Analyze This

By Small, Meredith F. | Natural History, October 1999 | Go to article overview

Analyze This

Small, Meredith F., Natural History

In the cause of conservation, everything from caviar to rhino dung is grist for the DNA laboratory.

Geneticist Vadim Birstein was carrying a can of caviar when he arrived at the Molecular Systematics Laboratories at the American Museum of Natural History. Ah, thought his colleague Rob DeSalle, here's some caviar because we've done such nice work.

But the caviar, it turned out, was a study specimen. Both Birstein and DeSalle analyze the DNA of living and extinct animals in order to illuminate evolutionary history. Their work on the fish-egg delicacy would launch a series of DNA comparisons of caviar purchased at gourmet shops all over Manhattan. Identifying the species of fish that the eggs came from, the researchers discovered that one-quarter of the cans were fraudulently labeled. Not surprisingly, cheaper fish eggs were sometimes being passed off as beluga sturgeon caviar, a very costly product. In addition, this so-called beluga caviar often came from highly endangered species of sturgeon from extremely fragile ecosystems-a matter of concern to many conservationists.

DeSalle's and Birstein's original interest in sturgeon DNA, however, was more theoretical. They initially saw it as a way to reconstruct a family tree. "We have representatives of every single species of living sturgeon on the face of the Earth in our tissue and genetic database," explains DeSalle. "We even have thirty to forty individuals of some of these species."

Another Museum researcher doing DNA studies is Joel Cracraft, of the Department of Ornithology. He uses DNA to evaluate the diversification of birds of paradise in the mountainous terrain of New Guinea. Cracraft's population sample includes blood and muscle from zoo specimens and tiny scrapings from the feet of birds in the Museum's collections of skins. Together, the modern material and the skins represent almost ninety different forms of birds of paradise-an array of specimens unavailable from the wild today.

Such theoretical research inevitably has implications for conservation biology, a field concerned with preserving biodiversity in the face of human environmental impact. Conservation decisions require answers to basic biological questions about the definition of species and how they evolve over time. DNA analysis enables conservation geneticists to make practical recommendations on such matters as the minimum population size required to avoid the perils of inbreeding and the targeting of particular species for preservation becaue of their great genetic diversity.

Molecular genetics researchers at three New York City institutions-the American Museum of Natural History, the Wildlife Conservation Society, and the New York Botanical Garden-have been sharing lab techniques and ideas to address a range of conservation-related subjects, from the population genetics of the black rhinoceros to the diversity of African violets. A procedure called polymerase chain reaction, or PCR, is the main research tool: PCR can create millions of copies of DNA from a minuscule amount of organic material.

In PCR, genetic start and stop signals are used to isolate a specific portion of a DNA strand. Usually the portion or portions selected are known to be highly variable and therefore useful in making comparisons. By subjecting the sample to chemical and temperature changes, the targeted lengths of DNA are duplicated again and again (a process called amplification), producing a large sample for testing. The genetic sequence of the sample is then compared with those of other known samples to identify variations in the genetic code, at least for that particular strand of DNA. Comparisons can be made between individuals, populations, or species.

The three New York City institutions are especially suited to employ PCR because they are great repositories of organic matter: the Museum has a vast collection of animal skins and skeletons; the Wildlife Conservation Society has access to hair, skin, blood, and other material from animals in captivity and in the wild; and the Botanical Garden houses an immense collection of dried plants as well as thriving exotic gardens. …

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