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A virgin crocodile made herself pregnant in a first for her species, researchers say

Researchers have identified the first known case of a crocodile making herself pregnant — and producing a fetus that was genetically identical to herself. The findings were published Wednesday by a team led by evolutionary biologist Warren Booth from Virginia Tech in Biology Letters, a journal published by the Royal Society.

In 2018, officials with the Parque Reptilandia in Costa Rica found 14 eggs in a female's enclosure. The crocodile had been in isolation since the age of 2, yet she still managed to lay a clutch of eggs at 18.

"Given the period of isolation from mates, these would normally be considered non-viable and discarded," the researchers wrote. But the officials gathered seven eggs that appeared viable and kept them in an incubator.

There were several signs that one of the eggs may be viable, Booth told CBS News.

"Viable eggs are often bright white, whereas infertile may be more yellowish," he said. "When held up to a flashlight, viable crocodile eggs will have a distinct band, whereas non-viable will simply glow yellow."

A crocodile swims in the Tarcoles River, the most polluted river in Central America, southwest of San Jose, Costa Rica, on November 21, 2022.
A crocodile swims in the Tarcoles River, the most polluted river in Central America, southwest of San Jose, Costa Rica, on November 21, 2022. Ezequiel Becerra/AFP via Getty Images

Costa Rica officials reached out to experts in the U.S. for consultation — ones that specialized in parthenogenesis. The term is derived from the Greek words "parthenos," meaning "virgin," and "genesis," meaning "origin," according to Encyclopedia Britannica.

Booth, and co-author Gordon Schuett of Georgia State University, had published multiple papers on the topic. As such, they were the "go-to people," Booth told CBS News.

Once considered rare, so-called virgin births have been documented among various species — including sawfish, snakes, sharks, and birds. The process, which is more common in the plant and insect worlds, allows a female organism to replicate itself without fertilization from a male.

In 2021, a study found that California condors can have virgin births. Researchers with the San Diego Zoo Wildlife Alliance said genetic testing confirmed that two male chicks that hatched in 2001 and 2009 from unfertilized eggs were related to their mothers. Neither was related to a male. In 2019, an anaconda housed with two other females gave birth. DNA testing would later confirm that the anaconda babies were reproduced through parthenogenesis.

In the case of the crocodile in Costa Rica, three months after workers found the eggs, none had hatched and only one egg was found to have a fully formed but nonviable fetus. DNA analysis would later determine that the fetus was 99.9% genetically identical to its mother.

Virgin births could be happening in crocodiles without anyone realizing, according to the researchers. 

"These findings, therefore, suggest that eggs should be assessed for potential viability when males are absent," they wrote.

The authors suggest that in these cases among reptiles, birds, and now crocodiles, there may be a common evolutionary origin.

"This discovery offers tantalizing insights into the possible reproductive capabilities of the extinct archosaurian relatives of crocodilians and birds, notably members of Pterosauria and Dinosauria," they write, referring to flying reptiles that have been described as "close cousins" of dinosaurs.

Booth told CBS News that crocodiles are at the base of a lineage known as the archosaurs, with the most recent members being birds. All of these creatures use the same complex form of parthenogenesis, or terminal fusion automixis. It is unlikely they all developed independently.

"The cool aspect is that in between crocodiles and birds are the pterosaurs and dinosaurs," he added. "Given that all of these lineages use the same mechanism, it is highly likely that pterosaurs and dinosaurs also had the capacity to produce parthenogenetically."

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