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.

Tags : sharks, sex, repoduction, parthenogenesis, oceans

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