By: Yvonne Liu
A Costa Rican female crocodile layed a clutch of eggs in January 2018. Except, she had been alone for 16 years.
When an isolated female crocodile lays eggs, the eggs are almost always infertile. However, the clutch layed by a crocodile at a Costa Rican zoo defied all expectations. Some of the eggs in the clutch looked normal, but one continued to mature. Unfortunately, life didn’t find a way and the resulting embryo was stillborn.
In a paper out on Wednesday, the baby crocodiles were declared parthenogens by a group of researchers.
Parthenogenesis is a form of asexual reproduction where the offspring are produced without a male, and the genetic material is entirely from the mother. Parthenogenesis is common in other animals such as king cobras, Sawfish, and California Condors, but this was the first time found in crocodiles.
“But it is also possible that parthenogenesis is simply a trait that doesn’t have enough downsides for evolution to weed it out, ” Dr. Booth said. “It is not necessarily a response to stress or even a lack of mates. In 2020, scientists discovered that lizards can mate and then lay clutches of eggs where some are normal offspring and some are parthenogens. This is Dr. Booth’s hunch: It’s an ability that can be switched on or off, and it is perhaps controlled by a single gene.”
So, could dinosaurs have given virgin birth as well, as the discovery of parthenogenesis in crocodiles suggests?
“What this tells us is it’s very likely that this also happened in pterosaurs and dinosaurs,” Dr. Booth said.”
DNA analysis is the most reliable way to confirm parthenogenesis since it allows scientists to tell parthenogenesis apart from a delayed conception. Delayed conception is when a female stores sperm for as long as six years before using it to fertilize eggs. There can be no certainty without the ability to retrieve dinosaur DNA and pterosaur DNA, which do not persist in fossils.
“We’ll never be able to prove they could do it,” Dr. Booth said. “But it suggests they had the ability.”