Parthenogenesis—also known as virgin birth—is a type of asexual reproduction in which a female's egg can develop into an embryo without sperm. Lizards do it. Swellsharks do it. Even water dragons do it. In a surprising twist, scientists found that California condors are also able to reproduce this way, reports Sara Harrison for Wired.
The California condor's population stooped dangerously low to 22 individuals in the 1980s. In a race to save the critically endangered species, scientists captured the remaining condors and began a captive breeding program that is still running. With such a small genetic pool and a fragile population, their breeding has to be meticulously planned and documented, reports Sarah Zhang for the Atlantic.
When scientists at the San Diego Zoo Wildlife Alliance were reviewing the birds' genetic data, they found something puzzling: Two male chicks, known as SB260 and SB517, didn't have genetic contribution from any males in the program, reports Jason Bittel for National Geographic. They published their findings this week in the Journal of Heredity.
"This is truly an amazing discovery. We were not exactly looking for evidence of parthenogenesis, it just hit us in the face," co-author Oliver Ryder, a geneticist at the San Diego Zoo Wildlife Alliance, says in a press release. "We only confirmed it because of the normal genetic studies we do to prove parentage."
Both condor chicks died before reaching sexual maturity, but other parthenotes—like domesticated turkeys, pigeons and chickens—usually die before hatching. SB260 only lived for two years before dying in 2003 in the wild, likely from malnourishment. SB517 was unusually small and remained in captivity until he died of a foot infection at nearly eight years old in 2017, reports Wired.
"They certainly weren’t, shall we say, shining specimens of the condor," Demian Chapman, a biologist at the Mote Marine Laboratory and Aquarium, tells the Atlantic.
California condors can live to about 60 years, and Ryder says parthenogenesis itself could have led to the parthenotes' early demise. The young birds may have developed genetic mutations that caused underlying problems, since they didn't have the genetic diversity that is added from the DNA of another parent, reports National Geographic.
Parthenogenesis is a rare occurrence, but some evidence suggests that females capable of parthenogenesis will reproduce this way when there aren't any mates around, which could happen with an imperiled population. Scientists suspect that's what pushed the critically endangered smalltooth sawfish to parthenogenesis in the wild. For that reason, it's more common for females in captivity to reproduce asexually if they don't have mates in their enclosure.
But in a puzzling twist to this theory, the female California condors who laid these two eggs were living with males, reports National Geographic. They mated with their partners before and after the parthenotes were born, leaving the team to wonder: Why would theses birds reproduce asexually? The researchers don't have an answer yet, but they're working on it.
"We only now have the genetic tools to look at this in detail," Ryder tells Isaac Schultz for Gizmodo. "Previously, parthenogenesis was really identified by seeing females who weren’t housed with males have offspring. But now we know the condor can have offspring while being housed with males and it begs the question, 'Is this going on more than we know?'"
It probably is, reports Wired. The team caught these two parthenotes while reviewing the genetic data, but there could be more. Because these births happened twice, at separate times and with different females, so it could be a recurring oddity, Ryder tells Wired.
"In their lifetimes, they weren’t even recognized to be parthenotes… we’re definitely keeping our eyes out anytime we get a batch of blood samples for testing," Ryder tells Gizmodo.
Ryder hopes that some parthenotes born in the past slipped past the team and grew to be healthy adults, which could benefit the species in the future, he tells Wired. Because for a species so imperiled—now with a population at about 500 individuals—every new egg counts.