GROWTH TEMPERATURE AND PHENOTYPIC PLASTICITY IN 2 DROSOPHILA SIBLING SPECIES - PROBABLE ADAPTIVE-CHANGES IN-FLIGHT CAPACITIES

In the sibling species Drosophila melanogaster and D. simulans, growth and development at constant temperatures, from 12 to 30 degrees C, re sulted in extensive variations of adult size and flight parameters wit h significant differences between species. Changes in body weight, tho rax length and wing length were nonlinear, with maximum values of each trait at lower temperatures for D. simulans than for its sibling spec ies. By contrast, the wing/thorax ratio and the wing loading varied mo notonically with growth temperature. These traits were negatively corr elated, the wing/thorax ratio decreasing with growth temperature while the wing loading increased. Wing/thorax ratio, which is easier to mea sure, thus appears as a convenient predictor of wing loading. During t ethered flight at the same ambient temperature, the wingbeat frequency changed linearly as a function of the wing moment of inertia. More in terestingly, the beat rate was strongly correlated with the increase o f wing loading at growth temperature above 13 degrees C. The likely ad aptive significance of these morphometrical changes for flight efficie ncy is discussed.