The shark and the virgin birth

Scientists have confirmed the second case of a virgin birth in a shark. In a study reported today in the Journal of Fish Biology, scientists said DNA testing proved that a pup carried by a female blacktip shark in a Virginia aquarium 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 mystery began 16 months ago after the death of Tidbit, a blacktip shark who lived for eight years at the Virginia Aquarium and Marine Science Centre without a male of the same species in sight. In May 2007, she died after she was given a sedative before undergoing a yearly checkup and the 25-centimetre shark pup was found during a necropsy. Scientists initially thought the embryonic pup a cross between Tidbit and a male of another shark species – something which has never been documented. However, DNA testing proved this not to be the case. Virgin birth has been proven in some bony fish, amphibians, reptiles and birds, and has been suspected among sharks in the wild. The scientists who studied the Virginia and Nebraska sharks said the newly formed pups acquired one set of chromosomes when the mother’s chromosomes split during egg development, then united anew. The scientists said their findings offer “intriguing questions” about how frequently automictic parthenogenesis occurs in the wild. AP