Vision and structural colouration of butterflies

PhD ceremony: Mr. P. Pirih, 16.15 uur, Academiegebouw, Broerstraat 5, Groningen

Title: Vision and structural colouration of butterflies

Promotor(s): prof. D.G. Stavenga

Faculty: Mathematics and Natural Sciences

Vision, body colouration and the visual environment of an animal may be tuned to each other. This thesis aims at connecting the three entities by studying insect vision, physiological optics of butterfly eyes and optics of butterfly wing colouration. Vision is an imaging sense, used for finding food, avoiding predators, seeing mates and rivals. Many insects detect colour and polarisation of light. Body colouration may serve to conceal or reveal, or to communicate territoriality and gene quality. Butterfly wing patterns are formed by coloured scales. Colouration is due to pigments and due to periodic chitin structures.

First, we study the physiology of light sensing in the fruitfly (Drosophila melanogaster). We show that the ratio of the visual pigment rhodopsin to the controlling protein arrestin impacts the dynamic range of phototransduction.

Second, we study the physiological optics of the eye of the Clouded Yellow butterfly (Colias erate). We describe three types of red pigment-lined rhabdoms. We classify the photoreceptors into nine classes with sensitivities peaking from ultraviolet to the far red. The expanded set may be used for colour vision in intraspecific interactions, foraging or host-plant identification.

Third, we study the optics of wings in purple-coloured, iridescent males from Coliadinae and Colotis groups (Pieridae). We relate the multilayer structure in the scales to the reflectance spectra. We measure the scattering patterns of single scales and wing patches with an imaging scatterometer. Scale curvature determines the spatial extent of the iridescence patterns, which may influence the visibility of the colouration signal.