How Did an Aquarium Stingray Get Pregnant without a Mate?

How did an aquarium stingray get pregnant without a partner?

TO Stephanie Pappas edited by Ginna Bryner

A stingray in a small aquarium in Hendersonville, North Carolina became pregnant despite living in the tank without a male stingray.

This seemingly miraculous event sparked rumors online that the waiting stingray, Charlotte, may have been impregnated by one of the small sharks that live in her tank at the Shark Aquarium and Laboratory. But experts say this is extremely unlikely, as is the idea that a lion and a wolf could have “she-wolf” (“she-wolf”?) cubs.

In fact, baby shark rays would be even more dramatic, says Damian Chapman, director of the shark and ray conservation program at Mote Marine Laboratory and Aquarium in Florida. The last common ancestor of cats and dogs lived about 45 million years ago. Sharks and rays diverged from each other at least 300 million years ago, according to Article for 2021 in the magazine Developmental biology.

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However, there is another explanation for Charlotte's impending motherhood, and it is no less strange: she almost certainly became pregnant – a phenomenon known as parthenogenesis.

“Very diverse species shark and stingrays are known to reproduce in this manner in captivity,” says Chapman, who studied the first known case parthenogenesis in the hammerhead sharkwhat happened in 2001. “We even have evidence that one species of stingray did this in the wild.”

Charlotte, round slope (urobatis conditions), has a noticeable bump (visible on both her bottom and back) and could give birth at any time, according to the Aquarium & Shark Lab, which is run by the nonprofit educational organization Team ECCO. Pregnancy was confirmed by ultrasound. Charlotte will be the first known round stingray to undergo parthenogenesis“,” says Cady Lyons, a research scientist at the Georgia Aquarium. “It's exciting that we have another documented case of this phenomenon in a new species,” says Lyons.

Researchers don't fully understand why parthenogenesis occurs and what triggers it. Here's how the process works: Inside the female's body, cell division produces sex cells, or gametes. This division, called meiosis, produces an egg that can eventually be fertilized. spermand three additional cells called polar bodies. The egg and each polar body contain half the set of genes necessary to create a new organism. In parthenogenesis, the polar body fuses with the unfertilized egg, causing it to form embryo.

This is different from cloning, Lyons warns, which would create an exact copy of the mother ray. In parthenogenesis, since both the egg and the polar body contain only parts of the mother's genome, the young end up being less genetically diverse than their mother. Some parthenogenetic species get around this problem by duplicating their genes before the sex cells divide: whiptail lizards Aspidoskelis get along great, reproducing this way. But in many other species that only occasionally undergo parthenogenesis, the offspring may not be as robust, Lyons says. “You can think of them as highly inbred people,” she adds.

Even the typical reproduction of a round stingray is whimsical. Female stingrays mate with several males in the spring, and three to four months later, litters are born from several different fathers, Lyons said. And they bathe their embryos in a kind of nutritious uterine fluid, not unlike mammalian milk, which gives them the impetus to survive once they are born. At birth, babies are less than three inches in diameter (about the diameter of a baseball) and are ready to fend for themselves.

“They're really cute,” Lyons says.

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