Female Sharks Reproduce With Out Dad!

Virgin births are possible in female sharks, accordingto a new study that determined a captive female bonnethead sharkreproduced without having been near a male in three years.Since other captive females — including a white spotted bamboo shark —have anecdotally accomplished the same feat, researchers conclude itis likely all shark species possess the ability.The recent determination, made possible through DNA analysis, actuallyapplies to the birth of a bonnethead shark (of the hammerhead family)that occurred six years ago at the Henry Doorly Zoo in Nebraska."It was a big surprise for us," zoo director Lee Simmons toldDiscovery News.Simmons added, "We brought in three female bonnetheads on December 15,1998, and on December 14, 2001, bang! One of them gave birth to an8-inch-long offspring."The pup unfortunately died the same day from internal injuries likelycaused by a stingray in the same exhibit that munched the wiry infantand then spit it out. Puzzled by the birth, Simmons and his team putthe offspring on ice and handed it over to the Guy Harvey ResearchInstitute at Nova Southeastern University.At this point Simmons said he considered all possibilities, includinga delayed pregnancy, which is possible in some insects that can storesperm and then give birth much later.Mahmood Shivji, director of the institute, and his team collectedtissue samples from all of the zoo's female bonnetheads. DNA analysis,which took several years, identified one female as the mother.Research on the perished pup found that it had no paternal DNA.Additionally, it possessed half of its mother's genetic diversity.Combined, the data indicates the mother gave birth through anon-sexual mode of reproduction known as automatic parthenogenesis.Shivji explained to Discovery News that this process involves thefemale creating an egg that contains fifty percent of the mother'sgenes. It is induced to behave as though it has been fertilized by atiny, genetically similar cell called a sister polar body.The resulting offspring therefore is doubly genetically disadvantaged."It had no father to provide genetic diversity, and it even lacks itsmother's full genetic makeup," Shivji said.He speculates that such births can only occur when females do not haveaccess to males, such as in a captive setting, or in the wild whenoverfishing depletes shark populations."We now are concerned, because if conditions prompt asexualreproduction in the wild, the species could be at an evolutionarydisadvantage," he said.While the new research, published in today's Royal Society BiologyLetters, represents a rare, documented case of an asexual birth in ashark, it's already known that certain birds, reptiles and amphibiansalso possess the ability.Shivji said it is significant that sharks can now be added to thelist, since they are the world's oldest living vertebrates, a group ofbackboned animals that also includes humans.Since humans and mammals lack the ability, he suspects it evolvedearly on in the vertebrate lineage, but was lost in some groups whenthey diverged from their common ancestor with sharks about 450 millionyears ago.