Sharks can reproduce without a mate

Female hammerhead sharks can reproduce without having sex, scientists confirm.

The evidence comes from a shark at Henry Doorly Zoo in Nebraska which gave birth to a pup in 2001 despite having had no contact with a male. Genetic tests by a team from Belfast, Nebraska and Florida prove conclusively the young animal possessed no paternal DNA, Biology Letters journal reports.

The type of reproduction exhibited had been seen before in bony fish but never in cartilaginous fish such as sharks. Parthenogenesis, as this type of reproduction is known, occurs when an egg cell is triggered to develop as an embryo without the addition of any genetic material from a male sperm cell.

The puzzle over the hammerhead birth was reported widely in 2001, but it is only with the emergence of new DNA profiling techniques that scientists have now been able to show irrefutably what happened.

The investigation of the birth was conducted by the research team from Queen's University Belfast, the Southeastern University in Florida, and Henry Doorly Zoo itself.

The scientists say the discovery raises important issues about shark conservation. In the wild, these animals have come under extreme pressure through overfishing and many species have experienced sharp declines.

If dwindling shark groups resort to parthenogenesis to reproduce because females have difficulty finding mates, this is likely to weaken populations still further, the researchers warn.