In 1983, Betsy Dresser boarded a plane in Los Angeles with delicate cargo taped under her arm: a test tube containing embryos from a rare antelope bred several days earlier at the Los Angeles Zoo.
After the four-hour flight, Dresser delivered the embryos to the Cincinnati Zoo, where they were successfully implanted into two other antelopes, one of them a different species. Two healthy calves were born nine months later and raised by their surrogate mothers.
Dresser's trip marked the start of what researchers say will one day be standard practice in the breeding of endangered species. Rather than moving animals themselves around the globe, they will be transported as embryos, sperm or eggs. Healthy species may be used to carry the embryos of the endangered.
The trend is part of an increasingly technical approach to saving wildlife from extinction by controlling a population's genetic makeup. The more genetically diverse a population, the better able it is to fight off disease and reproduce.
But as a species' number dwindles, animals resort to mating with relatives. This inbreeding can lead to birth defects, reproductive problems and susceptibility to disease.
Using genetic studies and reproductive technology, scientists now are attempting to choose which animals to reproduce based on their bloodlines. An animal that already has several offspring, even if endangered, will not be allowed to mate. Priority is given to animals with few relatives, because its genes are not well represented in a population.
Already, "frozen zoos" are being formed in zoos to store sexually reproductive cells for possible future breeding of rare animals. "You can keep thousands of animals in a small tank, frozen," said Dresser, research director of the Cincinnati Zoo.
While this high-tech approach may enhance endangered species protection, separate developments in genetic analysis could unwittingly jeopardize it. Recently, for instance, scientists found genetic evidence that indicated the endangered gray wolf in Minnesota mated with coyotes at one time.
Farm groups subsequently challenged the wolf's endangered classification. As a hybrid, the groups charged, the wolf does not merit protection under the federal Endangered Species Act. The matter is under review.
The growing emphasis on the genetic makeup of populations has vastly changed the way zoos breed animals.
"It's become an increasingly technical business," said Bob Seibels, who helps oversee the mating of the endangered Bali myna in captivity throughout North America. "If you had told me before that I would be looking at a computer screen for seven hours of the day, I wouldn't have believed you. I can actually call up two birds, and the computer will tell me whether they are a good (genetic) match."
Of all the developments in genetic manipulations of populations, Dresser's work is probably the most challenging. In one case, the embryo of an endangered Indian desert cat was transferred into a domestic cat. Two kittens were born. One died but the domestic cat raised the other as her own.
Dresser concedes that researchers do not know whether such transfers may somehow alter the endangered animal behaviorally, perhaps interfering with its ability to identify with its own species.
"There hasn't been enough of this done," she said. "But these animals grow up and reproduce naturally on their own. You have to suspect that they haven't changed that much, and indeed, (reproducing naturally) has happened to every one we have tried it on."
Reproductive technologies such as artificial insemination may one day be effective in maintaining genetic diversity of small, rare tiger populations in India, said Ulie Seal, chairman of the captive breeding group of the International Union for the Conservation of Nature.
For instance, he said, there are 18 tiger reserves scattered over India, with 25 to 50 tigers in each. Although the populations are "way too small for genetic diversity," moving tigers from one population to another for mating could be risky for the animals. A male tiger in a strange reserve may be quickly killed by another tiger protecting his turf, may wander off the reserve or even kill other tigers, according to Seal.
Reluctant breeders whose genes are nevertheless needed for a small population also could be made to reproduce through the use of artificial insemination and other reproductive technologies. Eventually, zoos might become storehouses of genes that would be transferred to wild populations through embryo transplants or artificial insemination.
"The loss of any individual group of animals will not compromise the survival of the species," Seal said. "The breeding stock will be available in captivity and will provide as many animals as needed to learn and accomplish the science of reintroduction," the return of captive-bred wildlife to their original habitat.