Science – Endangered California Condors May Be Reproduced Asexually, Study
The rare discovery arose as a result of efforts to preserve the species.
Conservation geneticists working to preserve endangered California condors have discovered two cases of chicks hatching from unfertilized eggs: the first known cases of so-called virgin births within the species.
This finding, included in a study published Thursday in The Journal of Heredity, is especially notable, as such cases are unusual among birds.
Parthenogenesis, the process by which females produce embryos that have not been fertilized by sperm, is more common among vertebrate species such as fish or lizards. Prior to the findings being made public on Thursday, other known cases of parthenogenesis among birds were limited to turkeys, finches and domestic pigeons, according to the San Diego Zoo Wildlife Alliance.
“Parthenogenesis is considered a rare phenomenon in birds,” said Oliver Ryder, co-author of the study and director of conservation genetics for the San Diego Zoo’s Wildlife Alliance. “We found out in California condors because we have such a detailed genealogical analysis of the entire population.”
California condors have long been an endangered species, with the world’s population falling to just 23 in 1982, according to the U.S. Fish and Wildlife Service. At the time, the agency removed all known California condors from nature and raised them in captivity.
The species, which by 2020 had 504 birds, has been closely monitored and studied for decades, leading to findings such as the one released Thursday, said Samantha Wisely, a conservation geneticist at the University of Florida who did not participated in the study.
The need to identify birds by sex to develop a successful breeding program led to the discovery of the two chicks.
Years ago, Dr. was asked. Ryder who developed a system to identify the sex of California condoms in captivity so that males and females look alike. He also had to identify close relatives among the birds so that they would not mate. So he created a genetic database for all California condors.
In 2013, Dr. Ryder’s team noticed some discrepancies in the database, which led to a reanalysis of all the birds in captivity. Dr. Ryder’s team discovered two male chicks, one born in 2001 and the other in 2009, that do not match any of the males ’genetic profiles. This meant that none of the male condors had fathered them.
“There was no paternal contribution,” Dr. Ryder said. “They only had genetic information from their mothers.”
The final clue that these chicks had developed from parthenogenesis was the fact that they were both male. Due to the genetic makeup of birds, female condors that reproduce on their own can only give birth to male condors.
In the past, parthenogenesis was thought to be a somewhat desperate form of reproduction, occurring when females were in low male populations or in environments with few members of their own species, said Dr. Wisely.
Condors in captivity, however, had mated with males in an enclosure, but were still reproducing by parthenogenesis.
According to Dr. Ryder, the discovery of “virgin births” in such a closely monitored bird population makes scientists wonder if more birds in nature reproduce by parthenogenesis than previously thought.
“For other species it seems to be a kind of last-ditch effort to save itself,” Dr. Wisely. “It will be very interesting to know the context in which it is happening in nature for birds.”
Another interesting aspect of parthenogenesis is that lethal genetic traits cannot be transmitted from the mother.
Still, Dr. Ryder said, some less favorable traits may still appear in offspring.
“Maybe they could, you know, not wear the handsome genes or something,” he said.