Science - Shark in 'virgin birth'

RICHMOND: Scientists have confirmed the second case of a “virgin birth” in a shark.

In a study reported on Friday in the Journal of Fish Biology, scientists said DNA testing proved that a pup carried by a female Atlantic blacktip shark in the Virginia Aquarium & Marine Science Centre contained no genetic material from a male.

The first documented case of asexual reproduction, or parthenogenesis, among sharks involved a pup born to a hammerhead at an Omaha, Nebraska, zoo.

The aquarium sharks that reproduced without mates each carried only one pup, while some shark species can produce litters numbering in the dozen or more. The scientists cautioned that the rare asexual births should not be viewed as a solution to declining global shark populations.

“It is very unlikely that a small number of female survivors could build their numbers up very quickly by undergoing virgin birth,” Mr. Chapman said.

The medical mystery began 16 months ago after the death of the Atlantic blacktip shark named Tidbit at the Virginia Beach aquarium. No male blacktip sharks were present during her eight years at the aquarium. In May 2007, the 152-cm, 43-kg shark died of stress-related complications related to her unknown pregnancy after undergoing a yearly checkup. The 25.4-cm shark pup was found during a necropsy of Tidbit, surprising aquarium officials. They initially thought the embryonic pup was either a product of a virgin birth or a cross between the blacktip and a male of another shark species — which has never been documented, Chapman said. Tidbit’s pup was nearly full term, and likely would have been quickly eaten by “really big sand tiger sharks,” he said.

The scientists said the new pups acquired one set of chromosomes when the mother’s chromosomes split during egg development, then united anew. Without the chromosomes present in the male sperm, the offspring of an asexual conception have less genetic diversity and, the scientists said, may be at a disadvantage for surviving in the wild. — AP