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Planet Earth

Virgin birth by Komodo dragons

Not Exactly Rocket ScienceBy Ed YongOctober 3, 2008 7:00 PM

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According to Christian lore, Mary gave birth to baby Jesus without ever having had sex with Joseph. A biologist might describe this as 'parthenogenesis', the Greek version of the more familiar phrase 'virgin birth'('parthenos' means virgin, and 'genesis' means birth). The New Testament aside, shunning fertilisation and giving birth to young through parthenogenesis is rare among higher animals, occurring in only one in every thousand species. Nonetheless, two Christmases ago, eight virgin births took place in the English town of Chester. The mother's name was Flora and she was a komodo dragon.

Komodo dragons are an endangered species in their island homes of >Indonesia. Fifty-two zoos around the world co-operate in a dedicated breeding programme that aims to boost the natural populations of these largest of lizards. In Europe, only two female dragons, both living in England, are sexually mature. One of these, Flora, lives at Chester Zoo where she has laid a clutch of 25 eggs despite never having been kept with a male.

Three of Flora's eggs tragically collapsed while they were being incubated, but this provided Phillip Watts and colleagues from the University of Liverpool with a chance to trace their origins. They analysed the genetic make-up of the lost eggs using genetic fingerprinting and found that their genomes matched those of their mothers.Children born through sex have two copies of every gene, one inherited from their father and one from their mother but the genomes of Flora's babies had two identical copies of every gene, a sign that every copy came from Flora alone.

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Watts found a similar situation in London Zoo, where a late female called Sungai had given birth to four healthy dragon-lings, over two years after she lost contact with a male. Scientists had suspected that the babies were the result of sperm that Sungai had stored during that time, but genetic tests confirmed that she was the sole parent.

This double-sighting of parthenogenesis in Komodo dragons suggests that this unusual strategy is not so unusual in these lizards. It could even be used to help populations weather hard times. Komodo dragons have Z and W chromosomes, rather than our Xs and Ys and in their case, it's individuals with a matching pair who are male (ZZ or WW), and those with a a mismatched pair who are females (WZ). As a result, parthenogenetic dragons are always male and when populations dwindle, they can kick-start numbers by mating with their own mothers.

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This strategy could cause large problems for conservationists. By causing all an individual's gene pairs to be identical, parthenogenesis achieves what inbreeding usually takes generations to do. In rare cases, it could help struggling populations to recover, but if dragon numbers become so small that parthenogenesis becomes the norm, reduced genetic diversity could push the species further towards extinction.

Zoos need to take heed as well. Females are usually kept apart from males, who are transferred between zoos to act as reptilian studs. This reduces the risk of aggression on the part of the larger males, but it could lead to a excessive number of virgin births. To save this magnificent animal, we need more research into how best to account for its new-found ability, and how best to breed a healthy, genetically diverse population. These lessons may apply to other species too - mere months after writing this article, the same thing happened with a captive hammerhead shark.

Reference: Phillip C. Watts, Kevin R. Buley, Stephanie Sanderson, Wayne Boardman, Claudio Ciofi, Richard Gibson (2006). Parthenogenesis in Komodo dragons Nature, 444 (7122), 1021-1022 DOI: 10.1038/4441021a

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