Biologists are looking at how a shark in a Great Lakes region aquarium gave "virgin birth" last year. Photo courtesy of Belle Isle Aquarium, Detroit.
A female shark in an aquarium in the Great Lakes region has apparently given virgin birth. Four shark eggs hatched last year and three of those babies are now growing normally. As the Great Lakes Radio Consortium’s Celeste Headlee reports, it may be some time before the cause can be determined, but the event is still a surprise for biologists:
Transcript
A female shark in an aquarium in the Great Lakes region has apparently given virgin birth. Four
shark eggs hatched last year and three of those babies are now growing normally. As the Great
Lakes Radio Consortium’s Celeste Headlee reports, it may be some time before the cause can be
determined, but the event is still a surprise for biologists:
Biologists have a technical term for virgin birth. It’s called parthenogenesis. Doug Sweet is the
Curator of Fishes at the Belle Isle Aquarium in Detroit. He says parthenogenesis is common in
invertebrates and some amphibians.
“Most vertebrate animals, the females will produce eggs even if the male is not around. And it’s
just a matter of… it’s a chemical trick, basically, to get that egg to develop into an individual
without a sperm activating it.”
But parthenogenesis has been totally unheard of for sharks, until now. Last year, the Henry
Doorly Zoo in Omaha, Nebraska, announced they thought a Bonnethead shark there had
reproduced by parthenogenesis. The baby lived less than 12 hours, though, and genetic tests were
inconclusive.
But when Doug Sweet saw the press release from the Henry Doorly Zoo about a possible virgin
birth, he thought he’d try an experiment. Sweet decided to incubate the eggs of his two female
bamboo sharks. Four of the eggs developed. Sweet says the sharks were acquired by the
aquarium before they had reached sexual maturity, and they have never been exposed to a male.
He says the likely conclusion is that these sharks are reproducing by parthenogenesis.
Two other explanations, though highly unlikely, are that the shark has both testicular and ovarian
tissue, and fertilized its own eggs or that sharks are capable of storing sperm for years and even
passing it down to their offspring. Sweet has sent small clippings from the sharks’ fins to the
Henry Doorly Genetics Lab. Testing has already begun, but Sweet says it could take more than a
year to get the results. In the meantime, Sweet says the facts remain the same: a female shark
has given virgin birth. If it is parthenogenesis, he says, it will have important implications for
biologists around the world.
“Parthenogenesis just hasn’t been considered to happen in sharks; it’s never been recorded. It may
be happening all the time out there, so this is kind of breaking news in the shark world.”
The two adult bamboo sharks and the offspring are currently on exhibit at the Belle Isle
Aquarium in Detroit.
For the Great Lakes Radio Consortium, I’m Celeste Headlee.