Test shows aquarium shark's pregnancy was a solo project

VIRGINIA BEACH

It doesn't take two to tango, as proved by a shark at the Virginia Aquarium & Marine Science Center that produced a baby without a father.

DNA analysis showed that the fetus carried only the mother's genes. This is the second proven case of so-called "virgin birth" in sharks, or parthenogenesis. The first case was in a hammerhead shark in a Nebraska facility, which was reported only a short time before the Virginia Aquarium baby was discovered, unborn, during a necro-psy on its mother.

The local shark was a blacktip named Tidbit that had been in captivity for about 10 years without a mate. She was in an exhibit with two other shark species, so the possibility of a hybrid pup was considered first. But DNA "fingerprint" testing showed otherwise, as reported today in the Journal of Fish Biology.

"There was absolutely no genetic material from a father," said lead author Demian Chapman of the Institute for Ocean Conservation Science at Stony Brook University in New York. "Every part of this fingerprint from the baby was a match for Tidbit."

Most interesting, Chapman said, was that the baby had only half the genetic diversity of the mother. In sexual reproduction, half of the baby's genetic material comes from the mother and half from the father. Tidbit's baby had half of the mother's material, which had joined with an identical half, also from the mother.

"It's pretty much as inbred as you can get," Chapman said.

The unborn pup was discovered during a necropsy on Tidbit. She had been sedated for a routine vet exam in May 2007 but did not respond well. Curator Beth Firchau swam in the tank alongside her until Tidbit suddenly bit her on the leg. The shark died a short time later.

Tidbit had been captured too young to have mated in the wild, Firchau said, and was kept behind the scenes for two years until she was big enough to join the other sharks on exhibit. Had she given birth in the exhibit, the pup probably would have been eaten by its mother or by another shark, she said, and the aquarium would never have known. That, in fact, is what happened to the Nebraska shark pup, which was killed by something in its tank shortly after it was born.

Other animals, including Komodo dragons, lizards, some insects and some birds, can reproduce without mating. But larger vertebrates had not been known to produce babies asexually until it was confirmed in sharks.

Even humans can produce such cells, but they turn into ovarian cysts instead of babies. Some scientists say that the human cells, because they contain genetic material from only the donor, could be used to create stem-cell lines for treatment of diseases such as Type I diabetes in that donor, but Congress has outlawed it.

No one knows what triggers parthenogenesis in sharks. Wild populations of sharks have been declining, mostly because of overfishing, and a shortage of males could prompt females to produce young asexually, but that raises concerns about health.

"It's kind of a crapshoot, last-ditch way to reproduce," Chapman said.

Such babies have only half the genetic diversity of sexually produced young and are more likely to express mutations or recessive genes, Chapman said. Also, in species such as the hammerhead and blacktip, which give birth to live young, only one baby is produced at a time through parthenogenesis, as opposed to litters of up to several dozen in sexual reproduction, and only females are born.

Chapman is now studying parthenogenesis in white-spotted bamboo sharks, which lay eggs.

"There is a value to sexual reproduction," Firchau said. "Variation and diversity is the spice of life. But, boy, isn't it neat to know that these creatures have the ability to throw the rule book out the window and keep going?"

Diane Tennant, (757) 446-2478, diane.tennant@pilotonline.com