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A crocodile in Costa Rica had a virgin birth. Here’s what that means

<i>imageBROKER/Alamy Stock Photo</i><br/>A new study has found an American crocodile pictured in Sirena
imageBROKER/Alamy Stock Photo
A new study has found an American crocodile pictured in Sirena

By Jackie Wattles, CNN

(CNN) — Scientists say they have documented the first virgin birth in a crocodile. And while the concept may sound bizarre to humans, this type of reproduction is not unheard of across the animal kingdom, according to researchers.

The crocodile in question, named Coquita, had been living alone in a Costa Rican zoo called Parque Reptilandia for 16 years before laying a very special clutch of eggs in 2018. One of those eggs was later found to contain a fully formed crocodile fetus, despite the fact that Coquita had lived virtually her entire life in isolation. There was almost no chance she had consorted with male crocodiles.

It was clear evidence — presented for the first time in a paper published in the journal Biology Letters on June 7 — that crocodiles are capable of a type of reproduction called parthenogenesis, in which unfertilized eggs can yield offspring.

It’s not uncommon for reptiles living in captivity to lay eggs, but “given the period of isolation from mates, these would normally be considered non-viable and discarded,” according to the study. But after shining a flashlight on the 14 eggs in Coquita’s clutch, experts determined seven could be viable and chose to artificially incubate them.

Ultimately, there was only one fully formed offspring among those seven viable eggs. It never hatched and was deemed stillborn.

But a scale from the fetus was shipped from Costa Rica to Dr. Warren Booth, a coauthor of the new study and a researcher at the Virginia Polytechnic Institute and State University. Booth — who has studied parthenogenesis for more than a decade — is the person that others in the reptilian world tend to call when they suspect an animal has reproduced without mating.

Booth was able to sequence the stillborn crocodile’s DNA and confirmed that it was indeed produced by parthenogenesis, with a genetic makeup that was a 99.9% match for its mother’s.

“These findings therefore suggest that eggs should be assessed for potential viability when males are absent,” the study noted.

Virgin births throughout history

Scientists have known for more than a century that some animals are capable of spawning offspring without male fertilization. Booth said the first instance on record was observed in pigeons, though viable fetuses were not immediately identified.

Parthenogenesis has since been observed in a vast array of different animal species, particularly in snakes. And it’s also been found in birds, lizards, turtles and sharks. Now, of course, crocodiles join the list.

Many of the offspring produced this way are very ill or weak, according to Booth.

They are, essentially, “highly inbred individuals,” he said.

The genetic cards tend to be stacked against animals formed by this type of reproduction, but “it’s not as if they all don’t survive,” Booth added. “Some of them certainly do.”

And offspring produced by parthenogenesis can go on to reproduce — either sexually or through more parthenogenesis, Booth said, though he noted that not all the research behind these observations has been published.

Research on this topic evolved slowly before picking up exorbitant speed in the 21st century with the advent of DNA sequencing technology, Booth added.

It’s very likely that thousands of species of birds, reptiles and other animals are capable of this type of reproduction. Many of the documented cases have been in animals kept in captivity.

“The reason it’s not documented a lot in natural populations (is) that people aren’t looking for it,” Booth said. But there’s an effort underway to mine the genes of wild animals to search for evidence of parthenogenic reproduction.

How parthenogenesis works

Parthenogenesis is not exactly immaculate conception. Any offspring produced in this manner shares most of its DNA with the mother.

And the process can only occur in animals with certain types of chromosomes and the ability to pass on genes in a specific manner.

In short, this type of reproduction can’t happen in humans or other mammals because they use a type of genomic imprinting that “requires a specific set of genes to be switched on by the male and a specific set of genes by the female” to form an embryo, Booth said.

At least, it can’t happen in mammals naturally, he noted.

Researchers have successfully created mice born by parthenogenesis in a lab, but they had to undergo “pretty extreme gene editing — switching on and switching off genes at the right time,” Booth said.

Crocodiles do not have sexual chromosomes at all, Booth added. And Coquita’s parthenogenically produced offspring — which was female — likely formed that way solely because of the temperature at which the egg was incubated.

Parthenogenesis: A possible common origin

Observing parthenogenesis in crocodiles is a fascinating discovery, Booth said, because the method they use is strikingly similar to that of birds and other reptiles.

“They are all using the exact same cellular mechanism for parthenogenesis,” Booth said. “A very complex mechanism like that is very unlikely to evolve independently.”

That means, he added, it’s probable that crocodiles and birds inherited this ability from their far, far distant relatives — the dinosaurs.

“It’s very likely that the dinosaurs and pterosaurs also had the ability to produce parthenogenetically,” he said, joking that it’s all very reticent of “Jurassic Park.”

Without DNA from dinosaurs, however, scientists will likely never be able to definitively prove that is the case.

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