Aug. 18, 1998 WEST LAFAYETTE, Ind. -- 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.
Unfortunately, the rare animals sometimes die off again, and the reintroduction isn't successful. Too often the cause may be the inevitable inbreeding that occurs in the small populations.
Gene Rhodes, a wildlife biologist at Purdue University, is improving the odds for these reintroduced species by making new use of a familiar scientific tool: biotechnology. Rhodes is comparing the genes of the introduced animals to reduce the chances of inbreeding.
"Almost every reintroduction program has stories of failures of local populations," Rhodes says. "One of the questions that biologists always ask is 'Could have this have been a genetic problem?'"
According to Rhodes, 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," Rhodes says. "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 inbreeding, 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 population of a species 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 says. "We've seen this with the cheetah, with the northern elephant seal, and potentially hundreds of other species."
Extreme inbreeding also can cause genetic problems. "With inbreeding you can get developmental problems such as actual structural problems -- missing legs, two heads, that sort of thing," Rhodes says. "The recessive lethal genes that are scattered through a population begin to come together and you start to see problems."
Rhodes counters the problems of inbreeding by identifying specific gene markers on an animal's chromosomes and then looking for the gene markers in other animals of the species. Wildlife biologists can then see if they need to introduce new animals to improve the genetic variability. For example:
- In Indiana, Rhodes is using these biotechnology techniques to improve the genetic profiles of introduced populations of wild turkeys. Once a population's genetic profile is determined, wildlife biologists establish satellite groups with different genetics to improve the genetic variability of the entire population. Currently Rhodes is able to sample the genetics by meeting hunters at state weigh stations during turkey hunting season, but he is investigating retrieving DNA from feathers and fecal samples.
- In Arizona, Rhodes has used mitochondria DNA analysis to develop a profile of the entire pronghorn antelope herd in the state. "Arizona has one threatened subspecies, one endangered subspecies, and one subspecies that's doing fine," Rhodes says. "We're not only trying to improve the genetics of the populations, but also to help the subspecies to keep their unique genes. We don't want to mix stocks that historically weren't mixed."
- In Florida, Rhodes is investigating the genetics of the model duck. The model duck is a native, nonmigratory species that is threatened not because of inbreeding, but because of hybridization with mallard ducks. The concern is that the model duck might fade away as a separate species. Rhodes is checking the genes of ducks used in breeding programs to make sure that they aren't hybrids.
According to Rhodes, the number of ways of looking at DNA is rapidly expanding. "Now we have the ability to look at the genetics of a large population in a short period of time, and the cost is coming down, too. Ten years ago this would have been very slow and too expensive.
"Its just like the space program, where we developed all of these new spin-off technologies from things that were needed for space travel," Rhodes says. "Wildlife biology has never been the focus of any of the big biology thrusts. The big genome mapping projects are spinning off technologies that are inexpensive enough that we can use them in wildlife management."
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