Fossil record analysis hints at the evolutionary origins of insect structural colors.

Researchers from Yale-NUS College in Singapore and University College Cork (UCC) in Ireland analyzed preserved scales from wing cases of two fossil weevils from the late Pleistocene era (approximately 13,000 years ago) to better understand the origin of the nanostructures of light scattering. present in current insects.

The researchers, led by Yale-NUS Assistant Professor of Science (Life Sciences) Vinod Kumar Saranathan and UCC paleobiologists, Drs. Luke McDonald and Maria McNamara, found that the wing cases of fossil weevils contained ‘ Preserved photonic diamonds, one of the many types of crystal as a nanoscopic structure that interacts with light to produce some of nature’s brightest and purest colors.

The outer covers of many insects comprise repeating units arranged in a crystalline formation that interacts with visible light to produce structural colors, which typically have an iridescent metallic appearance. For many of these insects, iridescent colors perform a variety of functions including camouflage, signaling potential mates, and predator warning. To date, the evolutionary history of these complex tissue structures has not been clearly defined. This study highlights the great potential of the fossil record as a means of discovering the evolutionary history of structural colors, not only in weevils but also in other insects, and paves the way for further research on the development of these scattering nanostructures. light and the vibrant colors they give rise to.

The researchers used powerful electron microscopes and state-of-the-art synchrotron X-ray scattering techniques and optical modeling techniques to identify and characterize a rare three-dimensional photonic crystal nanostructure in fossil weevil scales, the shades of blue and green of which are very similar to those of of modern weevils of the same genus, revealing a diamond-shaped arrangement. Instances of three-dimensional nanostructures are extremely rare in the fossil record. This study marks the second time such nanostructures have been found. The only other instance of such nanostructures found in the fossil record of another weevil was also discovered by Assistant Professor Saranathan and Dr. McNamara.

The fact that very similar green substrate match colors have been maintained for hundreds of thousands of generations suggests that the same selective pressures for camouflage have been acting on these weevils. This is consistent with a recent study by Professor Asst Saranathan and the weevil systematizer Dr. Ainsley Seago which suggests that weevil colors initially evolved to camouflage themselves among their leafy backgrounds, before diversifying for other functions such as pinpointing possible mates or deter predators.

Professor Asan Saranathan, who has a concurrent appointment at the Department of Biological Sciences at the National University of Singapore, said: “It is very interesting to discover that insects seem to evolve complex 3-D nanoscale architectures to escape predators by mixing with their background (usually brown or green). Only later do these colors diverge for other uses, such as signaling potential mates or as a warning to predators that the insect is not worth eating. ”