Shark Born From Virgin Birth (5/23/2007)

Hammerhead Shark taken whilst scuba diving at Cocos Island. - http://www.flickr.com/photos/98635529@N00/

On 14 December 2001, workers at Omaha's Henry Doorly Zoo, came to work to discover a mystery that went unsolved for six years. That day they discovered a new baby hammerhead shark, in a tank with only females.

For many years, different theories were tossed around:

• One of the females had been inseminated by a shark from a different species
• One of the females had been inseminated before being captured
• Female sharks have an organ that allows them to store sperm, but the sharks were isolated for three years

Initially Paulo Prodöhl of Queen's University Belfast in Northern Ireland expected to find that the shark was inseminated by another species or before being captured. At the time he had trouble believing asexual reproduction was possible in a shark.

Prodöhl is part of a group of researchers that determined that one of the females did reproduce asexually to produce the mystery shark.

The team, led by Demian Chapman of the Pew Institute for Ocean Science in the US, used a DNA fingerprinting techniques similar to those used in human paternity tests. Initially, this was to determine which of the three females was the mother.

In offspring that are created sexually, half the DNA comes from the mother and the other half from the father. After determining the mother, finding the father is just a matter of subtracting the mothers DNA markers and matching the remaining markers to the father. In this case there was no father, making it the first documented case of asexual reproduction in cartilaginous fish.

The discovery leaves mammals as the only vertebrates known to not be able to reproduce asexually.

The researchers believe the hammerhead shark was created by a type of asexual reproduction called automictic parthenogenesis, where an unfertilized egg is fertilized by a nearly identical cell known as the sister polar body.

Because the unfertilized egg and the polar body both contain only half of the mother's genes, the baby shark also only got half of its mother's genes.

The researchers believe this restriction of genetic diversity could be important to the survival of shark species if female hammerhead sharks switch to asexual reproduction when they are having trouble finding a mate.

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