The world is filled with examples of introduced exotic species such as African walking fish in Florida, rabbits in Australia and kudzu throughout the southeastern United States decimating native species and upsetting ecosystems. Until now, biologists studying these events have not seriously considered evolution as part of the strategy used by invading species.

But new evidence stemming from the accidental introduction into North and South America of an Old World fruit fly, which has exhibited one of fastest evolutionary changes ever recorded, may alter that perception.

Writing in this week's issue of the journal Science, a team of researchers from the University of Washington, Clarkson University in New York and the University of Barcelona report that the fly, Drosophila subobscura, which was introduced about two decades ago, has already evolved a wing size pattern that mimics that of established populations in Europe In the process, D. subobscura, a black fly less than one-eighth of an inch long, seems to be replacing native fruit flies in the Pacific Northwest.

"Humans are introducing plants and animals all around the globe and, in many cases, those introductions are wreaking havoc on native populations," said Raymond Huey, a UW evolutionary biologist and lead author of the study. "The dynamics of invasions become much more complicated if the invaders evolve rapidly. It is very likely that introduced invading species are evolving, and scientists typically have not appreciated how fast evolution can occur in an introduced species. This probably means native populations will be changing as well in response to introduced species."

D. subobscura is a temperate-zone fly native to a region stretching from Spain northward into southern Scandinavia and from North Africa eastward to the Middle East. In South America, it was first found near the Chilean port city of Puerto Montt in 1978. The flies quickly colonized much of coastal Chile, although sc
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Contact: Joel Schwarz
joels@u.washington.edu
206-543-2580
University of Washington
12-Jan-2000