An 18-year old female crocodile who languished alone without a mate in an enclosure at a wildlife park in Costa Rica surprised everyone by laying over a dozen eggs.
Obtained by Parque Reptilania at the age of two, the American croc - Crocodylus acutus - never mingled with its own kind. So, understandibly, the park's scientific team rushed to share their news of the asexual reproduction case with experts. A team from Virginia Polytechnic in the US was contacted. Seven of the eggs, which appeared to be fertile, were artificially incubated, yet did not hatch. One, though, contained a fully formed stillborn crocodile fetus.
After the experts in so-called "virgin births," referred to scientifically as "parthenogenesis," analyzed the DNA of the fetus - identified as female - they found it was more than 99.9% genetically identical to its mother. This was taken as further proof of self-impregnation.
"It is not uncommon for captive reptiles to lay clutches of eggs, given the period of isolation from mates, these would normally be considered non-viable and discarded. These findings therefore suggest that eggs should be assessed for potential viability when males are absent. Furthermore, given that (virgin births) can occur in the presence of potential mates, instances of this may be missed when reproduction occurs in females co-habited with males," the scientists stated in their research paper.
An egg would typically need a second set of chromosomes, but in cases of "virgin births," the egg fuses with the so-called "polar body," explained Warren Booth, an associate professor of urban entomology at Virginia Tech in the US and lead author of the study.
"Polar bodies are produced at the same time as the egg, and contain a set of chromosomes that are "nearly identical to the mother," Dr. Booth clarified, adding that, "It makes it feel like [the egg] has become fertilised, and as a result that starts the process of production of an embryo."
Many species, from small invertebrates like ants and bees, to birds, snakes, and sharks have had the ability to reproduce parthenogenetically for millions of years, research has shown. However, this is the first such recorded case involving a crocodile. As to why this process happens, there are a number of theories. According to one, it happens when a species feels its dwindling numbers signal possible extinction.
"This new evidence offers tantalizing insights into the possible reproductive capabilities of extinct relatives of crocodiles, notably the dinosaurs," the team of researchers concluded.