A Louisiana aquarium has a new star — and a mystery — on its hands after a baby shark was born in a habitat without any males.
The Shreveport Aquarium announced last week that Yoko the swell shark — named for "Onyoko," the Chumash word for shark — hatched on Jan. 3, about eight months after her egg was first discovered in a tank with only female inhabitants.
Not only that, it said, but its team "determined that the two female sharks present in the tank had not been in contact with a male in over 3 years."
"This situation is incredible and shows the resilience of this species," Greg Barrick, the aquarium's curator of live exhibits, said in the release. "It really proves that life ... uh ... finds a way."
Is it a miracle, a medical mystery or more? Scientists have two main theories.
The aquarium says Yoko's birth could be the result of either delayed fertilization or parthenogenesis, a rare form of asexual reproduction — in which offspring are identical copies of their mothers — that has been seen in certain kinds of plants and vertebrates.
Kevin Feldheim, the Pritzker Lab Manager at Chicago's Field Museum, told NPR by email that both explanations are possible, and genetic testing is needed to determine what actually happened.
Many kinds of female sharks can store sperm in their oviducal gland, he said, though scientists know relatively little about how long each species can do so.
In one of the longest known cases, scientists discovered in 2015 that a female brownbanded bamboo shark at a San Francisco aquarium had stored sperm for at least 45 months — it gave birth nearly four years after its last contact with a male.
Meanwhile, there have been published cases of parthenogenesis involving more than half a dozen shark species, Feldheim said, from the bonnethead to the common smooth-hound. With some, like the zebra shark and whitespotted bamboo shark, it has been documented in multiple aquariums.
Feldheim said the phenomenon has been documented only once in the wild (in the smalltooth sawfish) and continues to stump scientists.
"In general, we think parthenogenesis is a last ditch effort for a female to pass on its genes, so when a female is isolated from conspecific males, she is able to undergo parthenogenesis," he wrote. "How parthenogenesis kicks in or what cues the females use to begin the process remains to be discovered."
Yoko's future is uncertain too
The Shreveport Aquarium plans to seek confirmation through genetic testing once Yoko is the "suitable size" for a blood draw, likely in a few months.
Barrick told NPR that the aquarium will karyotype the sample — a type of genetic testing that examines the size, shape and number of chromosomes — and compare it to that of the two female swell sharks that could have laid the egg.
"We do not know which one laid it, but they both came to our facility at the same time from the same place," he explained.
Yoko is being monitored "off exhibit" for now, but has already made her social media debut. Barrick says the aquarium has fielded questions "basically every day" from people wondering when they can see her.
The aquarium says she will move out of quarantine to a larger tank when she is "old enough," and will share her progress on social media.
While it says Yoko is "currently thriving," it acknowledges that sharks born through these kinds of rare reproductive events often face "significant challenges."
According to the Smithsonian Institution's National Museum of Natural History, parthenotes "don't have the best track record when it comes to survivorship or fitness."
Feldheim said there seems to be variability between shark species on that front: While every zebra shark parthenote has died before reaching sexual maturity, one female whitespotted bamboo shark not only survived to sexual maturity but also gave birth through parthenogenesis.
"The simple answer is we don't know a lot," Feldheim added.
Whatever happens, the aquarium says, Yoko has already made her mark.
"Should Yoko's time with us be brief, it will still leave an unforgettable legacy, contributing invaluable insights to the study of shark reproduction and conservation efforts," it added.
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