Self-fertilization in a female crocodile, the first case in the world in these reptiles – Corriere.it

In Costa Rica at Parque Reptilaria in January 2018 they were surprised when a 18 year old female crocodile American (Crocodylus acutus), not to be confused with the alligator, had laid an egg: strange but not unusual. But they were shocked when they discovered that there was a fully developed fetus, but died before breaking the shell. The surprise was due to the fact that the female, who arrived in the reptile house at the age of 2, had always been kept separate from male specimens of her species. So she could not have been fertilized.

Parthenogenesis

Experts from the Virginia Polytechnic were then called to examine the case, and have now published the results on
biology letters, journal of the Royal Society. The genome of the crocodile fetus resulted 99.9% equal to that of the mother, therefore a clone of it. So there could only be one answer: the mother was self-fertilised or, in biological language, it was a case of facultative parthenogenesis in vertebrates. the first time in the world that it is documented in crocodiles, previously it has been reported in snakes (pythons, boas), lizards, some species of birds (turkeys, California condors) and in the subclass of fish which also includes sharks, rays and torpedoes. Parthenogenesis in vertebrates is also called virgin birth.

The reasons

According to the researchers, similar cases may be more frequent among crocodiles, only that so far they have always gone unnoticed. Biologists are uncertain in attributing the reasons for virginal births among vertebrates. A well-established hypothesis is that species capable of parthenogenesis resort to this possibility when they are in danger of extinction. But the possibility of parthenogenesis must be one characteristic that developed in a very ancient common ancestor in the evolutionary line of reptilestaking into account that the line of crocodiles separated from that of snake-lizards between 267 and 312 million years ago, but which also remained in the evolutionary line of dinosaurs and then transmitted to birds.

Sex determined by temperature

Crocodiles lack the gene for the sex of the unborn child, which instead is determined by the temperature at which the eggs ripen. As reported by the researchers of the Virginia Polytechnic, in the case of the American crocodile with temperatures below 30 degrees and above 35 from the eggs only females are born, with temperatures around 31.5% the majority of males born.