News is just coming to light about a momentous wildlife management event from last December. It involves a little black-footed ferret named Elizabeth Ann, who along with a horse named Kurt, inspired this week’s Wildlife Matters.
Black-footed ferrets have had a long, slow road back from the brink of total extinction. They are victims of their prey; prairie dogs were the target of farmers and ranchers on the prairie shot them, poisoned them, and destroyed their colonies early in the last century. To make matters worse, an exotic disease plague suppressed their numbers even more. By some estimates, the populations of prairie dogs were reduced from their original levels by as much as 95%. Sadly, the loss of the prey resulted in the loss of their primary predator, which didn’t have a suitable alternate prey species, and their numbers crashed. The ferret has the unfortunate distinction of being on the very first list of endangered species under the 1966 Endangered Species Preservation Act. Their numbers in the wild were so low, in fact, that they were considered extinct until 1981, when a small group of 18 individuals was discovered on private land in Wyoming. The animals were captured and set about the task of breeding in captivity to try to expand their numbers. The undertaking has been somewhat successful; 40 years later, there are about 300 ferrets living in captivity and about the same number again spread across 29 reintroduction sites in 12 states. However, when you grow hundreds of animals from such a small initial population, you risk genetic drift. Inbreeding of related individuals can result in a loss of diversity, increasing risk of disease, health problems, reduced reproductive capacity and early mortality.
When you have a geographically isolated population, you can introduce individuals from another location to infuse some diversity. In this case, there have been no other family groups discovered, so scientists have had to go back in time to bring genetic diversity into the population. This is where Elizabeth Ann comes into the picture. She is the exact genetic replicate of Willa, a ferret that died in 1988. Her genetic material was cryogenically preserved at that time with the hope that one day genetic science would advance enough to help bring endangered or extinct species back to life.
Elizabeth Ann is noteworthy, as the first Endangered Species clone in the United States. However, Kurt beat her to the punch. Last summer, a similar feat was accomplished with an endangered species of wild horse, known as Przewalski's horse, which was captive bred and reintroduced into the wilds of central Asia and eastern Europe. The foal born last summer, named Kurt, was fathered by a stallion that died in 1980 and had its cells preserved in the same facility at the San Diego Zoo. The hope is that Kurt will help bring fresh new genetic material and ensure the viability of Przewalski’s horse for years to come.
There is some difference between resurrection science, where efforts are being considered to bring extinct animals back into existence, and introducing genetic variety by cloning such individuals as Kurt and Elizabeth Ann. Cloning one unique individual using modern techniques is still extremely expensive, but if one individual can be introduced into an existing viable population and breed several times, it could well make a difference on a small scale over time. If you started with an initial population of zero, as is the case with de-extinction, you would need to clone a significant number of genetically distinct individuals to breed with each other. If you clone Kurt six times, you will get six identical Kurts, which is great if that is the goal; you could clone 28 more Elizabeth Anns, one for each separate ferret reintroduction site, and the end result will be significant genetic diversity over generations in geographically distinct populations.
Wisconsin has had to tackle the question of genetic drift with some of its own reintroduced wildlife species, such as fisher, pine marten, whooping crane, even elk. In each case, it can be difficult to determine the minimum number of distinct individuals needed to keep a population viable until it is too late. In some cases, such as with elk, genetically distinct individuals were introduced from another population to infuse fresh DNA into the population and give it a boost in numbers as well. Whether genetic science will ever become affordable enough to be used as a management tool to fight extinction is a question that remains to be answered.