In Chicago, one shark has shown that she doesn’t need a male to become a mother. Despite not being housed with a male for years, the female epaulette shark (Hemiscyllium ocellatum) produced a fertile egg that has now hatched.
Aquarium staff think that this apparent marine miracle is in fact all down to a process called parthenogenesis, a word originating from the Greek word “parthenos” meaning “virgin” and the Latin “genesis” meaning “birth”. Parthenogenesis can allow an embryo to develop from an unfertilized egg cell.
In this case, the female shark arrived at Brookfield Zoo aged 3 years old. Epaulette sharks typically reach sexual maturity around age 7, and this particular individual had not been housed with a male since 2019. In 2022, she began laying two to four infertile eggs a month – but one was carrying a little surprise, turning out to be fertile. The egg was incubated for five months and hatched on August 23.
“We are happy to report that our epaulette pup has been eating well on her diet of finely chopped capelin, minced squid tentacles, and other finely chopped seafood,” Mike Masellis, a lead animal care specialist at Brookfield Zoo, said in a statement.
So how can parthenogenesis happen in species that normally undergo sexual reproduction? Although some species only reproduce this way, such as the New Mexico Whiptail lizard (Aspidoscelis neomexicana), this is definitely not the case for sharks. One way is the egg becoming fertilized as it re-merges with a polar body – a small cell formed at the same time as the egg. However, as the offspring only has the mother’s genetic material, rather than benefitting from the genetic mixing that comes from sexual reproduction, this can cause some issues.
“Our colleagues at New England Aquarium have been a great resource as shark pups produced parthenogenetically can be very delicate,” explained Masellis.
This isn’t the first time parthenogenesis has been observed in sharks, or even this particular species – Brookfield Zoo explained that it has also happened in epaulette sharks at New England Aquarium, where Brookfield got their female sharks.
Parthenogenesis was observed in a hammerhead shark in 2007, and potentially in a smooth-hound shark in 2021. More recently, in 2022 a particularly choosy zebra shark had pups via parthenogenesis even though healthy males were available to do the job.
Epaulette sharks are fascinating creatures outside of their capability for virgin birth. Found around Australia and New Guinea, they are typically bottom feeders, and can “walk” around on their fins in search of food. Far from fish ambling around out of water being reserved for fictional works like Junji Ito’s Gyo, this shark species has actually been observed walking around on land.
“We are looking forward to guests being able to see the pup,” said Masellis.