Komodo dragon

Komodo dragon
Conservation status
Vulnerable  (IUCN 2.3)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Squamata
Suborder:	Sauria
Family:	Varanidae
Genus:	Varanus
Species:	V. komodoensis
Binomial name
Varanus komodoensis Ouwens, 1912

The Komodo Dragon, Komodo Monitor, or simply Komodo (Varanus komodoensis) is the largest living species of lizard, growing to an average length of 2-3 metres (approximately 6.5-10 feet). It is a member of the monitor lizard family, Varanidae, and only inhabits the islands of Komodo, Rinca (or Rintja), Padar, Flores, Gili Motang, Owadi and Samiin in central Indonesia.

Dragons were first documented by Europeans in 1910. Widespread notoriety came after 1912, in which Peter Ouwens, the director of the Zoological Museum at Bogor, Java, published a paper on the topic. In 1980, Komodo National Park was founded to help protect its limited population.

Physical description

In the wild, large adults tend to weigh around 70 kg (154 lbs). Captive specimens often weigh more. The largest verified wild specimen was 3.13 metres (10 feet 3 inches) long and weighed 166 kg (365 lbs), including undigested food. Komodo dragons have a tail that is as long as the body, as well as 52 serrated teeth that may be 1 inch (2.5 centimeters) in length. They have red, blood-like saliva, as they bite their own gums when they eat, thus creating an ideal culture for the virulent bacteria that live in their mouths. It also has a long, yellow, snake-like tongue. Males are larger than females, with skin color from dark gray to brick red. Females are more olive green, and have patches of yellow at the throat. The young are much more colorful by comparison, with yellow, green and white banding on a dark background.

Ecology and behavior

Komodo dragons are found exclusively in Indonesia, on the island of Rinca and on several islands of the Lesser Sunda archipelago. They prefer hot and dry places, and typically live in dry open grassland, savanna and tropical forest at low elevation. As poikilotherms, they are most active in the day, although they do exhibit some nocturnal activity. Komodo dragons are largely solitary, coming together only to breed and eat. They are capable of running rapidly in brief sprints, are excellent swimmers, and when young they climb trees proficiently through use of their strong claws. As they grow older, their claws are used primarily as weapons, as their great mass makes climbing impractical for adults.

For shelter, dragons dig holes that can measure from 3-6 feet wide (0.9-1.8 metres wide). Their sense of hearing is not particularly acute, and their visual discrimination (most especially of stationary objects) is poor. They use their tongue to detect taste and smell stimuli (as with many reptiles), which aids navigation in the dark. These lizards are apex predators, dominating the ecosystems in which they live.

Diet and feeding

A Komoodo dragon from Disney's Animal Kingdom

Komodo dragons are carnivorous. Although they eat much carrion, studies show that they also hunt live prey with a stealthy approach followed by a sudden short charge, during which they can reach up to 20 km/h (over 12 mph). Komodo dragons have not traditionally been considered venomous, but it has recently been suggested that they may produce a weak venom (Fry et al., 2006). In addition to the possible venom, dragons also possesses virulent bacteria in their saliva, of which more than 15 strains have been isolated. These bacteria cause septicemia in their victim; if an initial bite does not kill the prey animal and it escapes, it will commonly succumb within a week to the resulting infection. The lizard is able to locate its prey using its keen sense of smell, which can locate a dead or dying animal from a range of up to four miles. The Komodo dragon appears to be immune to its resident bacteria.

Feeding follows a social hierarchy - the dominant male eats first, with other dragons eating only when he is finished. Females however do not follow any set hierarchy and eat together. Komodo dragons eat by tearing large chunks of flesh while holding their food down with their forelegs then swallowing it whole. Their loosely articulated jaws and expandable stomachs allow them to eat up to 80 percent of their body weight in one meal, akin to a 200 lb man (90.7 kg) eating 160 lbs (72.6 kg) of food during one sitting.

The Komodo dragon diet is wide-ranging, and includes invertebrates, other reptiles (including smaller dragons), birds, bird eggs, small mammals, monkeys, wild pigs, goats, deer, horses and water buffalos. Occasionally they have been known to consume humans and human corpses. Over a dozen human deaths have been attributed to dragon bites in the last century, although there are reports of survivors of the resulting septicemia.

Conservation status

Komodo Dragons photographed on Rinca (wild but managed)

The Komodo dragon is a vulnerable species and is found on the IUCN Red List. There are approximately 6,000 living Komodo dragons. Their populations are restricted to the islands of Rinca (1,300) and Gili Motang (100) and several of the Lesser Sunda Islands, including Komodo (1,700) and Flores (perhaps 2,000). However, there are concerns that there may presently be only 350 breeding females.

Reproduction

Mating occurs between May and August, with the eggs laid in September. During this period, males fight over females and territory by grappling with one another upon their hind legs, with the loser eventually being pinned to the ground. During copulation, the male often scratches the female's back, sometimes even to the point of drawing blood. The female will lay her eggs in the ground or in tree hollows (thereby lending them a certain degree of protection). Clutches contain an average of 20 eggs which have an incubation period of 7 months. The hatchlings are born more or less defenseless, and many do not survive. Young Komodo dragons spend much of their first few years in trees, where they are relatively safe from predators. Dragons take about three to five years to mature, and may live for up to 30 years.

There are recorded examples of parthenogenesis (reproduction without the contribution of a male), a phenomenon also known to occur in some other reptile species.

Parthenogenesis

On December 20, 2006, it was reported that Flora, a captive Komodo dragon living in the Chester Zoo in England, is the second Komodo dragon to have fertilised her eggs herself, via the process of parthenogenesis. Scientists at Liverpool University in northern England verified that Flora had had no male help by means of genetic tests on three eggs that collapsed after being moved to an incubator. (Flora had never had physical contact with a male dragon.) Sungai, a Komodo dragon at London Zoo, laid a clutch of eggs in early 2006 after being separated from males for more than two years. Scientists initially assumed that she had been able to store sperm from her earlier encounter with a male (an adaptation known as superfecundation), but after being apprised of the condition of Flora's eggs, testing showed that Sungai's eggs were also produced without outside fertilisation.

Due to a ZW chromosomal sex-determination system (as opposed to a mammalian XY system), all progeny of Komodo dragon parthenogenesis are male. When a female Komodo dragon (with ZW sex chromosomes) reproduces in this manner, she provides her progeny with only one chromosome from each of her pairs of chromosomes, including only one of her two sex chromosomes. This single set of chromosomes is duplicated in the egg, which develops parthenogenetically. Eggs receiving a Z chromosome become ZZ (male) while those receiving a W chromosome become WW and fail to develop.

It has been hypothesised that this reproductive adaptation allows a single female to enter an isolated ecologic niche (such as an island) and by parthenogenesis produce male offspring, thereby establishing a sexually reproducing population (via reproduction with her offspring that can result in both male and female young).

Komodo dragons at Toronto Zoo

In captivity

Komodo dragons have long been great zoo attractions, where their size and reputation make them popular exhibits. One particularily interesting fact that has been observed in captive dragons is that many individuals display relatively tame behavior within a short period of time in captivity. Many incidents are reported where keepers have brought the animals out of their enclosures to interact with zoo visitors, including young children, to no harmful effect (Procter, 1928), (Lederer 1931). Dragons are also capable of recognizing individual humans. Ruston Hartdegen of the Dallas Zoo reported that their monitors reacted differently when presented with their regular keeper, a more or less familiar keeper, or a completely unfamiliar keeper (Murphy and Walsh, 2006).

However, even seemingly docile dragons may be unpredictably aggressive. In June 2001, a dragon seriously injured Phil Bronstein - executive editor of the San Francisco Chronicle and then-husband of film actor Sharon Stone - when Bronstein entered its enclosure at the Los Angeles Zoo.

Various zoos keep Komodo dragons in captivity, including:

UK

• Chester Zoo
• London Zoo
• Colchester Zoo

USA

• Disney's Animal Kingdom, Lake Buena Vista, Florida
• Busch Gardens, Tampa, Florida
• Woodland Park Zoo, Seattle, Washington
• Honolulu Zoo, Hawaii
• San Diego Zoo, San Diego, California
• Fort Worth Zoo, Fort Worth, Texas
• Miami Metrozoo, Miami, Florida
• Smithsonian National Zoological Park, Washington D.C.
• Sedgwick County Zoo, Wichita, Kansas
• Saint Louis Zoo, Saint Louis, Missouri
• Houston Zoo, Houston, Texas
• Denver Zoo, Denver, Colorado
• Cincinnati Zoo, Cincinnati, Ohio
• Zoo Atlanta, Atlanta, Georgia
• John Ball Zoological Garden, Grand Rapids, Michigan
• Memphis Zoo (Memphis, Tennessee)

Australia

• Taronga Zoo
• Australia Zoo

Netherlands

• Diergaarde Blijdorp, Rotterdam

Indonesia

• Gembira Loka Zoo, Yogyakarta

Japan

• Ueno Zoo, Tokyo

Media

Videos of Varanus komodoensis at Disney's Animal Kingdom Template:Multi-video start Template:Multi-video item Template:Multi-video item Template:Multi-video item Template:Multi-video end

See also

• Island gigantism
• Megalania prisca (huge extinct Varanid lizard)
• European dragon (the mythical dragon)
• Monitor lizard
• Parthenogenesis Virgin Birth recorded in Komodo dragon

Works cited

• Fry, B. G., Vidal, N., and Norman, J. A., 2006. Early evolution of the venom system in lizards and snakes. Nature 439: 584-588.
• King, Dennis & Green, Brian. 1999. Goannas: The Biology of Varanid Lizards. University of New South Wales Press. ISBN 0-86840-456-X
• Lederer, G. 1931. Erkennen wechselwarme Tiere ihren Pfleger? Wochenschr. Aquar.-Terrarienkunde 28: 636-638.
• Murphy, J., and Walsh, T., 2006. Dragons and Humans. Herpetological Review, 37: 269-275.
• Procter, J. B. 1928. On a living Komodo dragon Varanus komodensis Ouwens, exhibited at the Scientific Meeting, October 23rd, 1928. Proc. Zool. Soc. London 1928:1017-1019.

External links

• Woodland Park Zoo
• Komodo Dragon Central
• Discovery of venom in monitor lizards
• CNN NEWS: Virgin Komodo dragon is expecting
• National Geographic NEWS: Virgin Birth Expected at Christmas -- By Komodo Dragon
• BBC NEWS: 'Virgin births' for giant lizards (Komodo dragon)

Images

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  Two komodo dragons
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  Komodo dragon at Taronga Zoo