Polarizing optics in a spider eye

Abstract

Many arthropods including insects and spiders exploit skylight polarization for navigation. One of the four eye pairs of the spider Drassodes cupreus is dedicated to detect skylight polarization. These eyes are equipped with a tapetum that strongly plane-polarizes reflected light. This effectively enhances the polarization-sensitivity of the photoreceptors, improving orientation performance. With a multidisciplinary approach, we demonstrate that D. cupreus exploits reflective elements also present in non-polarizing tapetal eyes of other species such as Agelena labyrinthica. By approximately orthogonal arrangement of two multilayer reflectors consisting of reflecting guanine platelets, the tapetum uses the mechanism of polarization by reflection for polarizing reflected light.Polarizing optics in a spider eye AbstractMany arthropods including insects and spiders exploit skylight polarization for navigation. One of the four eye pairs of the spider Drassodes cupreus is dedicated to detect skylight polarization. These eyes are equipped with a tapetum that strongly plane-polarizes reflected light. This effectively enhances the polarization-sensitivity of the photoreceptors, improving orientation performance. With a multidisciplinary approach, we demonstrate that D. cupreus exploits reflective elements also present in nonpolarizing tapetal eyes of other species such as Agelena labyrinthica. By approximately orthogonal arrangement of two multilayer reflectors consisting of reflecting guanine platelets, the tapetum uses the mechanism of polarization by reflection for polarizing reflected light.

Disordered animal multilayer reflectors and the localization of light

“…These reflectors have been well described in the previous literature [3,16,21–25]. Figure 1 a is a transmission electron micrograph from Lepidoptus caudatus (silver scabbard fish), reproduced from [21], that shows the guanine crystals (the lighter streaks) and cytoplasm gaps (the darker surrounding media) that form a typical reflector.…”

“…In the skin and scales of fish [3,21–24] and the eyes of spiders [16,25] the layers are guanine crystals with cytoplasm gaps, in the iridophores of cephalopods the layers are protein platelets with cytoplasm gaps [3,26,27] and in butterfly wings the layers are chitin and air [4,28]. By controlling the values and the distribution of the layer thicknesses in the reflector, animals are able to produce both narrowband ‘coloured’ reflectivity (where the high- and low-index layers have approximately the same thicknesses throughout the near-periodic structure [2–4,26,27,29]) and broadband ‘silver’ reflectivity (where the high- and low-index layers have randomly distributed thicknesses about a mean value [3,21,22,24,30]).…”

The ocelli of Archaeognatha (Hexapoda): Functional morphology, pigment migration and chemical nature of the reflective tapetum

“…The determination of the chemical nature of multilayer reflectors has been performed by chromatography, UV-Vis spectroscopy and histochemistry (Zyznar and Nicol, 1971;Chae et al, 1996;Mueller and Labhart, 2010). In the present analysis we demonstrate that Raman microspectrometry is likewise an appropriate method that even has considerable advantages over the others.…”

“…fish, cats, mollusks, spiders, crustaceans and insects (for a review, see Schwab et al, 2002). Although crystals of various substances can form multi-layer reflectors, the best studied is guanine (Land, 1972;Mueller and Labhart, 2010;Hirsch et al, 2015;Bossard et al, 2016;Jordan et al, 2014Jordan et al, , 2012. Guanine or uric acid reflectors also cause color and color change phenomena in the integument of many animals, e.g.…”

Microstructural Organization of the Central Nervous System in the Orb-Web Spider Araneus ventricosus (Araneae: Araneidae)

“…Here, we could identify the only nerve arising from the protocerebrum is the optic nerve which composed of more than four pairs of neuropile masses in A. ventricosus. Although it has been known that the eyes of webbuilding spiders are primitive and can detect little more than light and dark (Land, 1985;Mueller & Labhart, 2010), but this orb-web spider also have well-organized neuropile masses, and the principle eyes have the most thick and abundant neuropiles comparing to other optic nerves connected with the lateral eyes. Previous research concerning the analysis of the postembryonic development has demonstrated that the number of neurons in Argiope spider's CNS remains the same at all stages of growth (Babu, 1985).…”