The contrasting genetic architecture of wing size and shape in Drosophila melanogaster.

Surprisingly little is known about the genetic architecture of body size in natural populations of Drosophila melanogaster. Using both generation means and triple-test-cross analyses, we investigated the genetic architecture of wing size (an indicator of body size) and wing shape in a naturally occurring body size cline. For wing size, we found significant epistatic genetic variance and evidence of past directional selection for increased body size. While wing shape also exhibits significant epistatic genetic variance, there was no indication of directional selection, suggesting instead a history of optimizing selection. Our results support the idea that epistatic variance may be more common in natural populations than was once suspected. Also, our results suggest substantial directional selection on wing size but not shape.