Altered fish's weak offspring

The genetic modifications that improve animals for human consumption also could doom populations if released into the wild, warn scientists from Purdue University, West Lafayette, Ind. Biologist Rick Howard and his colleagues have discovered a paradox that crops up when new genes are inserted into a fish's chromosomes to make the animal grow larger. While the genetically modified fish will be bigger and have more success at attracting mates, they also may produce offspring that are less likely to survive to adulthood. If this occurs, as generations pass, a population could dwindle in size and, potentially, disappear entirely.

The most common question posed about genetically modified organisms (also known as GMOs or transgenics) is whether they are safe for people to eat. When GMOs first were made commercially available in 1996, many food crops, such as corn and soybeans, were altered to produce substantially more yield than they do in nature. The debate on transgenics in supermarkets has yet to be resolved, and Howard indicates it could be drawing attention from an equally important issue: whether they are safe for the planet.

"With all the concern over whether transgenic food is safe for humans, the environment has been more or less left out of the picture," he points out.

As a step toward resolving this issue, Howard and his colleagues set out to examine the risk transgenic fish might pose to natural-bred populations. They chose to examine the Japanese medaka, a small species that breeds daily, because it would reproduce often enough for trends to emerge relatively quickly.

"We took several tanks and put a female into each one with two males--one natural, and one transgenic. The transgenic males were 83% heavier than the natural-bred males, so it was easy to distinguish which male was mating with the female."

Howard found that the larger transgenic males mated three times for every time the natural-bred males did--not surprising, considering the premium that female medakas place on male size. However, fewer of their young survived to adulthood. "We call this the 'Trojan gene effect,'" says Howard.

Over time, this effect could continue to multiply itself over generations, eventually decimating a population. "Imagine a pie, and you eat 30% of it every day," he says. "Half of it is gone in two days, and, within a week, less than one-tenth of it remains. It is conceivable that a similar effect could occur among fish populations if GMOs with 'Trojan genes' escape into the wild."

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