AR-News: (US)Fishy Alpha Males

[Masako Miyaji]

http://www.sciencenews.org/articles/20040306/food.asp

Week of March 6, 2004; Vol. 165, No. 10 
 
Fishy Alpha Males
Alexandra Goho

With the ocean's natural bounty declining around the
world, an increasing amount of fish consumed today,
such as most Atlantic salmon, is farmed. To further
boost the efficiency of fish farms, companies are
looking to raise fish genetically modified to have an
extra growth hormone gene that makes the fish grow
faster. Indeed, raising fast-growing fish inside
pens—whether kept inland or in ocean bays—can reduce
harvesting pressure on the wild fish populations that
are threatened. However, new research suggests that as
a way to protect wild fish stocks, such efforts may be
futile should some of these modified fish escape into
the environment.

Biologist Richard Howard and his colleagues at Purdue
University recently showed that genetically engineered
fish have the potential to replace some wild fish
populations. What's more, because the offspring of
modified fish are less viable, their replacement of
native fish could eventually drive entire species to
extinction. 

To investigate the effects of genetically engineered
fish on wild populations, the biologists looked at how
well males from both groups competed with each other
for the same mate. In this experiment, the researchers
used as their model Japanese medaka, a relatively
small fish that reproduces quickly. 

To create the genetically modified fish, the
researchers inserted into fertilized medaka eggs
copies of a salmon gene that codes for a growth
hormone. As a result, the modified fish grew to be 83
percent larger than their wild counterparts. 

Then the Purdue team conducted a series of mating
experiments in the lab. The researchers placed one
genetically modified male, one wild male, and a single
wild female in a 4.5-liter fish tank and then
monitored the fishes' mating behavior. Presumably
because of its larger size, the modified male was
typically more successful than the wild male at
attracting the female and fertilizing her eggs. 

Even though the genetically modified fish regularly
chased the wild ones away from the females, the wild
fish weren't entirely deterred from mating. They
quickly adopted new strategies. For instance, while
the modified male courted the female, the wild male
would sneak in and try to fertilize the female's eggs.
"At first, I thought it was an aberration," says
Howard. "But then it kept on happening. That literally
knocked my socks off." 

Despite their relentlessness, the wild fishes' hard
work resulted in little payoff. When the researchers
analyzed the DNA of eggs fertilized during the trials,
the results showed that 75 percent of all matings went
to the genetically modified males. The researchers
describe their results in the March 2 Proceedings of
the National Academy of Sciences. 

"This is a real concrete example of how [genetically
engineered] fish will have a mating advantage," says
Allison Snow, an evolutionary biologist at Ohio State
University. Should such modified fish escape into the
environment, these results suggest that they could
wipe out native fish, she says. 

Yet, another factor could lead to a species' demise
altogether. In a separate experiment, the Purdue
researchers observed that the offspring of genetically
modified medaka were less likely to survive into
adulthood than those sired by wild fish. Based on a
mathematical model, the researchers predict that as
transgenic fish would spread their genes throughout
the population, the medaka species would go extinct
after 50 generations. The researchers call this the
Trojan-gene effect. 

To what extent the results of these laboratory
experiments can predict what will happen in the wild
is unclear, says Howard. In certain salmon species, he
says, small males are prevalent and can compete
successfully with larger male fish by sneaking in
during competitive matings. Therefore, should a
genetically modified male find its way into the
environment, the large number of sneaking males
already in the population "should stop a Trojan gene,"
says Howard. 

However, whether a male fish becomes a large, dominant
fish or a small sneaker is determined very early in
the animal's development: Fish that have a rapid
growth rate early in life become sneakers instead of
dominant males. Because genetically modified fish also
grow rapidly early in life, "if they get out into the
wild, it's not really clear to me whether these guys
will all be sneakers or really large dominant males,"
says Howard. 

Still, the findings highlight the potential
environmental risks posed by the release, deliberate
or not, of genetically modified fish into the
environment. Over the past couple of decades,
researchers have genetically modified a number of
commercial crop plants, such as pest-resistant cotton
and herbicide-resistant corn. More recently,
researchers have been increasingly engineering
animals, such as mosquitoes that are poor transmitters
of malaria (SN: 5/25/02, p. 324: Available to
subscribers at
http://www.sciencenews.org/articles/20020525/fob3.asp)
and chickens that produce pharmaceuticals in their
eggs (SN: 4/6/02, p. 213:
http://www.sciencenews.org/articles/20020406/fob5.asp).


In response to the expanding practice, the Ecological
Society of America recently released a position paper
on genetically engineered organisms. While citing the
many benefits of such plants and animals, the report
calls for more rigorous risk assessment studies before
the organisms are released into the environment. The
report also recommends that genetically engineered
organisms be modified to prevent the transfer of
foreign genes to species in the wild. 

The firm Aqua Bounty is currently seeking approval
from the Food and Drug Administration to commercialize
the company's genetically engineered salmon. Aware of
the environmental concerns, the company's researchers
are developing ways of genetically modifying the fish
to make them sterile, as well as fast growers. 

Snow commends the company's efforts to prevent its
fish from reproducing in the wild but wonders whether
the technique will be 100 percent effective. "Can you
guarantee that all the fish are going to be sterile?"
says Snow, suggesting that it might not be possible.
Still, she says, it may be possible to keep these
genetically engineered organisms at "manageable and
very low levels that would cause no problems" in the
environment. 

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