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Data for: A hypothesis for robust polarization vision: An example from the Australian Imperial Blue butterfly, Jalmenus evagoras

Data files

May 19, 2022 version files 10.44 MB
Oct 15, 2022 version files 13.37 MB
Feb 09, 2023 version files 12.71 MB

Abstract

The Australian lycaenid butterfly, Jalmenus evagoras, has iridescent wings that are sexually dimorphic in both spectral reflection and degree of polarization, suggesting that these wing properties are likely to be important in mate recognition. We first describe the results of a field experiment showing that free-flying individuals of J. evagoras discriminate between visual stimuli that vary in polarization content in blue wavelengths but not in others. We then present detailed reflectance spectrophotometry measurements of the polarization content of male and female wings, showing that female wings exhibit blue-shifted reflectance, with a lower degree of polarization relative to male wings. Finally, we describe a novel method for measuring alignment of ommatidial arrays:  By measuring variation of depolarized eyeshine intensity from patches of ommatidia as a function of eye rotation, we show that a) individual rhabdoms contain mutually perpendicular microvilli; b) many rhabdoms in the array are rotated with respect to one another by as much as 45º; c) the rotated ommatidia are useful for robust polarization detection. By mapping the distribution of the ommatidial rotations in eye patches of J. evagoras, we show that males and females exhibit differences in the extent to which ommatidia are aligned. Both the number of rotated ommatidia suitable for robust polarization-detection, and the number of aligned ommatidia suitable for edge-detection, vary with respect to both sex and eye-patch elevation. Thus, J. evagoras exhibits finely-tuned ommatidial arrays suitable for perception of polarized signals, likely to match sex-specific life history differences in the utility of polarized signals.