Polarization Signals in Crustaceans and Insects

Polarization vision can accomplish complex visual tasks, including discrimination and contrast in biological signals such as sexual and social communication, defence, camouflage, and foraging. In the context of signalling, polarization vision can be particularly valuable in environments where the reliability of colour as a cue is low, such as deep water. Crustaceans and insects construct photoreceptors with regular arrays of microvilli that are intrinsically polarization sensitive. Polarization sensitivity can be used for tasks like navigation and orientation based on celestial polarization, as well as orientation to flat water surfaces using horizontal polarization. Polarization sensitivity and polarization vision differ in scale: polarization sensitivity applies to large-field processing such as navigation, while polarization vision applies to small-field target-associated processing such as signalling and contrast enhancement. This chapter focuses on the latter, examining linearly and circularly polarized signals from crustaceans and insects. We will cover the latest research on polarized signals, as well as review the foundational work in this field. Understanding signals requires an understanding of how the signal is generated, received and how it influences other organisms. When known, behaviour related to creating or receiving signals is described, along with research contributing to how signals are processed by the visual system. Cues will also be discussed, though not in depth, as they can serve as evolutionary precursors to signals. The earlier literature about polarization signals has been reviewed by Horváth and Varjú (Polarized light in animal vision—polarization patterns in nature. Springer, Heidelberg, Berlin, New York, 2004) and Marshall et al. (Chapter 19: Polarisation signals. In: Horváth G (ed) Polarized light and polarization vision in animal sciences. Springer: Heidelberg, Berlin, New York, pp 407–442).