Climate warming over the last quarter century is writ large in tiny fruit flies, according to a genetic analysis. In a species of fruit fly, the frequencies of so-called inversions, in which a piece of chromosome is flipped around, were observed decades ago to correspond to the latitude at which the flies were found. In nearly all the sites where the flies have recently been sampled--a span of three continents--the frequency of specific inversions has increased hand in hand with climbing temperatures. "It's a very clear signal that climate warming is going to have a big impact on our environment," says Raymond Huey of the University of Washington, co-author of a Science report published online August 31 that documents the change.

To date, the biological effects of climate change have shown up primarily in ecological patterns, such as the northerly spread of butterflies or the earlier flowering of plants and mating of animals. Corroborating those findings with genetic studies is more challenging because the needed data do not extend very far back for many organisms. One exception is the fruit fly, particularly Drosophila subobscura, a native of Europe that was introduced to the Americas in the late 1970s and early 1980s. Researchers sampled the fly's chromosomes at around the same time they appeared in North and South America, after having sampled them in Europe. They noted that inversions common to high (northern) latitudes occurred less frequently at low latitudes, and vice versa. Now Huey and his co-workers have resampled the flies in the same locations.

The low-latitude inversions have crept upward, appearing in the more northerly flies in 21 of 22 sites that have experienced warming, but not in four nonwarmed sites, they find. Flies in the warmed sites have the pattern of inversions that would previously have been found in their brethren one degree, or 70 miles, closer to the equator. Average temperatures in these sites have risen by half a degree Celsius since the earlier inversion samples were taken. The researchers speculate that the genetic change confers some protection against the heat, although migration may also play a role, says Huey. The result suggests that flies, with their short generation time, can cope genetically with climate change, he notes, whereas longer-lived organisms, such as large trees, are unlikely to be as flexible. "If you have some organisms able to keep up and others not, I think a lot of plant-animal interactions could be disrupted," Huey forecasts.