Wed Mar 21 13:41:34 2001 Pacific Time

UC Davis Study Links Intense Competition Among Fruit Flies to Evolutionary Process of Forming New Species

       DAVIS, Calif., March 21 (AScribe News) -- An experiment by University of
California, Davis graduate student Daniel Bolnick has captured evolution in
action, provided support for a long-standing hypothesis in evolutionary
biology, and could help explain how some new species arise from old ones.

       Using the fruit fly Drosophila melanogaster, Bolnick has shown that
intense competition between members of the same species can drive some
individuals into using different habitat niches. Biologists think that this
separation into niches marks the beginning of the process of forming a new
species.

       "It's a long-standing problem in evolutionary ecology," said Bolnick.

       "Dan's work represents a current spate of interest in looking for more
empirical evidence," said biologist Peter Wainwright, who is Bolnick's thesis
supervisor.

       The study is published in the March 22 issue of the journal Nature.

       When Charles Darwin arrived in the Galapagos Islands, he noticed that
there were many more species of finch in the small islands than on the mainland
of South America, said Bolnick. Biologists see the same result in other islands
and remote places where a single species has arrived and found itself with few
competitors.

       Animals and plants have to compete for resources both with other
species, and with individuals of their own species. These competitive forces
balance each other, said Bolnick. In a big environment such as a continent,
competition with other species is more important. But when a species -- for
example, a finch -- enters an environment such as a remote island with few
other species already present, competition within the species becomes more
important.

       Recent theoretical work shows that intense competition in the "middle"
of a population drives more variation at the edges, said evolutionary biologist
Sergey Nuzhdin. Bolnick's work provides experimental evidence for this, he
said.

       Bolnick set out to test this hypothesis by studying the effect of
competition on Drosophila fruitflies. He set up cages of flies with both normal
fly food and food tainted with different amounts of cadmium. Some cages had
less food available than others, increasing competition.

       At the beginning of the experiment, none of the flies would eat food
with any amount of cadmium. However, in cages with high competition, some flies
began to switch to the toxic food, and passed this characteristic to their
offspring. Within as few as four generations, groups of flies appeared that
were exploiting the different "niches" of the food supply by being able to
tolerate different levels of cadmium.

       The rate of evolution into niches was fastest in the cages with the
highest competition, said Bolnick.

       "The response was much faster than had been predicted," he said.

       Bolnick did not observe the formation of actual new species in the
experiment. Biologists think that separation into niches that tend not to
interbreed marks the beginning of the process.

       Biologists have two basic models for how new species form. In one model,
a group of individuals is physically isolated from the rest of the species, for
example by a mountain range. In the second model, the two groups continue to
live side by side, but one group adapts to a different "niche" within the
habitat.

       These ideas on competition and species formation were first put forward
in the 1970s, but new theories developed in the last five years have made it
possible to test them, said Wainwright.