Thu, May 24, 2007 - Page 7 News List

Shark reproduced without mating, researchers say


A hammerhead shark swims in a large tank at the Georgia Aquarium in Atlanta on Oct. 27, 2005. Researchers say sharks are capable of asexual reproduction.


A hammerhead shark that gave birth in a Nebraska aquarium reproduced without mating, a genetic analysis shows.

This form of asexual reproduction, called parthenogenesis, has been found in other vertebrate species, including some snakes and lizards. But this is the first time it has been documented in a shark.

Researchers from the Guy Harvey Research Institute at Nova Southeastern University in Florida and Queen's University Belfast found no male DNA in the female baby shark, which was born in December 2001 and died shortly after birth, apparently killed by another fish.

The mother was one of three female bonnetheads, a small hammerhead species, that had been captured in Florida and kept without male sharks for three years in the Henry Doorly Zoo in Omaha, Nebraska.

At the time of the birth, many scientists thought that the female had mated with another species, or that it had used sperm obtained years before. Female sharks are capable of storing sperm, although none have been known to store it as long as these sharks had been isolated.

But through the analysis "it was pretty clear that there was no male contribution," said Mahmood Shivji, director of the Guy Harvey Research Institute and author of a paper on the finding being published online today by the journal Biology Letters.

Instead, the female shark's own genetic material combined during the process of cell division that produces an egg. A cell called the secondary oocyte, which contains half the female chromosomes and normally becomes the egg, fused with another cell called the secondary polar body, which contains the identical genetic material.

Robert Hueter, director of the Center for Shark Research at the Mote Marine Laboratory in Sarasota, Florida, said the finding helped fill a gap in understanding of parthenogenesis, which has been found to occur in most vertebrate lines except mammals and, until now, cartilaginous fishes like sharks.

"These guys have proven their case," Hueter said of the Guy Harvey researchers.

Shivji said that after the bonnethead birth was reported, keepers at the Belle Isle Aquarium in Detroit reported similar virgin births.

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