Using whole-genome sequencing and bioinformatic analysis, scientists provide the first evidence of facultative parthenogenesis in a crocodilian — the American crocodile (Crocodylus acutus), a large and wide-ranging apex predator that occurs from Florida to Colombia, Venezuela and Peru.
An adult American crocodile (Crocodylus acutus) at La Manzanilla, Jalisco, Mexico. Image credit: Tomás Castelazo.
Facultative parthenogenesis is the ability of sexually reproducing species to generate offspring without genetic contributions of males.
Once considered rare, this reproductive mode has been documented across multiple vertebrate lineages, including both avian and non-avian reptiles (specifically snakes and lizards), and elasmobranch fishes, with notable examples in sharks, rays and sawfish.
“Part of this growth among vertebrates is attributable to awareness of the phenomenon itself and advances in molecular genetics/genomics and bioinformatics, and as such our understanding has developed considerably,” said Dr. Warren Booth, a researcher at Virginia Tech and Chiricahua Desert Museum, and colleagues.
“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 facultative parthenogenesis in vertebrates, crocodilians lack sex chromosomes and sex determination is controlled by temperature.”
In January 2018, the researchers discovered a clutch of eggs in the enclosure of an 18-year-old female American crocodile housed on public exhibit at Parque Reptilandia, Costa Rica.
This individual was obtained when it was two years old and maintained in isolation from other crocodilians for its entire life.
Of the 14 eggs laid, seven appeared to be fertile and were artificially incubated. After three months of incubation, the eggs had failed to hatch and were opened to assess their contents.
The offspring was found to have identical genotypes to the mother at greater than 99.9% of her homozygous loci, demonstrating a lack of paternal alleles.
This discovery offers tantalizing insights into the possible reproductive capabilities of the extinct non-avian dinosaurs and pterosaurs.
“The first ‘virgin birth’ in crocodiles could give insights into the reproductive capabilities of dinosaurs,” the authors said.
“One of the eggs contained a fully formed fetus which was genotypically identical to its mother.”
“Although these eggs didn’t hatch, this case offers tantalizing insights into the reproductive capabilities of extinct archosaurs.”
The team’s paper was published in the journal Biology Letters.
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Warren Booth et al. 2023. Discovery of facultative parthenogenesis in a new world crocodile. Biol. Lett 19 (6): 20230129; doi: 10.1098/rsbl.2023.0129
