In January 2018, a female crocodile in a Costa Rican zoo laid a clutch of eggs. This was strange: She had lived on her own for 16 years.
While crocodiles can lay sterile eggs that do not develop, some of these clutches appear to be completely normal. And one of them — in a plot twist familiar to anyone who’s seen “Jurassic Park” — went on to mature in an incubator. In this case, Life did not find a wayThe egg eventually produced a fully formed but stillborn baby crocodile.
in Research paper published Wednesday in the journal Biology LettersAnd A team of researchers reports that the baby crocodile was virginal – the product of a virgin birth, containing only genetic material from its mother. While parthenogenesis has been identified in creatures as diverse as King CobraAnd saw And California condorThis is the first time that crocodiles have been found. And because of where crocodiles fall on the tree of life, it means that pterosaurs and dinosaurs may also have been capable of such reproductive feats.
Here’s how a virgin birth happens: As an egg cell matures in its mother’s body, it divides repeatedly to produce a final product with exactly half of the genes an individual needs. Three smaller cytosolic sacs containing the chromosomes, known as polar bodies, are formed as by-products. Polar bodies usually wither. But in vertebrates that can perform parthenogenesis, a single polar body sometimes fuses with an egg, forming a cell that contains the necessary set of chromosomes to form an individual.
That’s what appears to have happened in the case of alligators, said Warren Booth, an assistant professor at Virginia Tech who has studied eggs. Dr. Booth is an entomologist whose main focus is bugs, but he was Wide margin in defining parthenogenesis. Sequencing the crocodile’s genome indicates that its chromosomes differed from their mother’s chromosomes at the tips, where there was little DNA recombination—a telltale sign of polar body fusion.
This is exactly what happens in parthenogenesis in birds, lizards and snakes, Dr. Booth said, noting that this group of animals inherited the ability from a common ancestor. But crocodiles evolved long before many modern animals parthenogenesis, which points to intriguing possibilities about the creatures that came between them.
“What this tells us is that it is very likely that this also occurred in dinosaurs and pterosaurs,” said Dr. Booth.
Why do animals produce parthenogens? Dr. Booth said that although some herbivores can survive to adulthood and mate, they are not always the healthiest. But the increasing ease of DNA analysis, making it easier to identify animals born in this way, has shown that they are not entirely rare.
“It’s a lot more prevalent than people think,” he said.
It is possible that parthenogenesis gives a species the ability to survive long periods when no partner is available. A new individual, which carries largely the same genes as its parent, may live long enough for a mate to arrive, allowing sexual reproduction, which tends to produce stronger offspring.
It’s also possible, Dr Booth said, that parthenogenesis is just a trait that doesn’t have enough negatives for evolution to eliminate. It’s not necessarily a response to stress or even a lack of friends. In 2020, scientists found out Lizards can mate and then lay clutches of eggs, some of which are natural offspring and some are inbred. That’s Dr. Booth’s hunch: It’s an ability that can be turned on or off, possibly controlled by a single gene.
So did dinosaurs do it, as the discovery of parthenogenesis in crocodiles suggests? Parthenogenesis is best confirmed by DNA analysis, a process that has allowed scientists to tell apart from late pregnancy, The female stores the sperm for up to six years before using it to fertilize the eggs. Without the ability to retrieve the DNA of dinosaurs and pterosaurs, which do not survive in fossils, there is no certainty.
“We’ll never be able to prove they can do that,” said Dr. Booth. “But it does indicate that they have the ability.”
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