How a lonely female leopard shark became pregnant without a mate

Leonie the leopard shark has given birth to a litter of pups despite being separated from her partner for more than three years. The Independent spoke to the scientists investigating the world-first case to find out how it happened

A shark has given birth in an Australian aquarium despite being separated from her long-term male partner, in what scientists say is the world’s first documented case of virgin birth of its kind.

Leonie the leopard shark’s parthenogenesis birth initially baffled her handlers, and has since made headlines around the world. Speaking to The Independent, the authors of a study into the case said she appears to have “adapted to her circumstances” – and that the process is one which could save her species.

Parthenogenesis is a natural process of asexual reproduction that involves the development of embryos without fertilisation. It is relatively commonly found in plants and invertebrate organisms, but incredibly rare among vertebrate species. Most of the cases which have occurred involve animals who have never given birth previously through sexual reproduction.

In 1999, Leonie was introduced to a captive mature male leopard shark at the Reef HQ Aquarium in Townsville, Australia. The couple started to mate in 2006 and produced several litters of viable offspring each year.

In 2012, as part of a study on their juveniles, the male was removed from the aquarium. Leonie continued to produce unfertilised eggs, in the same way as chickens do in good conditions, and two years later, staff found embryos developing in some of them.

None of those embryos survived. But in early 2016, more seemingly fertilised eggs were discovered and three of these hatched.

At first, researchers thought Leonie had been able to store sperm from her previous partner over the years, a method already observed in the carpet shark species and some vertebrates, such as the eastern diamond-backed rattlesnake (Crotalus adamanteus).

Dr Christine Dudgeon, who led the study for the University of Queensland’s School of Biomedical Sciences, told The Independent, “We examined the DNA of the eggs from the offspring produced from the last mating season and following the removal of male and could see that the DNA signatures changed.”

The test showed that the pups only carried cells from Leonie, meaning that the trigger for the switch to asexual reproduction was the loss of the male.

“She adapted to the circumstances. It shows us how flexible the shark’s reproductive system really is,” she added.

One of Leonie’s pups, sexually produced with its prior male partner and born in 2009, also hatched one egg in June 2016 without being exposed to any reproductively mature males.

It raises the prospect of Leonie’s ability to give birth asexually being passed on through the generations. In their study, Dr Dudgeon’s team speculate that parthenogenesis could have the evolutionary advantage of allowing a female strand of DNA to “hold on” until male partners become available.

At the moment, researchers don’t know if this phenomenon could occur in the wild. The switch from sexual to asexual reproduction has only ever been documented three times in any vertebrate organism. The other instances were recorded in a captive eagle ray and a captive boa constrictor.

The new case comes at a remarkable time, as the newly released IUCN Red List of Threatened Species included leopard sharks as “endangered”. The animals have been impacted largely by overfishing.

“Leonie the leopard shark has made a switch that could save her species,” said Dr Dudgeon.

Dr Dudgeon and the team will now follow the pups until they reach maturity to see if asexually produced zebra sharks can reproduce with a male partner. This would itself be key to the species’ longevity, as genetic diversity is reduced by generations of asexual reproduction.

The research about Leonie and parthenogenesis was published in online journal Scientific Reports, produced by the Nature Publishing Group.