http://www.washingtonpost.com/wp-dyn...052201405.html

Female Sharks Can Reproduce Alone, Researchers Find

By Juliet Eilperin
Washington Post Staff Writer
Wednesday, May 23, 2007; Page A02

A team of American and Irish researchers have discovered that some
female sharks can reproduce without having sex, the first time that
scientists have found the unusual capacity in such an ancient
vertebrate species.

Their report that sharks can reproduce asexually through the process
known as parthenogenesis is being published online today in the
British journal Biology Letters. Researchers have observed
parthenogenesis in certain species of birds, reptiles, amphibians and
bony fishes, but the new finding suggests that vertebrates' ability to
reproduce without sex evolved much earlier than scientists had
thought.

Scientists began their investigation after a female hammerhead shark
was mysteriously born at Omaha's Henry Doorly Zoo in December 2001, in
a tank that held three adult, female hammerheads but no males. The
seven-inch-long baby was killed within a day of its birth, apparently
because another fish in the tank, probably a stingray, attacked it.

Though the three females had been caught before they reached sexual
maturity and held in captivity for more than three years, researchers
initially thought one had stored sperm from a male shark before
fertilizing an egg. But the team -- which included scientists at Nova
Southeastern University in Florida, Queen's University Belfast and the
zoo -- determined that the baby shark's genetic makeup perfectly
matched one of the females in the tank, with no sign of a male parent.

Mahmood Shivji -- Nova Southeastern's Guy Harvey Research Institute
director and one of the paper's authors -- said that he and his
colleagues determined that a byproduct formed when sharks produce
eggs, known as a sister polar body, had fused with an unfertilized egg
to produce the baby shark, whose DNA had only half as much genetic
variability as the mother.

"Yes, indeed this is a virgin birth," Shivji said in an interview,
adding that this could help explain why other sharks have suddenly
been born in captivity, like a bamboo shark that appeared in Detroit's
Belle Isle Aquarium in 2002.

"We have now demonstrated that sharks are actually able to use an
alternative, previously unknown reproductive pathway, which is
parthenogenesis. The problem here is that this alternative
reproductive pathway results in offspring that have much lower genetic
diversity," he said.

The paper's lead author, Demian Chapman, who did the genetic analysis
while pursuing his doctorate at Nova Southeastern and now directs the
shark program at the Pew Institute for Ocean Science, said the reduced
genetic variability might pose a problem over time if males become
scarce under intense fishing pressure and females resort to asexual
reproduction. This, in turn, would result in "genetically
disadvantaged offspring," he said.

Still, Chapman added, the virgin birth does serve as a testament to
sharks' resourcefulness. Mammals cannot reproduce asexually.

"It just goes to show, life will find a way," he said, adding that
during his research in Belfast he bet several other scientists the
answer to the Omaha shark mystery would turn out to be something other
than parthenogenesis. "I lost so many pints of Guinness over that
one," he said.