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A female blacktip shark in Virginia fertilized her own egg without mating with a male shark, new DNA evidence shows. This is the second time scientists have used DNA testing to verify shark parthenogenesis—the process that allows females of some species to produce offspring without sperm.

The female shark, dubbed Tidbit, died during a routine physical exam before the pregnancy was identified.

A necropsy—an animal autopsy—after her death revealed she was carrying a near-term pup fetus that was about 12 inches (30 centimeters) in length.

Tidbit was caught in the wild when she was very young and reached sexual maturity in a tank at the Virginia Aquarium in Virginia Beach, where she lived for eight years.

"The interesting thing about that was there were no male blacktip sharks in the tank for the entire time of her captivity," said Demian Chapman, a researcher with the Institute for Ocean Conservation Science at Stony Brook University in New York.

"So the question is, where does this baby come from?" he asked.

Chapman is the lead author of a study on the female blacktip in the latest issue of the Journal of Fish Biology.

DNA fingerprinting

Chapman and his colleagues generated a DNA fingerprint for the mother shark and her pup fetus with a procedure identical to a human paternity test.

Ordinarily, a shark's DNA contains some genetic material from its mother and some from its father. Tidbit's pup, however, was not ordinary.

"Every part of the fingerprint of the embryo comes from the mother," Chapman said. "In other words, there is no genetic material from a father."

All non-mammal vertebrate species are theoretically capable of parthenogenesis, scientists say. Examples have been documented in komodo dragons , pythons, rattlesnakes, chickens, and turkeys.

Parthenogenesis is not possible in humans because if all the genetic material comes from the mother, certain genes will be switched off, and the embryo won't develop.

"For sharks in captivity, [parthenogenesis] has probably occurred more times than has been documented," says Robert Hueter, director of the Center for Shark Research at Mote Marine Laboratory in Sarasota, Florida.

The question then becomes, is parthenogenesis a type of developmental anomaly or a response to the female shark not having a mate in captivity?

"The fact that only one shark embryo was formed may suggest that this is more a case of an egg developmental aberration rather than a physiological response to the lack of a mate," said Hueter, who was not involved with the study.

No Variation

Normally, an embryo is formed when an egg containing half its chromosomes is fertilized by a sperm containing the other half.

When an egg cell is formed, a plant or female animal also produces three other cells called polar bodies. In the type of parthenogenesis observed in sharks, one of those cells behaves like a sperm and fertilizes the egg.

"But that cell is genetically identical to the egg," Chapman said. "So that's where you lose a lot of genetic variation."

Offspring produced by parthenogenesis are not exact clones of their mothers, however, because the genetic material is mixed differently.

Still, researchers believe the risk of congenital defects increases in animals whose DNA lack genetic variation.

"There's an increased risk of having a weakened immune system and there's a risk of reproductive abnormalities," Chapman said. "But in some cases, they'll be able to survive."

The scientists have not ruled out the possibility that increased stress from the abnormal pregnancy contributed to Tidbit's death.

The race is on to make commercial amounts of ethanol or other biofuels out of plant waste containing cellulose -- a fibrous component of plants that gives them structure. But some researchers are looking at a different option -- using cellulose to power microbial fuel cells, in which bacteria digest plant waste matter to create electricity directly.

These fuel cells could be used to charge batteries or power electrical devices.

Others are considering drawing power from microbes digesting human waste at wastewater treatment plants or manure from feedlot lagoons.

"Basically, we're converting cellulose into a different energy source than ethanol," said John Regan of Pennsylvania State University in University Park.

"It's not more efficient right now, but if you look at what's been done over the last decade, there has been about a five to six order-of-magnitude (100,000-1,000,000-fold) increase in power density."

What are Second Generation Biofuels?
Ethanol made from cellulose, as opposed to ethanol made from corn, is a second generation biofuel. The difference, and it's an important one, is that second generation biofuels use non-food residual biomass like the stems, leaves, wood chips, and husks, or they use non-food crops that can be grown without high energy inputs, like switchgrass.

Verenium's Cellulosic Ethanol Goals
Verenium wants to create cellulosic ethanol at $2 per gallon, which right now would make it fairly competitive with corn ethanol and regular gasoline.

But this demonstration plant is just the beginning: Next year, Verenium wants to built several commercial plants that would each produce 20 to 30 million gallons of cellulosic ethanol yearly. That's still a fairly small drop in the bucket of gasoline consumption, but it would be much better than corn ethanol, and certainly better than fossil fuels.

What to do with Corn Ethanol?
One question that remains is: What do we do with all that corn ethanol?

The best hope would be to convert corn ethanol biorefineries into second generation biofuel plants. That might or might not be possible on a technical level, but we suspect that on a political level it will be even harder. The farm lobby is very good at keeping subsidies forever. When food prices are low, they ask for subsidies, when prices are high (as now), they ask for more. So who knows if the fat corn ethanol subsidies will ever be repelled?

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