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Biology Articles » Reproductive Biology » No sex please, we're lizards

No sex please, we're lizards

A Komodo dragon (Varanus komodoensis) has astonished the scientific world by producing a clutch of eight viable eggs without any assistance from a male.

Fittingly, the baby dragons could hatch in time for Christmas in what would effectively be a virgin birth.

Parthenogenesis, the production of offspring without fertilization by a male, is carried out by King Edward potatoes, bees and greenfly but is rare in vertebrate species.

Now Phillip Watts of Liverpool University and colleagues have used genetic fingerprinting to reveal that parthenogenetic offspring have been produced by Flora the Komodo in Chester Zoo. Flora and her sister Nessie are now the only two sexually mature dragons in Europe.

Flora produced a clutch of eleven eggs in May of this year. Three failed to incubate, which provided embryonic material for DNA paternity tests. These revealed that there was no father, the scientists report today in the journal Nature.

The remaining eight eggs are developing normally and are expected to hatch after the usual incubation of between seven and nine months. Kevin Buley, Chester Zoo's curator of lower vertebrates and invertebrates and a co-author, said: "Although other lizard species are known to be able to reproduce without a male this is the first time this has ever been reported in Komodo dragons."

"Essentially what we have here is a 'virgin birth' and, because the eggs were laid back in May, the incubating eggs could hatch around Christmas time. We will be on the look out for shepherds, wise men and an unusually bright star in the sky over Chester Zoo."

Sungaï, a Komodo dragon at London Zoo, managed to produce four viable offspring more than two years after her last contact with a male and subsequently produced additional offspring sexually.

She arrived at London on loan from Thoiry Zoo in France last year and the clutch of eggs was laid more than two years since she had last lived with Thoiry's male, Kimaan, demonstrating that Komodo dragons can switch between asexual and sexual reproduction depending on the availability of a mate.

Sungaï died earlier this year.

The fact that Komodo dragons can switch back to normal reproduction, depending on the availability of mates, was unknown until now.

Richard Gibson, London Zoo's curator of herpetology, said: "I am delighted that the mysterious parentage of our Komodo dragon babies has been solved and that we have discovered something new to science at the same time. Knowing that the world's largest lizard can reproduce like this suggests that many other reptiles may also do this more often than we thought and may lead to changes in the way we manage this and other species in breeding programmes."

This discovery also has implications for understanding how reptiles are potentially able to colonise new areas.

"Theoretically a female Komodo dragon in the wild could swim to a new island and then establish an new population of dragons," said Mr Buley.

"The genetics of this type of parthenogenesis in lizards means that all her hatchlings would have to be male. These would grow up to mate with their own mother and therefore, within one generation, there would potentially be a population able to reproduce normally on the new island."

If a human virgin birth could occur, Jesus should have been a girl, not a boy, because all his genes must have come from Mary. She would only have the genetic wherewithal - in humans, a bundle of genes called the X chromosome - to make a female.

Not so for the Komodo. Sex determination is analogous to that of mammals, the difference being that the lizard's sex chromosomes are W and Z and it is the males, not females (as with humans) which have two of the same type of sex chromosome while the females are have one W and one Z. Thus with parthenogenesis, each egg only gets half of the mother's genetic material (that is a W or a Z chromosome, but not both) so only females are produced.

Komodo dragons are the largest lizards in the world, with adult males growing up to three metres in length and weighing up to 100kg. There are now believed to be fewer than 4000 Komodo dragons left on the planet. They survive on three islands in Indonesia - Komodo, Flores and Rinca - and are still under threat in certain areas. Komodo dragons are known to be excellent swimmers and can swim across the sea from one island to another. Although they are not considered to be poisonous, the saliva from a Komodo dragon contains deadly bacteria, ambushing and biting the legs and tendons of prey and track it for up to two days until it eventually dies. The first human inhabitants of Komodo were the Ata Modo. They believed that they were created at the same time as the Komodo dragon when a beautiful spirit woman Putri Naga gave birth to twins - one of the babies was a human child, the second a Komodo dragon. Males demonstrate ritual combat during breeding season by standing on their hind legs and wrestling.

Quoted from Telegraph News. December 21, 2006.


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