NEWSSCIENCE science.orgPHOTO: USFWS NATIONAL BLACK-FOOTED FERRET CONSERVATION CENTER
ing program. They captured 18 individuals,
but just seven survived to breed, putting
the species at risk of inbreeding, which can
erode reproductive fitness.ELIZABETH ANN owes her existence to a
chance meeting at a banquet in Montana.
In 1987, biologist Oliver Ryder was on the
lookout for animal cells to freeze. As a
young scientist in the 1970s, he had joined
a new effort, known as the San Diego Fro-
zen Zoo, that aimed to preserve genetic
material from a wide array of endangered
mammals, deep-frozen in liquid nitrogen.
At a conservation conference, Ryder struck
up a conversation with a Wyoming Game
and Fish veterinarian named Tom Thorne,
who told him about the black-footed ferrets’
plight. A couple of years earlier, Thorne had
sent a handful of black-footed ferret tissue
samples to the Frozen Zoo, but scientists
had managed to preserve a cell line from
just one: a male labeled Studbook #2. Ryder
suggested Thorne send more. Seven months
later, he received skin cells from a single fe-
male named Willa, which the zoo also suc-
cessfully banked.As those two cell lines sat in a freezer,
the ferret breeding program—which has
been led by the U.S. Fish and Wildlife Ser-
vice (FWS) since 1996—began to take off. To
date, it has produced some 10,000 ferrets,
many of which have been released into the
wild. The program has become a prominent
success story, but the ferret’s survival is still
far from a sure thing.
One threat is sylvatic plague, a deadly
bacterial disease introduced from Asia.
Inbreeding has also begun to take a toll
on the population, all descendants of just
seven animals. Genetic studies, Novak says,
show “they’re all superrelated. ... The mean
kinship falls between that of a sibling and
a first cousin.” As a result, they have accu-
mulated some potentially damaging muta-
tions, says genomic researcher Klaus-Peter
Koepfli with the Smithsonian Mason School
of Conservation. Some animals are born
with kinked tails and deformed sternums.
To shore up the ferrets’ genetic diversity,
researchers have turned ferret breeding
into an exacting science. A computer pro-
gram helps them assign a desirability rating
to each possible pairing, based on the ani-mals’ ancestry. Breeders have also relied on
artificial insemination with semen taken in
the 1990s from two standout males, known
as Scarface and Rocky. But semen is a finite
resource, says Pete Gober of FWS, who coor-
dinates the recovery programs.
So, in 2013, program managers turned
to Revive & Restore to see whether they
could bolster the population’s diversity by
transforming the Frozen Zoo’s small vials
of preserved cells into living, breathing fer-
rets. “We wanted to increase and maintain
as much genetic diversity as we could from
what little amount we had to begin with,”
Gober says.THE IDEA WAS to use a technology that didn’t
exist when the zoo had stored the samples:
somatic cell nuclear transfer. In this cloning
technology, technicians replace the nucleus
of an egg cell with a nucleus taken from a
body cell. A jolt of electricity encourages
the egg and nucleus to fuse and the cell toBiologists hope Elizabeth Ann, a cloned black-footed
ferret (above), will soon contribute to efforts to breed
the endangered species and restore it to grasslands.14 JANUARY 2022 • VOL 375 ISSUE 6577 135