24 May, 2007 l 0424 hrs ISTlREUTERS
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 in Northern Ireland 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.
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 S Shivji, director of the Guy Harvey Research Institute.
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 E Hueter, director of the Center for Shark Research 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.
View more random threads: