Crocodile lays eggs without fertilization, first case in the world

First case of a female crocodile that without mating with a male has managed to lay eggs, one of which contains a fetus genetically almost identical to the mother. The discovery, published in Biology Letters by a group of American researchers, opens up the possibility that this unusual reproductive mode may date back to the time of the dinosaurs.

Reproduction without fertilization (parthenogenesis) has already been documented in over 80 species of vertebrates, including snakes, sharks and lizards, but until now it has never been observed in crocodiles. To leave the researchers open-mouthed was an 18-year-old female Crocodylus acutus, kept in a reptile park in Costa Rica. After 16 years spent in captivity, without ever meeting a male, she managed to lay as many as 14 eggs of which seven, apparently fertile, were placed in the incubator. After three months of waiting, the eggs did not hatch and the eggs were analyzed to verify their contents. One of these contained a complete but not viable fetus.

Genetic analysis showed that it was a female with 99.9% identical DNA to that of the mother. In practice, in the absence of a male with whom to mate, the female crocodile would have fused two of its cells: an egg cell (which contained half of its chromosomes) and another species of cell with a halved chromosomal structure (this is the so-called 'polar body', a small cellular structure expelled from an oocyte, consisting of nuclear material and a small amount of cytoplasm). The fusion of the two cells would have implied even a minimal reorganization of the genetic material to fill the gaps due to the absence of the male genome: this would have led to generate an individual who is almost a clone of the mother.

Now that parthenogenesis has been documented in both crocodiles and birds, it is possible to hypothesize that their common ancestors, dinosaurs, may have had a similar reproductive ability.