The Komodo dragon (Varanus komodoensis), also known as the Komodo
monitor, is a large species of lizard found in the Indonesian islands of
Komodo, Rinca, Flores, Gili Motang and Gili Dasami. A member of the
monitor lizard family (Varanidae), it is the largest living species of
lizard, growing to a maximum length of 3 metres (9.8 ft) in rare cases
and weighing up to around 70 kilograms (150 lb). Their unusual size has
been attributed to island gigantism, since there are no other
carnivorous animals to fill the niche on the islands where they live.
However, recent research suggests that the large size of Komodo dragons
may be better understood as representative of a relict population of
very large varanid lizards that once lived across Indonesia and
Australia, most of which, along with other megafauna, died out after the
Pleistocene. Fossils very similar to V. komodoensis have been found in
Australia dating to greater than 3.8 million years ago, and its body
size remained stable on Flores, one of the handful of Indonesian islands
where it is currently found, over the last 900,000 years, "a time
marked by major faunal turnovers, extinction of the island's megafauna,
and the arrival of early hominids by 880 ka."
As a result of their size, these lizards dominate the ecosystems in
which they live. Komodo dragons hunt and ambush prey including
invertebrates, birds, and mammals. Their group behaviour in hunting is
exceptional in the reptile world.
The diet of big Komodo dragons mainly
consists of deer, though they also eat considerable amounts of carrion.
Mating begins between May and August, and the eggs are laid in
September. About twenty eggs are deposited in abandoned megapode nests
or in a self-dug nesting hole. The eggs are 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 about eight to nine years
to mature, and are estimated to live for up to 30 years.
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.
Contents
1 Etymology
2 Evolutionary history
3 Description
3.1 Senses
4 Ecology
4.1 Diet
4.2 Saliva
4.3 Reproduction
4.4 Parthenogenesis
5 History
5.1 Discovery by the Western world
5.2 Studies
6 Conservation
6.1 In captivity
7 See also
8 References
9 Further reading
10 External links
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).
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 ft 3 in) 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 centimetres (1 in) 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 bacteria that live in
its mouth. It also has a long, yellow, deeply forked tongue.
Senses
The Komodo dragon does not have an 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 color, but has poor visual
discrimination of stationary objects.
A Komodo dragon on Komodo Island uses its 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 the
Jacobson's organ, rather than using the nostrils. 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 (2.5–5.9 mi) away. 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
Foot and tail
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 solitary, coming together only to
breed and eat. They are capable of running rapidly in brief sprints up
to 20 kilometres per hour (12 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 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 serve as a strategic
location from which to ambush deer.
Diet
Komodo dragons on Rinca
Komodo dragons are carnivores. Although they eat mostly carrion, they
will also ambush live prey with a stealthy approach. 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 kilometres (6 mi). Komodo dragons have
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). A Komodo dragon 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 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 drinks by sucking water into its mouth via buccal
pumping (a process also used for respiration), lifting its head, and
letting the water run down its throat.
Saliva
A sleeping Komodo dragon. Its large, curved claws are used in fighting
and eating.
Auffenberg described the Komodo dragon as having septic pathogens in its
saliva (he described the saliva as "reddish and copious"), specifically
the bacteria: E. 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 and the use of
antibiotics. 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 these bacteria was noted by Fredeking:
"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. How the Komodo dragon
is unaffected by these virulent bacteria remains a mystery.
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. Hatching is an exhausting effort for the neonates, 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.
Parthenogenesis
Main article: Parthenogenesis
A parthenogenetic baby Komodo dragon, Chester Zoo, England
A Komodo dragon at London Zoo named Sungai laid a clutch of eggs in late
2005 after being separated from male company 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. On December 20, 2006, it was reported that Flora, a
captive Komodo dragon living in the Chester Zoo in England, was the
second known Komodo dragon to have laid unfertilized eggs: she laid 11
eggs, and seven of them hatched, all of them male. Scientists at
Liverpool University in England performed genetic tests on three eggs
that collapsed after being moved to an incubator, and verified that
Flora had never been in physical contact with a male dragon. After
Flora's eggs' condition had been discovered, testing showed that
Sungai's eggs were also produced without outside fertilization. On
January 31, 2008, the Sedgwick County Zoo in Wichita, Kansas became the
first zoo in the Americas to document parthenogenesis in Komodo dragons.
The zoo has two adult female Komodo dragons, one of which laid about 17
eggs on May 19–20, 2007. Only two eggs were incubated and hatched due
to space issues; the first hatched on January 31, 2008 while the second
hatched on February 1. Both hatchlings were males.
Komodo dragons have the ZW chromosomal sex-determination system, as
opposed to the mammalian XY system. Male progeny prove that Flora's
unfertilized eggs were haploid (n) and doubled their chromosomes later
to become diploid (2n) (by being fertilized by a polar body, or by
chromosome duplication without cell division), rather than by her laying
diploid eggs by one of the meiosis reduction-divisions in her ovaries
failing. 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); those receiving a W chromosome become WW
and fail to develop.
It has been hypothesized that this reproductive adaptation allows a
single female to enter an isolated ecological 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). Despite the advantages
of such an adaptation, zoos are cautioned that parthenogenesis may be
detrimental to genetic diversity.
History
Discovery by the Western world
Komodo dragon coin, issued by Indonesia
Komodo dragons were first documented by Europeans in 1910, when rumors
of a "land crocodile" reached Lieutenant van Steyn van Hensbroek of the
Dutch colonial administration. Widespread notoriety came after 1912,
when Peter Ouwens, the director of the Zoological Museum at Bogor, Java,
published a paper on the topic after receiving a photo and a skin from
the lieutenant, as well as two other specimens from a collector. Later,
the Komodo dragon was the driving factor for an expedition to Komodo
Island by W. Douglas Burden in 1926. After returning with 12 preserved
specimens and 2 live ones, this expedition provided the inspiration for
the 1933 movie King Kong. It was also Burden who coined the common name
"Komodo dragon."
Three of his specimens were stuffed and are still on
display in the American Museum of Natural History.
Studies
Komodo in the emblem of East Nusa Tenggara province
The Dutch, realizing the limited number of individuals in the wild,
outlawed sport hunting and heavily limited the number of individuals
taken for scientific study. Collecting expeditions ground to a halt with
the occurrence of World War II, not resuming until the 1950s and 1960s,
when studies examined the Komodo dragon's feeding behavior,
reproduction, and body temperature. At around this time, an expedition
was planned in which a long-term study of the Komodo dragon would be
undertaken. This task was given to the Auffenberg family, who stayed on
Komodo Island for 11 months in 1969. During their stay, Walter
Auffenberg and his assistant Putra Sastrawan captured and tagged more
than 50 Komodo dragons. The research from the Auffenberg expedition
would prove to be enormously influential in raising Komodo dragons in
captivity. Research after the Auffenberg family has shed more light on
the nature of the Komodo dragon, with biologists such as Claudio Ciofi
continuing to study the creatures.
Conservation
A basking Komodo dragon photographed at Disney's Animal Kingdom.
The Komodo dragon is a vulnerable species and is found on the IUCN Red
List. There are approximately 4,000 to 5,000 living Komodo dragons in
the wild. Their populations are restricted to the islands of Gili Motang
(100), Gili Dasami (100), Rinca (1,300), Komodo (1,700), and Flores
(perhaps 2,000). However, there are concerns that there may presently be
only 350 breeding females. To address these concerns, the Komodo
National Park was founded in 1980 to protect Komodo dragon populations
on islands including Komodo, Rinca, and Padar. Later, the Wae Wuul and
Wolo Tado Reserves were opened on Flores to aid with Komodo dragon
conservation.
Komodo dragons avoid encounters with humans. Juveniles are very shy and
will flee quickly into a hideout if a human comes closer than about 100
metres (330 ft). Older animals will also retreat from humans from a
shorter distance away. If cornered, they will react aggressively by
gaping their mouth, hissing, and swinging their tail. If they are
disturbed further, they may start an attack and bite. Although there are
anecdotes of unprovoked Komodo dragons attacking or preying on humans,
most of these reports are either not reputable or caused by defensive
bites. Only a very few cases are truly the result of unprovoked attacks
by abnormal individuals which lost their fear towards humans.
Volcanic activity, earthquakes, loss of habitat, fire,loss of prey due
to poaching, tourism, and illegal poaching of the dragons themselves
have all contributed to the vulnerable status of the Komodo dragon.
Under Appendix I of CITES (the Convention on International Trade in
Endangered Species), commercial trade of skins or specimens is illegal.
On Padar, a former population of the Komodo Dragon became extinct, of
which the last individuals were seen in 1975. It is widely assumed that
the Komodo dragon died out on Padar after a strong decline of the
populations of large ungulate prey, for which poaching was most likely
responsible.
In captivity
A Komodo dragon at Smithsonian National Zoological Park. Despite the
visible earholes, Komodo dragons cannot hear very well.
Komodo dragons have long been great zoo attractions, where their size
and reputation make them popular exhibits. They are, however, rare in
zoos because they are susceptible to infection and parasitic disease if
captured from the wild, and do not readily reproduce. In May 2009, there
were 13 European, two African, 35 North American, one Singaporean, and
two Australian institutions that kept Komodo dragons.
The first Komodo dragon was exhibited in 1934 at the Smithsonian
National Zoological Park, but it lived for only two years. More attempts
to exhibit Komodo dragons were made, but the lifespan of these
creatures was very short, averaging five years in the National
Zoological Park. Studies done by Walter Auffenberg, which were
documented in his book The Behavioral Ecology of the Komodo Monitor,
eventually allowed for more successful managing and reproducing of the
dragons in captivity.
A variety of different behaviors have been observed from captive
specimens. Most individuals are relatively tame within a short period of
time, and are capable of recognizing individual humans and
discriminating between more familiar keepers. Komodo dragons have also
been observed to engage in play with a variety of objects, including
shovels, cans, plastic rings, and shoes. This behavior does not seem to
be "food-motivated predatory behavior."
Even seemingly docile dragons may become aggressive unpredictably,
especially when the animal's territory is invaded by someone unfamiliar.
In June 2001, a Komodo dragon seriously injured a man when he entered
its enclosure at the Los Angeles Zoo after being invited in by its
keeper. He was bitten on his bare foot, as the keeper had told him to
take off his white shoes, which could have potentially excited the
Komodo dragon. Although he escaped, he needed to have several tendons in
his foot reattached surgically.
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