The > Science > A Species in a Second: Promise of DNA 'Bar Codes'

hen an astronaut sets foot on an alien planet and sees moving shadows in a nearby wood, he whips out a scanning device that immediately identifies the menacing life-form, flashing up a photo of its species and an assessment of its aggressive intent.

If such devices are standard equipment for visiting distant planets, why can't we have them here at home where we really need them? Less than a fifth of the earth's 10 million species of plants and animals have been cataloged, and taxonomists are backlogged with requests to apply their specialist knowledge to identification problems.

The wait for a simple way of identifying species may not be too much longer, if an idea known as DNA bar coding should prove as good as its advocates say. DNA bar coding depends on analyzing part of just one gene, the same gene in all cases, for every species. If and when a DNA bar code database of all terrestrial plant and animal species is established, a field biologist could take a tiny piece of tissue, like a scale or hair or leaf, from the unknown specimen, and feed it into a hand-held device for analysis. With a cellphone call to the database, the device would identify the species and present its photo and description.

DNA bar coding is the idea of Dr. Paul D. N. Hebert, a population geneticist at the University of Guelph in Ontario. It has attracted support from the Alfred P. Sloan Foundation of New York, where it has been championed by a program officer, Jesse H. Ausubel of Rockefeller University. In April a consortium of major natural history museums and herbariums started the Barcode of Life Initiative, a plan to create a DNA bar coding database that would be linked to identified specimens in their collections.

Such a system, if it works as promised, will help field biologists identify known species and assist immensely in the urgent task of cataloging unknown species before their ranks are decimated by extinction.

Public health authorities could identify whether mosquitoes were of a type likely to carry deadly diseases. Since bar coding works on tissues, inspectors could test animal feed for forbidden items likely to spread mad cow disease.

And because DNA bar codes can be obtained from museum specimens up to 20 years old, curators throughout the world could bar code their collections, making their priceless storehouses of taxonomic knowledge available to everyone and easily accessible.

Despite its promise and quick start, DNA bar coding has not yet won the unanimous support of a core constituency, the taxonomists and biologists who would be its principal creators and users. The resistance stems from doubt that DNA bar codes can distinguish between closely related species.

There may be other sources for the muted enthusiasm, like insiders' habitual reserve toward outsiders' help, and the traditional difference of perspective between those who study whole animals and those interested only in their DNA.

Two reports published in October demonstrated the striking power of DNA bar coding. In an article in The Proceedings of the National Academy of Sciences, a team led by Dr. Hebert and Dr. Daniel H. Janzen of the University of Pennsylvania showed that members of a Costa Rican butterfly species, Astraptes fulgerator, possessed a total of 10 bar codes. The finding meant that the butterflies were not a single species, as long assumed, but a complex of 10 species occupying overlapping territories.

Researchers had suspected something of the kind because the caterpillars looked quite different and preferred different food plants, as if each had long diverged away from a distant ancestral species. But all looked the same as adults, as if that particular appearance - livery that includes a splash of iridescent blue scales across the body and wings - carried such a survival advantage that none of the descendant species could stray from it.

In another article, in Public Library of Science Biology, Dr. Mark Stoeckle of Rockefeller University and colleagues developed DNA bar codes for 260 species of North American birds. They found that all had different DNA bar codes except four species in which two bar codes were present, suggesting in each case that a single species was really two.

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