Doling out DNA: biologists make their debut as molecular matchmakers for endangered species

Science News, Feb 4, 1989 by Rick Weiss

DOLING OUT DNA

What do you get when you cross two captured African elephants? If you're not careful, says conservation biologist John Patton, you may get nothing more than "a hybridized mess."

Patton is one of a handful of scientists who are trying to avoid that genetic Waterloo by applying state-of-the-art DNA "fingerprint" tests to endangered species in captive breeding programs.

In cooperation with the St. Louis Zoo and Wildlife Conservation International -- a conservation arm of the New York Zoological Society in New York City -- Patton is preparing a sort of dating-service database for the endangered elephant, whose numbers have been declining in recent years as it is increasingly poached for its tusks (SN: 5/21/88, p.333). His little black book of gneetic information should help biologists decide which individual African elephants now held in captivity should be mated to preserve the ideal degree of genetic variability within the species.

"I've been trying to understand what is this thing we call an African elephant," says Patton, a researcher at Washington University in St. Louis. But unlike the legendary blind men who had a similar quest and who came to disparate conclusions by getting a feel for an elephant's ears, trunk and tail, Patton is using microscopic samples of the animal's DNA to settle the issue once and for all.

DNA testing, which other researchers are applying to a growing number of species, is becoming increasingly important as zoos in the United States and other countries take on new roles as breeders of rare and endangered animals.

"Zoos are increasingly involved in trying to do something more than simply putting animals on display," says Susan Haig of the Department of Zoological Research at the National Zoo in Washington, D.C. "Zoos are starting to switch their whole way of thinking away from the Noah's ark phenomenon, where they want two kingfishers, two Guam rails, two of this and two of that. In general they are moving more in the direction of managing populations, and especially those of endangered species."

But when only a few of these exotic individuals have been captured and made available for breeding, problems can arise. In some cases, several adults may be close kin and thus likely to produce weakened offspring because of inbreeding. In other cases, breeders have mistakenly mated pairs of individuals that look like they belong to the same species but that in fact would never have mated in nature. That can lead to what biologists call "outbreeding depression" -- a weakening of the species due to a hypervariability of the genetic code.

"The problem with zoo biology is that too often, when you have relatively few animals brought in, you don't know where the hell they came from," Patton says. "Somebody may say it came from here or there or somewhere else, but mostly managers don't have the reference samples to double check and make sure things are even the same species."

And yet, Patton says, "zoos have freely been breeding these animals one to another until there's no real species that's left anymore. Instead, what they've got is a big hybridized mess that quite often gives reproductive problems down the road."

Until recently, population biologists relied mostly on morphology -- or physical appearance -- to lump animals into taxonomic groupings such as genus, species and subspecies. But appearances can be deceiving. So these naturalists are joining forces with molecular biologists to get a more precise handle on just how similar--and just how different--are the various individuals of a given species.

They use DNA fingerprinting to measure these differences. Developed only three years ago, it has already triggered a revolution in molecular genetics (SN: 4/23/88, p.262) and has begun to find its way into U.S. courtrooms because of its ability to link tiny bits of evidence such as hair or semen to accused murderers or rapists.

It calls for a cocktail of highly specific enzymes and molecular "probes" that can cut and label pieces of DNA bearing particular molecular sequences. Scientists apply these labeled DNA fragments to a gelatin strip that sorts the pieces by size. The result is an easy-to-read, black-and-white representation of an animal's genetic code that resembles the "bar codes" found today on the packaging of most grocery items. The scientists can then compare this bar code, or DNA fingerprint, with those of other animals to measure their degrees of genetic similarity. And with that information in hand, they can choose pairs of prospective parents that are not too alike and not too different.

"The single most important tool we have for management of gene-pool resources in zoos is our ability to know individuals as individuals and to establish and manipulate pedigrees," explains Oliver Ryder of the San Diego Zoo. "DNA fingerprinting is a very powerful technique that allows us the potential to very efficiently manage gene-pool resources."

Ryder has DNA fingerprinted all 28 California condors now held by scientists who hope to breed them in captivity. His fingerprinting efforts are part of a larger effort to save the severely endangered birds, none of which remains in the wild.