Subtle design changes control the difference in colour reflection from the dorsal and ventral wing-membrane surfaces of the damselfly Matronoides cyaneipennis

P Vukusic,A.G Orr,M.R Nixon

doi:10.1364/oe.21.001479

Abstract

The hind wings of males of the damselfly Matronoides cyaneipennis exhibit iridescence that is blue dorsally and green ventrally. These structures are used semiotically in agonistic and courtship display. Transmission electron microscopy reveals these colours are due to two near-identical 5-layer distributed Bragg reflectors, one placed either side of the wing membrane. Interestingly the thicknesses of corresponding layers in each distributed Bragg reflector are very similar for all but the second layer from each outer surface. This one key difference creates the significant disparity between the reflected spectra from the distributed Bragg reflectors and the observed colours of either side of the wing. Modelling indicates that modifications to the thickness of this layer alone create a greater change in the peak reflected wavelength than is observed for similar modifications to the thickness of any other layer. This results in an optimised and highly effective pair of semiotic reflector systems, based on extremely comparable design parameters, with relatively low material and biomechanical costs.

Highlights

Many biological systems are known to use periodic variations in refractive index on the submicron scale to produce a range of optical effects [1,2,3]
Transmission electron microscopy reveals these colours are due to two near-identical 5-layer distributed Bragg reflectors, one placed either side of the wing membrane
The thicknesses of corresponding layers in each distributed Bragg reflector are very similar for all but the second layer from each outer surface. This one key difference creates the significant disparity between the reflected spectra from the distributed Bragg reflectors and the observed colours of either side of the wing

Summary

Introduction

Many biological systems are known to use periodic variations in refractive index on the submicron scale to produce a range of optical effects [1,2,3]. Some species of Odonata exhibit a range of bright structural colours in their wing membranes and bodies [19,20,21]. The montane, stream-dwelling Bornean damselfly Matronoides cyaneipennis is interesting as the dorsal and ventral sides of its hind wing membrane reflect different colours. Both fore- and hind wings’ upper surfaces are deep blue, as is the lower surface of the hind wing; that of the forewing, is deep green. The forewing is coloured on its upper surface, but the underside reflects the same deep blue colour as on the dorsum of both wings

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