Transparency in butterflies and moths: structural diversity, optical properties and ecological relevance

Abstract

21In water, transparency seems an ideal concealment strategy, as testified by the variety of transparent 22 aquatic organisms. By contrast, transparency is nearly absent on land, with the exception of insect 23 wings, and knowledge is scarce about its functions and evolution, with fragmentary studies and no 24 comparative perspective. Lepidoptera (butterflies and moths) represent an outstanding group to 25 investigate transparency on land, as species typically harbour opaque wings covered with coloured 26 2 scales, a key multifunctional innovation. Yet, many Lepidoptera species have evolved partially or 27 fully transparent wings. At the interface between physics and biology, the present study investigates 28 transparency in 123 Lepidopteran species (from 31 families) for its structural basis, optical 29 properties and biological relevance in relation to thermoregulation and vision. Our results establish 30 that transparency has likely evolved multiple times independently. Efficiency at transmitting light 31 is largely determined by clearwing microstructure (scale shape, insertion, colouration, dimensions 32 and density) and macrostructure (clearwing area, species size or wing area). Microstructural traits -33 density, dimensions -are tightly linked in their evolution, with different constraints according to 34 scale shape, insertion, and colouration. Transparency appears highly relevant for vision, especially 35 for camouflage, with size-dependent and activity-rhythm dependent variations. Links between 36 transparency and latitude are consistent with an ecological relevance of transparency in 37 thermoregulation, and not so for protection against UV radiation. Altogether, our results shed new 38 light on the physical and ecological processes driving the evolution of transparency on land and 39 underline that transparency is a more complex than previously thought colouration strategy. 40 41

Developmental, cellular, and biochemical basis of transparency in the glasswing butterflyGreta oto

“…1G-I) (10,23). More recent studies have explored aspects of structural diversity, optical properties, phylogenetic distribution, and ecological relevance of transparency within a wide range of butterflies and moths, highlighting that transparency has evolved multiple times independently and may present evolutionary benefits (13,24,25).…”

“…Lepidoptera are proving to represent an excellent group to investigate transparency on land, but the developmental processes underlying wing transparency are currently unknown. This presents a gap in our understanding of lepidopteran wing evolution and diversification, as transparent butterflies and moths contain multitudes of intriguing scale modifications and sub-wavelength cuticular nanostructures (24,25). We therefore set out to explore the development of wing transparency in the glasswing butterfly Greta oto, which belongs to a diverse tribe (∼393 species) of predominantly transparent neotropical butterflies (26).…”

How Spectral Properties and Machine Learning Can Categorize Twin Species - Based on Diachrysia Genus

“…The overall characteristic of the spectrum of Diachrysia scales, especially glass scales, is very similar to the general spectrum of chitin presented by Apetroaei et al 58 . Glass scales are colorless and melanin-deprived 59 . Thus, chitin in glass scales seems to be the most important factor differentiating the siblings Diachrysia.…”

Mimicry drives convergence in structural and light transmission features of transparent wings in Lepidoptera

“…Erected scales (i. e., with a non-flat angle between the scale basis and the wing membrane) have been previously reported in the riodinid Chorinea sylphina (Dushkina, Erten, and Lakhtakia 2017) and in the nymphalid Parantica sita (Perez Goodwyn et al 2009). Here we describe, as Gomez et al (2020, in review) did for the first time, some species with coloured erected scales that are completely perpendicular to the wing membrane, such as in the ithomiine Methona curvifascia. Transparent scales have already been reported in the opaque papilionid Graphium sarpedon (Stavenga, Giraldo, and Leertouwer 2010) and as Gomez et al (2020, in review) we are describing them for the first time in transparent Lepidoptera.…”

“…Here we describe, as Gomez et al (2020, in review) did for the first time, some species with coloured erected scales that are completely perpendicular to the wing membrane, such as in the ithomiine Methona curvifascia. Transparent scales have already been reported in the opaque papilionid Graphium sarpedon (Stavenga, Giraldo, and Leertouwer 2010) and as Gomez et al (2020, in review) we are describing them for the first time in transparent Lepidoptera. Other means of achieving transparency reported in the literature are not observed among our species (e. g., wing membrane devoid of scales, Yoshida et al 1996).…”