The event was detailed this week by the San Diego Zoo Wildlife Alliance’s conservation scientists in the American Genetic Association’s Journal of Heredity.
The scientists explained that during a routine analysis of biological samples from the two condors in the San Diego Zoo Wildlife Alliance’s managed breeding program, they confirmed that each condor chick was genetically related to the respective female condor that laid the egg from which it hatched.
Neither bird was found to be genetically related to a male condor – and researchers tested 467 male condors in the breeding pool as potential fathers – even though the two mother condors, or dams, had been continuously housed with fertile male partners.
The find, the San Diego Zoo Wildlife Alliance said, was the first in any avian species where the female bird had access to a mate.
“This is truly an amazing discovery,” Oliver Ryder, the study’s co-author director of conservation genetics at San Diego Zoo Wildlife Alliance, said in a statement. “We were not exactly looking for evidence of parthenogenesis, it just hit us in the face. 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 dams, verifying our findings.”
In addition to the California condor parthenotes, both dams had also produced numerous offspring via sexual reproduction with their mates. One had 11 chicks and another who was paired with a male for more than 20 years had 23 chicks and reproduced twice more following the parthenogenesis.
Parthenogenesis – also known as a “virgin birth” – is a natural form of asexual reproduction in which an embryo that is not fertilized by sperm continues to develop, containing solely the genetic materials of the mother. The offspring are called parthenotes.
The process is relatively rare in birds and instances were confined mainly to domestic birds and normally observed in females who have no access to males.
California condors are a critically endangered species and the San Diego Zoo Wildlife Alliance said it was through the California Condor Recovery Program and genetics and genomics research that scientists were able to “cross-reference historical genetic records before confirming the outcome of this distinctive case of parthenogenesis.”
Although one chick died in 2003 at the age of 2 and the other in 2017 at the age of 7, the researchers said they would continue future genotyping efforts in the hopes of identifying other parthenogenetic cases.
“These findings now raise questions about whether this might occur undetected in other species,” Ryder said.
Breeding efforts to save California condors have produced more than 1,000 chicks and, following the reintroduction of some to the wild, the population has increased to more than 500 both in human care and free-flying in California, Arizona, Utah and Baja California.