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Ancient DNA Could Return Passenger Pigeons to the Sky

Genetic engineering could restore the once profuse North American bird after a century or more of extinction
passenger-pigeon-illustration


PASSENGER PIGEON: The numerous bird went from abundant to extinct in less than 100 years. 
Louis Agassiz Fuertes

The last lonely bird of a species that once numbered three billion or more died on September 1, 1914. Martha, as she was known, had been the last passenger pigeon since her mate George died in 1910. The last of a social species, she lived out her days in solitary confinement in a cage in the Cincinnati Zoo. Her corpse—stuffed and primped—can now be seen at the Smithsonian Institution.
 
But what if the passenger pigeon could be brought back?
 
That's the idea behind de-extinction. Take DNA harvested from specimens stuffed in museum drawers, like Martha. Figure out which genes matter and then use the fast growing field of genetic engineering to edit the DNA of a closely related species into some version of the extinct species. If all goes well, a chimera of the long-lost Martha could be born and, one day, flocks of passenger pigeons could be restored to the regrown eastern North American woodlands.
 
Would-be de-extinction pioneer Ben Novak is working at the University of California, Santa Cruz, to make this exact scenario come true. A joint venture between the Revive and Restore effort of The Long Now Foundation (an organization dedicated to long-term thinking) and the ancient DNA lab at U.C. Santa Cruz, Novak's effort is focused on acquiring genetic information from stuffed passenger pigeons and sequencing the genome of the closely related band-tailed pigeon. So far, 32 samples have had the genetic code in their mitochondria sequenced. All of the samples come from birds killed between 1860 and 1898, according to Novak. "That's right in the range when the bird was going extinct," he notes.
 
Outside efforts have helped as well, including nearly complete sequencing of three individuals that showed passenger pigeons have been through booms and busts before. "If passenger pigeons survived through several population bottlenecks during their evolutionary history, perhaps we don't need to create billions of them in order for their populations to be sustainable," notes paleogenomicist Beth Shapiro of U.C. Santa Cruz, whose lab hosts Novak and this effort.

"All of our birds are all very, very similar to each other—like everybody being cousins, essentially—which is the effect of this recent rapid population expansion," Novak adds. "What we're really interested in is figuring out when that population expansion happened."
 
If the population explosion happened more than 400 years ago, then it is unlikely that the European arrival in North America precipitated the boom that produced billions of birds, as some have suggested. To figure out when the last boom occurred will require finding DNA from fossil samples thousands of years old—a few of which Novak has begun to examine. With ancient samples and those from the 19th century, Novak and his peers could begin to piece together the actual ecology of the bird in the wild. And understanding how the passenger pigeon existed makes it more likely people could bring the bird back and have the species thrive in the woods that are available today as well as in the future as the climate changes. "Nothing in the data so far to shout at us to turn back now and not bring back the passenger pigeon," Novak says.
 
The team has not yet completed the band-tailed pigeon sequencing required to begin resurrecting the passenger pigeon, but experiments in cell cultures from the band-tailed pigeon may begin as soon as next year, Novak says. This work would be similar to experiments being done at Harvard Medical School to see if the woolly mammoth might be resurrected through its still living relative, the Asian elephant. And the passenger pigeon work may be helped along by similar germ cell efforts in the chicken and houbara bustard—a rare bird prized by oil sheikhs with the funds to attempt a genetic rescue.
 
If cell cultures thrive and genetic engineering works, the only remaining challenge would then be to teach the resulting hybrid band-tailed and passenger pigeons how to be passenger pigeons. This will likely even more challenging than the genetic work, given experience from rearing California condors with puppets or teaching cranes to migrate with ultralight airplanes. That’s why Revive and Restore, for one, is not putting all its de-extinction eggs in the passenger pigeon basket (as it were). The foundation-funded outfit might undertake a similar effort to revive the heath hen in Martha's Vineyard, if they can get funding from outside donors. But, assuming breeding, sequencing and cell-culture experiments go well, birds that carry the now extinct genes of the passenger pigeon could be flapping around a California facility by the end of the decade, according to Novak.
 
These de-extinction projects may prove too ambitious, however. Similar efforts that stretch back 30 years have so far failed to produce a quagga, an extinct species of zebra, although acquiring quagga genetics from museum specimens did kick off the entire ancient DNA field in 1984. And the 2003 experiment that resurrected a bucardo for seven minutes has yet to be repeated. Nevertheless, even the International Union for Conservation of Nature has set up a committee to examine how the genetics used for de-extinction might be used to preserve endangered animals and plants or bring them back if they die out.
 
De-extinction is not just for extinct species, after all. It could also be used to save a plant or animal that is on the verge of extinction. The black-footed ferret has been bred back from just seven viable individuals in the 1980s to thousands today, but the species may need a genetic transfusion to protect the new animals from the perils of inbreeding, which include reproductive problems, susceptibility to disease and genetic drift. So Revive and Restore has sequenced four ferret genomes, including two that had been stored in cell cultures from deep freeze at the Zoological Society of San Diego for the Frozen Ark Consortium, a global project to save the DNA and viable cells of endangered species. If genetic information from such frozen samples could be used to infuse robust genetics into a living population, it would be a first in the annals of conservation. "The northern white rhino has only four living individuals left. They are not viable," says Ryan Phelan of Long Now, who has petted the last individuals of this functionally extinct species. "Do we use genomic techniques and advanced genetic technology to keep that species alive or let it march over to the right on the continuum of extinction and become extinct?"
 
But there are advantages to work with an animal that is already extinct, not least of which is the absence of urgency. After all, Martha died 100 years ago. "If we succeed, the world gets a new organism," Novak says. "If we fail, we learn things that are valuable and the world isn't left with another extinct species."

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