HUEY, R.B.*; GILCHRIST, G.W.; BALANYA, J.; PASCUAL, M.; SERRA, L.: Rapid Evolution Redux: a Size Cline in South American Populations of an Introduced Fly

The introduction and rapid spread of the fly Drosophila subobscura along the west coasts of both North and South America just over two decades ago provide a remarkable opportunity to evaluate the repeatability and speed of evolution on a continental scale. In the native Old World populations, wing length increases clinally with latitude, as in many other Drosophila. In the North and South American populations, no cline in wing length was evident about one decade after the introduction. After two decades, however, the North American populations had evolved a size cline that had largely converged on the ancestral cline (2000, Science 287:308); and the quantified rate of evolution was one of the fasted ever measured. We recently collected introduced South America flies and find that they too have now evolved a latitudinal cline in wing length that is essentially parallel with the ancestral one. Nevertheless, clines in wing shape differ subtly among continents. Thus, evolution of a geographic cline in wing size is very fast and generally repeatable across contents; however, the details of how a given cline is achieved differs somewhat from continent to continent.