Transparent half wing
In those species, wing colour pattern typically consists of a mosaic of brightly coloured elements and transparent patches. Surprisingly, although most aposematic Lepidoptera species harbour brightly coloured patterns, some unpalatable (due to the presence of chemical compounds in their body), aposematic species exhibit transparent wing patches ( McClure et al., 2019). Therefore, mimicry selects for convergent (when a trait in different species evolves towards the same value) or advergent (when a trait of a given species evolves towards the trait value in another species) colourations, as perceived by predators. those occupying a similar position in the wing and harbouring similar colour) cannot be discriminated by birds, believed to be the main predators ( Bybee et al., 2012 Llaurens et al., 2014 Su et al., 2015 Thurman and Seymoure, 2016). Among such co-mimetic lepidopteran species, several studies using visual modelling have shown that analogous colour patches (i. Co-mimetic species (species that share a common aposematic colour pattern) are often distantly related, implying multiple independent evolution of the same colour pattern. Because of the positive frequency-dependent selection incurred on aposematic signals ( Greenwood and Cotton, 1989, Chouteau et al., 2016), aposematic species often engage in Müllerian mimetic interactions, whereby species exposed to the same suite of predators converge on the same colour pattern and form mimicry ‘rings’ ( Müller, 1879). Another type of anti-predator defence in Lepidoptera involving wing colour pattern is aposematism, where the presence of secondary defences is advertised by the means of bright and contrasted colour patterns. Wing colour patterns are involved in thermoregulation ( Dufour et al., 2018 Heidrich et al., 2018), sexual selection ( Kemp, 2007), and anti-predator defences, such as crypsis ( Cook et al., 2012 Endler, 1984 Webster et al., 2009), masquerade ( Skelhorn et al., 2010 Stoddard, 2012), disruptive coloration, and deflection of predator attacks ( Vallin et al., 2011).
Scales can contain pigments or generate structural colours, thereby producing colour patterns across the entire wing. Lepidoptera (butterflies and moths) are characterised by large wings typically covered by scales, as testified by the name of the order (after the ancient greek lepís - scale and pterón – wing). This study shows that transparency might not only enable camouflage but can also be part of aposematic signals. We reveal that while transparency is primarily produced by microstructure modifications, nanostructures largely influence light transmission, potentially enabling additional fine-tuning in transmission properties.
Underlying micro- and nanostructures are also sometimes convergent despite a large structural diversity. We show that transparency, as perceived by predators, is convergent among co-mimics in some mimicry rings. Here, we conducted a comparative study of wing optics, micro and nanostructures in neotropical mimetic clearwing Lepidoptera, using spectrophotometry and microscopy imaging. Surprisingly, some aposematic mimetic species have partially transparent wings, raising the questions of whether optical properties of transparent patches are also convergent, and of how transparency is achieved.
In Lepidoptera, aposematic species typically harbour conspicuous opaque wing colour patterns with convergent optical properties among co-mimetic species.
Müllerian mimicry is a positive interspecific interaction, whereby co-occurring defended prey species share a common aposematic signal.