Trojan Gene Spurs Extinction Warning
12/2/99
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Title: Trojan gene spurs extinction warning
Source: Environmental News Network
Status: Copyright 1999, contact source for permission to reprint
Date: December 2, 1999
Byline: Hillary Mayell
Researchers looking at genetically modified organisms - in this case
fish - warn that modifications that increase an organism's sex appeal
could lead to the extinction of the species' wild population, the
journal New Scientist reports today.
Dr. William Muir and Dr. Richard Howard, professors at Purdue
University, made the discovery while studying the ecological risks
associated with genetically modified organisms.
Plants are genetically engineered for resistance to herbicides and
pests, to make the stalk woodier, the leaves more tender and to
increase crop yields. Beef cattle, chickens and pigs are fed hormones
to make them gain weight faster and produce leaner meat, among other
characteristics.
Biologists have been studying the same kinds of approaches to farmed
salmon, and the research conducted by Muir and Howard exposed some
problems that are unique to fish populations because of the ability
of a genetically modified fish to spread its genes into a wild
population.
Working with medaka, a small Japanese fish, the researchers modified
the fish using human growth hormone. As expected, these transgenic
fish grew bigger faster and developed sexually earlier than wild
fish. But therein lies the Catch-22 that led the researchers to issue
their warning of a potential "Trojan gene" effect.
Among medaka, females choose their mates, and they choose larger
mates on a 4 -to-1 ratio. Transgenics - genetically modified
organisms - are known to have a lower viability than wild fish; fewer
survive to mating age. But in the lab, those that did survive were
getting all the matings, according to the researchers. This could be
catastrophic if a transgenic fish was accidentally released into the
wild.
"A transgene that simultaneously confers increased mating advantages
with reduced viability can easily drive a population to extinction,"
says Muir, which is why we called it the Trojan gene. Something that
looks good but can be totally devastating to a population. This
totally turns the Darwin theory on its head. Here you have a case
where the least fit individual (the transgenics) are getting the most
matings, which drives the genes into the population, while at the
same time, the reduced viability drives the population into
extinction."
The researchers developed a computer model to find out what would
happen if 60 transgenic individuals joined a wild population of
60,000 fish. The population became extinct within 40 generations,
though even a single transgenic fish would lead to the same result.
It would just take longer.
Genetic engineering of plants and other microorganisms has been
extremely controversial. These are some of the first experiments
using animals, and the researchers are concerned that their results
will contribute to the melee surrounding the issue.
"The kinds of transgenes that increase mating advantage - color,
size, in some cases scent - are the ones that can cause the problems.
There are genes that are quite safe and beneficial and this can be
determined in the lab. The so-called Enviropig, which was developed
in Canada and greatly reduces pollution by removing phosphorus from
the atmosphere is an example of a transgenic that is immensely
beneficial to agriculture," says Muir.
The study, titled "Possible ecological risks of transgenic organism
release when transgenes affect mating success: Sexual selection and
the Trojan gene hypothesis" was published in the Nov. 23 issue of The
Proceedings of the National Academy of Sciences.