Evolution may not be slow or random

Studies of fruit flies taking over the New World and stickleback fish adapting to Canadian lakes suggest that evolution can move fast and take predictable paths.

An Old World fruit fly, Drosophila subobscura, turned up in Chile in 1978 and seems to have liked the Americas. It has already spread as far north as Vancouver Island and as far east as Utah. George W. Gilchrist of Clarkson University in Potsdam, N.Y., warns that this interloper is crowding out a native fruit fly, although the public isn’t weeping at the tragedy yet.

Gilchrist and his colleagues checked flies in 11 North American sites in 1997 and 10 European ones in 1998. The team confirmed earlier reports that in Europe, D. subobscura grows longer wings in the north than in the south. Danish flies outspan their Spanish relatives by 4 percent, the team reports in the Jan. 14 Science.

Ten years after the fruit flies immigrated, there was no sign of such a pattern along coastal Chile, other researchers had found. Now, the pattern has emerged in North America. Whereas males differ only by 1 or 2 percent, higher-latitude female flies grow wings 4 percent longer than Californian females do.

Threespine sticklebacks, in the genus Gasterosteus, also show evolution marching down similar paths in similar places, according to Howard D. Rundle of the University of British Columbia in Vancouver and his colleagues.

Mitochondrial DNA of sticklebacks in Enos, Paxton, and Priest Lakes in coastal west Canada suggests that all the forms of the fish evolved from a common seagoing ancestor, the researchers report in the Jan. 14 Science. That ancestor seems to have yielded a pair of stickleback types in each lake, a larger one hunting invertebrates along the bottom at lake edges and another straining plankton out of the open water.

In more than 750 laboratory tests, the researchers found that fish were more likely to breed with their counterparts from another lake than with fish from a different habitat in their own lake.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.