SCIENCE science.orggenetic analysis shows she is 100% a black-
footed ferret.
This spring her creators hope to mate
Elizabeth Ann with a captive male. Any
offspring will still have Elizabeth Ann’s mi-
tochondrial DNA, with traces of domestic
ferret. To remove those traces, any male off-
spring will be paired with captive females,
producing kits that no longer carry the do-
mestic female’s mitochondrial DNA.
Successfully adding Willa’s genes to the
black-footed ferret gene pool via Elizabeth
Ann would likely “pack this huge biodiversity
punch,” Novak says. Genomic analysis
has found Willa’s DNA has 10 times more
unique alleles than DNA from any captive-
bred ferret. That means her chromosomes
will “introduce a whole new combination
[of traits] and higher level of genetic vari-
ants,” Koepfli says. That should slow the fer-
rets’ trajectory of reproductive decline.
To introduce even more genetic variation
into captive-bred ferrets, ViaGen aims to
create company for Elizabeth Ann. Scien-
tists there are fine-tuning the cloning pro-
cedure to make it more efficient and will try
to create the next batch of cloned ferrets in
spring 2023, to align with next year’s breed-
ing season.THE SUCCESSFUL USE of cloning in ferret
conservation is likely to attract attention—
and perhaps funding—for similar efforts in
other endangered species. But replicating it
won’t be easy. In part, that’s because species
that might benefit from cloning have to meet
numerous criteria. The best candidates, for
example, have both banked genetic material
at the ready and a less endangered close rela-
tive that can act as a surrogate. It also helps
to have funding and captive breeding infra-
structure in place. Few programs can meet
these prerequisites—yet.
Another obstacle is that, although the ba-
sic cloning process is the same for all mam-
mals, the technology has worked better in
some species than others, and “no one knows
why,” Durrant says. To increase the odds of
success, researchers often must develop a
unique “recipe” that addresses an animal’s
reproductive quirks, says Samantha Wisely,
a conservation geneticist at the University
of Florida who works with the black-footed
ferret program. “Reproductive technology is
super–species specific.”
Still, efforts to clone at least two other en-
dangered species are underway. One is the
Przewalski’s horse (Equus ferus przewal-
skii), a stocky wild horse that once roamed
across Europe and Asia. The species nearly
went extinct in the mid–20th century, and
all individuals alive today are descended
from just 12 animals. Luckily, nearly
300 cell lines have been stashed at theFrozen Zoo, and conservationists are now
trying to inject some of that lost genetic di-
versity into the modern population.
In 2020, researchers created Kurt, the
clone of a Przewalski’s horse whose cells
were frozen 40 years ago. Although he was
born several months before Elizabeth Ann,
he still has some growing up to do before
he’ ll be ready to breed. Kurt could be joined
by cloned siblings by spring of 2023.
The San Diego Zoo Wildlife Alliance is
also in the preliminary stages of trying to
clone the northern white rhino (Cerato-
therium simum cottoni), the most endan-
gered of several rhino subspecies. Just two
living northern white rhinos remain, andneither is capable of giving birth. As a first
step, scientists are working on techniques
to incorporate the northern white rhino ge-
nome into egg cells of a close relative, the
southern white rhino (C. simum simum).
And once the team hones its techniques,
“We certainly hope we can apply them to
the black rhino, the Sumatran rhino, and
maybe the Javan rhino,” Durrant says.
Some researchers are looking beyond
cloning, to other genetic technologies that
might help endangered species. Birds, for
example, can’t be cloned, but Revive & Re-
store recently formed a research consor-
tium to develop a technique that could fill
a similar role. It involves introducing pri-
mordial germ cells from an endangered spe-
cies into an embryo of a surrogate species,
such as a chicken. These germ cells then
migrate to the chicken’s gonads and become
sex cells. So, a male domestic chicken couldproduce the sperm of, say, an endangered
prairie chicken.
CRISPR gene-editing tools could also play
a role in conservation. Editing the genome
of black-footed ferrets so that they could re-
sist sylvatic plague, for example, could be a
game changer. Koepfli and collaborators are
now comparing the black-footed ferret ge-
nome with that of its domestic cousin, which
plague does not affect, in hopes of identify-
ing the genetic basis of resistance. But actu-
ally genetically modifying ferrets and then
setting them loose in the wild would require
extensive legal and ethical deliberations.
For now, Elizabeth Ann’s caregivers are
simply gearing up to pick her ideal firstmate. Every male ferret in the six breeding
facilities scattered across the United States
and Canada is getting intense scrutiny. In
part, that’s because Elizabeth Ann is likely
to have just a few good breeding years, and
annual litters average only three to five
kits. Breeders have decided that, first and
foremost, they need a proven gentleman—
they can’t risk an aggressive ferret hurting
their only clone. Excellent genes matter,
too. (That criterion could put a male re-
lated to Scarface or Rocky in the mix,
Novak muses.)
This month, they will develop a short list
and make their pick. If the best fit happens
to live across the country, they will fly him
to Colorado. They’ll collect a semen sample,
just in case they need it to artificially insem-
inate Elizabeth Ann. But they are hoping
that once they put the two ferrets together,
PHOTO: SAN DIEGO ZOO GLOBAL nature will simply take its course. j
At the San Diego Frozen Zoo, the cells of numerous endangered species are preserved in liquid nitrogen.
Cloning a mammal was not yet feasible when the zoo banked cells from two black-footed ferrets in the 1980s.14 JANUARY 2022 • VOL 375 ISSUE 6577 137