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Virgin dragon to give birth

Komodo dragonA Komodo dragon raised in captivity at a zoo in England is set to give birth over the holidays, despite never having mated or even being in contact with a male dragon. Flora, an eight-year old reptile, is expecting eight bouncing male baby dragons over the holidays. Another unmated Komodo dragon at London Zoo produced four live young earlier this year, according to a report in Nature.

Brad Shaffer, a professor of evolution and ecology at UC Davis who studies the evolution and genetics of reptiles and amphibians, says that there are several examples of “virgin birth” or parthenogenesis in other lizards and snakes, but not in the family of lizards to which Komodo dragons belong.

Most of these examples are fast-spreading “weed species,” such as house geckos in Hawaii or the whip-tail lizards in the American Southwest. They are typically hybrids that lose the ability to reproduce sexually and can only reproduce in this way.

Parthenogenesis allows for a rapid increase in numbers, Shaffer says. All the individuals in the population can produce young, “and you don’t waste time making males.”

But reproducing without sex has long term costs because there is no shuffling of genes between generations and harmful mutations can build up.

There is some evidence from zoos that reptiles housed in captivity for a long time can spontaneously produce fertile eggs, Shaffer says, citing work especially by Gordon Schuett at Arizona State University. A case was reported in a Burmese python in a Dutch zoo in 2003. But many reptiles can also store sperm for long periods of time, and researchers would need to check carefully that the animals had never, even accidentally, been in contact with another male of the same or a related species. Careful genetic analysis is needed to show that the offspring come only from the mother.

Shaffer adds: “Whether or not this represents an adaptation to island living in Komodo dragons is an interesting question. However, given the genetics of sex determination in these lizards, where the heterogametic sex is the female, the story seems to be that all kids from parthenogenetic births are males, so that would imply that it is a one-generation only phenomenon.”

Facts about the Komodo dragon, from the American Museum of Natural History: they can reach 10 feet long, weigh up to 300 pounds (especially after a meal), carry toxic bacteria in their mouths and can move with “alarming speed.”

How to catch a Komodo dragon (…very, very carefully).

More from Chester Zoo.

Update

The Nature paper does mention a possible case of parthenogenesis in a captive monitor lizard, which belongs to the same family as Komodo dragons. Also, the sex ratio of Komodo dragons in the wild is rather male-biased, perhaps implying that this is happening in the wild as well as in zoos.

4 Responses to Virgin dragon to give birth

  1. Camille says:

    “the story seems to be that all kids from parthenogenetic births are males,”

    I thought the offspring of parthenogenesis were always female. Where would the “y” chromosome come from if a female’s egg could start to develop into a baby on it’s own… that does happen but the offspring are females… did I read that quote above wrong?

  2. I do not know how you could leave out a discussion of Jurassic Park in association with this story. After all, Crighton’s premise for the problems on the island relates to parthenogenesis. The fictional scientists thought that by making all the dinosaurs female they could not reproduce. I guess they did not have someone like Brad to advise them. And then things go bad on the island due to parthenogenesis by the females. There is a mini discussion of this at a HHMI web site and I am sure there has been other stuff written about this.

  3. Andy says:

    The Pharyngula blog has a post on the sex determination issue. In humans, sex determination is set by X and Y chromosomes — XX is female, XY is male. In these lizards, sex is set by W and Z chromosomes, but the result is reversed: two different chromosomes (WZ) gives a female, ZZ is a male. In this case, because of the way the eggs have formed, they can apparently only be ZZ or WW, and WW do not develop, so there are only ZZ males.

    You’re right that animals that do have parthenogenetic reproduction usually produce all females, because then you can reproduce endlessly. Producing a generation of 100 percent males is not going to get you very far.

  4. Andy says:

    Re Jurassic Park… only in a Michael Crichton novel could scientists do something so dumb. I hope.

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