Animal's Blog

Komodo dragon

The Komodo dragon (Varanus komodoensis) is a venomous species of lizard that inhabits the islands of Komodo, Rinca, Flores, and Gili Motang in Indonesia. A member of the monitor lizard family (Varanidae), it is the largest living species of lizard, growing to an average length of 2 to 3 metres (6.6 to 9.8 ft) and weighing around 70 kilograms (150 lb). Their unusual size is attributed to island gigantism, since there are no other carnivorous animals to fill the niche on the islands where they live; their large size is also explained by the Komodo dragon's low metabolic rate. As a result of their size, these lizards dominate the ecosystems in which they live. Although Komodo dragons eat mostly carrion, they will also hunt and ambush prey including invertebrates, birds, and mammals.

Mating begins between May and August, and the eggs are laid in September. About twenty eggs are deposited in abandoned megapode nests and incubated for seven to eight months, hatching in April, when insects are most plentiful. Young Komodo dragons are vulnerable and therefore dwell in trees, safe from predators and cannibalistic adults. They take around three to five years to mature, and may live as long as fifty years. They are among the rare vertebrates capable of parthenogenesis, in which females may lay viable eggs if males are absent.

Komodo dragons were first recorded by Western scientists in 1910. Their large size and fearsome reputation make them popular zoo exhibits. In the wild their range has contracted due to human activities and they are listed as vulnerable by the IUCN. They are protected under Indonesian law, and a national park, Komodo National Park, was founded to aid protection efforts.

Etymology

The Komodo dragon is also known as the Komodo monitor or the Komodo Island monitor in scientific literature, although this is not very common. To the natives of Komodo Island, it is referred to as ora, buaya darat (land crocodile) or biawak raksasa (giant monitor).
Adult Komodo Dragon

Evolutionary history

The evolutionary development of the Komodo dragon started with the Varanus genus, which originated in Asia about 40 million years ago and migrated to Australia. Around 15 million years ago, a collision between Australia and Southeast Asia allowed the varanids to move into what is now the Indonesian archipelago, extending their range as far east as the island of Timor. The Komodo dragon was believed to have differentiated from its Australian ancestors 4 million years ago. However, recent fossil evidence from Queensland suggests that the Komodo dragon evolved in Australia before spreading to Indonesia. Dramatic lowering of sea level during the last glacial period uncovered extensive stretches of continental shelf that the Komodo dragon colonized, becoming isolated in their present island range as sea levels rose afterwards.

Description
Closeup of a Komodo dragon's skin

In the wild, an adult Komodo dragon usually weighs around 70 kilograms (150 lb),although captive specimens often weigh more. The largest verified wild specimen was 3.13 metres (10.3 ft) long and weighed 166 kilograms (370 lb), including undigested food. The Komodo dragon has a tail as long as its body, as well as about 60 frequently replaced serrated teeth that can measure up to 2.5 centimeters (1 inch) in length. Its saliva is frequently blood-tinged, because its teeth are almost completely covered by gingival tissue that is naturally lacerated during feeding. This creates an ideal culture for the virulent bacteria that live in its mouth. It also has a long, yellow, deeply forked tongue.

Senses

The Komodo dragon does not have a particularly acute sense of hearing, despite its visible earholes, and is only able to hear sounds between 400 and 2000 hertz. It is able to see as far away as 300 metres (980 ft), but because its retinas only contain cones, it is thought to have poor night vision. The Komodo dragon is able to see in colour, but has poor visual discrimination of stationary objects.
Komodo dragons video.wmv.OGG
Play video
A Komodo dragon on Komodo Island uses his tongue to sample the air.

The Komodo dragon uses its tongue to detect, taste, and smell stimuli, as with many other reptiles, with the vomeronasal sense using a Jacobson's organ, a sense that aids navigation in the dark. With the help of a favorable wind and its habit of swinging its head from side to side as it walks, Komodo dragons may be able to detect carrion from 4–9.5 kilometres (2.5–6 mi) away. The dragon's nostrils are not of great use for smelling, as the animal does not have a diaphragm. It only has a few taste buds in the back of its throat. Its scales, some of which are reinforced with bone, have sensory plaques connected to nerves that facilitate its sense of touch. The scales around the ears, lips, chin, and soles of the feet may have three or more sensory plaques.

The Komodo dragon was formerly thought to be deaf when a study reported no agitation in wild Komodo dragons in response to whispers, raised voices, or shouts. This was disputed when London Zoological Garden employee Joan Proctor trained a captive specimen to come out to feed at the sound of her voice, even when she could not be seen.

Ecology


The Komodo dragon prefers hot and dry places, and typically lives in dry open grassland, savanna, and tropical forest at low elevations. As an ectotherm, it is most active in the day, although it exhibits some nocturnal activity. Komodo dragons are largely solitary, coming together only to breed and eat. They are capable of running rapidly in brief sprints up to 20 kilometres per hour (12.4 mph), diving up to 4.5 metres (15 ft), and climbing trees proficiently when young through use of their strong claws. To catch prey that is out of reach, the Komodo dragon may stand on its hind legs and use its tail as a support. As the Komodo dragon matures, its claws are used primarily as weapons, as its great size makes climbing impractical.

For shelter, the Komodo dragon digs holes that can measure from 1–3 metres (3–10 ft) wide with its powerful forelimbs and claws. Because of its large size and habit of sleeping in these burrows, it is able to conserve body heat throughout the night and minimize its basking period the morning after. The Komodo dragon typically hunts in the afternoon, but stays in the shade during the hottest part of the day. These special resting places, usually located on ridges with a cool sea breeze, are marked with droppings and are cleared of vegetation. They also serve as a strategic location from which to ambush deer.

Diet

Komodo dragons are carnivores. Although they eat mostly carrion, they will also ambush live prey with a stealthy approach, a technique that has allowed the Komodo dragon to capture even the most lethal prey, such as the King Cobra. When suitable prey arrives near a dragon's ambush site, it will suddenly charge at the animal and go for the underside or the throat. It 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 9.5 kilometers (6 miles). Komodo dragons have also been observed knocking down large pigs and deer with their strong tail.

Komodo dragons eat by tearing large chunks of flesh and swallowing them whole while holding the carcass down with their forelegs. For smaller prey up to the size of a goat, their loosely articulated jaws, flexible skull, and expandable stomach allow it to swallow its prey whole. The vegetable contents of the stomach and intestines are typically avoided. Copious amounts of red saliva that the Komodo dragons produce help to lubricate the food, but swallowing is still a long process (15–20 minutes to swallow a goat). Komodo dragons may attempt to speed up the process by ramming the carcass against a tree to force it down its throat, sometimes ramming so forcefully that the tree is knocked down. To prevent itself from suffocating while swallowing, it breathes using a small tube under the tongue that connects to the lungs. After eating up to 80 percent of its body weight in one meal, it drags itself to a sunny location to speed digestion, as the food could rot and poison the dragon if left undigested for too long. Because of their slow metabolism, large dragons can survive on as little as 12 meals a year. After digestion, the Komodo dragon regurgitates a mass of horns, hair, and teeth known as the gastric pellet, which is covered in malodorous mucus. After regurgitating the gastric pellet, it rubs its face in the dirt or on bushes to get rid of the mucus, suggesting that it, like humans, does not relish the scent of its own excretions.
A young Komodo dragon photographed on Rinca feeding on a water buffalo carcass

The largest animals generally eat first, while the smaller ones follow a hierarchy. The largest male asserts his dominance and the smaller males show their submission by use of body language and rumbling hisses. Dragons of equal size may resort to “wrestling”. Losers usually retreat though they have been known to be killed and eaten by victors.
Komodo excrement is mostly white as the stomach is not capable of digesting the calcium found in the bones of the animals they eat.

The Komodo dragon's diet is wide-ranging, and includes invertebrates, other reptiles (including smaller Komodo dragons), birds, bird eggs, small mammals, monkeys, wild boar, goats, deer, horses, and water buffalo. Young Komodos will eat insects, eggs, geckos, and small mammals. Occasionally they consume humans and human corpses, digging up bodies from shallow graves. This habit of raiding graves caused the villagers of Komodo to move their graves from sandy to clay ground and pile rocks on top of them to deter the lizards. The Komodo dragon may have evolved to feed on the extinct dwarf elephant Stegodon that once lived on Flores, according to evolutionary biologist Jared Diamond. The Komodo dragon has also been observed intentionally startling a pregnant deer in the hopes of a miscarriage whose remains they can eat, a technique that has also been observed in large African predators.

Because the Komodo dragon does not have a diaphragm, it cannot suck water when drinking, nor can it lap water with its tongue. Instead, it drinks by taking a mouthful of water, lifting its head, and letting the water run down its throat. When it comes to hunting the lizard is very picky, but will eat any type of carrion.

Venom

Auffenberg described the Komodo dragon as having septic pathogens in its saliva, specifically the bacteria: Escherichia coli, Staphylococcus sp., Providencia sp., Proteus morgani and P. mirabilis. He noted that while these pathogens can be found in the mouths of wild Komodo dragons, they disappear from the mouths of captive animals, due to a cleaner diet. This was verified by taking mucous samples from the external gum surface of the upper jaw of two freshly captured individuals. Saliva samples were analyzed by researchers at the University of Texas who found 57 different strains of bacteria growing in the mouths of three wild Komodo dragons including Pasteurella multocida. The rapid growth of this bacteria was noted by Friedking: "Normally it takes about three days for a sample of P. multocida to cover a petri dish; ours took eight hours. We were very taken aback by how virulent these strains were". This study supported the observation that wounds inflicted by the Komodo dragon are often associated with sepsis and subsequent infections in prey animals.

In late 2005, researchers at the University of Melbourne speculated that the perentie (Varanus giganteus), other species of monitor, and agamids may be somewhat venomous. The team believes that the immediate effects of bites from these lizards were caused by mild envenomation. Bites on human digits by a lace monitor (V. varius), a Komodo dragon, and a spotted tree monitor (V. scalaris) all produced similar effects: rapid swelling, localized disruption of blood clotting, and shooting pain up to the elbow, with some symptoms lasting for several hours.

In 2009, the same researchers published further evidence demonstrating that Komodo dragons possess a venomous bite. MRI scans of a preserved skull showed the presence of two venom glands in the lower jaw. They extracted one of these glands from the head of a terminally ill specimen in the Singapore Zoological Gardens, and found that it secreted a venom containing several different toxic proteins. The known functions of these proteins include inhibition of blood clotting, lowering of blood pressure, muscle paralysis, and the induction of hypothermia, leading to shock and loss of consciousness in envenomated prey. As a result of the discovery, the previous theory that bacteria were responsible for the deaths of komodo victims was disputed.

Kurt Schwenk, an evolutionary biologist at the University of Connecticut finds the discovery of these glands intriguing, but considers most of the evidence for venom in the study to be "meaningless, irrelevant, incorrect or falsely misleading". Even if the lizards have venomlike proteins in their mouths, Schwenk argues, they may be using them for a different function, and he doubts that venom is necessary to explain the effect of a Komodo dragon bite, arguing that shock and blood loss are the primary factors.

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. These males may vomit or defecate when preparing for the fight. The winner of the fight will then flick his long tongue at the female to gain information about her receptivity. Females are antagonistic and resist with their claws and teeth during the early phases of courtship. Therefore, the male must fully restrain the female during coitus to avoid being hurt. Other courtship displays include males rubbing their chins on the female, hard scratches to the back, and licking. Copulation occurs when the male inserts one of his hemipenes into the female's cloaca. Komodo dragons may be monogamous and form "pair bonds", a rare behavior for lizards.
A Komodo dragon with its long tail and claws fully visible

The female lays her eggs in burrows cut into the side of a hill or in the abandoned nesting mounds of the Orange-footed Scrubfowl (a moundbuilder or megapode), with a preference for the abandoned mounds. Clutches contain an average of 20 eggs which have an incubation period of 7–8 months. The female lies on the eggs to incubate and protect them until they hatch around April, at the end of the rainy season when insects are plentiful. Hatching is an exhausting effort for the pups, who break out of their eggshells with an egg tooth that falls off soon after. After cutting out the hatchlings may lie in their eggshells for hours before starting to dig out of the nest. They are born quite defenseless, and many are eaten by predators.

Young Komodo dragons spend much of their first few years in trees, where they are relatively safe from predators, including cannibalistic adults, who make juvenile dragons 10% of their diet. According to David Attenborough, the habit of cannibalism may be advantageous in sustaining the large size of adults, as medium-sized prey on the islands is rare. When the young must approach a kill, they roll around in fecal matter and rest in the intestines of eviscerated animals to deter these hungry adults. Komodo dragons take about three to five years to mature, and may live for up to 50 years.


source: www.wikipedia.com