Abstract
Müllerian mimicry is a positive interspecific interaction, whereby co-occurring defended prey species share a common aposematic signal. In Lepidoptera, aposematic species typically harbour conspicuous opaque wing colour patterns with convergent optical properties among co-mimetic species. 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. Here, we conducted a comparative study of wing optics, micro and nanostructures in neotropical mimetic clearwing Lepidoptera, using spectrophotometry and microscopy imaging. We show that transparency, as perceived by predators, is convergent among co-mimics in some mimicry rings. Underlying micro- and nanostructures are also sometimes convergent despite a large structural diversity. We reveal that while transparency is primarily produced by microstructure modifications, nanostructures largely influence light transmission, potentially enabling additional fine-tuning in transmission properties. This study shows that transparency might not only enable camouflage but can also be part of aposematic signals.
Highlights
IntroductionLepidoptera (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)
Lepidoptera are characterised by large wings typically covered by scales, as testified by the name of the order
Regarding chromatic contrasts, six mimicry rings out of 10 comprise co-m imetic species exhibiting smaller chromatic contrast than expected at random and three out of them comprise co-m imetic species with smaller chromatic contrast than expected given the phylogeny (Figure 1C, Figure 1—figure supplement 2). These results suggest that in some cases the similarity in transparent patches between co-mimetic species is due to convergent evolution but we cannot rule out that for some mimicry rings similarity could be due to shared ancestry
Summary
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). Wing colour patterns are involved in thermoregulation (Dufour et al, 2018; Heidrich et al, 2018), sexual selection (Kemp, 2007), and anti-p redator 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) 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. 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
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