In this project the PIs will study wing colors in butterflies. The brilliant colors found on the wings of butterflies have attracted attention from biologists and physicists alike. Many of these colors are due to light interacting with the nano-structures on the surface of the wing scales. In particular the aim of this project is to focus on a group of closely related species that have remarkably different colors, and have a known evolutionary history. This will allow the PIs to examine the smallest amounts of morphological change in a scale's structure that can produce a change in color. The PIs will combine descriptive and theoretical approaches coupled to experimental methods to fully understand how structural colors are produced in this group of butterflies. They will pursue two main approaches: The first approach will involve a comparison of wing scale color and associated morphology across the butterfly genus Bicyclus. The second approach will target a change in scale color using artificial selection in replicate lines of Bicyclus anynana butterflies, and describe the associated morphological changes in the nano-structure of the scales. The PIs will train graduate and undergraduate students, many of them women, as well as actively participating in a variety of outreach activities that are aimed at the broader public. One of the PIs will participate in established Yale education outreach programs to local high schools and middle schools. The PIs will also produce an interactive web-based animation showing how diverse structural colors evolved in a close group of butterflies, and disseminate the results from their findings broadly.
The brilliant colors found on the wings of butterflies have attracted attention from biologists and physicists alike. Many of these colors are due to light interacting with the nano-structures on the surface of the wing scales. Most studies to date have examined the scales of single specimens from a small number of distantly related species. We have focused our attention on a group of closely related species that have remarkably different colors, and have a known evolutionary history. This allowed us to examine the smallest amounts of morphological change in a scale’s structure that can produce a change in color. We have combined descriptive and theoretical approaches coupled to experimental methods to fully understand how structural colors are produced in this group of butterflies. We have taken two main approaches: The first approach involves a comparison of wing scale color and associated morphology across the butterfly genus Bicyclus. Structural colors such as purples and blues have arisen multiple times independently in this group of butterflies. We found that similar morphological architectures have been adopted by different species within a single genus of butterflies to produce the same structural colors. The second approach is targeting a change in scale color using artificial selection in replicate lines of Bicyclus anynana butterflies, and identifying the associated morphological changes in the nano-structure of the scales. We have performed detailed analysis of the nano-structures of the different butterfly species and selection lines using spectrophotometric measurements, and electron microscopy, coupled with theoretical/computational analysis of the optic properties of the wing scales. We have combined all this information to produce exact models of how the colors are being produced and how color has evolved across selected populations of B. anynana, and across Bicyclus species. Intellectual merit: we performed the first artificial selection on a structural color using butterflies. We demonstrated rapid evolution of violet structural color from ultra-violet brown scales in Bicyclus anynana butterflies with only six generations of selection. Furthermore, we identified the structural changes responsible for color evolution, which involve changes in the thickness of a chitin lamina in individual wing scales. By examining other violet-banded species that occur naturally in the Bicyclus genus, we found the colors are produced via the same mechanism and thus may have evolved via similar scale modifications. We believe that the knowledge obtained from this research project will facilitate the judicious design of synthetic nanomaterials for photonics applications. Broader impacts: This is a collaboration between two women faculty, Hui Cao in the Applied Physics Department, and Antonia Monteiro in the Ecology and Evolutional Biology Department of Yale University. They have cross-trained two PhD students, four undergraduate students and three postdoc fellows in Optical Physics and in Evolutionary Biology. Among them, there are four women and one minority. Cao has actively participated in a variety of outreach activities that are aimed at the broader public. She has given public lectures on structural coloration in nature at US undergraduate institutions and international summer schools. Our findings about structural color have attracted much media attention and been reported by the National Geographic, the National Public Radio, the Discovery Channel, the New York Times, etc.
