The Daughterless Gene

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“The Plot to Kill the Carp” by Todd
Woody, in
Wired (Oct.
2002), 520 Third St., 3rd Fl., San Francisco, Calif. 94107–1815.


Eight years ago, Australian wildlife officials were
alarmed to discover environmentally destructive European carp—which
are already dominant in mainland Australia’s waterways—swimming
among the rare native fish in Tasmania’s Lake Crescent. Carp, writes
Woody, a Sydney-based journalist, are “the Borg of the fish
world.” Uprooting aquatic vegetation, they turn clear-running water
muddy, depriving native fish of food, light, and oxygen.


Authorities held the rapidly multiplying Lake Crescent
invaders in check by lowering the lake’s water levels and denying
them space to spawn. But Australian scientists now believe they have a
better solution: “daughterless” genes.


“Biologists have long known that female fish
develop when an enzyme called aromatase transforms androgen into
estrogen,” notes Woody. If aromatase were chemically blocked, fish
could be made to produce only males. Biologist Ron Thresher and his
colleagues developed a gene to do exactly that. As carp injected with
daughterless genes produce single-sex offspring, “the population of
each targeted river or lake will eventually drive itself to
extinction.”


That’s the idea, at least. The scientists have
already proved they can develop a daughterless gene for the zebra fish, a
two-inch cousin of the carp. Next comes the destructive, fast-breeding
mosquito fish. If that effort is successful, work on the daughterless carp
will begin.


Skeptics such as Bob Phelps, director of the
Australian Gene Ethics Network, worry about the unknowable consequences of
releasing “millions of genetically engineered fish into complex
ecological systems.” Woody describes “the nightmare scenario:
Daughterless carp somehow escape to other parts of the world and breed with
dozens of closely related species. Or they evolve in unforeseen ways into
superpests.” Thresher, however, says the daughterless carp would be
introduced to a target population only gradually over many years, so there
would be plenty of time to halt the process if something went awry.


With the continuing spread of destructive alien
species around the world, defensive genetic technologies are also likely to
spread, says Woody. Scientists and regulators who are dealing with the
influx of alien species in North America’s Great Lakes, for example,
are interested in the new technologies as a way of dealing with invaders
such as the big head carp, a 50-pound monster from China.


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