A Komodo dragon named Flora proved last week that you don't always have to wait for your prince to start a family. Though she lives in the Chester Zoo in England with just her sister, Nessie, the 8-year-old virgin laid a clutch of fertile eggs last spring. After a long incubation period, five baby Komodos finally hatched.
Though it came as a surprise, it's no miracle, say biologists. Nor is it a threat to male Komodo dragons. Though males in other species have died out when females learned to reproduce without them, the quirks of dragon sex chromosomes ensured that all Flora's offspring came out male.
Scientists suspect that female Komodo dragons have always had the ability to bear sons on their own in a pinch. Such a trick could prove a handy adaptation in the Komodo's natural Indonesian island habitat. If you're founding a new colony and don't happen to have males around, you can always make some yourself.
Despite their reproductive flexibility - and a fearsome bite that kills prey from blood poisoning over several days - these 200-plus-pound reptiles are no match for human encroachment. Some scientists estimate there are just 4,000 individuals left in the world, all living on just three islands: Komodo, Flores and Rinca.
While Flora is the first documented virgin dragon to hatch babies, she's not the first female to reproduce without the help of a male. Last spring another dragon, Sungai, hatched four healthy offspring though she hadn't been near a male in well over a year.
Sungai might have qualified as a reformed virgin, so scientists couldn't rule out that she stored sperm from an old boyfriend she lived with at another zoo. Turtles, after all, can store viable sperm for years.
But the case was settled last fall, when a lab in Liverpool analyzed DNA from Sungai and her babies, as well as from Flora and several of her eggs that had collapsed. The tests showed that both dragons laid their eggs with no genetic input from a male.
"This is a fascinating story - just because it happened," said Michael Majerus, a Cambridge University biologist.
Majerus says virgin births are documented in about 70 species of vertebrates as well as countless insects.
In some of those cases the eggs fail to divide all their genes in half. Normally, we and Komodos and most other animals carry two slightly different copies of each gene, one from our mothers and one from our fathers. These get divided in half in eggs and sperm.
If eggs keep a full complement instead, the babies may come out as clones of the mother.
But in Flora's case, the eggs do divide the mother's genetic material in half. Then that half gets Xeroxed to make a second, identical copy. So these new baby dragons are not clones and they carry two identical copies of every gene.
While some scientists fear that sexless reproduction hurts genetic diversity, Majerus says it isn't all bad. Each of us carries about five lethal mutations, he said, ones that would kill us before we got a chance to reproduce if we weren't covered by a second copy of the same gene. But these baby dragons can't pass on any lethal mutations since all their genes come in two identical copies. If one were lethal, they'd be dead.
So the sons of Flora can't be carrying any silent lethal mutations. They may one day meet females and contribute to the next generation.
That they're not clones also explains why the offspring all came out male. In Komodo dragons, like birds, butterflies and some other reptiles, the female has two different chromosomes, dubbed Z and W, while males have two W's. (This is the reverse of our situation in which males carry two different chromosomes, an X and a Y, and females have two X's.)
So when Flora divided her chromosomes in half to make eggs, each one got either a Z or a W. When she copied those, the self-fertilized eggs got either WW (male) or ZZ (which don't survive).
In a mammal the situation would be reversed, so if you were to attribute any famous cases of virgin births to parthenogenesis, you'd have to accept that the offspring would all be girls.