At an aquarium in Queensland, Australia, a zebra shark (Stegostoma fasciatum) named Leonie gave birth to pups in April 2016. Although interesting for aquarium goers, the births wouldn’t have garnered much attention from scientists if it weren’t for the small fact that Leonie hadn’t mated with a male zebra shark since 2012. Thus, according to Science Alert, Leonie made history as the first known case of a shark shifting from sexual to asexual reproduction who had mated before.
In the past, scientists have occasionally observed “virgin births” occurring with animals such as rays, sharks and various reptiles. However, these animals had never mated with a male.
According to CNN, the only other animals to have shifted from sexual to asexual reproduction in captivity are a boa constrictor and an eagle ray. Yesterday, Christine Dudgeon, a biologist at the University of Queensland, published a report on Leonie unusual reproductive shift.
After the zebra shark gave birth with no mate, Dudgeon and her team initially considered two possibilities. Their first thought was that Leonie might have used sperm stored in her body, an occurrence which has been documented in the past. The other option was parthenogenesis, or asexual reproduction.
When they performed genetic testing on Leonie’s pups, the results showed an elevated homozygosity, which means more genes were identical, suggesting the asexual theory more likely than stored sperm.
Dudgeon stated in the New Scientist that asexual reproduction in sharks can take place when the eggs of a female are fertilized by a nearby cell known as a polar body. Since this cell also contains the genetic material of the mother, Dudgeon mentioned this leads to “extreme innerbreeding,” which means it’s not a good strategy in the long run because it reduces adaptability and genetic diversity in future generations.
However, for the zebra shark Leonie and others like her, the strategy still comes in handy when a man is hard to find. Dudgeon believes the strategy may be used to pass down the mother’s genes from generation to generation until a male finally shows up.
Dudgeon also noted asexual reproduction may not be as rare as it sounds, scientists just haven’t thought to look for it. For now, scientists in Australia are waiting for Leonie’s pups to reach sexual maturity before taking the study further. Although zebra sharks, also known as leopard sharks, were once common in tropical waters around the world, they have recently been listed as endangered on the IUCN Red List of Threatened Species.
By Rebeccah Dean
Photo Courtesy University of Queensland