Shedd's zebra shark gives birth through rare parthenogenesis, or 'virgin birth'

CHICAGO (WLS) -- At six and a half feet long zebra sharks are one of the largest species at Chicago's Shedd Aquarium. The endangered animals, which are native to Indonesia, have been a fixture at the Wild Reef exhibit since it opened almost 20 years ago.

"They started reproducing in 2004 and have produced over 100 offspring over 15 years," said Lise Watson, assistant director of animal operations and habitat. "We've had one of the most successful breeding programs anywhere around the world with the species."

The pups were all conceived with the help of male sharks, or so they thought, until genetic testing was done on the offspring of a zebra shark named Bubbles. She is the first known at the Shedd to reproduce by a process called parthenogenesis, meaning "virgin birth," in which Bubbles fertilized an egg with her own genetic material.

"We always considered parthenogenesis basically like a Hail Mary. A female that wasn't with males and she is trying to pass on her genes," Watson said.

While zebra sharks are a species that can reproduce asexually, it is rare. Researchers said it's even more unusual that Bubbles chose parthenogenesis even though she was exposed to three mature breeding males.

"Now the question becomes why," said Kevin Feldheim, Field Museum lab manager. "Why is it that she did not like them, were they not pretty enough? We don't know."

Feldheim said the question must be answered for the survival of zebra sharks. He said virgin birth pups have low rates of survival; the two born to Bubbles both died.

"If parthenogenesis is occurring at a very high rate that is not a good thing, because we want a lot of genetic variation of the individuals we put back into the wild," he said.

The Shedd Aquarium plays a key role worldwide in the conservation of zebra sharks. The extremely rare discovery about Bubbles was recently published in a new study.

Through continued genetic testing and observation, researchers at the Shedd and Field Museum are hopeful questions about the biology of zebra sharks will be answered someday. Researchers said their new study is just the beginning.