Staff at the Shreveport Aquarium in Louisiana were astonished by the birth of a baby swell shark named Yoko. The young shark hatched in a tank that housed only two female sharks, which had not come into contact with a male for over three years. Yoko's unexpected arrival left marine experts puzzled and intrigued.
Yoko hatched on January 3rd and is now "thriving" under the care of dedicated aquarists. The immediate question surrounding her birth is how it was possible without the presence of a male. Two possible explanations were proposed: either parthenogenesis occurred, allowing a female to produce offspring on her own, or delayed fertilization, where eggs are fertilized long after mating.
Parthenogenesis is a phenomenon in which an embryo develops from an unfertilized egg, and it was documented in some vertebrates, including sharks. Wild animals generally do not reproduce through parthenogenesis, making Yoko's birth extraordinary. Alternatively, delayed fertilization has been observed in some sharks, where fertilization could occur long after a mating encounter, possibly involving stored sperm from over three years ago.
To determine the exact cause of Yoko's birth, the aquarium plans to conduct DNA tests on the pup when she is large enough in a few months' time. "We are very excited to confirm in the next few months whether this is parthenogenesis or delayed fertilization," said Greg Barrick, curator at the Shreveport Aquarium. He added, "It really proves that life... uh... finds a way," referencing the 1993 film Jurassic Park.
Young sharks born through such rare reproductive events often face challenges to survive and tend to live shorter lives. The aquarium recognizes the inherent risks associated with Yoko's unusual birth circumstances but reports that she is currently "thriving" under their care. Yoko is being closely monitored and kept away from public view, but the aquarium is sharing her progress on social media until she is old enough to move to a larger tank.
The swell shark (Cephaloscyllium ventriosum) is endemic to the coastal waters of the eastern Pacific Ocean and is oviparous, meaning it lays eggs. Swell sharks are known for their ability to inflate their bodies to twice their normal size using seawater as a way of deterring predators. The egg from which Yoko hatched was first noticed about eight months ago, but estimates suggest it could have been laid up to two months before it was discovered. The gestation period for a swell shark is nine to twelve months, depending on water temperature, raising questions about the timeline for Yoko's conception.
Parthenogenesis was recorded in species such as fruit flies, turkeys, pythons, and Komodo dragons. In 2006, parthenogenesis was first documented in Komodo dragons when female individuals in two British zoos gave birth to offspring without mates. Some suggest that endangered animals may reproduce through parthenogenesis more often because finding a mate has become more difficult.
In nature, some animals delay the development of their embryos to wait for better conditions to have offspring, which may explain Yoko's mother's situation in captivity. However, it is unclear why there would be delayed fertilization in this case, as conditions for offspring are good in captivity.
It is not completely clear what triggers certain species to undergo parthenogenesis, and many aspects of this process remain unknown. The birth of Yoko is not only a biological curiosity but also contributes to scientific knowledge and shark conservation efforts. "Although Yoko's time with us may be brief, she will still leave an unforgettable legacy, providing invaluable knowledge to the study of shark reproduction and conservation efforts," Barrick added.
To learn more, the staff will soon conduct genetic testing on the shark once she is large enough for a blood test, likely after a few months. "This DNA analysis will provide definitive confirmation of whether the hatchling is a product of parthenogenesis or delayed fertilization," the Shreveport Aquarium stated.
While most species of sharks give birth to live young, swell sharks usually release fertilized eggs into the water, a phenomenon that is rare in vertebrates. The egg cases are sometimes referred to as mermaid's purses, and they attach to features such as rocks or algae, allowing the shark embryo inside to grow and later hatch from the egg.
Yoko is named after the Chumash word "onyok," meaning "shark," not after the famous Japanese artist. Cases like Yoko's shed light on sharks' evolutionary adaptations. "Parthenogenesis is very rare in nature," as emphasized by Jutarnji List.
Colin Stevenson, head of education at Crocodiles of the World in Brize Norton, explained, "Komodos can reproduce normally, but from time to time, they give birth to a parthenogenetic dragon. The trick is to understand what triggers this phenomenon."
The article was written with the assistance of a news analysis system.