Second 'Virgin Birth' Documented in Shark

Oct. 10, 2008 -- The first documented virgin shark birth seemed like an odd miracle, but now a second female has become pregnant sans daddy, adding to the evidence that female sharks don't always need a male to conceive, according to a new study.

Virgin birth, scientifically known as parthenogenesis, has previously been proven in certain amphibians, reptiles, birds and bony fish. It's now suspected that most, if not all, female sharks possess the ability.

"Parthenogenesis may not have evolved in sharks," Demian Chapman, who led the research, told Discovery News. "It may just be an occasional mistake that sometimes occurs when eggs are left unfertilized."

Chapman, a shark scientist with the Institute for Ocean Conservation Science at Stony Brook University, explained that during egg production, a female shark produces four cells. Only one of these becomes the egg. Another of the four is called "the sister polar body," which is a close genetic match to the egg.

During parthenogenesis, according to Chapman, "the sister polar body fuses with the egg and injects its chromosomes into it."

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"Therefore, it acts like a sperm and triggers the development of an embryo," he said.

The discovery in this case is bittersweet, since the virgin shark in question, a female blacktip shark named "Tidbit," died after living for eight years without a male companion at the Virginia Aquarium.

An autopsy upon her death revealed that she was pregnant with a single offspring. DNA testing of the unborn offspring showed that it contained no genetic material from a father.

A paper outlining the findings appears in the latest issue of the Journal of Fish Biology.