Varanus prasinus

Geographic Range

Varanus prasinus , commonly known as the Emerald Tree monitor, is found in tropical lowland environments ranging from the Torres Strait to islands adjacent to New Guinea (Planka and King, 2005). Of related species, Varanus prasinus has the largest distribution, since it occupies the entire island of New Guinea as well as surrounding areas (Köhler and Wicker, 2017). They are not known to migrate, but there have been unconfirmed sightings of these lizards in some other areas such as the Cape York Peninsula (Köhler and Wicker, 2017).

• Biogeographic Regions
• australian australian
  • native native

• Other Geographic Terms
• island endemic island endemic

Habitat

Varanus prasinus lives at low elevations (from sea level to 830 meters in tropical island habitats) (Planka and King, 2005). Emerald tree monitors live up to their name and are commonly found in rain forests, mangroves, and cocoa plantations (Greene, 1986) because of their arboreal lifestyle. Their habitat is heavily forested and these monitors are mostly found in the trees as that is where they find prey, escape predation, and also lay their eggs (Greene, 1986). Individuals of this species obtain much of their water from the air around them, so they are found in humid, tropical environments (Fischer, 2012).

• Habitat Regions
• tropical tropical
• terrestrial terrestrial

• Terrestrial Biomes
• forest forest

• Wetlands
• swamp swamp

• Other Habitat Features
• riparian riparian

Physical Description

Varanus prasinus is a medium sized monitor species and has some unique characteristics compared to some of the other members of the family Varanidae . The average size is approximately 800 mm in total, with an average snout-vent length of 290 mm and an average tail length of 510 mm, although the largest recorded Varanus prasinus individual was measured to be 1,140 mm in total (Pianka and King, 2005). Males do tend to be slightly larger than females. Although Emerald monitors have not been specifically studied for sexual dimorphism, a study of the related Varanus indicus found monitor lizards to have perhaps the largest difference in size of males to females because of the longer growth period male varanids exhibit (Frynta et al., 2010). One of the most important and most unique characteristic is an extremely long (typically around 1.75 times the snout-vent length) prehensile tail (Köhler and Wicker, 2017). This adaptation is due to their arboreal lifestyle. Additionally, they possess specialized feet for climbing. The bottoms of their feet are covered in larger scales which aid the monitors in climbing and gaining traction while in trees. Their long, slender fingers for grasping end in extraordinarily sharp claws that help them move, climb, and catch prey (Greene, 1986). V. prasinus are easily recognizable by their vibrant emerald coloration, although that can vary to a lighter yellow-green and even a turquoise color. Sometimes a darker dorsal coloration is seen as well (Greene, 1986). ). Varanus prasinus are born looking almost identical to their parents; the only noticeable difference being size in the young compared with adults (Frynta et al., 2010). There is no sexual dimorphism in size noticed in hatchlings (Frynta et al., 2010). Historically, all of the monitor lizards in the area of Greenland, Australia and the islands of New Guinea were described as Varanus prasinus . However, due to differences in coloration, scale shape, and some specific cranial morphologies (Quayle et al., 2015) new species of the same genus have been described. One of which is the Varanus beccarii which is similar in size and shape but is characterized by a dark black coloration. Similarly, Varanus macraei has dark scales with unique blue rings of color (Pianka and King, 2005). Varanus prasinus are born looking almost identical to their parents; the only noticeable difference being size in the young compared with adults (Frynta et al., 2010). There is no sexual dimorphism in size noticed in hatchlings (Frynta et al., 2010).

• Other Physical Features
• ectothermic ectothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger

Development

Monitor lizards ( Varanidae ) are often studied because of the rapid growth they exhibit (Frynta et al., 2010). After hatching from eggs, both male and female lizards experience extremely rapid growth up to approximately 12 months. After that initial growth; females tend to stop growing or experience a drastic reduction in growth rate while males continue to grow and develop for several additional months. This results in large size differences between the sexes (Frynta et al., 20120). Females are thought to experience this early reduced growth because of their sexual maturation and transition from using energy to grow and mature to using energy to prepare for reproduction (Frynta et al., 2010). Although there is no evidence to suggest that Varanus prasinus young experience temperature-dependent sex determination, many closely related species in the genus Varanus that do (Valenzuela, 2004).

Reproduction

There is little information about Varanus prasinus mating systems. Documentation of captive breeding attempts of a similar species Varanus beccarii showed heavy pursuit of the female by the introduced male and aggressive courtship behavior (Fischer, 2012). Males of a similar species, Varanus tristis , follow the scent of a female for about 800 yards to mate (Sweet and Pianka, 2003). Emerald tree monitors return to their solitary lifestyle after mating. There is no recorded data on whether V. prasinus is monogamous or polygamous.

The general reproductive behavior of the Varanus prasinus has been primarily studied in captive environments and there is relatively little information known. Emerald tree monitors are oviparous, laying eggs in clutches of 2 to 4 (King and Pianka, 2015). They can breed and have up to three clutches in a year (King and Pianka, 2015). A study of the closely related Varanus beccarii found that the female laid eggs the morning after copulation (Fischer, 2012). Varanus beccarii have also been observed to mate while hanging onto the side of their enclosure (King and Pianka, 2005), most likely associated with their arboreal nature. Varanus prasinus eggs typically incubate from 154 to 190 days and the young typically don't reach sexual maturity until about 2 years (King and Pianka, 2005). Overall, there has been a very low success rate seen in captive monitor lizards when it comes to breeding (Fischer, 2012).

• Key Reproductive Features
• iteroparous iteroparous
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• induced ovulation induced ovulation
• fertilization fertilization
• oviparous oviparous

Typical of reptile species, the Varanus prasinus has limited parental investment in the care of young. There is little to no record of protection or investment from the parent to the young. However, there is evidence to show that female Emerald tree monitors do provide a food source and protection for young previous to hatching. A clutch of eggs in Papa New Guinea was observed to hatch in an arboreal termite nest (Greene, 1986). This provides protection for the eggs as well as a source of food once they hatch. This is similar to behavior exhibited by Lace monitors, or Varanus varius . They have been observed to lay eggs in active termite mounds and then return at the end of the incubation period to help reopen the mound and release the hatchlings (Sweet and Pianka, 2003). This suggests a slightly higher level of parental investment, however it is unknown whether the Emerald tree monitor also returns to the termite nests.

• Parental Investment
• precocial precocial
• female parental care female parental care
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female

Lifespan/Longevity

Although relatively little is known about the lifespan of V. prasinus in the wild, a wide range of individuals have been studied and compared in captivity. It was found that individuals of the Varanus prasinus species live an average of 14.4 years in captivity (Mendyk, 2014). The oldest recorded captive Emerald monitor lizard was 25 years old at time of death (Mendyk, 2014). Interestingly, wild caught females who have successfully reproduced live, on average, more than twice as long as wild caught females who were unable to successfully reproduce (Mendyk, 2014).

Behavior

Varanus prasinus have many adaptations that allow them to spend most of their lives in trees. They are the only monitor lizard with a prehensile tail, which allows them to be highly arboreal (Köhler and Wicker, 2017). They rarely come down to the forest floor as most of their needs are met in an arboreal habitat. They catch prey in trees and are believed to leap from one tree to the next when a predator approaches (Greene, 1986). Because of this arboreal lifestyle, very little is actually known about the behaviors of Varanus prasinus in particular, although other monitor lizards have exhibited behavior that suggests high intellectual and processing abilities (Pianka and Sweet, 2003). In particular, Varanus prasinus have exhibited interesting behavior in relation to feeding habits. They have been observed to hit their prey against other objects to kill them before lacerating and devouring them (Greene, 1986). As far as is known, Varanus prasinus are solitary and mainly diurnal (Pianka and King, 2005).

• Key Behaviors
• arboreal arboreal
• scansorial
• diurnal diurnal
• motile motile
• solitary solitary

Communication and Perception

Little is known about the communication and perception of Varanus prasinus , however monitor lizards are known to be excellent trackers based on chemical cues (Sweet and Pianka, 2003). Monitor lizards interpret these chemicals using their vomeronasal organs, which are two sensory receptors on the roof of their mouth. In order to do this, they sense the chemicals with their tongue which then transfers to the receptors (Sweet and Pianka, 2003). Monitor lizards have been known to use chemical cues to search out prey and mates over long distances (Sweet and Pianka, 2003).

• Communication Channels
• chemical chemical

• Perception Channels
• chemical chemical

Food Habits

The largest part of the diet consists of small invertebrates (Greene, 1986), including katydids ( Tettigoniidae ), which are both the most abundant prey item (Greene, 1986). Grasshoppers ( Caelifera ) were also seen at higher rates in the contents of the studied stomachs (Greene, 1986). Other prey includes centipedes ( Chilopoda ), spiders ( Araneae ), and a few coleopteran larvae (Greene, 1986). Although primarily insectivores, Emerald tree monitors also eat small arboreal or semi-arboreal vertebrate mammals, such as Melomys moncktoni (King and Pianka, 2005). TEmerald tree monitors use their long claws for more than just climbing. Observations of feeding behavior in captive V. prasinus revealed the effective technique these lizards exhibited to kill and eat rodents. They rake and disembowel their prey with their extraordinarily sharp claws after first biting them around the nape of their neck and slamming them against the nearest surface (Greene, 1986). Although Emerald tree monitors requires a relatively low prey to predator mass ratio (Greene, 1986), they have adaptations that make them extremely effective hunters. Emerald tree monitors consume relatively large prey in comparison to other monitor lizards (Quayle et al., 2015). Feeding on larger prey allows them to conserve energy by requiring less frequent feedings. The specific morphology of their skull contributes to their ability to feed on larger prey. They have an elongated crania and mandibles; which are potential adaptations to help dispel strain on the organism during predation and feeding (Quayle et al., 2015).

• Primary Diet
• carnivore carnivore
  • eats terrestrial vertebrates
  • insectivore insectivore

• Animal Foods
• mammals
• insects
• terrestrial non-insect arthropods

Predation

Varanus prasinus are considered to be top predators in their area so no species have been confirmed as predators of this lizard. However; there is evidence that larger, placental carnivores may pose a threat (Koch and Boehme, 2014). Young are vulnerable before they hatch, which is why it is thought that females lay eggs in arboreal termite nests for protection (Greene et al., 1986).

Ecosystem Roles

Varanus prasinus , like other monitor lizards, play a predatorial role in their ecosystem (Koch et al. 2012). They prey on many insects and small vertebrates (Greene, 1986), which may help control pests within their area. Additionally, female Emerald Tree Monitors may lay clutches in arboreal termite nests, where the hatchlings then feed on termites, creating a parasitic relationship with the termites (Greene, 1986).

Economic Importance for Humans: Positive

Humans mainly benefit from this species because they are widely traded internationally both as pets and for zoos. They are one of, if not the most, popular monitor lizard species in the international pet trade, with over 4,000 individuals exported from 1977-2010 (Koch et al. 2012). Additionally, Varanus prasinus pelts have been used to make leather products to be sold in China (Koch et al., 2012).

• Positive Impacts
• pet trade pet trade
• body parts are source of valuable material
• research and education

Economic Importance for Humans: Negative

There are no known adverse effects of Varanus prasinus on humans.

Conservation Status

Since Varanus prasinus has such a wide geographic range compared to other Varanoid lizards, it is considered under Least Concern with the IUCN red list (IUCN, 2016). They are not listed under the United States Endangered Species Act list, although they are federally protected in Indonesia. This protects first generation (wild caught) Varanus prasinus individuals from being exported (Koch et al., 2012). However, laws in Indonesia are not thoroughly enforced, leading to many wild-caught species being sold into the pet trade despite the protection (Koch et al., 2012). They are listed under appendix II with CITES because of the prolific pet trade of Emerald monitor lizards and the need to closely monitor that trade.

Additional Links

Encyclopedia of Life

Contributors

Jillian Krynock (author), Colorado State University, Peter Leipzig (editor), Colorado State University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

Böhme, W., E. Arida. 2012. Pressing Problems: Distribution, Threats, and Conservation Status of the Monitor Lizards (Varanidae: Varanus spp.) of Southeast Asia and the Indo-Australian Archipelago. Herpetological Conservation & Biology , Vol. 8 Issue 3: 1-66.

D, F. 2010. "Ontogeny of sexual size dimorphism in monitor lizards: males grow for a longer period, but not at a faster rate." (On-line). National Center for Biotechnology Information. Accessed February 18, 2018 at https://www.ncbi.nlm.nih.gov/pubmed/21110717 .

Koch, A., W. Boehme. 2014. A review of the subgenus Euprepiosaurus of Varanus (Squamata: Varanidae): morphological and molecular phylogeny, distribution and zoogeography, with an identification key for the members of the V. indicus and the V. prasinus species groups. ZOOTAXA , Vol. 1472 Issue 1: 1-28.

Köhler, J., R. Wicker. 2017. New findings on the relationships among New Guinea tree monitor lizards of the Varanus prasinus (SchleGel, 1839) complex. Herpetozoa , Vol. 30 Issue 1: 9-20.

Quayle, M., T. Jessop, S. Wroe. 2015. The Relationship between Cranial Structure, Biomechanical Performance and Ecological Diversity in Varanoid Lizards. PLoS ONE , Vol. 10 Issue 6: 1-27. Accessed February 10, 2018 at http://eds.a.ebscohost.com.ezproxy2.library.colostate.edu/ehost/detail/detail?vid=0&sid=ca265743-d089-4e7b-86dc-43936cba7f47%40sessionmgr4010&bdata=JkF1dGhUeXBlPWNvb2tpZSxpcCx1cmwsY3BpZCZjdXN0aWQ9czQ2NDA3OTImc2l0ZT1laG9zdC1saXZl#AN=103568574&db=aph .

2005. Varanoid Lizards of the World . Bloomington, Indiana: Indiana University Press.

1986. Diet and Arboreality in the Emerald Monitor, Varanus prasinus, with Comments on the Study of Adaptation. Fieldiana , 31: 7-28. Accessed February 26, 2018 at https://ia800204.us.archive.org/35/items/dietarborealityi31gree/dietarborealityi31gree.pdf .

2014. Life expectancy and longevity of varanid lizards (Reptilia:Squamata:Varanidae) in North American zoos. Zoo Biology , Vol. 34 Issue 2: 139-152.

International Varanid Interest Group. 2012. Notes on the Husbandry and Breeding of the Black Tree Monitor Varanus (Euprepiosaurus) beccarii (Doria, 1874). Biawak , vol. 6 Issue 2: 79-87.

2004. Temperature-dependent sex determination. Pp. 987 in Temperature-dependent Sex Determination in Vertebrates , Vol. Vol. 70 Issue 3. Journal of Fish Biology: Wiley Blackwell. Accessed April 24, 2018 at http://www.public.iastate.edu/~nvalenzu/Valenzuela_Publications/Valenzuela2004_ReptilianTSD_Chapt09.pdf .

2003. The Lizard Kings. Natural History , Vol. 112 Issue 9: 40-45.