PhD defence Juliana Sosa Espinosa
Juliana Sosa Espinosa (GREEN/BPE)
Promotores: Prof. S. Verhulst, Prof. M.A. Giraldo Cadavid (University of Antioquia), Prof. D.G. Stavenga; copromotor: Dr C.J. van der Kooi
Shedding light on Morpho butterfly wings
Iridescence and directional displays
Morpho butterflies are renowned for their brilliant blue, iridescent displays, produced by intricate wing scale nanostructures. However, not all species exhibit these vibrant colours, which suggests pronounced interspecific variation in scale morphology and pigmentation. While the generation of structural colour through multilayered ridges has been well documented, difference in the directionality of these displays received little attention. This thesis investigates how specific scale morphologies shape the directional and polarised nature of iridescence in Morpho butterflies, and explores its potential role in visual communication.
To understand display directionality across the genus Morpho, detailed analyses were performed on both wing sections and individual scales, using morphological imaging, spectrophotometry and imaging scatterometry. Results show that directionality arises from a combination of scale-level features including curvature, scale superposition, ridge orientation and density, the presence of windows, and multilayer tilt relative to the wing surface. These structural traits modulate the spectral and angular properties of iridescence, influencing how the wing display is perceived. Additionally, distinct polarisation signatures were characterised, and a mechanistic classification of the iridescent strategies across the genus is proposed. These findings expand our understanding of Morpho structural colouration and offer new insights into its ecological relevance.
Given that iridescent signals are inherently directional, their potential communicative function was explored using M. helenor as a model species. Optical analyses were integrated with behavioural observations. Males were significantly more likely to approach pinned conspecifics when viewed through a polariser compared to a neutral filter, suggesting that polarised iridescence may serve a communicative function.