Fruit flies rock the evolutionary clock

Magnified ballet: A microscopic image of two female fruit flies, D. subobscura, shows their difference in size. The smaller fly, left, is from Valencia, Spain. The larger fly is from Aarhus, Denmark.

January 28, 2000
Web posted at: 9:25 a.m. EST (1425 GMT)

By Environmental News Network staff

Scientists have found evidence that the non-native fruit fly, D. subobscura, introduced to North and South America from Europe 20 years ago, is adapting to its new environment almost overnight. The alien fly has replaced as much as 95 percent of native fruit-fly species and has developed a wing size pattern that mimics that of established populations in Europe.

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Evolution

Occupying temperate Europe for the past 10,000 years, D. subobscura developed a geographic pattern of producing larger individuals in areas of higher latitude. The wings of fruit flies in Denmark, for example, are 4 percent longer than those from Spain.

Measurements of fruit flies introduced to North America show that D. subobscura evolved a similar pattern in less than two decades. Like their counterparts in Europe, North American fruit flies found in higher latitudes were four percent larger than those found in lower latitudes.

"Scientists typically have not appreciated how fast evolution can occur in an introduced species," Raymond Huey, an evolutionary biologist at the University of Washington and lead author of the study.

In combating invasive species, scientists have not considered evolution as a factor because it was thought to occur at a pace much slower than the invasion, Huey explained. "Now, for the first time, scientists are looking at the ecological consequences of an invasive species from an evolutionary standpoint," he said.

Biological invasions occur when a plant or animal relocates to a new, favorable environment. Eliminating other competitors, predators or diseases, the species can rapidly expand its habitat, crowding out and otherwise harming native species. Many scientists believe the spread of exotic species is one of the most serious yet least known threats to biodiversity.

Non-indigenous animals, plants and microbes cost the U.S. $123 billion a year in management, according to ecologists at Cornell University. Introduced insects alone cost $20 billion annually.

While the invasive D. subobscura does not pose an immediate threat to humans, its rapid adaptation to North and South America adds new ammunition in the ongoing battle between science and invasive species.

"The dynamics of invasions become much more complicated if the invaders evolve rapidly," Huey said. "This study shows that an invader can in fact evolve very quickly, in just a few years, and potentially have a big impact.

"Imagine that you were trying to defend your country against an invading army. You assess the army's size strength and fire pattern as a strategy for a counterattack. But if in time it takes you to come up with a counter attack, the army has changed, your counter might not work as well. That's what real risk here is."

Huey noted that rapid evolution is of particular concern with insects because they regenerate several times a year.

Other members of Huey's research team include George Gilchrist, a professor of biology at Clarkson University, and Luis Serra, an evolutionary biologist at the University of Barcelona.

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