Study finds brilliant green-blue colours in 13,000-year old fossil insects
Vivid colours produced by photonic diamonds
University College Cork (UCC) scientists have discovered 13,000-year-old fossil insects with brilliant green-blue colours produced by microscopic photonic ‘diamonds’.
These tiny structures produce the brightest and purest colours in nature and are used by insects today to produce striking visual signals. The evolution of photonic diamonds, however, is poorly understood.
Top: Fossil scales from 13,000-year-old weevils preserving bright blue, green and yellow hues. Bottom: Electron microscope images reveal the microscopic photonic ‘diamond’ structure responsible for producing these colours, which are believed to have been used for camouflage. Image credits: Luke McDonald and Maria McNamara (UCC).
Remarkably, the fossil insects preserve ancient photonic diamonds within scales on their outer surface. Unlike many of today’s insects, which are thought to use photonic diamonds for mating displays or displays of fitness, the green hues of the fossil weevils probably functioned as camouflage.
The fossil insects examined were from ancient lake sediments from Lobsigensee in Switzerland. The study was led by UCC palaeobiologists Drs Luke McDonald and Maria McNamara in collaboration with applied physicist Dr Vinod Saranathan, an expert in biological photonic systems, from YaleNUS College in Singapore.
Study leader Dr McDonald said, “This is only the second time that 3D photonic crystals have been reported from the fossil record. We identified the microscopic structures in the fossil scales using powerful electron microscopes. The photonic ‘diamonds’ in the fossils interact with wavelengths of light to produce vivid colours.”
Senior author Dr McNamara said, “The fossil record is potentially a treasure trove of information on the evolution of these structures, but it’s largely an untapped resource. More work on fossils will help us understand how these incredibly complex tissue structures evolved and how their functions may have changed through deep time.”
Artist’s impression of the weevil.
Dr Saranathan, who structural and optical analyses using particle accelerator X-rays and modelling, added, “It is very interesting to discover that insects first seem to evolve complex 3D nanoscale architectures in order to escape predators by blending in with their background (usually brown or green). Only later do these colours diverge for other uses such as signalling potential mates or as a warning to predators that the insect is not worth eating.”
The study is published today in the journal Biology Letters.
McDonald, L.T., Narayanan, S., Sandy, A., Saranathan, V., McNamara, M.E., 2020. Brilliant angle-independent structural colours preserved in weevil scales from the Swiss Pleistocene. Biology Letters, 16, 20200063. DOI: https://doi.org/10.1098/rsbl.2020.0063.
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