Preventing Wildlife from GENETIC CRASH-AND-BURN.

• Position: Brief Article

Group by group, animals such as pronghorn antelope and wild turkeys that once disappeared from America's landscape are returning as wildlife biologists reintroduce them to their native areas. Sometimes, though, the reintroduction isn't successful and the species becomes extinct. Too often, the cause may be the inevitable inbreeding that occurs in small populations. Gene Rhodes, a wildlife biologist at Purdue University, West Lafayette, Ind., is improving the odds for these reintroduced species by making new use of biotechnology. He is comparing the genes of the introduced animals to reduce the chances of inbreeding.

Some species have gone extinct when they reached a genetic point beyond which they could not recover. "You could say that about almost any species that has disappeared. Take, for example, a species like the passenger pigeon. We know that the species declined because of hunting for the feathers. However, even after the hunting was banned, the species crashed. The population was too small to recover." After being hunted to the edge of extinction, the problem for the pigeon became one of limited genetic variability. "What difference does this make?," Rhodes asks. "Genetic variation is the currency of evolution. By having a variety of genes in the population, the animals have the ability to adapt to their environment."

When environmental factors change, such as a harsh winter or a new disease spreading through the area, some individual animals will survive if the population is large enough because they are slightly different from the other animals. If the population has undergone in-breeding, however, the genes of the animals will all be nearly similar. If the genetics aren't right for the new environmental conditions, the entire population may disappear.

When the number of animals gets small enough to threaten the species, wildlife biologists say it has gone through a population bottleneck. "We're only working with a fraction of the total genetic variation that once was there," Rhodes explains. "We've seen this with the cheetah, with the northern elephant seal, and potentially hundreds of other species."

Extreme inbreeding also can cause adverse genetic conditions. "With inbreeding you can get developmental problems such as actual structural problems--missing legs, two heads, that sort of thing. The recessive lethal genes that are scattered through a population begin to come together and you start to see problems."

Rhodes counters...