First ever instance of 'virgin birth' recorded in crocodiles

This virgin birth process is known as facultative parthenogenesis, in which embryos grow from unfertilized eggs.
Mrigakshi Dixit
Representational image.
Representational image.

Michel VIARD/iStock 

For the first time, a female crocodile was found to have laid eggs without mating. 

In 2002, a two-year-old American crocodile(Crocodylus acutus) was placed in an isolated enclosure at the Parque Reptilandia Park in Costa Rica. The crocodile lived there for the next 16 years by itself. 

Workers at the reptile park were taken aback in January 2018 when they discovered the crocodile guarding a clutch of 14 eggs in the enclosure. 

The one-on-kind discovery gives insights into the evolutionary origins of this trait, reported Live Science.

The first-ever virgin birth in crocodiles

The park's management contacted Virginia Tech researchers, who advised waiting for the eggs to hatch. 

The team waited for months, but none of the eggs hatched on their own, so they opened them. Six of the eggs were packed with unrecognizable content, most likely yolk, and immature cells. However, one egg yielded a completely developed fetus that died at full term. 

They went on to undertake genetic testing, which revealed that the female fetus was nearly similar to the mother. 

The genetic sequencing of samples collected from the heart of the fetus and the mother's skin indicated a 99.9 percent DNA match. This also proved that the fetus lacked a father, and the offspring were produced by asexual reproduction.

The authors emphasize that the fetus's early demise does not suggest that asexual reproduction progeny cannot live full lives. In certain cases, such offsprings reach maturity and even reproduce normally.

The process of embryo formation

This virgin birth process is known as facultative parthenogenesis(FP), in which embryos grow from unfertilized eggs. The embryo formed after the female's egg united with one of its own byproducts known as the second polar body. 

This type of asexual reproduction has been observed in some species of birds, snakes, lizards, sharks, and turkeys. 

It had never been discovered among Crocodilia before. This discovery suggests that crocodiles may have adopted this peculiar reproduction method that may be traced back to dinosaurs —  the ancestors of these reptiles and birds. 

Birds and crocodilians descended from archosaurs, which include dinosaurs and pterosaurs. It also suggests that dinosaurs and pterosaurs may have reproduced without males some millions of years ago. 

However, it is unknown why some female reptiles, fish, and birds spawn asexually. It may not be completely attributed to a dearth of males, since it can occur even when males are present hanging around the female. 

One possible explanation might be the function of a gene that is activated by hormones. More investigation is needed, according to the authors, to determine the specific cause of virgin births.

The study has been published in the journal Biology Letters

Study Abstract:

Over the past two decades, there has been an astounding growth in the documentation of vertebrate facultative parthenogenesis (FP). This unusual reproductive mode has been documented in birds, non-avian reptiles—specifically lizards and snakes—and elasmobranch fishes. Part of this growth among vertebrate taxa is attributable to awareness of the phenomenon itself and advances in molecular genetics/genomics and bioinformatics, and as such our understanding has developed considerably. Nonetheless, questions remain as to its occurrence outside of these vertebrate lineages, most notably in Chelonia (turtles) and Crocodylia (crocodiles, alligators and gharials). The latter group is particularly interesting because unlike all previously documented cases of FP in vertebrates, crocodilians lack sex chromosomes and sex determination is controlled by temperature. Here, using whole-genome sequencing data, we provide, to our knowledge, the first evidence of FP in a crocodilian, the American crocodile, Crocodylus acutus. The data support terminal fusion automixis as the reproductive mechanism; a finding which suggests a common evolutionary origin of FP across reptiles, crocodilians and birds. With FP now documented in the two main branches of extant archosaurs, this discovery offers tantalizing insights into the possible reproductive capabilities of the extinct archosaurian relatives of crocodilians and birds, notably members of Pterosauria and Dinosauria.

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