Researchers in Costa Rica have recorded the first virgin birth in a crocodile.
In 2002, a two-year-old American crocodile (Crocodylus acutus) named Coquita was put in an enclosure in Parque Reptilandia, where she had no contact with other reptiles for 16 years, according to a recent 2023 Biology Letters study. Zookeepers found 14 of her unhatched eggs in January 2018 and brought them to an incubator.
Seven of the eggs were fertilized, but only one contained a fully developed, “stillborn” fetus, the study says. After some testing, researchers found its heart tissue had over a 99.9 per cent genetic match with the mother’s skin tissue.
Joshua Feltham, a Fleming College herpetologist who has spent years studying reptiles in Costa Rica, says this is the first time asexual reproduction has been recorded in a crocodile.
During development, crocodile mothers give their babies half their genetic information through eggs, throwing away the other half to make space for the sperm’s genetic information. In rare circumstances, however, the egg can reclaim the second half it threw away. While Feltham says this is usually a random occurrence, some snakes, lizards, and other reptiles are known to reproduce with only the mother’s information when their ratio of males to females is off balance.
Feltham says this could have happened with Coquita as a result of her isolation, but other theories would need to be disproven first. “When these kinds of things happened in the past, researchers attributed it to sperm storage, and we know that reptiles can store sperm for relatively long periods of time,” he says.
He adds that some instances were debated because they involved immature reptiles who could not yet reproduce, meaning they also couldn’t store sperm. He says Coquita is likely one of these instances.
Dr. Brenna Levine, an assistant professor at Kean University, is one of the study’s authors, and the American researcher who wrote the code analyzing DNA from the fetus’s and mother’s tissue samples. She agrees with Feltham, saying the longest time a reptile has been recorded storing sperm is six years.
“It’s very possible there’s longer sperm storage out there… so if we had found long-term sperm storage over 16 years that would have been really significant,” she says, adding that Coquita’s captivity at an immature age helped them rule out this possibility.
Feltham says some reptiles, including species of geckos and salamanders, can naturally reproduce through “kleptogenesis.” The Canadian blue-spotted salamander, for example, is a female-only species that gives 99.9 per cent of its own genetic information to its offspring. It still needs sperm from any male salamander species to start the reproduction process, but it discards the sperm’s genetic information during development.
Kleptogenesis doesn’t happen with crocodiles, says Levine. She says the only reasonable explanation for Coquita’s pregnancy is asexual reproduction, or “facultative parthenogenesis,” which is more common in invertebrates and some species of birds and snakes.
Feltham and Levine say this finding could provide insight into how reproduction works for dinosaurs, since they’re part of the same archosauria reptile class as crocodiles. Levine adds that it’s strong evidence asexual reproduction is an ancestral trait they all share, which would be significant for evolutionary biologists.
“The evolution of sex and why it occurs is one of those huge questions for scientists,” Levine says. “This advances our understanding of that evolution.”