Shark gives "virgin birth"
Washington, Oct 12 : Scientists have used DNA testing to verify that a female
blacktip shark in Virginia, US, fertilized her own egg without mating with a male shark, a
process which has been dubbed as "virgin birth".
According to a report in 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.
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 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," he added.
According to scientists, all non-mammal vertebrate species are theoretically capable of
parthenogenesis. Examples have been documented in komodo dragons, pythons, rattlesnakes,
chickens, and turkeys.
"For sharks in captivity, parthenogenesis has probably occurred more times than has
been documented," said Robert Hueter, director of the Center for Shark Research at Mote
Marine Laboratory in Sarasota, Florida.
"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," he added.
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.
Ends AK
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--ANI
