Desert monitor

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Desert monitor
Caspian monitor (Varanus griseus caspius)

Least Concern  (IUCN 3.1)[1]
CITES Appendix I (CITES)[2]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Family: Varanidae
Genus: Varanus
Subgenus: Psammosaurus
Species:
V. griseus
Binomial name
Varanus griseus
(Daudin, 1803)
Synonyms
  • Psammosaurus arabicus Hemprich & Ehrenberg, 1899
  • Psammosaurus griseus Sixta, 1900
  • Psammosaurus terrestris Rablrückhard, 1881
  • Tupinambis arenarius Geoffroy, 1827
  • Tupinambis griseus Daudin, 1803
  • Varanus arenarius Duméril & Bibron, 1836
  • Varanus griseus griseus De Lisle, 1996
  • Varanus scincus Merrem, 1820
  • Varanus terrestris Schinz, 1834
  • Varanus (Psammosaurus) griseus Mertens, 1942

The desert monitor (Varanus griseus) is a species of monitor lizard of the order Squamata found living throughout North Africa and Central and South Asia. The desert monitor is carnivorous, feeding on a wide range of vertebrates and invertebrates.[3]

Description

Body features

Desert monitors normally display a variety of body coloration from light brown and yellow to grey. They average about one meter in length, but can reach total body lengths of almost two meters. These lizards can also have horizontal bands on either their backs or tails, along with yellow spots across their backs. Their young are normally a brightly coloured orange and have distinctive bands across their backs which may be lost as they mature. Their

molting in which they shed their outer layer of skin to expand their overall body size. For adults, this process can take several months and happens around three times per year. Their skin is adapted to the desert environment where they live, and they are excellent swimmers and divers and have been known to enter the water occasionally to hunt for food.[4]

Subspecies

Three subspecies have been described:[5]

  • V. g. griseus (grey monitor)
  • V. g. caspius (Caspian monitor)
  • V. g. koniecznyi (Indian desert monitor)

Varanus griseus griseus

Grey monitor (Varanus griseus griseus), the nominate subspecies

V. g. griseus (grey monitor) has five to eight narrow grey bands on its back, as well as 19-28 bands on its tail. Its tail is more rounded that those of the other subspecies, and the final size of the adult depends on which

mammals.[3]

It can be found in north Africa (from Morocco and Mauritania east to Egypt and Sudan), the Arabian Peninsula (although appearing to be absent from Bahrain), southeastern Turkey, Syria, Israel, Palestine, Lebanon, Jordan and Iraq.[6]

Varanus griseus caspius

Caspian monitor (Varanus griseus caspius)

V. g. caspius (Caspian monitor) has five to eight bands on its back, 13-19 bands on its tail, a plain tail tip, and about 143 rows of scales in the middle section of its body. The Caspian monitor is found from the eastern shore of the

islets of the Aral Sea. They can be found at elevations up to 800 meters in the Kopet Dag Mountains, northern Iran
, western and southern Afghanistan and as far as south as western Pakistan. It is best-known from the secretions of Turkmenistan, Kazakhstan, Uzbekistan, Kyrgyzstan and Tajikistan.

They are found in barren areas of mainly sand and/or clay soils, and occasionally in wooded areas. Their diets include numerous invertebrates, small lizards and birds, bird eggs, young

cobras and vipers. They are strong diggers and can easily build burrows that are several feet long.[3]

Varanus griseus koniecznyi

V. g. koniecznyi (Indian desert monitor) has three to five bands on its back, 13-19 bands on its tail, a plain tail tip, 108-139 rows of scales on its midsection, and a broader and flatter head when compared to the other subspecies. This subspecies has the smallest body of the three. It is mainly found in Pakistan and west-central India, including the states of Gujarat, Rajasthan, Madhya Pradesh and Maharashtra, and probably others.

Due to climatic variations, the Indian subspecies has, reportedly, not been observed engaging in

invertebrates and insects, but will also include smaller lizards, rodents, birds, and their chicks and eggs, and various other small vertebrates.[3]

Lifestyle

Desert monitors goes into hibernation from about September to April. In April is a mass exodus from their hibernation, and they become most active between May and July. During the middle of the day, the lizards mainly stay in their burrows and only come to the desert surface to search for food. The monitor lizards require approximately 3 to 4 full hibernation periods (years) to reach their full size (about 55–65 cm excluding their tails) and at least 3 hibernation periods before they become sexually mature. The overall lifespan of desert monitors in the wild does not normally exceed around 8 years in both males and females.[7]

Importance of body temperature

Desert monitors are cold-blooded

predator while their body temperature is less than 21 °C, they will not flee, but will instead hold their ground and become extremely aggressive.[citation needed
]

The body temperature of desert monitors depend mainly on the outside

environment (time of day, season, etc.). Their internal temperatures begin warming up before they even leave their burrows through conductive heat gain, and their temperatures rapidly rise once they begin basking in the morning sun and reach their highest point in the noonday heat. The specific body temperature of desert monitors can vary depending on the average temperatures of the country they live in, but their maximum body temperature does not usually exceed 38.5 °C even when basking in the sunlight. Males are generally more active and have a higher average body temperature than the females. The body temperature of the lizard during hibernation is 15.0 to 30.5 °C, but in many areas, the average body temperature during hibernation is around 16-18 °C.[8]

The species is one of the few monitor lizards that tolerate relatively cold temperatures, being present as far north as south-west Kazakhstan.[9]

Reproduction

Desert monitor reproduction normally takes place between May and July. Copulation occurs in May and June, and the lizards normally lay their eggs from the latter part of June through the beginning of July.[7] The eggs are incubated at temperatures from 29 to 31 °C, and hatch after an average of 120 days. At birth, the baby lizards have a total length of around 25 cm.[10]

Feeding, hunting, and diet

Like most monitor lizards, desert monitors are

eggs, or fish, but it will also prey on other small mammals, reptiles, birds, amphibians, insects, or other invertebrates, if the opportunity presents itself.[11]

Venom

Although venom was once thought to be unique to

snakes, Gila monsters, and beaded lizards, this is no longer the case. Monitor lizard bite wounds often suffer more than just laceration damage. These aftereffects of monitor bites were once thought to be due to oral bacteria alone, but recent studies have shown that venom glands are in the lower jaws of most if not all species. [12][13]

Degree of envenomation depends on how long the animal is able to bite down and chew on its target to work venom into the wound. Envenomation appears to induce a neurotoxic effect, causing immediate paralysis in rodents (but not birds). In humans, envenomation from the species causes nausea and vomiting, dizziness, muscle pain of eventually the entire body, accelerated heartbeat, complicated breathing, and diarrhea, with symptoms appearing after as little as 20 minutes, but ending after around 24 hours, although itching of the bite area can potentially persist for 2 months at least. An unusual lack of inflammation has been noted. [14]

Along with assistance in immobilizing prey, the venom contains protease, which is known to cause blood clotting disorders, but also helps to digest food through breaking down proteins. Hyaluronidase within the venom has a similar digestive effect, increasing the production of digestive enzymes. [14]

Conservation

Desert monitors are not threatened in much of its habitat, although a great deal of the land previously inhabited by the subspecies V. g. caspius has been turned into farmland, which puts pressure on the species. Around 17,000 skins of this lizard are involved in commercial trade every year. The species is listed under Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) meaning commercial international trade is prohibited. In northern Africa, central Asia, and parts of India, the species is unprotected from hunting laws and is still hunted commercially.[15]

Captivity

These lizards rarely do well in captivity and at most live only a few years. On occasion, when their living requirements can be specifically met, they have been documented to live for more than 17 years, although they never become docile, and never become accustomed to being handled.[3] In captivity, their environments should mirror those of many ground-dwelling animals, as well as their natural desert habitat. They require lower temperatures to hibernate during the winter, along with warmer temperatures during the summer months, and their diets in captivity should be similar to their diets in the wild.[10]

Distribution

The desert monitor has a wide distribution across many countries and regions. It can be found in Jordan, Turkey, Morocco, Algeria, Tunisia, Libya, Egypt,[8][16] Israel, Syria, Lebanon, Iraq, Oman, Turkmenistan, Kazakhstan, Uzbekistan, Tajikistan, Kyrgyzstan, Western Sahara, Mauritania, Mali, Niger, Chad, Sudan, Afghanistan, Iran (including the Kavir desert), Pakistan, and northwest India. Its type locality is Dardsha, located on the coast of the Caspian Sea.[3][10]

Skull of Varanus griseus

References

  1. doi:10.2305/IUCN.UK.2021-2.RLTS.T62252A3110663.en
    . Retrieved 20 February 2022.
  2. ^ "Appendices | CITES". cites.org. Retrieved 2022-01-14.
  3. ^ a b c d e f Bennett, D. ‘’Desert Monitor, Grey Monitor’’, A Little Book of Monitor Lizards, Viper Press, 1995
  4. ^ Pianka, Eric R., Dennis King, and Ruth Allen. King. Varanoid Lizards of the World. Bloomington: Indiana UP, 2004. Print.
  5. ^ Mertens, R, "Über die Rassen des Wüstenwarans (Varanus griseus)", Senckenb. Biol. 1954, 35, 353-357
  6. ^ Ilgaz, Çetin (January 15, 2007). "The morphology and distribution of Varanus griseus (Daudin, 1803) (Reptilia: Sauria: Varanidae) in southeastern Anatolia". Russian Journal of Herpetology. 15 (3): 173–178 – via ResearchGate.
  7. ^ a b Smirina, E.M., and Tsellarius, A. Yu. Aging, Longevity, and Growth of the Desert Monitor Lizard, Russian Journal of Herpetology, Vol. 3 No. 2, pp. 130-142, 1996
  8. ^ a b Ibrahim, Adel A. A radiotelemetric study of the body temperature of Varanus griseus in Zaranik Protected Area, North Sinai, Egypt, Egyptian Journal of Biology, Vol. 2, pp.57-66, 2000
  9. S2CID 216922134
    .
  10. ^ a b c Varanus griseus (Daudin 1803) Desert Monitor" Archived 2010-06-10 at the Wayback Machine
  11. ^ Arbuckle, Kevin. Ecological Function of Venom in Varanus, with a Compilation of Dietary Records from the Literature, Biowak, Vol. 3(2), pp. 46-56, 2009
  12. PMID 31067768
    .
  13. PMID 19451641
    .
  14. ^ a b Zima, Yuliya (December 2019). "On the Toxicity of the Bite of the Caspian Gray Monitor Lizard (Varanus griseus caspius)". Biawak. 13 (2): 115–118 – via ResearchGate.
  15. ^ Gale Group. ‘’Desert Monitor’’ Archived 2012-04-25 at the Wayback Machine, 2001
  16. ISBN 978-9774249792
    .

External links
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