Effect of globalisation on children's mental health

<h3>Abstract</h3> Structural color is a pervasive natural phenomenon, caused by photonic nanostructures that refract light. Diverse organisms employ structural color to mediate ecological interactions and create specific optical effects such as iridescence. Despite its importance for living systems, the developmental, genetic, and evolutionary processes that generate structural color largely remain mysterious. Here, we focus on simple photonic structures, thin film reflectors, in the lower lamina of <i>Junonia</i> butterfly scales. We present multiple lines of evidence that the thickness of the lamina quantitatively controls lamina color, which is an important determinant of overall wing color, even when pigments are also present. First, in a lineage of buckeye butterflies artificially selected for blue wing color for 12 generations, a thicker lamina resulted in a color shift from brown to blue. A similar lamina thickness increase explains the appearance of blue scales in butterflies with mutations in the <i>optix</i> wing patterning gene. Finally, lamina thickness variation underlies the color diversity that distinguishes seasonal variants, sexes, and species throughout the genus <i>Junonia</i>. Thus, quantitatively tuning a single dimension of the existing scale architecture allows butterflies to evolve a broad spectrum of hues over both microevolutionary and macroevolutionary time frames. Because the lower lamina is an intrinsic component of typical butterfly scales, our findings imply that lamina structural color influences wing color in most butterflies. <h3>Significance Statement</h3> Structural colors, which result from photonic nanostructures that refract light and can create iridescence, are an important tool for many organisms. We use thin films, which are morphologically simple nanostructures that generate structural color in the lower lamina of butterfly scales, to dissect how photonic structures evolve. By combining interspecies comparisons with two different experimental approaches—artificial selection on wing color, and genetically engineered mutation of the <i>optix</i> wing patterning gene—we demonstrate that lamina thickness controls the wavelength (hue) of the structural color. These lamina structural colors are ubiquitous in the genus <i>Junonia</i>, and determine wing color along with pigments. Our results suggest that lamina structural colors probably exist in most butterflies, and that tuning lamina thickness facilitates wing color evolution.