Model for the evolutionary diversification of eyespot size and color composition. A and D, phenotypes representing presumed 'ancestral' and 'derived' eyespot patterns, respectively. B and E, schematics illustrating the strength of the focal signal (size of the black dot) and the level of threshold response (shading of the wing background) for the two phenotypes. In C, eyespot foci at two positions on an 'ancestral' wing surface (x-axis) produce the same amount of a diffusing morphogen (brown curve). The threshold concentration of morphogen inducing black pigment formation (black horizontal line) is higher than the gold-inducing threshold (yellow horizontal line). Size and color composition are the same for both eyespots. In F, eyespot foci on a 'derived' wing surface produce different amounts of the morphogen signal (brown curves) and consequently differ in total size. When the threshold for black pigment production is increased, both eyespots are proportionately 'golder,' since threshold concentration is a property of the whole wing surface. G-K, Bicyclus wing patterns illustrating variation in eyespot color composition (across species, but not within a wing surface) and size (across species and individual eyespots). G, eyespots relatively black (B. analis); H, eyespots relatively gold (B. buea); I-K, clear individualization of eyespot size but not color composition within a wing surface (left to right: B. italus, B. maesseni, B. milyas).
Allen et al. BMC Evolutionary Biology 2008 8:94 doi:10.1186/1471-2148-8-94