Lone zebra shark surprises scientists with pups

A zebra shark surprised researchers in Australia when she hatched a trio of eggs three years after she was last paired with a mating partner, according to a study published Monday in Scientific Reports.

Leonie the shark was separated from her partner in 2013, but in April 2016 managed to hatch the eggs. It is the first known time that a shark has switched from sexual to asexual reproduction, according to scientists at the University of Queensland.

"We thought she could be storing sperm, but when we tested the pups and the possible parent sharks using DNA fingerprinting, we found they only had cells from Leonie," said Christine Dudgeon, research officer at the University of Queensland's School of Biomedical Sciences. "Leonie adapted to her circumstances, and we believe she switched because she lost her mate."

Leonie was captured in the wild in 1999 and first introduced to a male shark at the Reef HQ aquarium in Queensland. The pairing wasn't fruitful until scientists again paired the two in 2006. Leonie started laying eggs in 2008 and continued to produce litters until 2013, according to researchers.

In 2013, Leonie's daughter, Lolly, was added to her tank. The next year, both sharks laid eggs.

"Much like a chicken, they will lay eggs if the conditions are good, whether they are fertile or infertile," Dudgeon told The Guardian Australia.

Despite the lack of male sharks, six of Leonie's 47 eggs had live embryos inside. However, by the third month of incubation, all six had died.

Again, both sharks laid eggs last year. Four of them hatched – three from Leonie's clutch and one from Lolly's.

It's incredibly rare for females of a species to switch from sexual to asexual reproduction. There are only two other documented cases, according to The Guardian. An eagle ray who was separated from her partner for a year managed to reproduce and a boa constrictor asexually reproduced, although she was caged with a male boa constrictor, according to the newspaper.

It's not clear what caused Leonie to switch from sexual to asexual reproduction.

"What we want to know now is, could this occur in the wild and, if so, how often does it?" Dudgeon said. "This has big implications for conservation and shows us how flexible the shark's reproductive system really is."

However, she warned The Guardian, the switch is unlikely to herald a turning point for the endangered species. She described the case to the newspaper as similar to "a severe case of inbreeding."

Scientists will watch Leonie's offspring to determine whether they can reproduce despite their odd beginnings.

"You lose genetic diversity with generations of asexual reproduction, so we'll be seeing if these offspring can mate sexually themselves," Dudgeon said.