How this stingray may have gotten pregnant without a mate
No sex? No problem. At least not for Charlotte the stingray.
Image: Team ECCO
Fans from around the world are patiently waiting for a pregnant stingray at a North Carolina aquarium to give birth.
This stingray, named Charlotte, took over the internet earlier this year when The Aquarium and Shark Lab by Team ECCO revealed that she had become pregnant despite having a mate. The aquarium that Charlotte lives in doesn’t even have a male stingray. So, how could this be possible?
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Researchers call this kind of asexual reproduction parthenogenesis. “Sisters are doing it for themselves,” says Kady Lyons, a researcher from Georgia Aquarium.
This kind of reproduction can happen in certain species of reptiles, birds and fish, including the zebra shark. However, it has never been documented in this kind of stingray before–the round stingray.
What might have happened in this case is that, instead of the egg and sperm each bringing half of the DNA, the mother’s body filled in the other half of the genetic material that is typically provided by the sperm.
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But where does the other genetic material actually come from? Ovaries produce eggs through a process called meiosis, where the cells split. This process results in three to four cells. One of these cells will become the egg, and the two or three smaller cells become what are called polar bodies. “The other three cells will typically die and won’t result in anything,” says Lyons. “But in parthenogenesis, what we think is happening is that the egg cell is fusing with one of those other polar bodies to restore the full complement of DNA.”
The DNA of this newly fused egg/polar body is not exactly a carbon copy of the mother’s DNA. The chromosomes are shuffled around a little bit, meaning that the offspring aren’t perfect clones of the mother. Lyons tells NOVA, “Think of them as a highly inbred individual, basically.”
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It has been suggested that a shark could have actually impregnated Charlotte the stingray, but Lyons says that that kind of interspecies breeding is unlikely. “So the puzzle pieces are being mixed from different puzzles, and you’re not going to make a complete picture that way. In that whole range of steps that you would have to go through to actually have a viable offspring, it’s not something I think is going on.”
In the wild, the round stingray is actually known to mate with multiple males and have litters with mixed sireship. “It’s interesting that this species is shown to reproduce parthenogenetically. It’s really neat that we can add that to its reproductive repertoire.”
Charlotte the stingray may be carrying as many as four pups. It was predicted that she would give birth as early as late February, but the wait is still on.
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