Adaptation and constraint in the evolution of Drosophila melanogaster wingshape

We have taken advantage of parallel instances of natural selection on body size in Drosophila melanogaster to investigate constraints and adaptation a ffecting wing shape. Using recently developed techniques for statistical sh ape analysis, we have examined variation in wing shape in similar body size clines on three continents. Gender-related shape differences were constant among all populations, suggesting that gender differences represent a deve lopmental constraint on wing shape. In contrast, the underlying shape varie d significantly between continents and shape change within each cline (i.e. , between small and large body size populations) also varied between contin ents. Therefore, variation at these two levels presumably results from eith er drift or natural selection. Functional considerations suggest that shape variation between the continents is unlikely to be adaptive. However, clin e-related shape change, which we show has a significant allometric componen t, may be adaptive. The overall range of wing shape variation, across a lar ge range of wing size, is extremely small, and the possibility that wing sh ape is subject to stabilizing selection (or canalization) is discussed.