Shark gives virgin birth

October 11th, 2008 - 12:27 pm ICT by ANI  

National Geographic

Washington, Oct 11 (ANI): 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 sharks 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. (ANI)

Related Stories

Tags: , , , , , , , , , , , , , , , , , , ,

Posted in National |