In 1981, scientists found only one small wild population of Black-footed Ferrets in Wyoming. Wildlife organizations, including zoos, have since brought this critically endangered species back from just 18 individuals to more than 2,600 in the wild today. This summer, the Smithsonian Conservation Biology Institute (SCBI) broke the genetic bottleneck facing the species by using semen that had been cryopreserved for 10 to 20 years to artificially inseminate live female ferrets. This breakthrough will increase the number of black-footed ferrets born in human care while enhancing genetic diversity within the species.
The United States Fish and Wildlife Service (USFWS) developed and oversees the Black-footed Ferret Recovery Program. The Association of Zoos and Aquariums’ Species Survival Plan (SSP) manages the Black-footed Ferret breeding program with a breeding population composed of about 300 animals. For this study, all the males were managed either at SCBI or at the USFWS National Black-Footed Ferret Conservation Center. Scientists collected semen samples from adult Black-footed Ferrets that ranged in age from one to six years old. All females were solely managed at SCBI.
Initially, scientists used fresh semen to artificially inseminate females who failed to naturally mate with males, resulting in 135 kits. With just a few founders to rebuild an entire species, early managers of the Black-footed Ferret recovery program knew that genetic diversity could be lost. Loss of genetic variation can lead to increased sperm malformation and lower success of pregnancy over time. Researchers routinely collected and preserved Black-footed Ferret semen for later use as part of standard operating procedures.
Read more about Black-footed Ferret breeding and see more photos below.
SCBI was the first institution to develop a successful laparoscopic artificial insemination technique for Black-footed Ferrets. Females are induced ovulators, which means that mating causes the ovary to release its eggs. SCBI researchers developed a hormone treatment that artificially causes ovulation to occur. Scientists then deposited the male’s fresh or frozen-thawed sperm directly into the female’s uterus. Animal care staff closely monitored potentially pregnant females by taking weight measurements and remotely monitoring the nest boxes via closed-circuit cameras.
During the 2008 breeding season, SCBI scientists used semen samples from four male Black-footed Ferret donors that had been frozen for 10 years. After using population data to determine the optimum genetic pairings, sevarel females were inseminated. Two became pregnant and gave birth to two kits. In the years that followed, subsequent AIs incorporated semen that had been cryopreserved up to 20 years, also resulting in successful pregnancies. Six of the eight kits produced 32 offspring and grand offspring by natural mating. More significantly, researchers found that incorporating these individuals into the population enhanced overall genetic diversity and lowered measures of inbreeding over time.
“Our findings show how important it is to bank sperm and other biomaterials from rare and endangered animal species over time,” said Paul Marinari, senior curator at SCBI. “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.”
Black-footed Ferret populations fell into drastic decline in the 20th century as the Great Plains were altered for agriculture, and the Ferrets’ primary food source – Prairie Dogs – were eradicated. Black-footed Ferrets were thought to be extinct until a small population was discovered in South Dakota in 1964. Nine Ferrets were captured in hopes of starting a captive breeding program, but the last surviving Ferret in captivity died in 1979. The small Wyoming population discovered in 1981 meant that Black-footed Ferets had a second chance. With the new technology pioneered by SCBI, scientists are working hard to ensure that the Black-footed Ferret’s second chance is not lost.