Australia's Reef HQ aquarium had hoped to scale back its shark breeding program. Its female sharks had other ideas. Over the course of six years, Leonie the zebra or leopard shark had produced more than two dozen offspring before she was separated from her mate in 2012. But in 2016, Leonie—who hadn't been introduced to another male—laid eggs that produced hatchlings, reports New Scientist. While sharks are known to store sperm for up to four years, per the Guardian, these hatchlings contained DNA from Leonie only. In essence, she made the offspring herself, marking the first time a switch from sexual to asexual reproduction had been witnessed among sharks, researchers explain in Scientific Reports.
Asexual reproduction itself is not unheard of, with species including snakes, rays, turkeys, Komodo dragons, and, of course, sharks known to be capable of it. But it usually occurs only when the females have had no male partners. (In fact, one of Leonie's offspring who'd never shared a tank with a male also produced hatchlings.) Only two other animals, a boa constrictor and an eagle ray, have been known before Leonie to have switched from sexual to asexual reproduction. That was a "really big surprise," researcher Christine Dudgeon tells the Brisbane Times. It's likely a trait used only in extreme circumstances because any offspring would be at a disadvantage with only their mother's DNA. "Having half of this genetic diversity means they are probably not able to continue this lineage very far into the future," says Dudgeon. (Read about a snake's virgin birth.)