A role of Ultrabithorax in morphological differences between Drosophila species

The mechanisms underlying the evolution of morphology are poorly understood (1,2). Distantly related taxa sometimes exhibit correlations between morpho logical differences and patterns of gene expression(3-8), but such comparis ons cannot establish how mechanisms evolve to generate diverse morphologies . Answers to these questions require resolution of the nature of developmen tal evolution within and between closely related species. Here I show how t he detailed regulation of the Hox gene Ultrabithorax patterns trichomes on the posterior femur of the second leg in Drosophila melanogaster, and that evolution of Ultrabithorax has contributed to divergence of this feature am ong closely related species, The cis-regulatory regions of Ultrabithorax, a nd not the protein itself, appear to have evolved. This study provides expe rimental evidence that cis-regulatory evolution is one way in which conserv ed proteins have promoted morphological diversity(1).