Scientists have successfully implemented a never-before-used technique for helping recover a critically endangered species: thawing out frozen, 20-year-old semen, and impregnating females through artificial insemination, according to a new study.
At one time, the black-footed ferret was found all along the Great Plains of North America, from Canada to Mexico, but it barely escaped extinction in the early 1980s when the last 24 surviving animals in the wild were rounded up by the US government in an attempt to recover the species. Six of the ferrets died shortly after, leaving just 18 animals to repopulate the species.
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Conservationists at the time were willing to try anything they could think of to help bring the species back from the brink, according to Paul Marinari, the senior curator of animal operations at the Smithsonian Conservation Biology Institute, who has worked on the black-footed ferret restoration program for more than 20 years. This multi-pronged effort included pulling semen samples from the remaining males of the species and freezing those samples in liquid nitrogen for later use.
“From day one, the National Zoo and the Smithsonian were on board to do the early science,” Marinari said. “They were coming out every year with a new crop of scientists looking into different ways to freeze semen, different ways to thaw semen, different ways to store it, and trying to develop these techniques for this exact purpose.”
Through years of captive breeding, the program—led by the US Fish and Wildlife Service with the help of dozens of other organizations—was able to gradually bring the population back up into the hundreds and even release some populations into the wild. However, breeding from an initial pool of just 18 ferrets meant the species was becoming increasingly inbred.
“With increased inbreeding, we can start to see a lot of detrimental effects to the animals,” said Marinari. “There’s lower semen quality. There’s a greater impact from diseases. So, the more genetic diversity and time we can give to our captive population, the better.”
That’s why, in 2008, Marinari and his colleagues decided it was time to thaw out some of that 80s ferret spunk. They assessed the genetic makeup of their current ferret population and compared it to the genetic records of the sperm samples they had from the original population to mix-and-match partners that would be the most genetically diverse. Between 2008 and 2011 they used artificial insemination to successfully impregnate five female ferrets with frozen semen that was between ten and 20 years old, resulting in the birth of eight baby ferrets, or kits.
Not only was this technique a success as far as increasing the population, but more importantly it provided a way to increase the genetic diversity in a species that was becoming more and more inbred. Gene diversity was enhanced by 0.2 percent (which is a lot, in this case) and measures of inbreeding were reduced by 5.8 percent, according to the study on the technique published Thursday in Animal Conservation.
This genetic diversity also had a trickle down effect: six of the eight kits eventually produced 32 babies and grandbabies through natural breeding, all of which maintained greater genetic diversity compared to the rest of the captive population:
Blue dots show the level of inbreeding for non-artificially inseminated ferrets while red dots show the level of inbreeding for the population resulting from the ferrets that were artificially-inseminated with the frozen semen. Source: Animal Conservation
Now the conservation team is being even more vigilant in collecting samples from the current population so they can use this technique again in five to 10 years, Marinari told me. There are currently about 300 captive black-footed ferrets and between 300 and 500 wild ferrets. That’s a huge improvement from where the species was 25 years ago, but still a long way from being out of the woods. The continued use of multiple techniques—including artificial insemination using old, frozen semen—will be necessary to ensure the survival of the species.
Marinari hopes his research will act as a signal for other conservationists to start collecting and freezing samples from all kinds of species, even those that aren’t yet at risk, to build a veritable Noah’s ark of frozen jizz.
“The time to do it is when you still have all of that genetic diversity in the wild,” Marinari said. “And the problem with a lot of breeding centers and a lot of zoos is we have limited space. We don’t have that problem when it comes to liquid nitrogen samples. We can store millions and millions of samples. We can’t house millions and millions of animals.”
