Stories tagged parthenogenesis
A modern blacktip shark: living a modern life on her own.Courtesy Albert Kok
*The original headline here was "Immaculate conception observed. In a shark." However, it was pointed out to me that "immaculate conception" and "virgin birth" really aren't the same thing. I changed it, but I resent the implication that I don't know the difference. Just because I get things wrong all the time, it doesn't mean that I was wrong about this. Not, you know, necessarily.
It looks like lady sharks have won another battle of the sexes. The sex war had been fought to a standstill, a stalemate siege, if you will, with the male army relying on the “well, you’ll need us eventually” tactic.
Apparently this isn’t necessarily the case. Deep inside the female Fortress of Celibacy, a devious plan was being hatched: virgin birth.
(Many types of sharks, it should be noted, give live birth, like mammals, instead of laying eggs.)
There have, in fact, been two documented cases of ladies-only shark reproduction. The first was in the Omaha Zoo, where a female hammerhead shark unexpectedly gave birth to a baby shark (called a “pup”) in her tank. Unfortunately, some of the other sharks (of a different species) in her tank immediately ate the pup. Whoops. But DNA tests were done on the… leftover chunks of the pup, I guess, and they showed that the baby did not have a father.
The other case happened in May of last year, with the research results being released this last week (hey, sometimes science stays out all night and gets up late, so give it a break). A blacktip shark named Tidbit had been living at the Virginia Aquarium and Marine Science Center for the last eight years, with no contact with males sharks of her species. When Tidbit died mysteriously last May, an autopsy revealed her nearly full-term pregnancy (the stress-related complications of which were probably what did her in). The shark pup had died as well—and aquarium staff believed that it would have been eaten by the tiger sharks in the same tank anyway had it actually been born—but genetic testing revealed it to be Tidbit’s child, and Tidbit’s alone.
Scientists studying the bizarre pregnancies believe that the pups got all the required chromosomes when the mother’s egg split, and then reunited—a process called "parthogenesis.”
Single-sex reproduction, it’s believed, might be an adaptation to situations when there are too few male sharks in a wild population. It’s rare enough, however, that it would be very unlikely that sharks could survive through pathogenesis alone. The process results in a lack of genetic diversity as well, which could leave individuals vulnerable to congenital disorders.
So, ladies, I salute your ingenuity, but you’re not rid of us yet.
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Ms. Komodo dragon says: "I want to be alone.": Photo courtesy stuartmoulder at Flickr.
Early last year a visiting Komodo dragon at the London Zoo laid a clutch of viable eggs that mystified zookeepers. The female dragon, Sungai, had been brought to England from Paris in hopes that she’d mate with one of the male Komodo dragons there. Unfortunately, she gave birth before she had a chance to meet her potential suitor.
Scientists clamored to explain the apparent immaculate conception. Sungai’s last known sexual encounter had been two years previous, but it was speculated that perhaps she was able to store the sperm for later use.
But now it turns out that it was indeed a virgin birth. Genetic tests done at the University of Liverpool shows that the DNA in all the offspring came from just the mother. The research appeared in the recent issue of the journal Nature
The asexual reproduction process displayed by the lizard is known as parthenogenesis, a Greek word meaning “virgin birth”.
“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,” said Richard Gibson, curator of herpetology at the Zoological Society of London.
“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 programs.”
Parthenogenesis has been known to take place in some reptiles but never the Komodo dragon species (Varanus komodoensis). The lizards can grow up to nine or ten feet in length, and are known to bite their prey with choppers full of lethal, bacteria-ridden saliva that slowly kills them
Sungai has since died, but another Komodo dragon, named Flora, at the Chester Zoo in England has laid eggs that are expected to hatch next month. And Flora has never met a male Komodo in her life. Tests done on three of her eggs that collapsed confirm the make-up of the DNA all derive from Flora.
Parthenogenesis is distinct from cloning. All of Flora’s offspring will be male because female Komodo dragons carry only dissimilar chromosomes (W and Z), so when one of their eggs divides it’s comprised only of similar chromosomes, either all W or all Z. (In humans it’s the male that carries the dissimilar chromosomes).
“This discovery has very important implications for understanding how reptiles are potentially able to colonize new areas. Theoretically, a female Komodo dragon in the wild could swim to a new island and then establish an entirely new population of dragons,” said Kevin Buley, curator of lower vertebrates and invertebrates at the Chester Zoo. “Essentially what we have here is an immaculate conception.”
Flora’s brood could hatch just in time for Christmas.
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