Measuring and Modelling Structural Colours of Euphaedra neophron (Lepidoptera: Nymphalidae) Finely Tuned by Wing Scale Lower Lamina in Various Subspecies

SIMPLE SUMMARY: Butterflies are best known because of their coloured wings. The colours are not for decorative but for crucial purposes within their reproductive strategy. One of these is sexual signalling, where the colours used for communication prior to mating are not chemical (based on pigments), but physical (based on nano-sized architectures). The genus Euphaedra belongs to the most diverse butterfly genera in forests of the Afrotropical Region, where many species are amazingly coloured. However, in the narrow forest belt along the Indian Ocean coast, Euphaedra is represented by only two species, one of them is the gold-banded forester (E. neophron) which expresses various physical colours. We investigated the coloration mechanism of this species, with our findings confirming that their structural colours are generated by the thickness of the laminae of the individual scales covering the wing surfaces. The colours are characteristic for all geographically distinct populations, currently recognised by scientists as subspecies. However, these do not show any clinal pattern or reflect climatic changes; therefore, we speculate that the various populations respond to new variables randomly tuning their colours. ABSTRACT: The nymphalid butterfly Euphaedra neophron (Hopffer, 1855) is the only structurally coloured species representing the genus along the Indian Ocean coast in East Africa and Southern Africa, with a distribution from southern Somalia to the Kwa-Zulu-Natal region of South Africa. The range of E. neophron is subdivided to several, geographically distinct populations, currently recognised as subspecies by taxonomists on the basis of violet, blue, and green-coloured morphs. We investigated the optical mechanism of all these morphs by various materials science techniques. We found that the structural colour is generated by the lower lamina of the cover scales and the different colours are tuned according to their thickness, which was also proved by modelling. The colour tuning of the different subspecies does not reflect any clinal pattern, be it geographical or altitudinal.