Chinese water dragon
| Chinese water dragon | |
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| At Khao Yai National Park in Thailand | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | Squamata |
| Suborder: | Iguania |
| Family: | Agamidae |
| Genus: | Physignathus Cuvier, 1829 |
| Species: | P. cocincinus
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| Binomial name | |
| Physignathus cocincinus Cuvier, 1829
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| Native range of Physignathus cocincinus | |
Physignathus cocincinus is a species of
Chinese water dragons are large diurnal lizards adapted for dense subtropical forests replete with unpolluted streams. They are semi-arboreal, roosting at night on branches overlooking streams, which offer an escape route when the lizards are disturbed. Arthropods are their main source of food, though worms, snails, vertebrates, and plants make up a notable portion of the diet as well. Males are territorial towards each other and bear display features such as crests and jowls. Females are oviparous and reproduce sexually in the wild, though at least one captive Chinese water dragon is known to have reproduced via parthenogenesis. Physignathus cocincinus is related to Australasian lizards in the subfamily Amphibolurinae. One amphibolurine, the Australian water dragon (Intellagama lesuerii) is so anatomically and ecologically similar to Physignathus cocincinus that it was once (erroneously) placed in the same genus.
Feral populations introduced to
Taxonomy
The species and genus were first described by
During the 19th and 20th centuries, several other species of agamid lizards were placed in Cuvier's genus Physignathus. These have been reclassified into separate genera, leaving Physignathus with only the original species P. cocincinus remaining. For example, the Australian water dragon (Intellagama lesueurii) was known as Physignathus lesueurii for much of its history.[10]
According to most genetic analyses, Physignathus cocincinus is the
Description
Adult Chinese water dragons are large and robust lizards; males can grow up to 90 cm (3 feet) in total length, including the tail. Chinese water dragons show distinct
_male_(7783192098).jpg)
Coloration is usually a shade of bright green, though they can take on a brown or grey hue when stressed. In juveniles, the body has vibrant green or turquoise diagonal stripes, which may fade with maturity. Most of the tail is ornamented with thick bands of alternating light green and dark brown. In some individuals a dark stripe stretches between the eye and the ear. In most areas the undersides are pale in color, but the throat takes on a more colorful shade of yellow or orange, especially in adult males. Scales on the cheek and lower jaw may acquire a blue or pink coloration in adults.[5][3]
Distribution
Native range
Chinese water dragons are native to the subtropical forests of southern China (Guangdong, Guangxi, and Yunnan provinces) and Southeast Asia (Vietnam, Laos, portions of Cambodia, eastern Thailand).[2][5][6] There are also unconfirmed[5] reports from Myanmar.[6]
Introduced populations
An introduced population of Chinese water dragons have established themselves in Hong Kong, probably from released pet animals.[15][16] The first reports came from Tsing Yi Island in 2004,[15] though the Hong Kong population likely originated from several releases.[17] Since 2010, another breeding population has been established in New Taipei City, Taiwan. Hundreds of the lizards were culled from 2013 to 2017 over concerns about their impact on native Taiwanese wildlife.[18] Introduced individuals (but not breeding populations) have also been reported from Malaysia and Florida.[17][18][5]
Habitat
Chinese water dragons are most commonly found within dense closed evergreen forest along the banks of freshwater streams.[19][5] They live in a humid climate with mild seasons: average humidity levels of 40–80% and temperatures ranging from 80–90 °F (26–32 °C). Their reliance on undisturbed forest streams indicates that, despite their wide extent of occurrence in southeast Asia, Chinese water dragons are a geographically restricted species.[5] They can be found between elevations of around 50 meters (164 ft) and 820 meters (2690 ft), though their density and abundance decline strongly above around 270 meters (885 ft).[6][20][5]
Despite their preference for undisturbed habitat, Chinese water dragons are common in the urban parks of Hong Kong. Nevertheless, they show a systematic preference for areas with streamside boulders, taller trees, and a denser canopy. Though all sampled individuals have streams within their territory, less than half of first-hand recordings occur within close proximity (< 5 meters) to a stream. Males prefer to defend wide or deep streams while female territories occupy more dry land. Rocks and concrete structures are frequented for basking spots. Orchards are avoided, since they offer no benefits for protection (relative to dense forests) or heat retention (relative to concrete).[16]
Behavior and ecology
Chinese water dragons are diurnal (active during the day) and forage for prey within small territories in the morning and midday. They are also semi-arboreal (spending much of their time in trees or plants). Adult males in particular tend to rest during the night on tree limbs overlooking streams. If threatened, a Chinese water dragon will leap or run to the nearest stream and either swim to safety or remain submerged for up to 90 minutes.[20][16][5]
In Hong Kong, the average territory size is about 1800 m2, with a small daily range of about 5 meters on average. Male territories generally do not overlap with each other, arguing that males are much more territorial than females. Movement and range patterns appear to be similar between the hot and wet summer and the relatively cool and dry winter, unlike most other subtropical reptiles. This may be an unintentional artefact of the fact that Hong Kong's dry season during the study interval (2015–2016) was unusually warm and wet.[16] Captive male water dragons are very aggressive towards each other while females and juveniles are more tolerant.[5]
Diet
Chinese water dragons are omnivorous and will readily supplement their diet with non-toxic vegetables or fruits in captivity. Nevertheless, their diet consists mainly of insects with occasional small vertebrates, eggs, and snails.[3][18] Introduced Chinese water dragons in Taiwan are known to prey on native lizards, frogs, snakes, and mice.[18][5]
According to a 2018 survey in Central Vietnam, Chinese water dragons persist on a diverse variety of terrestrial invertebrates. Termites, ants, orthopterans (grasshoppers and crickets), earthworms, and spiders all make up a significant portion of the diet, along with insect larvae, snails, and various other prey items. Plant material was eaten very rarely by the subjects of this study,[4] though other accounts testify that plants make up a significant portion of the diet in the wild.[5]
Reproduction and life history
Chinese water dragons are oviparous, with a clutch of 5 to 16 eggs buried in sandy riverbanks near the end of the dry winter. The eggs hatch two or three months later in the early part of the wet summer.[2][5] Maturity is met within the first year, and the generation length is about 6 years.[2] Captive females may breed several times per year.[5] Healthy captive Chinese water dragons have a life expectancy of 10 to 15 years, though some can exceed 20 years of age.[3][5]
Though they
Threats and conservation
Though locally abundant in some areas, the Chinese water dragon faces persistent unrestrained threats and a steadily declining wild population. It is listed as Vulnerable in Vietnamese conservation lists, and Endangered in Thailand and China.
Population dynamics
At one site in Cambodia the species experienced a 50% population decline in 18 years, while a 2007 estimate considered the entire Vietnamese population to have declined by 20% over the previous decade.[2][5] Based on these estimates, the species as a whole may be declining by 30% every 18 years.[2]
A 2017 population survey in Thua Thien Hue Province, Vietnam estimated that up to 250 individuals in total were present at the 11 sampled sites (combined). This is far below the several thousand expected to sustain long-term genetic diversity for a species restrained to narrow riparian habitats. Sites sampled in June 2017 show a slightly lower population and a higher relative proportion of females and sub-adults relative to the same sites in April 2017. Adults were uncommon in both months while juveniles were most common in April, maturing into a large sub-adult cohort by June. Chinese water dragons in Thua Thien Hue occur at moderate to high densities, up to 2.6 per 100 meters in April 2017.[6]
Somewhat different patterns were observed in a 2014–2016 survey in
Hunting and the pet trade
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The most severe threat to the species is harvesting for meat and the
Wild water dragons are captured and sold as pets on social media platforms for both Vietnamese customers and the international markets of Europe and the United States.[6] In Vietnam, about five times as many Chinese water dragons are sold for meat compared to those sold as pets.[20] Exports to Europe began in 1975 and have accelerated in recent decades.[5] From 2010 to 2018, a stable average of around 7,000 live Chinese water dragons per year were exported to the European Union. Approximately 89% came from Vietnam, though information on their production (wild caught or captive bred) is available for fewer than 13% of recorded exports to Europe.[20]
Exports to the United States are even higher despite recent declines: an average of 81,000 per year from 2002 to 2011, and around 48,000 per year from 2013 to 2017. Practically all water dragons exported to the United States are Vietnamese in origin. At least 95% are wild caught while around 3% are reportedly captive bred in Vietnam.[20] It is probable that some individuals sourced from Vietnam were actually collected from other nations, simply using the ports of Vietnam as a transit hub.[20][5] Captive breeding is a viable but limited conservation strategy; Chinese water dragons breed readily in captivity, though not at a high enough rate to counteract demand.[2][5] There is no direct evidence that captive breeding programs in Vietnam are in operation, despite claims of captive-bred exports.[5]
Habitat loss
A smaller threat, though still impactful, is degradation or removal of the forested stream habitats which water dragons rely on.[2][5] In Thua Thien Hue, illegal logging and a major highway construction project are likely partially responsible for losses in the Nam Dong and A Luoi districts. These pressures are less prevalent in the uplands of Phong Dien district, which seems to not experience the same degree of population decline.[6] Logging and expansion of agricultural and tourism infrastructure also contribute to the paucity of suitable habitats in Northern Vietnam. Coal mining, stream pollution, and climate change may also threaten the species, as reported for ecologically similar reptiles in the region, such as the Chinese crocodile lizard (Shinisaurus crocodilurus).[20][5]
Despite its common name, the Chinese water dragon is exceedingly rare in China, where it is threatened by dam construction on top of the same pressures as the Vietnamese populations. Suitably undeveloped habitats are uncommon in Cambodia and Laos. The few Chinese water dragons present in Thailand are stable and locally abundant thanks to their range lining up with protected areas such as Khao Yai National Park and Namtok Phlio National Park.[2][5]
Gallery
Wild individuals
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A juvenile in Cambodia -
In southern Vietnam -
A juvenile in Seka district, Thailand -
At Namtok Phlio NP, Thailand -
At Khao Yai NP, Thailand -
At Khao Yai NP, Thailand -
At Khao Yai NP, Thailand -
Detailed view of the head (Khao Yai NP, Thailand)
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Captive individuals
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At Warsaw Zoo -
AtBasel Zoo -
![At Palmiarnia Poznańska [pl]](//upload.wikimedia.org/wikipedia/commons/thumb/2/2e/654303_Pozna%C5%84%2C_palmiarnia_07.JPG/270px-654303_Pozna%C5%84%2C_palmiarnia_07.JPG)
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AtAmsterdam Zoo -
At Aalborg Zoo -
Detailed view of the head (Toronto Zoo)
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![At Palmiarnia Poznańska [pl]](/File:654303_Pozna%C5%84,_palmiarnia_07.JPG)
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_Aalborg_Zoo.jpg)
References
- ^ a b "Appendices | CITES". cites.org. Retrieved 2023-03-01.
- ^ a b c d e f g h i j k l m Stuart, B., Sumontha, M., Cota, M., Panitvong, N., Nguyen, T.Q., Chan-Ard, T., Neang, T., Rao, D.-q. & Yang, J. (2019). "Physignathus cocincinus". The IUCN Red List of Threatened Species.
{{cite web}}: CS1 maint: multiple names: authors list (link) - ^ a b c d e f g h "Asian water dragon". Smithsonian's National Zoo & Conservation Biology Institute. 8 September 2017.
- ^ S2CID 216909990.
- ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af "CoP19 Prop. 14" (PDF). CONVENTION ON INTERNATIONAL TRADE IN ENDANGERED SPECIES OF WILD FAUNA AND FLORA, Nineteenth meeting of the Conference of the Parties. November 2022.
- ^ ISSN 1314-3301.
- ^ PMID 31166974.
- ^ Cuvier, M. [Georges] le Baron (1829). Le règne animal distribué d'après son organisation, pour servir de base à l'histoire naturelle des animaux et d'introduction à l'anatomie comparée. Tome 2 (in French) (2 ed.). Déterville et Crochard. p. 41.
- ^ Uetz, P.; Freed, P.; Aguilar, R.; Reyes, F.; Hošek, J. (eds.). "Physignathus cocincinus". The Reptile Database. Retrieved 2023-09-12.
- ISSN 1175-5334.
- ^ PMID 12118407.
- ^ PMID 15297599.
- ^ ISSN 0024-4066.
- PMID 21787873.
- ^ a b To, Allen (2005). "Another alien has landed: the discovery of a wild population of water dragon, Physignathus cocincinus, in Hong Kong" (PDF). Porcupine. 33 (November): 3–4.
- ^ S2CID 211828808.
- ^ S2CID 242176811.
- ^ PMID 30914838.
- ^ "Chinese Water Dragon". World Association of Zoos and Aquariums. Archived from the original on 3 January 2015. Retrieved 18 August 2012.
- ^ S2CID 225308238.
- ^ Burns, Mercedes (Dec 26, 2020). "Parthenogenesis: How females from some species can reproduce without males". Ars Technica. Retrieved Jan 10, 2021.
External links
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