Last Glacial Period that ice sheets were at their greatest extent. Ice sheets covered much of Northern North America, Northern Eur ...
, around 21,000 years ago, crested and marbled newts likely survived in warmer refugia mainly in southern Europe. From there, they recolonised the northern parts after glacial retreat. The study also showed that species range boundaries shifted, with some species replacing others during recolonisation, for example the southern marbled newt which expanded northwards and replaced the marbled newt. Today's most widespread species, the northern crested newt, was likely confined to a small refugial region in the Carpathians during the last glaciation, and from there expanded its range north-, east- and westwards when the climate rewarmed.


Hybridisation and introgression

The northern crested newt and the marbled newt are the only species in the genus with a considerable range overlap (in western France). In that area, they have patchy, mosaic-like distributions and in general prefer different habitats. When they do occur in the same breeding ponds, they can form hybrids, which have intermediate characteristics. Individuals resulting from the cross of a crested newt male with a marbled newt female had mistakenly been described as distinct species ''Triton blasii'' de l'Isle 1862, and the reverse hybrids as ''Triton trouessarti'' Peracca 1886. The first type is much rarer due to increased mortality of the larvae and consists only of males, while in the second, males have lower survival rates than females. Overall, viability is reduced in these hybrids and they rarely backcross with their parent species. Hybrids made up 3–7% of the adult populations in different studies. Other ''Triturus'' species only meet at narrow zones on their range borders. Hybridisation does occur in several of these contact zones, as shown by genetic data and intermediate forms, but is rare, supporting overall
reproductive isolation The mechanisms of reproductive isolation are a collection of evolutionary mechanisms, behaviors and physiological processes critical for speciation. They prevent members of different species from producing offspring, or ensure that any offspring ...
. Backcrossing and
introgression Introgression, also known as introgressive hybridization, in genetics is the transfer of genetic material from one species into the gene pool of another by the repeated backcrossing of an interspecific hybrid with one of its parent species. Intr ...
do however occur as shown by mitochondrial DNA analysis. In a case study in the Netherlands, genes of the introduced Italian crested newt were found to introgress into the
gene pool The gene pool is the set of all genes, or genetic information, in any population, usually of a particular species. Description A large gene pool indicates extensive genetic diversity, which is associated with robust populations that can surv ...
of the native northern crested newt. The two marbled newt species can be found in proximity in a narrow area in central Portugal and Spain, but they usually breed in separate ponds, and individuals in that area could be clearly identified as one of the two species. Nevertheless, there is introgression, occurring in both directions at some parts of the contact zone, and only in the direction of the southern marbled newt where that species had historically replaced the marbled newt (see also above, '' Glacial refugia and recolonisation'').


Threats and conservation

Most of the crested and marbled newts are listed as species of " least concern" by the International Union for Conservation of Nature, but population declines have been registered in all assessed species. The Danube crested newt and the southern marbled newt are considered " near threatened" because populations have declined significantly. Populations have been affected more heavily in some countries and species are listed in some national red lists. The Anatolian, Balkan and the Macedonian crested newt, recognised only recently, have not yet been evaluated separately for conservation status.


Reasons for decline

The major threat for crested and marbled newts is habitat loss. This concerns especially breeding sites, which are lost through the upscaling and intensification of agriculture, drainage, urban sprawl, and artificial flooding regimes (affecting in particular the Danube crested newt). Especially in the southern ranges, exploitation of groundwater and decreasing spring rain, possibly caused by global warming, threaten breeding ponds. Aquatic habitats are also degraded through pollution with agricultural pesticides and fertiliser. Introduction of
crayfish Crayfish are freshwater crustaceans belonging to the clade Astacidea, which also contains lobsters. In some locations, they are also known as crawfish, craydids, crawdaddies, crawdads, freshwater lobsters, mountain lobsters, rock lobsters, mu ...
and predatory fish threatens larval development; the
Chinese sleeper The Chinese sleeper (''Perccottus glenii''), also known as the Amur sleeper, is a species of freshwater sleeper native to Amur River basin in eastern Asia with introduced populations in other regions of Eurasia. It is currently the only known mem ...
has been a major concern in Eastern Europe. Exotic plants can also degrade habitats: the
swamp stonecrop ''Crassula helmsii'', known as swamp stonecrop or New Zealand pigmyweed, is an aquatic or semiterrestrial species of succulent plant in the family Crassulaceae. Originally found in Australia and New Zealand, it has been introduced around the wor ...
replaces natural vegetation and overshadows waterbodies in the United Kingdom, and its hard leaves are unsuitable for egg-laying to crested newts. Land habitats, equally important for newt populations, are lost through the replacement of natural forests by plantations or clear-cutting (especially in the northern range), and the conversion of structure-rich landscapes into uniform farmland. Their limited dispersal makes the newts especially vulnerable to
fragmentation Fragmentation or fragmented may refer to: Computers * Fragmentation (computing), a phenomenon of computer storage * File system fragmentation, the tendency of a file system to lay out the contents of files non-continuously * Fragmented distributi ...
, i.e. the loss of connections for exchange between suitable habitats. High concentrations of road salt have been found to be lethal to crested newts. Other threats include illegal collection for pet trade, which concerns mainly the southern crested newt, and the northern crested newt in its eastern range. The possibility of hybridisation, especially in the crested newts, means that native species can be genetically polluted through the introduction of close species, as it is the case with the Italian crested newt introduced in the range of the northern crested newt. Warmer and wetter winters due to global warming may increase newt mortality by disturbing their hibernation and forcing them to expend more energy. Finally, the genus is potentially susceptible to the highly pathogenic fungus '' Batrachochytrium salamandrivorans'', introduced to Europe from Asia.


Conservation measures

The crested newts are listed in Berne Convention Appendix II as "strictly protected", and the marbled newts in Appendix III as "protected". They are also included in Annex II (species requiring designation of special areas of conservation; crested newts) and IV (species in need of strict protection; all species) of the EU habitats and species directive. As required by these frameworks, their capture, disturbance, killing or trade, as well as the destruction of their habitats, are prohibited in most European countries. The EU habitats directive is also the basis for the
Natura 2000 Natura 2000 is a network of nature protection areas in the territory of the European Union. It is made up of Special Areas of Conservation and Special Protection Areas designated under the Habitats Directive and the Birds Directive, respectively ...
protected areas, several of which have been designated for the crested newts. Habitat protection and management is seen as the most important element for the conservation of ''Triturus'' newts. This includes preservation of natural water bodies, reduction of fertiliser and pesticide use, control or eradication of introduced predatory fish, and the connection of habitats through sufficiently wide corridors of uncultivated land. A network of aquatic habitats in proximity is important to sustain populations, and the creation of new breeding ponds is in general very effective as they are rapidly colonised when other habitats are nearby. In some cases, entire populations have been moved when threatened by development projects, but such
translocations In genetics, chromosome translocation is a phenomenon that results in unusual rearrangement of chromosomes. This includes balanced and unbalanced translocation, with two main types: reciprocal-, and Robertsonian translocation. Reciprocal translo ...
need to be carefully planned to be successful. Strict protection of the northern crested newt in the United Kingdom has created conflicts with local development projects; at the same time, the charismatic crested newts are seen as flagship species, whose conservation also benefits a range of other amphibians.


References


External links

* {{Taxonbar, from=Q310391 Amphibians of Asia Amphibians of Europe Extant Eocene first appearances Amphibian genera Taxa named by Constantine Samuel Rafinesque