The California condor, a critically endangered vulture that was once extinct in the wild, has unexpectedly high genetic diversity, according to researchers, who say this increases the bird's chance of adapting to climate change and other anthropogenic modifications to the environment.
In a study published Thursday in Current Biology, the researchers sequenced the full genetic code of the California condor, or Gymnogyps californianus, as a first step toward better understanding its evolutionary history and biology, which will inform ongoing conservation efforts.
"California condors are the largest flying North American bird; they're very charismatic," said study lead author Jacqueline Robinson, a postdoctoral scholar at the Institute for Human Genetics at the University of California, San Francisco. "In the mid-20th century, people started to become very concerned that the population size had become so small — to the point that, by the early '80s, there were only a couple dozen birds left in existence."
But thanks to an intensive captive-breeding program over the past few decades, hundreds of birds have been reared and released back into the wild. From just 22 individuals in 1982, the population has soared to about 200 in captivity and more than 300 in the wild, some of which were recently up to mischief on a California woman's property.
A common assumption about species that have been to the brink and back is that they have low genetic diversity as a result of inbreeding, Robinson said.
"Inbreeding is a real concern, in part because you lose genetic diversity, but also in part because it can result in negative health consequences," she said. "In captive breeding programs for conservation purposes and in conservation in general, you want to avoid inbreeding as much as possible."
To gain a better understanding of California condor genetic diversity and evolutionary history, Robinson and her colleagues sequenced the full complement of genes, or genome, of the species.
About 20% of the California condor genome showed signs of previous inbreeding that likely occurred in the wild prior to the captive breeding program. Mating with related individuals is more common in smaller populations because family members are more likely to encounter one another, so this finding suggests that condor numbers had already fallen before human activities that nearly wiped them out.
According to Robinson, the fossil record shows that the Californian condor could once be found across North America. But by the 1900s, its range had shrunk to areas along the Pacific Coast. One hypothesis for this decline is the mass extinction of the so-called Pleistocene megafauna, because these large animals may have been an important food source for scavengers like the condors.
Another key finding from the study was that, outside of the regions of the genome linked with inbreeding, there was a "surprisingly" high level of genetic variation, Robinson said. This finding supports the idea that condor populations were once much larger but decreased over geologic time.
According to Robinson, high genetic variation is a hopeful sign for the persistence of this species.
"Since the population size of California condors is still quite low, they are in a precarious position because they remain in danger of extinction if their numbers start to decline," Robinson told The Academic Times. "It's encouraging that they have a decent amount of genetic diversity because it increases the chance that they may be able to leverage that diversity to adapt to a changing environment. If they had very low genetic diversity, the probability of evolving adaptations would be lower."
Robinson said that this work could be extended to aid conservation management of wild condor populations.
"We have condors at various release sites in California, Utah, Arizona and Mexico. So we could detect whether those populations are very isolated or if individuals are moving between these areas and exchanging genetic material," she said. "I'm kind of excited about that: being able to use genomic information for monitoring to keep an eye on whether any inbreeding is happening in the future."
The genome could also help researchers identify specific gene variants that may be beneficial or detrimental to the birds. One example is a genetic disease called chondrodystrophy, a lethal form of dwarfism that afflicts some captive-reared California condors.
"I think a major goal would probably be to identify, if possible, the gene underlying that disease, and then maybe you can manage breeding more effectively to reduce the prevalence or predict if it's going to show up," Robinson said.
For comparison with related species, the researchers also sequenced the genome of the Andean condor, a South American species classified as vulnerable. They also looked at a previously published genome of the turkey vulture, a common species found across the Americas.
Of the three birds, the California condor had the greatest genetic diversity, indicating that this now-rare species once had a bigger population than the Andean condor and even the highly abundant turkey vulture.
"There's been this reversal of fortune that we can see by looking at patterns of genetic diversity in these different species," Robinson said.
But despite the California condor's brush with extinction, fortune might yet favor this species.
"I think in a lot of cases there's this mentality that once the population size [of a species] becomes very small, they're kind of doomed to experience inbreeding depression or they're doomed to go extinct. And I just don't agree with that notion whatsoever," Robinson said. "We can choose to do something about it. And I certainly think it's worth it. They've spent decades with puppets, hand-rearing these condor chicks; a huge amount of time, money and effort went into saving the species — but we still have them."
The study, "Genome-wide diversity in the California condor tracks its prehistoric abundance and decline," published May 13 in Current Biology, was authored by Jacqueline A. Robinson, University of California, San Francisco; Rauri C.K. Bowie, University of California, Berkeley; Olga Dudchenko, Baylor College of Medicine and Rice University; Erez Lieberman Aiden, Baylor College of Medicine, Rice University, ShanghaiTech and University of Western Australia; Sher L. Hendrickson, Shepherd University; Cynthia C. Steiner, Beckman Center for Conservation Research; Oliver A. Ryder, Beckman Center for Conservation Research and University of California, San Diego; David P. Mindell, University of California, Berkeley; and Jeffrey D. Wall, University of California, San Francisco.