The American study, on an Atlantic blacktip shark housed in a Virginia aquarium, showed that the female had managed parthenogenesis - the ability to reproduce without having mated with a male.
The project team used DNA analysis similar to that used in human paternity testing. They were alerted to launch the study after the adult aquarium blacktip, called Tidbit, was found to be pregnant despite the fact that she had remained in captivity, with no contact with males, since shortly after her own birth in the wild.
This followed the discovery, in May last year, of parthenogenesis by a hammerhead aquarium shark in Omaha, Nebraska.
'It is now clear that parthenogenesis occurs in sharks other than just hammerheads,' said the group's report author Dr Demian Chapman, of the Institute for Ocean Conservation Science at New York's Stony Brook University. His view was that 'this is something female sharks of many species can do on occasion'.
The blacktip is closely related to the tiger, bull and dusky sharks. 'This raises intriguing questions about how frequently this may occur in the wild in this group of heavily fished sharks,' said joint researcher Dr Mahmood Shivji, Director of the Guy Harvey Research Institute and Professor at Florida's Nova Southeastern University.
'It is possible that parthenogenesis could become more common in these sharks if population densities become so low that females have trouble finding mates.'
But, warned Chapman, this was in no way a panacea for the ills of overfishing. 'It is very unlikely that a small number of female survivors could build their numbers up very quickly by undergoing virgin birth,' he said.
The sharks' parthenogenesis occurs when the mother's chromosomes split during egg development and, instead of combining as normal with split chromosomes from a male's contributed sperm, combine instead with a copy of themselves.
Resultant offspring feature reduced genetic diversity, which can be a disadvantage in environmental adaptation.
A study report on the Virginia blacktip's parthenogenetic birth has been published in the Journal of Fish Biology. |
