In a rather peculiar case, two California condor chicks reportedly hatched from what appeared to be unfertilized eggs, in a rare case of parthenogenesis in birds and the first ever recorded for a California condor. The one-of-a-kind study was published in the Journal of Heredity.
California condors (Gymnogyps californianus) are the last surviving members of the genus Gymnogyps, and are among the world’s most endangered birds. By 1987, these birds were considered extinct in the wild, as rapid conservation efforts in the United States led to the capture of the then-last surviving 27 members of the species. Recently, US-led conservation efforts had successfully reintroduced some of these condors back into the wild, and their numbers now reach upwards of 500; nowadays, though, they still remain classified as “Critically Endangered” by the International Union for the Conservation of Nature (IUCN).
Among the efforts needed to conserve these beautiful birds is monitoring how these birds breed; after all, doing so helps conservationists plan out ways to proliferate what few California condors we have left. Part of the standard procedure for efforts like these is a genetic analysis of all condor chicks hatched; the data from these will help scientists monitor which pairs of condors produced which offspring, as well as other metrics like population size and familial aspects. This particular study, however, revealed two particular specimens of condors that left scientists scratching their heads.
The two “dad-less” condors in question had already passed away; one of them died at the age of 2, and died all the way back in 2003; the other, aged 8, died back in 2017. These two particular California condors gave scientists a real brain workout, as they appeared to have had no fathers.
Said lead author Oliver Ryder, Kleberg Endowed Director of Conservation Genetics at the San Diego Zoo Wildlife Alliance: “This is truly an amazing discovery. We were not exactly looking for evidence of parthenogenesis—it just hit us in the face.”
Parthenogenesis pertains to the phenomenon wherein female animals produce an embryo without the aid of a sperm cell from a male counterpart. Being essentially a form of asexual reproduction, parthenogenesis is often observed on plants and some invertebrates; it is, however, rare in animals like amphibians and reptiles. The study by Ryder and team appears to be the first-ever recorded instance of parthenogenesis in birds.
Ryder followed: “We only confirmed it because of the normal genetic studies we do to prove parentage. Our results showed that both eggs possessed the expected male ZZ sex chromosomes, but all markers were only inherited from their [mothers], verifying our findings.” (Due to how genetics work for condors, condors that reproduce via parthenogenesis are expected to only produce male offspring, which this study seemingly proved.)
Thing is, the California condor mothers who hatched the two-of-a-kind offspring weren’t exactly out of dating matches, either. They had lived alongside and around several males who were certainly available for mating while in the conservation enclosure. In fact, these females had already mated with male condors—both before and after hatching these “dad-less” condor chicks.
“Parthenogenesis is considered to be a rare phenomenon in birds,” said Ryder in a statement to The New York Times. “We discovered it in California condors because we have such a detailed genealogical analysis of the entire population.”
In another statement to The New York Times by University of Florida conservation geneticist Samantha Wisely, who’s unrelated to the study: “For other species it seems to be sort of a last-ditch effort to save themselves. It will be really interesting to know the context in which it’s happening in the wild for birds.”
Of interesting note is the fact that these California condors are considered evolutionary anachronisms, in that they seem to have evolved to survive on ecological systems that no longer exist. Scientists think these condors evolved to become scavengers, or carnivores that survive on the meat of animals that had already died, due to the amount of carrion produced by the giant animals that once roamed the lands below their skies. These megafaunal animals have since gone extinct, leaving scavengers like the California condor to feed off other sources of carrion, like dead sea creatures that wash ashore in coastal areas like California.
(Read up on similar conservation stories on modernsciences.org, including topics such as the two newly-discovered pit viper species in Asia as well as the last surviving member of the Fernandina giant tortoises.
References
- Endangered condor chicks hatch from unfertilized eggs in species first. (2021, November 1). New Atlas. https://newatlas.com/biology/california-condor-asexual-reproduction-parthenogenesis/
- Fahy, C. (2021, October 30). Endangered california condors can reproduce asexually, study finds. The New York Times. https://www.nytimes.com/2021/10/30/science/san-diego-zoo-condor-virgin-births.html
- Galetti, M., Moleón, M., Jordano, P., Pires, M. M., Guimarães, P. R., Pape, T., Nichols, E., Hansen, D., Olesen, J. M., Munk, M., Mattos, J. S. de, Schweiger, A. H., Owen-Smith, N., Johnson, C. N., Marquis, R. J., & Svenning, J.-C. (2018). Ecological and evolutionary legacy of megafauna extinctions. Biological Reviews, 93(2), 845–862. https://doi.org/10.1111/brv.12374
- Kooser, A. (2021, October 29). Scientists surprised to discover California condors hatched chicks from unfertilized eggs. CNET. https://www.cnet.com/news/surprise-discovery-california-condors-hatched-chicks-from-unfertilized-eggs/
- Ryder, O. A., Thomas, S., Judson, J. M., Romanov, M. N., Dandekar, S., Papp, J. C., Sidak-Loftis, L. C., Walker, K., Stalis, I. H., Mace, M., Steiner, C. C., & Chemnick, L. G. (2021). Facultative parthenogenesis in california condors. Journal of Heredity, esab052. https://doi.org/10.1093/jhered/esab052
- Wetzel, C. (2020, August 25). How some animals have ‘virgin births’: Parthenogenesis explained. National Geographic. https://www.nationalgeographic.com/animals/article/parthenogenesis-how-animals-have-virgin-births
