A Louisiana aquarium has a new mystery to unravel after a baby shark was born in a habitat with no males present. The Shreveport Aquarium announced that Yoko, a swell shark, hatched on January 3, eight months after her egg was discovered in a tank with only female sharks. What makes this case even more intriguing is that the two females in the tank hadn’t been in contact with a male for over three years.
“This is extraordinary and demonstrates the resilience of this species,” said Greg Barrick, the aquarium’s curator. “It really shows that life… uh… finds a way.”
The aquarium is exploring two main theories for Yoko’s birth: delayed fertilization or parthenogenesis, a rare form of asexual reproduction where offspring are genetic clones of their mother. Both phenomena have been observed in various plants and animals, including sharks.
Kevin Feldheim, the Pritzker Lab Manager at the Field Museum in Chicago, explained that both possibilities are plausible, and genetic testing is needed to confirm what happened. Some female sharks can store sperm in their oviducal gland, and scientists know little about how long sperm can remain viable. In one case, a female brownbanded bamboo shark at a San Francisco aquarium gave birth nearly four years after its last contact with a male.
Parthenogenesis has also been recorded in several shark species, such as the bonnethead and the zebra shark, though it has been documented in the wild only once, in the smalltooth sawfish. Feldheim described parthenogenesis as a “last-ditch effort” for females to pass on their genes when isolated from males, but the triggers for the process remain unclear.
Yoko’s future is uncertain, and the aquarium plans to confirm the method of her reproduction through genetic testing once she’s large enough for a blood draw, likely in a few months. The aquarium will analyze the genetic sample using karyotyping, which examines the size, shape, and number of chromosomes, comparing it to those of the two female sharks that might have laid the egg.
Yoko is being kept “off exhibit” for now but has already made her social media debut. She will eventually move to a larger tank once she’s old enough. Though she is currently thriving, the aquarium acknowledges that sharks born through such rare reproductive events often face significant challenges. Parthenotes, offspring from parthenogenesis, typically struggle with survival and fitness, according to the Smithsonian Institution’s National Museum of Natural History.
Feldheim also noted the variability between species in terms of survivability. While zebra shark parthenotes have not survived to sexual maturity, a female whitespotted bamboo shark not only survived but also reproduced through parthenogenesis.
Despite the uncertainty about Yoko’s future, the aquarium is already celebrating her as a significant contribution to shark reproductive research and conservation efforts. “Even if Yoko’s time with us is brief, her legacy will leave an indelible mark on science,” they said.