Jurassic Park is probably not the most realistic film in its portrayal of genetics and its possibilities, and probably not the most realistic of dinosaurs like the velociraptor or the tyrannosaurus either. But perhaps, by coincidence, he hit on a no less relevant aspect of these animals: the females could have come to reproduce without the need for a male.
The key, in the crocodiles. A team of researchers has observed something never seen before in crocodiles: laying eggs without the need for a male. It happened in a park in Costa Rica, where a female American crocodile (Crocodylus acutus) laid a series of eggs without having had prior contact with males.
Although none of the eggs hatched, the experts who studied the event observed that some of the eggs contained fetuses that were significantly advanced in gestation. This is not entirely surprising, since it is estimated that only 3% of eggs laid without paternal input are viable in species in which parentogenesis has been observed.
The ability of a species to reproduce from a single parent (the female in principle) is rare, but not new. This form of asexual reproduction, based on the laying of unfertilized eggs, is called parentogenesis.
Parentogenesis. In this form of reproduction, the female replaces the male’s gamete with a haploid cell of her own (also a type of cell that contains a single set of chromosomes, in contrast to conventional cells that have a set of paired chromosomes).
In the so-called terminal fusion automixis, this haploid cell is in charge of fertilizing the egg (another reproductive cell with a series of unpaired chromosomes). The cell responsible for fertilizing the egg is a kind of residual cell created in the ovaries during the process of producing eggs.
This cell contains enough genetic information to complement the egg, but in both cases the genetic information comes from the mother, making the offspring genetically almost identical to the mother, virtually a clone.
Life makes its way. Examples of parentogenesis are rare, but some of them seem to point to dinosaurs as animals with this ability. Reptiles, dinosaurs and other animals such as pterosaurs and birds (the latter as a member of the dinosaur group from a taxonomic point of view) belong to the clade of archosaurs (Archosauria).
Dinosaurs would fall somewhere between birds and crocodiles on the evolutionary tree. Parentogenesis has already been described both in birds (such as the turkey) and in other reptiles somewhat further removed from dinosaurs (such as snakes). The fact that there are several species in this environment of the “tree of life” that have this ability, make experts think that it could be common in dinosaurs.
A not so strange phenomenon. Parentogenesis was a phenomenon originally described in plants and invertebrates. However, over the years, experts have been detecting more and more cases in vertebrates.
There are already more than 80 species where this phenomenon has been observed, which is not limited to sauropsids (the taxonomic class that groups reptiles, dinosaurs, birds…). Parentogenesis has also been observed in some fish such as rays and sharks. Of course, experts also rule out the possibility that it occurs in mammals.
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Imagen | Shelly Collins
