In 2017, a zebra shark named Leonie in Australia gave birth to three baby sharks after being separated from her mate for five years. Studies found no evidence of a paternal genetic contribution. The wild-caught shark hadn’t been exposed to a male in at least three years but still gave birth to a normally developed, live female. The first recorded evidence of parthenogenesis in a cartilaginous fish (which includes sharks, rays, and skates) occurred in 2001 with a captive hammerhead shark. According to Dudgeon, “this is an extreme form of inbreeding.” These animals need genetic diversity to make sure that it continues to adapt to an ever-evolving environment.ĭudgeon now plans to monitor the pups development through maturity to see if they can eventually reproduce on their own or find a mate.Parthenogenesis, a form of asexual reproduction where embryos develop from unfertilized eggs, has been observed in captive female animals that are separated from males for extended periods of time. It’s important to note however, that there could be serious consequences to this survival tactic, and it may just prove to be a short term solution. It might be happening in the wild but it’s never been recorded in this species before,” Dudgeon adds. “One reason why we haven’t seen it before could be because we haven’t been looking for it. The question is, is this phenomenon exclusive to animals kept in captivity, or is it also something that could occur in the wild? This could prove to be a critical survival mechanism for the species, especially since it has been identified as an endangered species by the IUCN Red List.
There are only two other instances of this occurrence – from an eagle ray and a boa constrictor, and both were held in captivity. In the case of Leonie, who was placed in a different tank from her mate after the pair was producing too many pups for the staff to handle, Dudgeon believes that the shark was simply adapting to her new circumstances. It seems captivity may play a role in this evolutionary shift. In Leonie’s case, she went from breeding with with Leo (the pair have more than 20 offspring), to asexually producing three pups years after she was moved away from her partner. So why all the fuss about Leonie giving birth asexually if other sharks have done the same thing? Well, in other cases where sharks produced asexually, there was no history of sexual reproduction at all. They'd only ever reproduced asexually. It’s more common among plants and invertebrate animals, but it has been known to occur among sharks and lizards. This phenomenon is extremely rare, but parthenogenesis – a process that prompts the development of embryos without the need for fertilization – does happen. Christine Dudgeon of University of Queensland’s School of Biomedical Sciences. 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 Dr. "In April 2016 Leonie hatched three eggs, despite having no access to a mating partner for three mating seasons.
During the years in between, Leonie shared a tank with other female sharks, with no male contact – meaning Leonie just made history by becoming the first shark scientists have successfully observed making the switch from sexual to asexual breeding.
But in April 2016, Leonie gave birth to three pups. In 2013, Leonie, a female zebra shark in a Queensland aquarium, was separated from her breeding partner, Leo.
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