Brief Communication: Polarized light as a butterfly mating signal

Abstract

Iridescent butterfly scales are visually stunning structures that reflect highly saturated colour. They also create an array of non-chromatic optical phenomena, such as polarization, polarization mixing and highly directional flashes (1,2) but the ecological purpose of these effects is unclear (3,4). Here we show that polarized light is used in mate recognition by Heliconius butterflies, a genus that is known to rely on visual cues in sexual selection and speciation (5). This terrestrial example of exploitation of polarized light may have adaptive value in dense forest, where illumination varies greatly in spectrum and intensity.