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No Daddy Shark in sight: Zoo greets a cute shark pup after apparent parthenogenesis
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What if the song "Baby Shark" stopped after just two stanzas?
For non-fans of the catchy tune, that might sound like a dream. For a real-life Mommy Shark in Illinois, it's reality: She produced a baby without a Daddy Shark.
The epaulette shark pup hatched this summer at Brookfield Zoo, just west of Chicago. Its mother has been at the zoo since 2019; in that time, she's never shared a tank with a male.
It's a rare case of parthenogenesis, a type of asexual reproduction, according to the zoo.
The female shark had not been living among males
"Beginning in 2022, the adult female shark began laying two to four, typically infertile eggs, each month," the zoo said in a news release. "One of those eggs was fertile, and following a five-month incubation the pup hatched and has been behind the scenes being monitored by staff."
Sharks, we'll remind you, are fish and not mammals, although some shark species do give birth to live young.
The virgin-born pup is now 2 months old, measuring about 6 inches. It could grow to become an adult 2-3 feet long when fully grown.
"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," the zoo's Mike Masellis, a lead animal care specialist, said. "We are looking forward to guests being able to see the pup."
It's also cute as a button: Epaulette sharks exist at the intersection of cute and interesting, with distinctively large false eye spots resembling epaulettes. They're famous for being able to walk — on the seafloor and on coral, but also on land.
Asexual reproduction was only recently seen in sharks
The zoo says this is the second known case of apparent asexual reproduction producing an epaulette shark pup in an accredited zoo or aquarium. That other case was reported at the New England Aquarium in Boston — where the Chicago Zoo acquired its adult epaulette females.
Staff at the Brookfield Zoo say they've been getting tips on nursing the young pup through its first months from their colleagues at the New England Aquarium.
Parthenogenesis is well documented in insects and reptiles, and it's been seen in birds and fish. But it wasn't until fairly recently that it was confirmed in sharks.
Most notably, about 22 years ago, female bonnethead sharks, a type of hammerhead, produced "astonishing virgin births" at the Henry Doorly Zoo in Nebraska, "despite the prolonged absence of male sharks," as an academic study stated.
In that case, genetic analysis of the sharks showed that the baby had no evidence of any paternal DNA.
Parthenogenesis cuts out the middle man
The specific type of asexual reproduction seen in sharks is called automictic parthenogenesis.
Rather than combining an egg with sperm, this form of reproduction uses a polar body — a byproduct of germ cells that undergo meiosis to produce eggs. Polar bodies contain chromosomes, but they're normally absorbed back into the female's body.
When a shark undergoes parthenogenesis, "one of the polar bodies that should have been absorbed under normal circumstances of sexual reproduction didn't get reabsorbed and actually acted like a sperm and fused with the cell that was actually going to become an egg," as shark expert Mahmood Shivji told NPR about those earlier cases, back in 2007.
The result is a fertilized egg with the normal complement of chromosomes — but it doesn't have all of the genetic diversity that sexual reproduction would bring.
The baby bonnethead shark that triggered that big discovery two decades ago met with a sad end: It was attacked and killed hours after it hatched. The epaulette baby is more fortunate, and it recently went on display in the zoo's Living Coast exhibit.
Copyright 2023 NPR. To see more, visit https://www.npr.org.
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