THERMAL EVOLUTION OF GROWTH EFFICIENCY IN DROSOPHILA-MELANOGASTER

Drosophila melanogaster shows geographic dines in body size, with gene tically larger flies being found further from the equator and at highe r altitudes. In the laboratory, evolution at lower temperatures result s in genetically larger flies, and development at low temperature incr eases adult body size. This study demonstrates that when newly hatched larvae from laboratory temperature selection lines were raised on fix ed amounts of food (yeast) at the same temperature, larvae from the li nes with the cold evolutionary history required less food to produce a given size of adult. Larvae from both high- and low-temperature selec tion lines required more food, however, to make a given size of adult when grown in the cold than when grown in the hot. The opposite associ ations between growth efficiency and adult body size seen with evoluti on or development at low temperature are puzzling, and suggest that di fferent mechanisms may underlie the size changes. Since environmental and evolutionary effects of temperature on body size seem to be widesp read among ectotherms, some basic aspects of thermal physiology must b e involved.