Tusk Tales

A trail of DNA may lead us to the killers of Africa's elephants

By Eric Scigliano|Sunday, June 05, 2005
RELATED TAGS: EXTINCTION

In a cluttered ground-floor laboratory at one corner of the University of Washington’s Seattle campus, Sam Wasser hunches over a gray toaster-size instrument. “This is it,” he says. “This is what makes it all possible.” The device is a liquid-nitrogen-cooled mill that can pulverize a piece of tusk without destroying its DNA. Genetic detectives can then use that information to determine where in the vast continent of Africa the elephant lived and died. Over the next few months, Wasser and his team hope to unravel the origins of the largest load of contraband ivory ever seized and furnish international investigators with the data they need to crack the criminal networks that continue to devastate Africa’s elephant herds.

elephant-tusk-l
elephant-tusk-l
John Clark

Tusks grow throughout an elephant’s life and can weigh up to 130 pounds. One study noted that the average weight of a traded tusk dropped from 22 pounds in 1979 to 7 pounds in 1990.

Such knowledge is essential if African countries and their supporters hope to enforce the ban on international ivory trading enacted 16 years ago. The agreement was reached to stem the slaughter of the herds, whose numbers had dropped from 1.3 million in 1979 to just over 600,000 in 1989. For a few years, poaching declined, herds began recovering, and in 1997 USA Today proclaimed that “the illegal ivory trade has been virtually wiped out.”

The declaration proved premature. Smugglers became more sophisticated and poachers more covert. Elephant kills on the savanna are easy to spot and count. But as logging opened up vast swaths of Central African rain forest, poachers increasingly targeted elusive forest elephants under a green canopy that hid their kills from aerial surveillance.

The African elephant population is estimated to be about 500,000, but experts fear that the killing in some

elephant-tusk-r
elephant-tusk-r

As poachers kill off males with the largest tusks, elephants with shorter tusks—younger males and females—become more frequent targets.regions may even exceed the slaughter of the late 1970s. “There are vast areas in Central Africa where the habitat is intact but empty,” says Richard Ruggiero, the U.S. Fish and Wildlife Service’s program officer for African elephant conservation. “There are no animals left.”

In June 2002 Singapore customs agents seized the largest haul of contraband ivory ever: 6 1/2 tons, including 535 tusks and 42,000 ivory cylinders used to make hanko, prestigious signature stamps that can fetch hundreds of dollars each. Investigators discovered that the ivory had been sent from Zambia—which has tried and failed to obtain special permission to sell stockpiled ivory—through Malawi and on to South Africa, a country that later won approval for a onetime sale. The cargo was then shipped to Singapore and was on its way to Yokohama. Investigators suspect that at least some of the booty came from the chaotic, poacher-plagued Democratic Republic of the Congo, but they need definitive clues about its origins.

“If that seizure came from 25 different places, that would tell us the smuggling network is quite sophisticated,” says Bill Clark, an enforcement officer at the Nature and Parks Authority in Israel who is assigned to Interpol’s wildlife-smuggling investigation. “If it came from only two or three, the population there is getting hit very heavily, but the network is not so extensive.” Tracing the origins of smuggled ivory, he says, would help investigators determine “the magnitude of the trade, the structure of the criminal syndicates running it, and the dynamics of the smuggling operations.”

Clark knew of Wasser’s research on elephant genetics, so last August, after completing the necessary formalities, he sent samples from the Singapore seizure to Seattle.

Ever since the ivory-trading ban took effect, scientists have labored to decipher the tales tusks might tell. First to try was a South African team led by Nikolaas van der Merwe, a professor of natural history at the University of Cape Town. South Africa has a special interest in solving the puzzle. In the 1990s, South Africa and four other southern African countries had repeatedly sought and occasionally won permission to sell ivory from their better-protected and sometimes overpopulated herds. But Kenya and other nations complained that legal sales would give cover to contraband shipments because officials had no way of knowing where the ivory actually came from—where, for example, a tiny nation like Burundi, with no elephants of its own, got the thousands of tusks it exported in the 1980s.

elephant-statue
elephant-statue
John Clark

This carved figure, which stands about four inches high, was found in a shipment of contraband ivory seized in Los Angeles in 1981. The collection was later given to the Oregon Zoo.

The South Africans wanted a “fingerprint” that would distinguish their ivory. They began by looking at isotopes of several elements in ivory. The difference between using DNA analysis and isotope tracking is a variation on the nature versus nurture debate: DNA records an organism’s genetic inheritance, and isotopes reflect the composition of the environment in which it grows. Trees and shrubs are rich in carbon-12, and tropical grasses are rich in carbon-13. The proportions of the isotopes in ivory reflect the diets of the elephants. Nitrogen isotopes vary with rainfall, reflecting the climate elephants inhabit. And the radioactive isotope strontium-87, which scientists use to date rocks, varies with the age of rock in soil.

By overlaying isotope ratios of these three elements, the South Africans were able to distinguish ivory not only from different regions and countries but also from parks as few as 150 miles apart. They proposed an isotope map of Africa.

But the map kept changing. In 1995 U.S. researchers found that carbon isotope ratios in elephants at Amboseli National Park in Kenya had shifted over decades, reflecting changes in the elephants’ diet as they crowded into the park to escape poaching, ate up the park’s trees, and switched to grass. Nitrogen ratios proved a “blunt” measure, says paleontologist Paul Koch of the University of California at Santa Cruz. He and his colleagues got different carbon and nitrogen readings at different points along a single molar. As the tooth grew, it recorded a diary of changing environment and diet.

Other researchers began looking to DNA. Prompted by the Wildlife Conservation Society, a young Kenyan-born biologist named Nick Georgiadis embarked on what he called “a long and wonderful hike” across 10 African countries, taking biopsy-dart samples from 600 elephants. He and his colleagues extracted mitochondrial DNA from the samples and screened it for specific markers, using a technique called restriction mapping. The results appeared to detect different markers in elephants from different regions—a first step toward a continent-wide genotype map. But a second look was deflating. Elephants were just too mobile; too much gene flow had occurred, especially between East and South African elephants, to preserve distinctive genetic signatures.

Georgiadis’s work did, however, prove valuable. Taxonomists and field biologists had long wondered just how different Africa’s two designated elephant subspecies—the familiar, widespread savanna elephants and the elusive forest elephants—actually were. With their round ears, sloping brows, and straight, downward-pointing tusks, the forest elephants certainly look different. Georgiadis concluded that the two lines diverged several million years ago, but he needed more evidence. He arranged for further analysis at the National Cancer Institute’s Laboratory of Genomic Diversity. There, with help from Wasser and his colleagues in Seattle, geneticist Al Roca sequenced introns—vestigial sections of DNA from the nucleus that accumulate mutations quickly because they don’t code for any physical traits—and confirmed that forest and savanna elephants diverged at least 2.6 million and probably more than 3 million years ago—long enough to render them separate species.

Since then, Smithsonian Institution biologist Lori Eggert has gathered mitochondrial evidence suggesting that West Africa’s elephants are so genetically distinct that they may constitute another species. Such findings aren’t just academic; recognizing distinctive populations could bring them additional legal protection. But such protection is only as good as its enforcement—and mitochondrial DNA, like isotopes, had failed to provide investigators the ivory fingerprints they needed to expose poaching and smuggling networks.

Where the elephants were

elephant-map
elephant-map
Graphic by Don Foley

Biologists recognize two elephant species in Africa, and both are larger than their Asian counterpart. But the forest elephants (orage area) of Central and West Africa are smaller than elephants on the savanna. They also have smaller ears and straighter tusks.

Savanna elephants (green area) range over a greater region than forest elephants (purple area shows where hybrids of the two species occur). A 1999 report estimated that at the peak of the ivory trade poachers took 1,000 tons of ivory from Africa each year.

While Georgiadis assembled his samples in Kenya, Wasser laid the groundwork for the next breakthrough in neighboring Tanzania. Wasser hadn’t come to Africa to work on elephants; he was there studying how female baboons curtail their reproduction when resources grow scarce, and he was interested in measuring changes in the hormones that regulate stress and reproduction. To chart this process, Wasser and his colleagues devised a new, noninvasive method—tallying hormone metabolites in feces.

Extracting information from fecal samples is now an important conservation tool, but it was new ground in early 1985. Using drug-sniffing dogs retrained to sniff out scat, Wasser tracked grizzly bears in Washington’s Cascade Range, pumas and jaguars in Brazil’s Central Highlands, and even right whales in the North Atlantic. Dogs can distinguish the scat of 18 different species, detect samples from great distances on land and sea, and search much faster and more thoroughly than humans. Once he gets the scat, Wasser says, he “can tell you if it was a female via DNA, and from hormones how stressed the animal was, and if it was a female, whether she was pregnant—all without ever seeing her.”

While chasing baboon scat, Wasser stumbled upon elephant poaching. “I spent years in one of the most heavily poached regions of Africa,” he says. “I became totally disgusted with the ivory trade.” And he realized how the methods he’d developed might help combat it. Forest elephants, which travel in smaller groups in dense foliage, are much harder to track and dart than their brazen savanna cousins. Fecal sampling and DNA analysis might provide much-needed information on their numbers and movements.

Eventually, by drawing on Georgiadis’s tissue collection, Lori Eggert’s West African samples, and the gleanings of other on-site collectors, Wasser’s team at the Center for Conservation Biology at the University of Washington assembled a bank of 354 tissue samples and 491 fecal samples, collected from 45 locations in 23 countries, that together account for over 85 percent of Africa’s surviving elephants. They extracted and amplified DNA from these samples, concentrating on microsatellites, repetitive noncoding DNA sections that rapidly accumulate genetic changes. Where the mitochondrial DNA that Georgiadis analyzed provides just a single locus for comparison, Wasser’s team compared up to 16 loci in each microsatellite sample—and the regional differences they found did not evaporate upon closer inspection.

By comparing the frequency of markers in samples taken from known locations, they managed to assemble a map of elephant gene flow across the continent. They tested this map by using it to deduce the origins of samples from undisclosed locations—and found they could place half these samples within 300 miles of their points of origin and 80 percent within 600 miles.

Last fall Wasser’s team began analyzing tusks from the Singapore seizure. Figuring out the origins of 75 randomly selected tusk samples would prove the first real-world test of the genetic detection method. To get to this point, the sleuths had managed to succeed where other investigators had failed; they had figured out how to successfully extract high-quality DNA from ivory, and they had done so by picking up a few tips from orthodontists and forensic scientists. Wasser surmised that because tusks are just massively overgrown teeth, they should harbor DNA in remnants of the odontoblastic cells that form dentin. And when he consulted a forensic dental laboratory in British Columbia, he found that superfreezing would avoid the DNA-wrecking heat of ordinary drilling and pulverizing. When Wasser and collaborator Kenine Comstock pulverized tusk samples in their nitrogen-cooled device, they found them shot through with DNA.

elephant-print
elephant-print
This footprint of Packy, a 43-year-old male Asian elephant at the Oregon Zoo, measures about 20 inches across. While the memories of elephants are legendary, their sensory abilities are equally impressive, if poorly understood. They can, for example, detect through their feet seismic signals being emitted by other elephants up to 20 miles away.
John Clark

The DNA is not evenly distributed, however, because it is organized into tubules, says Wasser. “You can have one spot blank next to another spot that’s loaded.” Blind strikes mean additional sampling and more expense, but they don’t invalidate the approach. “When we get profiles from the ivory, they’re beautiful—much clearer than from scat, which has a lot of [organic] noise.”

The final question is: Will the technique prove a reliable weapon against smugglers? “We’re not there yet,” says Stephen O’Brien, director of the Laboratory of Genetic Diversity, who headed the earlier forest-versus-savanna study. “If you have only 80 percent confidence about where ivory comes from, that’s not good enough to make explicit recognition. That’s not good enough to get us anywhere in court. I think the gene flow [between elephant populations] has occurred so recently, there’s not much of a prospect of establishing different genotypes.” Ruggiero of the U.S. Fish and Wildlife Service is more hopeful, but he warns: “Sam still has to prove the reliability of ivory detection. He needs to have 20 pieces from different collection points in one place,” and identify their sources in double-blind tests, just as his team did with tissues and dung. Importing those samples for testing would be a bureaucratic and legal nightmare.

Other elephant watchdogs worry that DNA tracking will prove too effective and spur more ivory trading by permitting legal sales—just as the South Africans hoped. “It’s a double-edged sword,” says Julian Newman, a senior campaigner with the London-based Environmental Investigation Agency, which has tracked the ivory trade extensively. “It’s a useful technology from my point of view. But it’s also a justification for the trade.” Paula Kahumbu, a science adviser to the Kenyan government, which opposes all ivory sales, views the new techniques more warily: “The suggestion that this DNA fingerprinting will, in essence, be used as a tool to help authorities to facilitate the ivory trade is scary. Since U.S. Fish and Wildlife financed the study, it means that the U.S. government and taxpayers are paying for reopening the ivory trade.”

Wasser contends that critics on both sides miss the point. He thinks DNA tracking may ultimately curb ivory sales because it can reveal whether dealers are telling the truth about where their ivory comes from. And like Clark, he foresees that DNA data will be more important as investigative intelligence than as trial evidence. “We’re not talking about a beyond-reasonable-doubt standard,” he explains. “The appropriate analogy is paternity testing. There, you can’t say ‘This is the father’ with absolute certainty. But you can exclude everyone else it might be.”

Clark thinks, nevertheless, that genetic profiling may one day help convict, not just catch, smugglers. “We might have ivory from a suspect’s premises in Africa. What if it matches the DNA of ivory seized in Singapore?”

Combining testing techniques is another possibility. Researchers would subject the same ivory samples to both genetic and isotope testing and compare results. The two approaches are “complementary,” says geochemist Thure Cerling of the University of Utah. “Stable isotopes are most useful in eliminating possible source regions [for ivory], rather than identifying a single one.” But isotopes overlaid with DNA tracking might provide firmer, finer-grained identifications than either could alone—if the practitioners of both techniques can collect a large enough database. They still have a big continent to map.

“We’re all working cooperatively, mainly because the criminals work cooperatively,” says Clark, “like gangsters during Prohibition.” He hopes that analyzing the ivory flow will “identify weak points in the network, where it might be attacked. It’s been done in the past. In 1998 an analysis of criminal trafficking in reptiles led us to a Malaysian dealer. He was monitored until he made a mistake and got nailed and extradited to the United States. He pleaded guilty to 40 violations of wildlife laws, and he’s now serving 71 months in prison, without parole. I’d like to get a few ivory dealers that way too.”

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