Stingray experts explain Charlotte's 'immaculate conception' - and why the North Carolina aquarium doesn't know when she'll actually give birth

Charlotte the stingray’s immaculate conception that has captivated marine wildlife enthusiasts worldwide now has a scientific explanation.

While the stingray conceived her pups without a male mate, experts said her pregnancy is not so uncommon -  and attributed it to parthenogenesis, the scientific term for a virgin birth.

Parthenogenesis is common in sharks and stingrays and occurs when the mammal has been in isolation for long periods and effectively produces a clone of itself.

Charlotte is on display at the Aquarium & Shark Lab in Hendersonville, North Carolina, which previously speculated she was impregnated by a white-spotted bamboo shark that was supposedly in the tank with her.

The aquarium has been saying the stingray is set to give birth 'any day now' since last month and the uncertainty is likely due to them not knowing exactly when the embryo developed. 

Stingray experts say Charlotte's 'miracle birth' is most likely due to parthenogenesis - a scientific term for virgin birth

Another, more unlikely scenario, for Charlotte's immaculate conception is that stingrays can carry sperm for up to a year. But she has been in isolation for too long for this to be a possibility, experts say

There is only one other possible explanation for Charlotte’s ‘miracle birth,’ according to Dr. Christopher Lowe, a professor of marine biology and director of the Shark Lab at California State University.

‘They can become pregnant without observed mating with a male in two ways,’ Lowe told Dailymail.com.

The first is that ‘many species of sharks and rays can store sperm for at least up to one year,’ but said this is unlikely because Charlotte has been on her own for too long.

‘Turns out that parthenogenesis is more common in sharks and rays than we previously thought, so this is the most likely explanation,’ Lowe said, adding that ‘a quick DNA test will confirm if the female produces viable young.’

Kevin Feldheim, a researcher at Chicago’s Field Museum who is a parthenogenesis expert told Dailymail.com that Charlotte's case is the first time parthenogenesis has been documented in her species, making it the 15th species to be documented altogether. 

The aquarium has been relaying regular updates on Charlotte’s condition, saying there is no sign of the pups yet, although an ultrasound showed she’s carrying as many as four offspring.

Researchers say Charlotte's ultrasound shows she's carrying up to four pups

Certain animals are capable of reproducing through 'facultative parthenogenesis' in which the egg is fertilised with cells from the mother rather than by a male 

However, the team has so far been unable to provide a date for when Charlotte is expected to give birth.

Lowe said it’s ‘probably because they don’t know exactly when she started developing an embryo, and we don’t know if parthenogenesis requires longer gestation periods.’

Round stingrays typically have a shorter gestation period compared to other species, with their pregnancy lasting three to four months depending on the temperature of the water.

He added that ‘the more and longer some species are kept in captivity, the more we learn about oddities like this.’

It’s hard to know the due date because it's difficult to determine how far into the pregnancy the stingray was when she conceived, Lowe said.

Ultrasounds are typically conducted in late-term pregnancies, Lowe said, so they could only tell the stingray was pregnant about one month before it gave birth.

The Aquarium & Shark Lab announced Charlotte’s ‘miracle birth’ in a Facebook post early last month, sparking global interest in how the stingray could have conceived on her own, going so far as to suggest she was impregnated by a shark.

The Aquarium & Shark Lab suggested Charlotte could have been impregnated by a shark, but experts said that's impossible

Feldheim said his guess is the aquarium 'made that as a kind of an offhand comment, but for whatever reason, the idea of a ray-shark hybrid really took off.' 

READ MORE: What is a virgin birth? Step-by-step graphic reveals how a female stingray was able to get pregnant - despite living alone 

Certain animals like sharks and snakes are capable of producing healthy offspring without ever mating, through a process known as parthenogenesis. 

In a separate interview, Feldheim told NBC News that the theory that a shark impregnated the Charlotte might have propelled her story into the global spotlight, but it has no basis in reality.

‘The divergence between sharks and stingrays is 350 million years. And as a comparison, the divergence between humans and platypus is 180 million years,’ he told the outlet.

‘The shark scientists were not really happy with that press release. No one would even think of that as an option,’ he added.

Kady Lyons, a research scientist at the Georgia Aquarium in Atlanta told AP News the theory is impossible because the animals’ substantially different sizes mean they wouldn’t match up anatomically and neither would their DNA.

A round stingray like Charlotte measures between 10 and 22 inches in width while the white-spotted bamboo shark – which was reportedly in the tank with Charlotte – measures between 24 and 37 inches long.

‘We should set the record straight that there aren’t some shark-ray shenanigans happening here,’ Lyons told the outlet.

‘There’s nothing unnatural about asexual reproduction, Mercedes Burns, a biologist at the University of Maryland, Baltimore County told NBC News.

‘Invertebrates or fishes are doing amazing things in their lifetimes in order to reproduce successfully.’