THENEWYORKER,JANUARY18, 2021 35
sand eggs at a go.) The resulting toadlets
were intentionally released into the re-
gion’s rivers and ponds.
It’s doubtful that the toads ever did
the sugar cane much good. Cane beetles
perch too high off the ground for a
boulder-size amphibian to reach. This
didn’t faze the toads. They found plenty
else to eat, and continued to produce
toadlets by the truckload. From a sliver
of the Queensland coast, they pushed
north, into the Cape York Peninsula, and
south, into New South Wales. Some-
time in the nineteen-eighties, they crossed
into the Northern Territory. In 2005, they
reached a spot known as Middle Point,
in the western part of the Territory, not
far from the city of Darwin.
Along the way, something curious
happened. In the early phase of the in-
vasion, the toads were advancing at the
rate of about six miles a year. A few de-
cades later, they were moving at the pace
of twelve miles a year. By the time they
hit Middle Point, they’d sped up to thirty
miles a year. When researchers measured
the individuals at the invasion front, they
found out why. The toads had signifi-
cantly longer legs than the toads back in
Queensland, and this trait was heritable.
The Northern Territory News played the
story on its front page, under the head-
line “SUPER TOAD.” Accompanying the
article was a doctored photo of a cane
toad wearing a cape. “It has invaded the
Territory and now the hated cane toad
is evolving,” the newspaper gasped. Con-
tra Darwin, it seemed, evolution could be
observed in real time.
Cane toads are not just disturbingly
large; from a human perspective, they’re
also ugly, with bony heads and what looks
like a leering expression. The trait that
makes them truly “hated,” though, is that
they’re toxic. When an adult is bitten or
feels threatened, it releases a milky goo
that swims with heart-stopping com-
pounds. Dogs often suffer cane-toad poi-
soning, the symptoms of which range
from frothing at the mouth to cardiac
arrest. People who are foolish enough to
consume cane toads risk winding up dead.
Australia has no poisonous toads of
its own; indeed, it has no native toads
at all. So its fauna hasn’t evolved to be
wary of them. The cane-toad story is
thus the Asian-carp story inside out,
or maybe upside down. Invasive Asian
carp are wreaking havoc in America
because nothing eats them; cane toads
are a menace in Australia because just
about everything eats them. The list of
species whose numbers have crashed
due to cane-toad consumption is long
and varied. It includes freshwater croc-
odiles, which Australians call “freshies”;
yellow-spotted monitor lizards, which
can grow more than five feet long; north-
ern blue-tongued lizards, which are ac-
tually skinks; Australian water dragons,
which look like small dino-
saurs; common death ad-
ders, which, as the name
suggests, are venomous
snakes; and king brown
snakes, which are also ven-
omous. By far the most win-
ning animal on the victims
list is the northern quoll, a
sweet-looking marsupial.
Northern quolls are about
a foot long, with pointy
faces and spotted brown coats. When
young quolls graduate from their moth-
er’s pouch, she carries them on her back.
In an effort to slow down the cane
toads, Australians have come up with all
sorts of ingenious and not-so-ingenious
schemes. The Toadinator is a trap fitted
out with a portable speaker that plays
the cane toad’s song, which some com-
pare to a dial tone and others to the thrum
of a motor. Researchers at the Univer-
sity of Queensland have developed a bait
that can be used to lure cane toad tad-
poles to their doom. People shoot the
toads with air rifles, whack them with
hammers, bash them with golf clubs,
purposely run them over with their cars,
stick them in the freezer until they so-
lidify, and spray them with a compound
called HopStop, which, its manufacturer
assures buyers, “anaesthetizes toads within
seconds” and dispatches them within an
hour. Communities organize “toad-bust-
ing” militias. A group called the Kim-
berley Toad Busters has recommended
that the Australian government offer a
bounty for each toad eliminated. The
group’s motto is “If everyone was a toad
buster, the toads would be busted!”
At the point that Tizard got inter-
ested in cane toads, he’d never actually
seen one. Geelong lies in southern Vic-
toria, a region that the toads haven’t yet
conquered. But one day, at a meeting, he
was seated next to a molecular biologist
who studied the amphibian. She toldhim that, despite all the busting, the toads
kept on spreading. “She said it was such
a shame, if only there was some new way
of getting at it,” Tizard recalled. “Well,
I sat down and scratched my head.”
He went on, “I thought, Toxins are
generated by metabolic pathways. That
means enzymes, and enzymes have to
have genes to encode them. Well, we have
tools that can break genes. Maybe we can
break the gene that leads to the toxin.”
As luck would have it, a team
at the University of Queens-
land, led by a chemist named
Rob Capon, had recently iso-
lated a crucial enzyme be-
hind the toxin.
Tizard brought on a
postdoc, Caitlin Cooper, to
help with the mechanics.
Cooper has shoulder-length
brown hair and an infectious
laugh. (She, too, is from
somewhere else—in her case, Massachu-
setts.) No one had ever tried to gene edit
a cane toad before, so it was up to Coo-
per to figure out how to do it. Cane-toad
eggs, she discovered, had to be washed
and then pierced just so, with a very fine
pipette, and this needed to be done
quickly, before they had time to start di-
viding. “Refining the microinjection tech-
nique took quite a while,” she told me.
As a sort of warmup exercise, Coo-
per set out to change the cane toad’s
color. A key pigment gene for toads
(and, for that matter, mammals) codes
for the enzyme tyrosinase, which con-
trols the production of melanin. Coo-
per reasoned that disabling this pigment
gene should produce toads that were
light-colored instead of dark. She mixed
some eggs and sperm in a petri dish,
microinjected the resulting embryos
with various CRISPR-related compounds,
and waited. Three oddly mottled tad-
poles emerged. One of the tadpoles died.
The other two, both male, grew into
mottled toadlets. They were christened
Spot and Blondie. “I was absolutely rapt
when this happened,” Tizard told me.
Cooper next turned her attention to
“breaking” the toads’ toxicity. Cane toads
store their poison in glands behind their
shoulders. In its raw form, the poison
is merely sickening. But, when attacked,
toads can produce the enzyme that
Capon isolated—bufotoxin hydrolase—
which amplifies the venom’s potency a