In January 2018, at Parque Reptilaria in Costa Rica, they were surprised when an 18-year-old female American crocodile (Crocodylus acutus), not to be confused with the alligator, laid an egg: strange but not unusual. However, they were amazed to discover that inside was a fully developed fetus, which died before it could break open the shell. The surprise was due to the fact that the female, who entered the reptile house when she was two years old, was always kept separate from male specimens of her species. So she couldn’t have been fertilized.
parthenogenesis
As a result, experts from Virginia Polytechnic were called in to investigate the case. They have now published the results in Biology Letters, a journal of the Royal Society. The genome of the crocodile fetus was 99.9% identical to that of the mother, so it was a clone of it. So there could only be one answer: the mother self-fertilized or, in biological terms, it was optional parthenogenesis in vertebrates. It is the first time in the world that it has been documented in crocodiles. It has been previously reported in snakes (pythons, boas), lizards, some bird species (turkey, California condor) and in the fish subclass that includes sharks. Rays and torpedoes. Parthenogenesis in vertebrates is also called “virgin birth”.
The reasons
According to the researchers, similar cases could occur more frequently in crocodiles, but so far they have always gone unnoticed. Biologists are not sure what causes virgin births in vertebrates. One accepted hypothesis is that species capable of parthenogenesis resort to this possibility when threatened with extinction. But the possibility of parthenogenesis must be a trait that evolved in a very ancient common ancestor in the reptilian lineage, given that the crocodile lineage split from the snake-lizard lineage 267 to 312 million years ago, when the dinosaur evolutionary lineage was discovered and then transmitted to birds.
Gender is determined by temperature
Crocodiles lack the gene for the sex of the unborn child, which is instead determined by the temperature at which the eggs mature. As the researchers at Virginia Polytechnic report, only females are born in the American crocodile at temperatures below 30 degrees and over 35 from the eggs, at temperatures around 31.5% most of the born males are.