Can the narrow red bands of dragonflies be used to perceive wing interference patterns?

Mikkel Brydegaard,Samuel Jansson,Marcus Schulz,Anna Runemark

doi:10.1002/ece3.4054

Abstract

Despite numerous studies of selection on position and number of spectral vision bands, explanations to the function of narrow spectral bands are lacking. We investigate dragonflies (Odonata), which have the narrowest spectral bands reported, in order to investigate what features these narrow spectral bands may be used to perceive. We address whether it is likely that narrow red bands can be used to identify conspecifics by the optical signature from wing interference patterns (WIPs). We investigate the optical signatures of Odonata wings using hyperspectral imaging, laser profiling, ellipsometry, polarimetric modulation spectroscopy, and laser radar experiments. Based on results, we estimate the prospects for Odonata perception of WIPs to identify conspecifics in the spectral, spatial, intensity, polarization, angular, and temporal domains. We find six lines of evidence consistent with an ability to perceive WIPs. First, the wing membrane thickness of the studied Odonata is 2.3 μm, coinciding with the maximal thickness perceivable by the reported bandwidth. Second, flat wings imply that WIPs persist from whole wings, which can be seen at a distance. Third, WIPs constitute a major brightness in the visual environment only second after the solar disk. Fourth, WIPs exhibit high degree of polarization and polarization vision coincides with frontal narrow red bands in Odonata. Fifth, the angular light incidence on the Odonata composite eye provides all prerequisites for direct assessment of the refractive index which is associated with age. Sixth, WIPs from conspecifics in flight make a significant contribution even to the fundamental wingbeat frequency within the flicker fusion bandwidth of Odonata vision. We conclude that it is likely that WIPs can be perceived by the narrow red bands found in some Odonata species and propose future behavioral and electrophysiological tests of this hypothesis.

Highlights

INTRODUCTION AND BACKGROUNDAnimal vision differs from ours with respect to the numbers and central wavelengths of the spectral bands
We conclude that wing interference patterns (WIPs) from thick film interference may, judged by the extensive experimental data examined, be spectrally revolved by the vision of Odonata
The magnitude of the WIP signal is considerable compared to surroundings, the degree of linear polarization is greater than that from the surroundings, and polarization can be sensed by Odonata with narrow red bands

Summary

Introduction

INTRODUCTION AND BACKGROUNDAnimal vision differs from ours with respect to the numbers and central wavelengths of the spectral bands. Narrow red bands of Odonata reported are 32 nm broad, four times narrower than expected from Maximov and Peitsch’s reportings (see values in Figure 1a; Maximov, 1988; Meinertzhagen, Menzel, & Kahle, 1983; Peitsch et al, 1992; Yang & Osorio, 1991). Most bands are broad and capture photons with a wide range of energies. This is sufficient for contrasting most spectral features in the environment (Campbell, 2011; Cronin et al, 2014). While certain dragonflies have the narrowest bands reported from the animal kingdom, there is no explanation to the benefits of narrow bands. We investigate the possibility that they use these bands to perceive wings of other dragonflies—the only natural objects reflecting such narrow band light

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Results

Conclusion