In a First, Shark Switches from Sexual to Asexual Reproduction
A zebra shark in Australia loses her mate and, after years alone, has more pups anyway.
A zebra shark named Leonie has done something never before documented in a shark species: After having produced pups the old-fashioned way, she switched to asexual reproduction, hatching eggs without the help of a mate.
Scientists with Australia's University of Queensland (UQ) observed the change at the Reef HQ Aquarium and have documented it in a new study in the journal Scientific Reports.
While other sharks have reproduced without a mate, in a process called parthenogenesis, in which embryos develop without fertilization, the researchers there say Leonie is the first shark documented to have once produced offspring via mating and then jumped to doing so without a mate.
Up until 2013, Leonie had been documented breeding pups successfully with a mate. However, the duo had to be separated to solve space issues during a slow-down of the breeding program at the aquarium, CNN reported.
Leonie had no intervening males in her life, during the next three mating seasons, but in summer 2016 the news came that she had hatched three eggs anyway.
Now, genetic analysis of the 2016 hatching has ruled out other factors and confirmed that Leonie indeed had a parthenogenic birth, making her "switch" from sexual to asexual reproduction a shark first.
"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," explained the study's lead researcher Christine Dudgeon, in a statement.
So-called "virgin births" are not new to sharks. "It's much like a chicken: They lay eggs whether they are fertilized or not, if the conditions are good," Dudgeon told CNN. They happen in other animals too, such as snakes, insects, lizards, and other types of fish.
Dudgeon and her colleagues think Leonie simply adapted to her circumstances, once she'd lost her mate.
Next, the UQ scientists plan to study Leonie's pups - all female, as the shark could only pass on her own genetic information - to see if they will be able to reproduce with a partner.
"You lose genetic diversity with generations of asexual reproduction, so we'll be seeing if these offspring can mate sexually themselves," added Dudgeon.
They also want to know more about sharks switching to asexual reproduction in the wild - if and how often that occurs. "One reason why we haven't seen it before could be because we haven't been looking for it," Dudgeon said. "It might be happening in the wild but it's never been recorded in this species before."
Zebra sharks are classified as endangered, so reproduction by any method was welcome news to the scientists.
"This has big implications for conservation and shows us how flexible the shark's reproductive system really is," said Dudgeon.
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