“…Variation in resistance to environmental stress has been observed among related species and populations of Drosophila from climatically different regions, particularly for heat (Hosgood and Parsons, 1968; Parsons, 1979;Coyne et al, 1983), and cold shock resistance (Jefferson et al, 1974; Tucic, 1979;Marinkovic et al, 1980;Kimura, 1982;Fukatami, 1984;Heino and Lumme, 1989;Hoffmann and Watson, 1993), and this variation appears to be an evolutionary response to the environment (Hoffmann and Parsons, 1991;Loeschcke et al, 1994). Success in selecting for stress resistance indicates that a significant additive genetic component also is present within populations (Morrison and Milkman, 1978; Kilias and Alahiotis, 1985; b; Jenkins and Hoffmann, 1994; Krebs and Loeschcke, 1996).…”