64.2 Jan. 7 Innovative Optics of Bright Wing Colors in Pierid Butterflies: Morphological Determinants and Implications for Use as Visual Signals MOREHOUSE, Nathan I.*; RUTOWSKI, Ronald L.; VUKUSIC, Peter; Arizona State University; Arizona State University; University of Exeter email@example.com
Animal color signals have been traditionally classified as either pigment based or structurally generated. However, little work has addressed the interplay between structures and pigments in color production, which has caused important interactions between these two color producing mechanisms to be overlooked or misunderstood. We have tested the hypothesis that collections of pigment molecules may in some cases act as structural scatterers, thereby increasing reflection of light wavelengths they do not absorb. We demonstrate that in pierid butterflies, pterin pigments are deposited within wing scales as oblong granules. These granules have been implicated as optical scatterers. Using both correlative and manipulative studies of the optical properties of single pierid wing scales, we probed the contribution of pterin granule arrays to backscattering of light from single scales. Our results support two conclusions: 1) the presence of pterin granules increases the reflectance of wing scales, and 2) denser granule arrays reflect more light than wing scales with less dense granule collections. Because male wing scales contain more pterin granules than do those of females, the sexual dichromatism found in many pierid species may be explained by differences in wing scale pterin deposition. Additionally, the color pattern elements produced by these pterins are known to be important during mating interactions in a number of pierid species. Therefore, we discuss the potential relevance of our results within the framework of sexual selection and color signal evolution.