Many insect visual systems are comprised of dedicated neuronal circuits that allow for perceiving, processing, and integrating different modalities of light in order to orient or even navigate within visually complex environments. In addition to intensity or chromatic cues, many insects can utilize the linear polarization of light as a separate modality (Labhart, 2016) for orientation. For instance, polarized
reflections can signal specific surface properties, aiding in the detection of water bodies, finding oviposition sites, or localizing prey. Additionally, due to scattering of sunlight in the atmosphere, a celestial polarization pattern is created that can be used by many insects as a reference for both orientation and navigation. Here in this thesis, Manuscript I provides an overview over polarization vision in insects, by summarizing the current knowledge (as of 2017) on anatomical and physiological adaptions of insect visual systems and their behavioral implications in different species (Mathejczyk & Wernet, 2017). To experimentally study visual orientation and navigation in insects, I designed affordable and highly modular behavioral assays, which are described in Manuscript II (Mathejczyk & Wernet, 2020).
These assays provide a quantitative behavioral readout in response to panoramic intensity and chromatic patterns or to polychromatic linearly polarized light presented dorsally, when insects are either walking on a spherical treadmill or flying in a magneto-tether. This publication provides 3D model data and building instructions for those modular assays, including an easy-to-build tethering station and a low-cost temperature and humidity control. All code for tracking and data analysis was also made available online to aid the scientific community in establishing and modifying the presented assays in the spirit of open science. In this publication, I further demonstrate the setup’s functionality and versatility by describing opto-motor responses of walking and flying flies to rotating panoramic intensity patterns as well as behavioral responses to rapid e-vector switches of polarized light presented dorsally in flying Drosophila melanogaster. Using the setup described in Manuscript II, I assessed polarotactic responses in flying Drosophila in response to a constantly rotating e-vector presented dorsally, under open-loop conditions (Mathejczyk & Wernet, 2019). I found that flying flies align their body axis in response to linearly polarized UV, but not under polarized green or depolarized UV light. Every fly chose an arbitrary preferred heading relative to a celestial e-vector and most flies were able the keep those headings at least over the course of several minutes. Taken together, these findings confirm that Drosophila can utilize wavelength-specific skylight polarization for orientation and suggest that in Drosophila celestial polarization vision might serve an underlying dispersal strategy, optimizing chances of survival and reproduction on a population level
