Theory indicates that non-linear selection (e.g., stabilizing, disruptive, or correlational selection) on traits can result in epsitasis for fitness even when alleles have additive affects on traits. In a paper recently published in Nature Ecology and Evolution, we demonstrate this in a field experiment with Timema stick insects. In particular, we show that color is determined mostly by alleles with additive effects, but that selection for crypsis favors color combinations resulting in epistasis for fitness. This in turn results in a rugged fitness landscape with respect to the color loci.

See our blog post for more thoughts and background on the paper.