'Virgin' shark birth in Virginia

From our friends at the Greenspace blog:

The first time it happened, scientists thought it might be a fluke. A female hammerhead shark residing at a zoo in Omaha, Neb., had not been in contact with male sharks for at least three years and yet experienced a "virgin birth." She delivered a single pup.

But it has happened again, according to today's issue of the Journal of Fish Biology. This time, a blacktip shark, similar to the one pictured above, had spent nearly her entire eight years at either the Virginia Aquarium without any male companionship from her kind. And again, in what some religions might call a miracle, and what science calls "parthenogenesis," she produced a single pup. Using DNA fingerprinting techniques used in human paternity tests, scientists have determined that in this case, as well as the hammerhead in Omaha, the solitary offspring contained no genetic material from a father.

"It's reasonable to assume that female sharks can do this on occasion," said Demian Chapman, a shark scientist with the Institute for Ocean Conservation Science at Stony Brook University in New York. "I'm sure this happens in the wild, but haven't been able to prove it yet. There's no reason that keeping a shark in captivity would cause a fundamental change in the reproductive system."

Sharks have suffered steep declines in all of the world's oceans, either inadvertently caught by fishing nets and hooks or targeted for shark fin soup marketed as a delicacy in China. Some scientists have suggested that this may be a last-ditch way for severely depleted populations to reproduce if their numbers fall so low that males cannot find females.

Yet parthenogenesis, derived from the Greek words for "virgin birth", has limits. First, he said, female sharks can have large litters of young, but in these documented cases only produced one pup. In addition, the offspring have reduced genetic diversity, putting it at a disadvantage in the wild.

Parthenogenesis has been observed in dozens of species, in some birds, amphibians and fish. This asexual reproduction occurs when an egg cell is triggered to develop as an embryo without the addition of any genetic material from a male sperm cell.

Before these recent discoveries, scientists presumed that sharks reproduced exclusively by internal insemination. Indeed, some sharks can store sperm for months, but not long enough to be responsible for these cases.

Sharks are an ancient species, with origins dating back 400 million years. "On the face of it, sharks were the first vertebrates to invent what we call sex, penetrative insemination," Chapman said. "We can learn a lot from studying them."

Chapman is trying to rewrite the book on shark sex, often a brutal affair that involves biting with sharp teeth and sometimes death. "It's taken us a long time to figure out that a female doesn't need a male," Chapman said. "You couldn't blame them for reproducing asexually because the sex is often quite violent."

-- Kenneth R. Weiss

Photo: Blacktop shark. Credit: Matthew D. Potenski, MDP Photography

Comments

[John]

It's getting really annoying, and old, that media outlets keep linking parthenogenesis to key terms that throwback to the Biblical account. One, because in parthenogenic-capable organisms it's definitely not a miracle, nor does any religion or religious group I know of say it is as "And again, in what some religions might call a miracle".

Sheesh.

[Ben Burns]

Its Shark Jesus come to save the sharks from damnation?

[Sandy Smith]

Besides, partogenesis has never been proven to occur in mammals.

[Sandy Smith]

Besides, partogenesis has never been proven to occur in mammals.

[Dylan]

100% agree with the above commenter, is it insecurity that is causing the journalist here to start the article with a bizarre miracle analogy to parthenogenesis? In any case the reference weakens his integrity in the purely scientific scope of the article.

[Tom]

I agree that it's unprofessional for scientists to use this information to try and explain how Jesus was born. We don't need science to tell us what happened two thousand years ago. We have first hand historical records from people who were alive and saw what happened with their own eyes. That's always going to be the most accurate data available.

[big fig]

But it truly is a miracle; THE MIRACLE OF LIFE...

[johndoe@johndoe.com]

beef, it's whats for dinner

[Nik]

Or maybe they use that phrase because it connects with a lot of people? Hmmm.....could be.....but then again, I'm no journalist.

[Science Colin]

Look under the sharks skirt and you will see it has gone hermaphrodite. Most female plants and animals can do this if you isolate them from the opposite sex and put them under the right stress. Never underestimate nature when it comes to procreation.

[Matt]

I think that if they want to find out if this is happening in the wild they should be doing random testing on sharks to see if they have no genetic material from a father.

[David Gonzalez]

They say Parthenogenisis is impossible in humans, yet I would think given the way technological advances occur, I would not be surprised if it became possible in the future through genetic engineering using DNA of creatures that do have occurences of Parthenogenisis.. This would start to coincide with the biblical account of the virgin birth as to say, yes it is possible. Kind of makes for an interesting twist...does it not?

[M]

"We don't need science to tell us what happened two thousand years ago. We have first hand historical records from people who were alive and saw what happened with their own eyes." And people can't possibly be tricked or fooled?? Magicians do it all the time! I agree that the religious reference undermines the scientific integrity of the article, but the author is not a scientist, he is a journalist, there are no educational credentials after his name. That's his job is to editorialize...but don't rip on scientists for the spin journalists put on their stories. No credible scientist would take scientfic information and arbitrarily relate it to religion and folklore (YES I said "folklore").

[James Jihulya]

It sounds unclear. That sharks are about to be exterminated by fishing and other causes yet they can reproduce asexually! Science should tell us what triggers parthogenesis. Is it being solitary? Or do sharks detect that they are depleted then they start reproducing asexually. If they could detect then they could reproduce enormously to counteract the decline Then if that is the case we should not be worried nature will solve the problem of sharks decline.