West of Pahrump, Nevada, in a corner of the Mojave Desert a couple thousand feet above Death Valley, a warm aquifer provides a home for one of the world’s rarest animals. It’s a tiny silvery-blue fish, smaller than your pinkie toe, and in the past 50 years it has survived real-estate speculators, death threats, congressional battles, and human screwups. The Devils Hole pupfish—Cyprinodon diabolis—is nothing if not tenacious.
But the biggest existential threat to the pupfish comes from its own DNA. Once upon a time, pupfish lived in a sprawling lake. Around 20,000 years ago, water levels dropped, the landscape turned to desert, and the pupfish ended up in disconnected ponds. Today, nine different species are scattered across the Southwest, and half of them are endangered. Devils Hole is the worst case; as of September 2012, there were 75 fish left. Thousands of years of adaptation have left the Devils Hole pupfish able to live only in one very particular environment: It needs 90-degree water, low oxygen, and a shallow submerged ledge on which to spawn. It’s hard enough being endangered; being endangered and picky is a deadly combination.
Endangered, picky, and unlucky? Even worse. Beginning in the 1970s, government scientists built three pools to contain backup populations of Devils Hole pupfish as a final hedge against extinction. At two of these refuges, pumps, valves, and other mechanical bits malfunctioned repeatedly, killing most of the fish. In one case, lightning struck a transformer. But at the third site, called Point of Rocks, something more interesting happened. Somehow a few pupfish of a different species managed to infiltrate the refuge and—to put it politely—their DNA quickly spread through the population. After about half a decade, every fish in the pool was descended from the invaders, who gave their offspring telltale genes and an extra set of fins. Wildlife officials moved all the hybrids to a hatchery, where, unlike captive Devils Hole pupfish, they couldn’t stop making babies. “There were floor-to-ceiling tanks of these hybrid fish,” says Andy Martin, an evolutionary biologist at the University of Colorado at Boulder who led the research into the hybrids’ DNA. “This was a population that had been sputtering away, and now it was going like mad.”
To Martin, the fact that an influx of new genes caused a population explosion suggested what was wrong: “genetic load,” a glut of defective DNA that accumulates in a small population. On the upside, that diagnosis suggests a cure—a way to save the species. Martin has a plan to bring the fish back from the brink. But to the kind of people who have battled extinctions in the past, his solution is heresy.
For half a century, conservationists have seen themselves as preservationists: Protect species X as it exists in place Y at time Z. Of course, nature has no such compunctions. Evolution is change. So the way to save the Devils Hole pupfish, Martin says, is to introduce genes from its cousin, the Ash Meadows Amargosa pupfish—C. nevadensis, the same little Casanova from the refuge—which is native to a spring just a few miles away. Martin wants to take one or two and drop them in with their endangered relatives. That simple act would have profound implications. It would protect the Devils Hole pupfish by rewriting its genome.
Whether or not you care about pupfish, this plan represents a major philosophical change in how we think about our relationship with nature—because it doesn’t end with the pupfish. It ends with us becoming architects, engineers, and contractors for entire ecosystems. The old approach involved fencing off swaths of wilderness and stepping aside. In the new order, we’d be the stewards not just of land or wildlife but of individual chromosomes. So far, in the world of Devils Hole pupfish conservation, Martin has run into a wall of no. But around the world, in other places where other species are in trouble, the answer, increasingly, is yes.
In 1995, Florida wildlife officials flew eight female cougars (Puma concolor stanleyana) from Texas to breed with their hometown Florida panthers (Puma concolor coryi), a local variety on the brink of extinction. The panther project met with passionate resistance, but it worked. Population numbers have tripled since then. (Of course, their habitat is increasingly covered in asphalt, and the cats often meet their end in a splattery heap on the highway. But at least their genes are hardy and their testicles are more likely to fully descend.)
Still, the Florida panther project isn’t exactly like what Martin proposes to do with pupfish. The pumas were two different subspecies. Martin wants to cross two separate species. That’s supposed to be a no-no. In fact, by one definition of what constitutes a species, it shouldn’t even be possible. Scientists have long thought of species as reproductively isolated units. In the days before Darwin, if two animals couldn’t produce fertile offspring, it meant they were different species. Then things got complicated. In the late 1800s, Darwin and naturalist Alfred Russel Wallace, who independently proposed the idea of natural selection, both said the sterile-offspring definition wasn’t enough. Over the next century, evolutionary biologists from Theodosius Dobzhansky to Ernst Mayr ladled on new criteria. Mate choice, physiology, geography, invisible genetic differences—all these might distinguish species.
But it turns out that biology doesn’t even adhere to those categories. For example, the ability to reproduce can evolve far more slowly than other traits. So when one species branches off from another, it may still be able to breed with its relatives up the evolutionary tree. “It raises the question, what really is a species? It’s very hard to clearly articulate,” says M. Sanjayan, lead scientist for the Nature Conservancy. “There are lots of things that can breed together but look morphologically and genetically different.”
That means scientists triaging endangered species might have more options than they thought. Three decades ago, ornithologists made a last-ditch effort to save the dusky seaside sparrow by breeding it with a related bird. (They failed; the last one died at Walt Disney World Resort on June 17, 1987.) Or take rhinos: Sanjayan is part of an initiative to save the northern white rhinoceros—the last eight until recently lived in zoos. The hope is to breed it with the more abundant southern white rhinoceros, which, depending on whom you believe, is either a different species or a different subspecies. It’s anyone’s guess whether the northerners and southerners will choose to mate.
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Attack of the Mutant Pupfish
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