Attack of the Mutant Pupfish
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.
http://www.wired.com/wiredscience/2012/11/mf-mutant-pupfish/
