for National Geographic News
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. (Read about the first time.)
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.
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."
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