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Radhika Sharma

on 1 April 2014

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Transcript of KOMODO DRAGONS

Komodo dragons are a member of the Varanoidea clade. This clade consists of one genus, Varanus, Latin for “monitors”, and 73 species of monitor lizards.These lizards are typically large with long necks, an elongated snout, and a snake-like tongue used to detect scent particles. They also tend to favor warm climates.

Varanoidea is a subset of the Anguimorpha clade, its closest relatives being the Xenosauridea, or knob-scaled lizards, and the Anguidae, consisting of the slowworms, glass lizards and alligator lizards. As you can see in this phylogeny, the Dibamidae, Amphisbaenia, and Serpentes clades have not been given a definitive place.

Monitor lizards are a part of the Squamata clade, consisting of lizards and snakes. These organisms descended from a common ancestor of the dinosaurs; a member of the subclass Diapsida which split into Lepidosaurmorpha, the ancestors to moderns snakes and lizards, and Archosauromorpha, the ancestors to modern crocodiles and birds.

Around 15 million years ago, an ancestor of the Varanidae reached Australia. This ancient species split into Varanus Komodoensis, the Komodo Dragon, 4 million years ago.
Komodo dragons are found on the volcanic Lesser Sunda Islands of Komodo, Flores, Rinca and Gili Motang in Indonesia.

Habitat of the Komodo Dragon
These small islands have relatively few resources, and yet the Komodo Dragon has evolved into the largest living species of lizard at an average weight of 90-155 pounds.
Evolutionary biologists theorize that the presence of pigmy elephants and stegodonts on the Indonesian islands created selection pressure for larger sizes of dragons.
The larger the dragon, the more likely they would be to take on large prey.

Komodo Dragon Size
The Komodo Dragon diet is mostly wild animals of the savana. They eat wild pigs but sometimes even attack a buffalo! Komodos can eat dozens kilograms of meat in one meal! They can eat up to 80 percent of their weight body in one time.
They are cannibalistic too with the babies and young Komodo dragons!
Biologists have observed animals being unusually quiet and quick to go into shock after being bitten, suggesting the Komodo Dragon utilizes some form of venom.
Komodo Dragons also have an absurdly high kill rate (90%)
One very popular theory explaining this high kill rate is the bacteria-as-venom theory.
This theory claims that the Komodo Dragon’s saliva contains various bacteria that causes sepsis in the event of a bite.

Bacteria as Venom
Bacteria is acquired through:
Sick prey and carrion
Other Komodo Dragons (through feeding in groups, eating prey killed by another Komodo Dragon)

Bacteria as Venom Critiques

The theory was based on two studies, neither of which were performed by microbiologists.
Komodo Dragons have been observed cleaning their mouths after feeding, which would be counter-productive if they used bacteria as a weapon.
Further studies have suggested that Komodo Dragons have no more oral bacteria than other carrion eaters. More studies have shown that Komodo Dragons have venom, which is a more likely explanation.
Although males tend to grow larger and bulkier than females, no obvious morphological differences mark the sexes. One subtle clue does exist: a slight difference in the arrangement of scales just in front of the cloaca.
Most mating occurs between May and August. Dominant males can become embroiled in ritual combat in their quest for females.
The mystery continues...
In 2006, the only two sexually mature Komodo Dragons in Europe laid viable eggs.
Flora laid a clutch of 11 eggs, 8 being viable
Sungai laid a clutch of 22 eggs, 4 of which were viable.
All of the viable eggs were male, and neither dragon had seen a male dragon in years

The Monitor Lizard
Computer simulations of the Komodo Dragon’s bite has shown that the Komodo Dragon has a bite force of 39N, 6.5 times less than the 252 N produced by the bite of an Australian saltwater crocodile with comparable skull size. Komodo Dragons bite and pull on prey in order to compensate for their weak bite force.

Other Theories-The Water Buffalo
One of the largest animals eaten by a Komodo Dragon is the Water Buffalo. Since they are such big prey, they are unlikely to be killed in one bite, and have been used as support for the bacteria-as-venom theory.
Biologists are too afraid to get near the Komodo’s Mouth to draw any real conclusions

Evolutionary biologists theorized that Komodo females evolved this trait in order to start a new population after a monsoon washes the female on an isolated island. In this way, parthenogenesis helps protect variation in the event of genetic drift


From the greek, Parthenos (virgin) genesis (birth)

Bull JJ, Jessop TS, Whiteley M (2010) Deathly Drool: Evolutionary and Ecological Basis of Septic Bacteria in Komodo Dragon Mouths. PLoS ONE 5(6): e11097. doi:10.1371/journal.pone.0011097
Luntz, S. 2013 Komodo Dragon Myth Slain. Australasian Science 34 (7): 1
Yam, P. Strange but True: Komodo Dragons Show that "Virgin Births" Are Possible. Scientific America [Internet0. 2006 Dec 28 [cited 2014 Mar 30] Available from http://www.scientificamerican.com/article/strange-but-true-komodo-d/
http://en.wikipedia.org/wiki/Komodo_dragon (pictures)

Our Theory
Life Cycle

Don’t take care of young.

1 female to every 3 males-considering that eggs are the limiting factor, why would natural selection favor this sex ratio?

A very rare feature amongst vertebrae (.1 percent or 70 species)
During the formation of egg cells, a mini-ovum is formed containing a duplicate copy of the egg cell’s DNA.
This “polar body” is normally discarded after the egg cell is formed.

In Komodo Dragons, this polar body can act as a sperm cell, effectively fertilizing the egg with a second set of the same DNA

Parthenogenesis and Sex ratio

Komodos sex chromosomes consist of a “W” and a “Z,” unlike humans, who have “X” and “Y” chromosomes.
Also unlike humans, Komodo females have one of each sex chromosomes (ZW) and Komodo males have two copies of the Z chromosome.
Since Komodo females are ZW, the egg cells contain either a Z or a W chromosome, if a W-egg is fertilized by its polar body, the zygote is WW, and therefore non-viable. If a Z-egg is fertilized, the offspring is male.

Water Buffalo were introduced to the islands 300 years ago, and therefore still retain their old instincts to flee to a body of water when threatened. Their normal habitat is much colder, and predators would have to risk hypothermia to hunt them down. In the Lesser Sunda Islands, not only is the water warm, it is full of bacteria.

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