In what has been described as the "perfect experiment," evolutionary biologists at the University of Chicago replaced a single gene in fruit flies and discovered a mechanism by which two different "races" begin to become different species, with one group adapted to life in the tropics and the other suited to cooler climates. The tropical group was more tolerant of starvation but less tolerant of cold. The temperate group was less able to resist starvation but better adapted to cool weather.

The altered gene also changed the flies' pheromones, chemical signals that influence mating behavior. As a result, the researchers show in the Dec. 5 issue of Science, the two groups of flies are not only fit for different environments but may also be on their way to sexual isolation, a crucial divide in the emergence of a new species.

"This study directly connects genetics with evolution," said Chung-I Wu, Ph.D., professor and chairman of ecology and evolution at the University of Chicago and director of the study. "For the first time, we were able to demonstrate the vast importance in an evolutionary context of a small genetic change that has already occurred in nature."

"We had the luxury," added co-author Tony Greenberg, Ph.D., a postdoctoral student in Wu's laboratory, "of watching the essential event in Darwinian evolution, the first step in the origin of a new species. We were quite impressed, that this simple alteration played such a dramatic role, both adapting flies to a new environment and changing their sex appeal. Once two groups become sexually isolated, there's no turning back."

The scientists used a new technique to knock out one gene from fruit flies and then replace it with one of two slightly different versions of the same gene.

They focused on a gene called desaturase2 that plays a role in fat metabolism. Flies from Africa and the Caribbean, where there is tremendous competition for food but cold temperatures a
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Contact: John Easton
jeaston@uchospitals.edu
773-702-6241
University of Chicago Medical Center
4-Dec-2003

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