NEOTENY AND PAEDOMORPHOSIS IN TRITURUS(

This page is a work-in-progress regarding paedomorphosis in Triturus sensu lato.

Neotenous male Triturus (=Mesotriton, Ichthyosaura) alpestris. Photo by Will Atkins.

Neotenous female Triturus (=Mesotriton, Ichthyosaura) alpestris. Photo by Will Atkins.

Neotenous female Triturus (= Lissotriton) italicus.

NEOTENY, PAEDOMORPHOSIS AND PROGENESIS

Newts showing both adult and larval features are often referred to as 'neotenous' or 'paedomorphic'. Gould (1977) defines three terms relating to this phenomenon:

• Paedomorphosis (Garstang, 1922- "shaped like a child"): the displacement of ancestral features to later stages of the ontogeny of descendants.
• Progenesis (Giard, 1887- "generation before [the ancestral time]"): paedomorphosis produced by an acceleration of maturation.
• Neoteny (Kollmann, 1885- "retention of young features"): paedomorphosis produced by a retardation of somatic development.

Neoteny has also been subdivided into "partial" and "total" neoteny (e.g. Ingram, 1929). "Total neoteny" refers to individuals that reach sexual maturity while retaining larval features, with "partial neoteny" referring to those in which the larval stage is prolonged.

In addition, "facultative neoteny" or "facultative paedomorphosis" describes animals which are able to metamorphose under certain conditions; "obligate neoteny" or "obligate paedomorphosis" describes animals which are unable to metamorphose under any condition [REF].

OVERWINTERING

Overwintering appears to be common in European newt larvae. Bell & Lawton (1975) estimated that 38% of all metamorphs in a population of T. vulgaris in Oxfordshire had overwintered before metamorphosis. They suggest that any larvae in this population that fail to reach 35mm in length before mid-September will overwinter, and metamorphose in the following spring. Despite this high rate of overwintering, no paedomorphic individuals were found.

PAEDOMORPHISM AND COLOURATION

The amphibian pituitary gland secretes melanocyte-stimulating hormone (MSH) and thyroid-stimulating hormone (TSH). MSH stimulates melanocytes to produce melanin (resulting in long-term darkening of the skin) and to disperse melanin (resulting in short-term darkening). TSH stimulates the thyroid gland to produce thyroxine, which induces metamorphosis. Pituitary gland malfunction thus has the potential both to retard metamorphosis and to lighten colouration. Gilled light-coloured individuals of T. vulgaris have been found on occasion- photographs have been published by Wisniewski (1989) and Smith (1951). Baker (2006) depicts a similarly-coloured T. cristatus.

SPECIES ACCOUNTS

Triturus alpestris (=Mesotriton alpestris, Ichthyosaura alpestris)

The alpine newt shows the strongest tendency towards paedomorphosis of any of the European newts, with many known paedomorphic populations. Denoel et al. (2001) summarise their distribution; the map above is based on their data. With the exception of one population in southern Germany, all paedomorphic individuals were found in the southern part of the species' range. They suggest that this tendency towards paedomorphosis is at least partly genetic, as suitable habitats for paedomorphosis occur throughout their range. Occurence of paedomorphosis in T. a. apuanus in its normal range (in 47% of populations, according to Andreone & Dore (1991)), in captive groups (M. Morgan, personal communication; Chris Michaels, personal communication) and in introduced animals outside their normal range (Atkins, 2012) would seem to support this.

A number of alpine newt subspecies have been described from paedomorphic individuals. Radovanovic (1951, 1961) described three subspecies based on paedomorphic individuals from Montenegro: montenegrinus from Lake Bukumirsko, piperianus from Lake Kapetanovo and Lake Manito, and serdarus from Lake Zminicko. Though these are described as 'neotenic' subspecies, metamorphic individuals are invariably present in these populations. Radovanovic's description of montenegrinus stated that 3-4% of specimens were 'fully developed', and Denoel et al. summarise the proportion of paedomorphic individuals found at these localities:

Location	Country	subspecies	% paedomorphic
Lake Bukumirsko	Montenegro	montenegrinus	75-96
Lake Kapetanovo	Montenegro	piperianus	<75
Lake Zminicko	Montenegro	serdarus	48-51

Sotiropolous et al. (2001) suggested that the morphological characters used in the description of the subspecies merely represent differences between paedomorphic and metamorphic individuals- for example, gilled individuals invariably have a wider head. More recent research (Sotiropoulos et al., 2007) shows that these subspecies are genetically very close to the metamorphic populations found nearby (currently regarded as T. a. alpestris), and hence may not represent valid subspecies.

Triturus cristatus

• Baker (2006) depicts a paedomorphic individual captured in southern England, with what he describes as 'leucistic' colouration. He suggests 'failure of pituitary action'.
• Jehle et al. (2011) depict a paedomorphic individual, of adult size, but larval colouration, found in a garden pond in Bavaria.
• Gislen & Kauri (1959) describe a single T. cristatus larva from a highland area of Sweden, which failed to metamorphose after 2 years in captivity, still having gills at a length of 94mm. Paedomorphic T. vulgaris were found at the same location.

Triturus carnifex

• Fasola and Canova (1992) found a single male and a single female paedomorphic adult in a sample of 197 crested newts in the Piacenza province of Northern Italy. Though described as T. cristatus, the location suggests T. carnifex.

Triturus macedonicus

• Kalezic et al. (1994) described a population in Montenegro where approximately 10% of the population were paedomorphic, all of these being males. Though described as T. carnifex at the time, this location falls within the range of what is now regarded as T. macedonicus.

Triturus dobrogicus

• Mester et al. (2013) describe a single paedomorphic female T. dobrogicus caught in Hungary.

Triturus karelinii

• I have not located any records of paedomorphosis in the T. karelinii group (including T. arntzeni, T. ivanbureschi).

Triturus marmoratus

• I have not located any records of paedomorphosis in T. marmoratus.

Triturus pygmaeus

• Ceacero et al. (2010) describe eight paedomorphic T. pygmaeus caught in a cistern, apparently of both sexes.
• Fuentes et al. (2010) describe a collection of 11 paedomorphic specimens of T. pygmaeus, apparently all male.

Triturus vittatus

• Kaya et al. (2008) collected four paedomorphic female T. vittatus (= Ommatotriton ophryticus) from Sakarya, Turkey, which produced fertile eggs when mated with normal males.
• Skorinov et al. (2009) report a single paedomorphic female T. vittatus (= Ommatotriton ophryticus) from Abkhazia in the Caucasus.

Triturus italicus

• Scillitano et al. (2004) found paedomorphic individuals in 12% of 154 sites surveyed throughout the species' range.
• Corsetti et al. (2005) found paedomorphic individuals at the far north west of the species' range.
• The image at top is of a female paedomorphic T. italicus (=Lissotriton italicus) raised by myself. This animal laid a number of infertile eggs before metamorphosing in its second summer.

Triturus boscai

• Ceacero et al. (2010) report a single paedomorphic male T. boscai (=Lissotriton boscai).

Triturus montandoni

• I have not located any records of paedomorphosis in T. montandoni (=Lissotriton montandoni).

Triturus helveticus

• Denoel (2007) states that there are numerous paedomorphic populations of T. helveticus (=Lissotriton helveticus) around Larzac, in southern France.
• Frazer (1983) quotes van Gelder (1972) who trapped 87 male and 280 female paedomorphic T. helveticus (along with 239 normal adults) at one site in the Netherlands.
• Griffiths (1996) states that neotenous T. helveticus have also been found in Germany.
• Dodd & Callan (1955) report a number of neotenous T. helveticus of both sexes taken from a pond in Scotland. These animals all exhibited pathology of the thyroid gland, which the authors suggest may have been due to agricultural contamination.

Triturus vulgaris
There are many records of paedomorphic T. vulgaris (=Lissotriton vulgaris) throughout its range, though these seem to usually represent what Griffiths (1996) describes as 'exceptional individuals in otherwise normal populations'. The list below makes no attempt to be exhaustive.

• Banks (1985) caught 3 paedomorphic newts, apparently of both sexes, in a sample of 27 in northern England. He suggested that low water temperatures might be responsible.
• Leeke (1990) described a pond in southern England where about 15% of the adult newts observed were paedomorphic. A captured female laid fertile eggs. Unpublished observations indicate that paedomorphs occured in other nearby ponds; the majority appeared female, with only one male observed.
• Litvinchuk et al. (1996) recorded 48 female and 2 male paedomorphic individuals of T. v. lantzi in a collection of 84 newts from Abkhazia, Georgia. Males and females were found to be sexually fertile, and paedomorphic individuals were reported from the same site several years in succession. They also reported several paedomorphic T. v. vulgaris from St. Petersburg, apparently exhibiting thyroid pathology.
• Gislen & Kauri (1959) examined six male and one female paedomorphic T. vulgaris, from three locations in Sweden. Two of these locations were highland areas where year-round low temperatures would mean that larvae were unable to metamorphose in their first year. Paedomorphic T. cristatus were also found at one of these locations.
• Dzukic et al. (1990) summarise paedomorphic populations of T. vulgaris (as well as T. alpestris) in the former Yugoslavia- 17 known locations are listed, from sea level to 1350m altitude, with all but one being in the Dinaric karst along the Adriatic coast. They report that some of these karst populations are up to 50% paedomorphic.
• Gvozdik et al. (2013) observed a population in the Czech Republic where a visual sample of 70 newts included 67 paedomorphic individuals, with only two being male. In a group taken into captivity, male courtship was observed, and females produced eggs. However, all of this group metamorphosed within 45 days of capture.

REFERENCES

Andreone, F., & Dore, B., 1991. New data on paedomorphism in Italian populations of the Alpine Newt, Triturus alpestris (LAURENTI, 1768) (Caudata: Salamandridae) Herpetozoa 4(3/4): 149-156. [PDF]

Atkins, W., 2012. Continental Types in the Pool. (Sep 2013).

Baker, J., 2006. A partially neotenous Great crested newt, Triturus cristatus. Herpetological Bulletin 98: 29-31.

Banks, B., 1985. Observations on neoteny in the smooth newt. British Herpetological Society Bulletin 12: 37-38.

Bell, G., & Lawton, J. H., 1975. The Ecology of the Eggs and Larvae of the Smooth Newt (Triturus vulgaris (Linn.)). The Journal of Animal Ecology 44(2): 393-423. [PDF]

Ceacero, F., Donaire-Barroso, D., Garcia-Munoz, E., Beltran, J. F., & Tejedo, M., 2010. On the occurrence of facultative paedomorphosis in the three newt species of Southern Iberian Peninsula (Amphibia, Salamandridae). Amphibia-Reptilia 31: 571-575. [PDF]

Corsetti, L., Ragno, R., & Romano, A., 2005. Triturus italicus (PERACCA, 1898) in the Lepini Mountains: new north-western range limit. Herpetozoa 18(1/2): 87-88 [PDF]

Denoel, M., 2007. Priority areas of intraspecific diversity: Larzac, a global hotspot for facultative paedomorphosis in amphibians. Animal Conservation 10(1): 110-116. [ABSTRACT]

Denoel, M., Duguet, R., Dzukic, G., Kalezic, M., & Mazzotti, S., 2001. Biogeography and ecology of paedomorphosis in Triturus alpestris (Amphibia, Caudata). Journal of Biogeography 28(10): 1271-1280. [ABSTRACT]

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Dzukic, G., Kalezic, M. L., Tvrtkovic, N., & Djorovic, A., 1990. An overview of the occurrence of paedomorphosis in Yugoslav newt (Triturus, Salamandridae) populations. British Herpetological Society Bulletin, 34:16-22.

Fasola, M. & Canova, L., 1992. Feeding habits of Triturus vulgaris, T. cristatus and T. alpestris (Amphibia, Urodela) in the northern apennines (Italy) Bolletino di zoologia 59(3): 273-280. [PDF]

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Gislen, T. & Kauri, H., 1959. Zoogeography of the Swedish amphibians and reptiles. Acta Vert 1: 193-397.

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Gvozdik, V., Javurkova, V., & Kopecky, O., 2013. First evidence of a paedomorphic population of the smooth newt (Lissotriton vulgaris) in the Czech Republic. Acta Herpetologica 8(1): 53-57, 2013. [PDF]

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Kalezic, M. L., Cvetkovic, D., Djorovic A., & Dzukic G, 1994. Paedomorphosis and differences in life-history traits of two neighboring crested newt (Triturus carnifex) populations. Herpetological Journal 4: 151-158.

Kaya, U., Sayim, F., Baskale, E., & Cevik, I. E., 2008. Paedomorphosis in the banded newt, Triturus vittatus (Jenyns, 1835). Belg. J. Zool. 138(2): 196-197. [PDF]

Kollman, J., 1885. Das Ueberwintern von europaischen Frosch- und Triton- larven und die Umwandlung des mexikanischen Axolotl. Verh. Naturf. Ges. Basel 7: 387-398.

Leeke, C., 1990. An Occurrence of Neotenous Smooth Newts (Triturus vulgaris) in Cambridgeshire. British Herpetological Society Bulletin 31: 28.

Litvinchuk, S. N., Rudyk, A. M., & Borkin, L. J., 1996. Observations of Paedomorphic Newts (Triturus vulgaris) from the Former Soviet Union. Russian Journal of Herpetology 3(1): 39-48. [Abstract]

Mester, B., Cozma, N., & Puky, M., 2013. First observation of facultative paedomorphosis in the Danube crested newt(Triturus dobrogicus Kiritzescu, 1903) and the occurrence of facultative paedomorphosis in two newt species from soda pans of the Danube-Tisza Interfluve (Kiskunsag National Park, Hungary). North-Western Journal of Zoology 9(2): xxx-xxx. [PDF]

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Scillitani, G., Scalera, R., Carafa, M., & Tripepi, S. 2004. Conservation and biology of Triturus italicus in Italy (Amphibia, Salamandridae). Italian Journal of Zoology 71 (supplement 1): 45-54. [PDF]

Skorinov, D. V., Novikov, O., Borkin, L. G., & Litvinchuk, S. N., 2009. Two New Cases of Paedomorphosis in the Caucasian Newts: Ommatotriton ophryticus (The First Record) and Lissotriton vulgaris lantzi. Russian Journal of Herpetology 16(1): 16-18. [ABSTRACT]

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Sotiropolous, K., Tomovic, L., Dzukic, G., & Kalezic, M. L., 2001. Morphological differentiation of the alpine newt (Triturus alpestris) in the Balkans: taxonomic implications. Herpetological Journal 11: 1-8.

Sotiropoulos, K., Eleftherakos, K., Dzukic, G., Kalezic, M. L., Legakis, A. & Polymeni, R. M., 2007. Phylogeny and Biogeography of the Alpine Newt Mesotriton alpestris (Salamandridae, Caudata), Inferred from mtDNA Sequences. Molecular Phylogenetics and Evolution 45: 211-226. [ABSTRACT]

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