They used to roam right across the Great Plains of America, hunting the prairie dogs that made up the vast majority of their diet. But in the early 1980s, the black-footed ferret was reduced to just a few dozen individuals and so the decision was made to take them all into captivity and start a breeding program. It got to the point where there were only 18 in existence, so alongside breeding the ferrets conventionally and using insemination of fresh semen, the choice was also taken to freeze some of the remaining males' sperm.
Fast forward 20 years, and scientists from Lincoln Park Zoo, along with help from many other institutions, have managed to successfully inseminate females and produce kits, or baby ferrets, using the frozen sperm from the long-dead males. This is seen as a critical step in proving that frozen semen from critically endangered species can still be viable decades later, and genetically vital in populations that have become worryingly inbred as their numbers have dwindled.
“Our study is the first to provide empirical evidence that artificial insemination with long-stored spermatozoa is not only possible but also beneficial to the genetic diversity of an endangered species,” explained David Wildt, lead author of the paper published in Animal Conservation. “What we've done here with the black-footed ferret is an excellent example of how sperm preservation can benefit species recovery programs.”
After being declared extinct in the wild in 1987, conservationists have managed to build up the number of ferrets from the surviving 18 they held in captivity. It’s thought the main reason they petered out in the wild in the first place was due to the extensive prairie dog control implemented by farmers who’d settled on the Great Plains. The rodents are thought to contribute up to 91% of the ferret’s diet, and so when its main prey base was decimated, the ferrets also suffered.
Since then, the ferret population has been managed extensively, and currently there are thought to be around 300 in captivity, with around 500 breeding adults that have been reintroduced into the wild at various sites in both the U.S. and Canada. This is despite having bred over 6,000 of the animals since 1987. One of the major problems facing the ferrets after being descended from just 18 individuals is inbreeding. This is why it is important to freeze samples of sperm from all possible breeding males, to preserve as much genetic diversity as possible.
“Our findings show how important it is to bank sperm and other biomaterials from rare and endangered animal species over time,” says Paul Marinari, senior curator at the Smithsonian Conservation Biology Institute. “These 'snapshots' of biodiversity could be invaluable to future animal conservation efforts, which is why we must make every effort to collect, store and study these materials now.”