A groundbreaking discovery has been made by researchers – the first documented case of a female crocodile impregnating herself and producing an offspring that is genetically identical to her. The team, led by evolutionary biologist Warren Booth from Virginia Tech, published their findings in Biology Letters, a journal published by the Royal Society.
In 2018, staff at Parque Reptilandia in Costa Rica found 14 eggs in the enclosure of a female crocodile. Surprisingly, she had been kept in isolation since the age of 2 and still managed to lay a clutch of eggs at 18.
“Under normal circumstances, eggs laid by a crocodile isolated from mates would be considered non-viable and discarded,” the researchers noted. However, seven eggs that appeared viable were collected and placed in an incubator.
According to Booth, there were several indicators that one of the eggs could be viable. “Viable crocodile eggs are usually bright white, while infertile ones tend to have a yellowish appearance,” he explained. “When held up to a flashlight, viable eggs will show a distinct band, while non-viable eggs will glow yellow.”
Costa Rican officials sought the expertise of parthenogenesis specialists in the U.S., reaching out to Booth and co-author Gordon Schuett of Georgia State University. Both researchers had previously published papers on the subject and were considered the go-to authorities in the field.
Although virgin births were once thought to be rare, they have been observed in various species such as sawfish, snakes, sharks, and birds. While more commonly seen in the plant and insect kingdoms, parthenogenesis allows female organisms to reproduce without fertilization from males.
In 2021, it was discovered that California condors can also undergo virgin births. Genetic testing confirmed that two male chicks hatched in 2001 and 2009 from unfertilized eggs were biologically related to their mothers, with no male involvement. Additionally, an anaconda housed with two other females gave birth in 2019, and DNA analysis later confirmed that the anaconda babies were the result of parthenogenesis.
In the case of the crocodile in Costa Rica, after three months, none of the eggs had hatched except for one that contained a fully formed but non-viable fetus. DNA analysis revealed that the fetus was 99.9% genetically identical to its mother.
The researchers suggest that virgin births may be occurring in crocodiles without detection. “These findings suggest the need to assess the potential viability of eggs even in the absence of males,” they recommended.
Furthermore, the authors propose that there may be a shared evolutionary origin for reptiles, birds, and now crocodiles in terms of this phenomenon. “This discovery provides fascinating insights into the reproductive capabilities of ancient relatives of crocodiles and birds, including members of the Pterosauria and Dinosauria,” they wrote. Pterosaurs and dinosaurs are often referred to as close cousins.
Booth explained that crocodiles are at the base of the archosaurs lineage, with birds being the most recent members. All of these creatures employ the same complex form of parthenogenesis, known as terminal fusion automixis. It is highly unlikely that this mechanism developed independently in each lineage.
“The interesting aspect is that between crocodiles and birds are the pterosaurs and dinosaurs,” he added. “Given that all of these lineages use the same mechanism, it is highly probable that pterosaurs and dinosaurs also had the ability to reproduce through parthenogenesis.”
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