Think of it as evolution in action

Joseph S. Barrera III joe at
Mon Dec 15 02:30:04 PST 2003

Plus: how flies cuddle...

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Subject: 	[>Htech] Eureka: Changing one gene launches new fly species
Date: 	Sat, 13 Dec 2003 11:05:30 -0500 (EST)
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Changing one gene launches new fly species
   Contact: John Easton
   [2]jeaston at
   [3]University of Chicago Medical Center

Study also ties sex appeal to cold tolerance

   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

   "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 are not a
   problem, have one version of ds2. Flies from cooler climates, where
   there is less competition for food but greater temperature variation,
   have a smaller, inactive version of ds2.

   The same gene plays a role in the production of cuticular hydrocarbons
   -- waxy, aromatic compounds that coat the abdomen of female flies. A
   male fly, in a romantic mood, strokes the female's abdomen with his
   feet, which have sensors that recognize specific hydrocarbons, like a

   In a previous report, Wu's laboratory found most males with the
   temperate version of the ds2 gene preferred females with the same
   gene; tropical males preferred tropical females.

   "Developing increased cold tolerance was an important step for flies
   that migrated out of Africa to Europe and Asia," Wu said. The change
   in pheromones, which altered patterns of sexual attraction, "was a
   by-product of adaptation to colder weather."

   Fruit flies have a migratory history similar to humans. They
   originated in Africa, spread to Europe and Asia and went on to
   populate the world. As with humans, there is greater diversity within
   African flies than between flies from Africa and other continents.

   Although fruit flies have been a favorite model for the study of
   genetics since the early 20th century, recognition of consistent
   differences between tropical and temperate flies came only in 1995.
   The discovery, however, "has allowed a lot of analysis of the
   evolution of adaptive traits," Wu said.

   "But this was the first time we have been able to study the process
   from the very beginning," he added, "to watch the first steps as one
   species begins to split into two, then seals the bargain by increasing
   sexual isolation. This is the essence of biodiversity."

   Additional authors include Jennifer Moran from the Wu lab and Jerry
   Coyne of the University of Chicago. The National Institutes of Health
   and the National Science Foundation funded the study.


   2. mailto:jeaston at

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