Crouching variation revealed.

The term 'phenotypic capacitance' was introduced nearly 15 years ago to describe the strain-specific effects of impairing Hsp90, a molecular chaperone, in the fly Drosophila melanogaster (Rutherford & Lindquist 1998). In one genetic background, Hsp90 depletion caused deformed eyes, whereas in other genetic backgrounds, the wings or abdomens or other aspects of morphology were affected. Hsp90 was therefore viewed as acting like a capacitor, allowing genetic differences to build up and to be released at a later time. In the years since, it has been debated whether capacitance is a laboratory curiosity or a major force in evolution. In this issue of Molecular Ecology, Takahashi (2013) presents evidence, from high-resolution morphometric analysis of fly wings, that a large number of other capacitors exist in D. melanogaster, and that the variation they reveal can be quite subtle. His results advance our understanding of capacitance and contribute to a new view of its role in evolutionary adaptation.