A virgin birth is expected this Christmas, though this particular nativity scene will be set in a zoo instead of a stable.

That's because the virgin in question is Flora the Komodo dragon, a giant lizard at Chester Zoo in England that has laid fertile eggs despite never having had a mate.

DNA tests confirmed Flora was the sole parent, says Chester Zoo curator of lower vertebrates Kevin Buley.

"Essentially what we have here is an immaculate conception," he said, adding that the eggs could hatch as soon as Christmas.

"We will be on the look-out for shepherds, wise men, and an unusually bright star in the sky over Chester Zoo," he joked.

Flora, along with another female Komodo dragon from the London Zoo, represent the first known cases of virgin birth in the world's largest lizard, according to researchers.

The two reptiles are examples of a process called parthenogenesis, in which offspring are produced without fertilization by a male, according to a report in the current issue of the journal Nature.

Single-parent reproduction is hardly ever seen in such complex animals, having been documented in just 0.1 percent of vertebrates, the study team says.

The finding that Komodo dragons are capable of self-fertilization may open the way for many more such discoveries in other animals, says team member Richard Gibson, curator of herpetology at the London Zoo.

Virgin birth, he says, is "considered a very rare phenomenon, but the fact that we've got these two lizards suggests it's not as rare as we thought. We recorded it in two unrelated females within the space of a year in two different collections."

Survivor Island, Without Sex

Like Flora, the Komodo dragon at the London Zoo, named Sungai, was also shown by genetic tests to be the sole parent to her offspring, which hatched last April.

"We thought it was a very long shot but that we ought to check it out," London Zoo's Gibson said. "We were able to rule out sexual reproduction completely."

In parthenogenesis, an unfertilized egg develops into an embryo using its two sets of maternal chromosomes.

The unusual process is most commonly known in smaller invertebrates, such as aphids and zooplankton. But it is occasionally recorded in much larger animals, including some reptiles and amphibians.

The main drawback to this mode of reproduction is that populations can become genetically very similar, making them more vulnerable to disease and less able to adapt to change, such as altered climate conditions or new predators.

But there may have been an important advantage to Komodo dragons having fatherless young, the study team says.

The reptiles are native to islands in Indonesia, where female castaways could have need to start new colonies on their own, the researchers say.

"If a female gets swept off her desert island to a new desert island where there are no other dragons, then she can reproduce parthenogenetically," Gibson said.

Males Only

The offspring of such virgin births are all male, because of the genetics involved in self-fertilization in lizards, Gibson explained.

"When the offspring reach sexual maturity, the mother can reproduce with her own sons, and you're back to a sexually reproducing population," Gibson said.

Parthenogenesis has been found in a number of other unexpected animals in recent years, he added.

"It was recorded in a python a couple of years ago," he said. "Turkeys can do it, and it's also happened in fish."

Previous suspected cases of virgin births in zoo animals include a white spotted bamboo shark at the Belle Isle Aquarium in Detroit.

When the female shark laid a clutch of eggs in 2002, six years after her last contact with a male, aquarium staff assumed they were infertile. Yet the eggs later hatched.

Gibson says such cases raise the question of whether this phenomenon is happening in wild animals as well as those in captivity.

But he thinks it unlikely that parthenogenesis can shed any light on how the Virgin Mary gave birth in a manger.