The extensive diversity of colorful patterns in butterflies and moths (Lepidoptera) have influenced studies in a variety of fields, including evolutionary biology, ecology, and bioinspired photonics. The primary unit for color in Lepidoptera is the wing scale cell and the underlying mechanism for a particular color can be due to either pigmentation from a biochemical pathway, or due to the physical architecture of scales manipulating wavelengths of light, known as structural color. To better understand processes underlying structural scale modifications, my dissertation focuses on a unique coloration strategy: wing transparency within Lepidoptera. Numerous species of Lepidoptera develop wings that allow light to pass through so that objects behind them can be distinctly seen, which has engendered a common notion that these species are “invisible” in the context of camouflage to go undetected by predators. However, my lab and collaborators hypothesize that transparency is a much more complex coloration strategy, playing roles in visual communication through light polarization and iridescence. Terrestrial transparency also entails challenging optical requirements and the morphological, physiological, and genetic mechanisms involved are virtually unknown. During my expedition to the Smithsonian Tropical Research Institute (STRI) in Gamboa, Panama, I was successfully able to collect and established a colony of glasswing butterflies at the local insectaries. The facilities at STRI also offer state-of-the-art molecular laboratories, where I was able to perform dissections of pupal wings at known time-points, stain wing tissue with fluorescent markers such as DAPI and phalloidin to visualize nuclei and scale cytoskeletal modifications, and preserve remaining tissue for downstream genomic and RNA experiments. Results thus far indicate that glasswing butterflies become transparent by modifying the ploidy levels in scale cell nuclei, as transparent regions of the wing have smaller and more spaced-out cells, and phalloidin stainings reveal that modifications to F-actin during scale growth likely plays a role in the peculiar "forked" bristles present on glasswings, which allows light to pass through to the membrane of the wing which harbors anti-reflective nanostructures. This has been a critical first step to employ experiments investigating the development of transparency, including gathering material for comparative transcriptomics and functional modifications via CRISPR-cas9 genome editing. The results from this expedition and future work on the established colony can now feed into comparative analyses, help elucidate the genetic drivers of scale structural complexity, and provide insight into the evolution of terrestrial transparency.
August 30, 2018