Post by Ceratodromeus on Jun 25, 2016 2:05:53 GMT 5
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Reptilia
Order: Squamata
Suborder: Lacertilia
Family: Varanidae
Genus: Varanus
Subgenus: (Varanus)
Species: V.panoptes
Subspecies{1}
Varanus panoptes horni - from New guinea
Varanus panoptes panoptes - from Northern Australia
Varanus panoptes rubidus - from Western Australia
A mitochondrial DNA analysis published in 2006 concluded that the New Guinea argus monitors(V.p.horni) are more closely related to animals from Northern Australia(V.panoptes) than to the Western subspecies(V.p.rubidus){2}. In the past, taxonomy between the sand goanna(Varanus gouldii) was greatly confused, but has since been corrected.
Description
The argus(or yellow spotted) monitor is one of the largest species of varanid occuring in Australia, only behind the perentie and lace monitor. These larger representatives of Australian varanids all occur in the Varanus subgenus, whilst the dwarf species occur in the Odatria subgenus. The argus monitor is a heavily built species with a dark brown body coloration typically, though the rubidus subspecies is more of a red coloration that enables it to blend in with the red sands of its habitat. The markings of the species are a light yellow, and the rows of spots that gave the species its alternative common name can be found running down the entire dorsal section of the body. The underside of the animal is a yellow coloration as well, with darker coloration speckled intermittently.
Sexual dimorphism is present, with the males growing to larger sizes overall; in Varanoid lizards of the world the highest recorded mass given for adult males is ~7kg, whilst the authors remark females "typically 1.5kg, rarely above 2kg"{1}. The largest recorded mail had a snout-ventral measurement of 740mm, whilst the largest recorded female had a snout-ventral measurement of 570mm; this large female weighed 2.6kg{1,4}. In a paper overlooking the morphology of western australian varanids, the snout ventral length mean for adult V.p.rubidus (both male and female, this study makes no distinction between sexes) was 350mm(13.7in) with a tail length of 564mm(22.2in) from a sample of 17 animals, whilst for adult V.p.panoptes the mean snout ventral length for adult animals was 252mm(9.9in), with a tail lengthh of 251.7mm(9.9in) from a sample of 12 animals{5}.
Distribution
Varanus panoptes is a fairly wide spread species of monitor lizard, with V.p.horni being found in New Guinea to the western race V.p.rubidus being found in the arid deserts of western Australia. This species also occupies a wide variety of habitats. not only is this evident because of their widespread distribution, but it can also be found in the subspecies. Along the coast of Fog bay, Australia, a Telemetry study was conducted on the habitat preferences of Varanus panoptes panoptes. It was observed that of the sexteen monitored animals, beaches, dunes, salt flats and marshes were heavily utilized; the beaches were utilized so the lizards could exploit nests of sea turtles{4}. Another common name for V.panoptes is the floodplain goanna, as this is another type of habitat this species utilizes frequently, as are savanna woodlands and of course urban habitats{1}.
They are mostly a diurnal, terrestrial species in nature. However they, like other members of the Varanus genus, show a flexibility allowing them to utilize trees and even shallow waters while foraging for food. They are active most of the year, but their period of activity is highly pronounced in the dry season when they make use of congregations of prey{1}. Observations on wild animals appear to indicate that they go into aestivation in June{8}.
Dietary habits
The argus monitor is a generalist predator, grabbing and swallowin any animal it thinks it can overpower. Scat analysis of coastal V.p.panoptes show that they generally feed on small mammals(Rattus rattus, Hydromys chryogaster, Melomys burtoni, Macropus agilis), small lizards(Carlia spp, Ctenotus spp, pygopodidae), snakes(Boiga irregularis), eggs & hatchlings of sea turtles(Natator depressus), crustaceans, and insects{4}. They have also been documented taking to the water and pulling out freshwater mussels(Velesunio sp.){6}.
It is a known predator of snakes; in addition to the apparent predation of a brown tree snake, the argus monitor has also been documented feeding on keelback(Tropidinophis mairii) file snakes(Acrochordus sp.), water pythons(Liasis fuscus), and common tree snakes(Dendreaphis punctulata); in one particularly fascinating instance a young yellow spotted monitor attacked and killed a central netted dragon(Ctenophorus reticulatus), using a tree stump to help get the equally large lizard down its throat.
V.p.rubidus has also been recorded feeding on the carcasses of kangaroos{7}.
During the time period of 2005-2006, There was a high mortality rate noticed in telemetry studies conducted on the argus monitor, a species with a naturally very low mortaility rate. Researchers tied this to the ingestion(or attempted predation) of the invasive cane toad. One particular instance to further this theory was the remains of a large, 5kg individual with a cane toad found in close proximity to the head, bearing teeth marks{3}. However in the past year steps have been taken to train young argus monitors to avoid the deadly toad, in hopes of avoiding population declines.
Reproduction
There is little in the way of literature documenting the reproduction habits of the argus monitor, in Varanoid lizards of the world the authors note copulation(and enlarged testes in the males) were observed in July{1}. However in a paper published in 2014, observations on wild argus monitors using communal burrowing systems suggest that copulation and egg laying occur earlier in the year; apparent gravid females were observed in April, as were clutches of eggs, which numbered 8-10{8}.
Parthenogenesis is widely published for members of Varanus, and V.panoptes is no exception. Two females, both in captive situations with no access to males after they were aquired, laid several clutches of eggs though most of them were infertile or did not come to full term; there is one notable exception to this though, that hatched out in 2011{9}. Another instance occurred some years earlier in 1999, when a female that had not ever been housed with a male in a 4-5 year period, produced a male offspring with a DNA fingerprinting almost identical to the maternal animal{10}.
Mortality
Adult Argus monitors do not have very many documented predators, there is one widely publicized photo of a perentie(Varanus giganteus) taking an adult argus monitor, and and another of a black headed python(Aspidites melanocephalus) eating a large adult;cannibalism has also been documented for the species{11}. Ingestion of cane toads also represents a thread to populations of toad naive Varanus panoptes. Potential predators include feral/domestic dogs, dingoes, large raptorial birds. The young are susceptible to a large array of small carnivores.
References
{1} Pianka, Eric R., Dennis King, and Ruth Allen King. Varanoid lizards of the world. Indiana University Press, 2004.
{2} Fitch, Alison Jane, Amanda E. Goodman, and S. C. Donnellan. "A molecular phylogeny of the Australian monitor lizards (Squamata: Varanidae) inferred from mitochondrial DNA sequences." Australian Journal of Zoology 54.4 (2006): 253-269.
{3} Ujvari, Beata, and Thomas Madsen. "Increased mortality of naive varanid lizards after the invasion of non-native can toads (bufo marinus)." Herpetological Conservation and Biology 4.2 (2009): 248-251.
{4} Blamires, Sean J. "Habitat preferences of coastal goannas (Varanus panoptes): are they exploiters of sea turtle nests at Fog Bay, Australia?." Copeia 2004.2 (2004): 370-377.
{5} Thompson, Graham G., and Philip C. Withers. "Comparative morphology of western Australian varanid lizards (Squamata: Varanidae)." Journal of Morphology 233.2 (1997): 127-152.
{6} Shannon, R., and ROBERT W. Mendyk. "Aquatic foraging behavior and freshwater mussel (Velesunio sp.) predation by Varanus panoptes panoptes in Central-Western Queensland." Biawak 3.3 (2009): 85-87.
{7} Bennett, D. A. N. I. E. L. "A note on Varanus panoptes rubidus (Storr 1980) in Wanjarri, Western Australia." British Herpetological Society Bulletin 39 (1992): 28-30.
{8} Doody, J. Sean, et al. "Cryptic and complex nesting in the yellow-spotted monitor, Varanus panoptes." Journal of Herpetology 48.3 (2014): 363-370.
{9} WIechmann, Ralf. "Observations on parthenogenesis in monitor lizards." Biawak 6.1 (2012): 11-21.
{10}Lenk, P., et al. "A parthenogenetic Varanus." Amphibia-Reptilia 26.4 (2005): 507-514.
{11} DIET, UROSTROPHUS VAUTIERI Brazilian Steppe Iguana. "TROPIDURUS HYGOMI. PREDATION. Tropidurus hygomi is one." Herpetological Review 44 (2013): 3.
