Scientists Marvel at the First ‘Virgin Birth’ Documented in a Crocodile

Over the years, some species of birds, fish, and other animals have been observed to experience parthenogenesis, or the ability to reproduce without mating. Now, scientists have documented the phenomenon in a newcomer: Crocodylus acutus, or the American crocodile.

In a paper published in Biology Letters, researchers have detailed the discovery of a female crocodile in a Costa Rican zoo that’s been in captivity for 16 years without a mate. In January 2018, she laid 14 eggs. This isn’t unusual, as such eggs can be sterile. Of the 14, seven were found to be fertile and were remanded to an incubator. One of those eggs held a surprise: a stillborn female baby crocodile. DNA testing confirmed it was a 99.9 percent match to the mother.

Parthenogenesis occurs when chromosome-filled polar bodies that typically disappear instead fuse with the egg, providing the necessary recipe for offspring in the absence of sperm. Though rare, parthenogenesis does occur and may persist when species need to reproduce in the absence of a mate to guarantee its survival.

But that may not be the whole story. When two California condors reproduced in captivity in 2021, they experienced parthenogenesis even though they were housed with males. Parthenogenesis occurred even though it wasn’t strictly necessary.

The discovery in crocodiles is intriguing in and of itself, but it also opens up the possibility that dinosaurs might have also been capable of the same biological trick.

The crocodile joins a small but eclectic group including snakes, lizards, and sharks that have demonstrated the ability. And while stillbirths or other abnormalities frequently occur, some parthenogens have been observed to achieve adulthood, including turkeys and boa constrictors.