Research Spotlight—Insect Polarization Vision: Peripheral And Central Mechanisms

Abstract

AbstractThe ability to detect linearly polarized light is used by insects for spatial orientation, object identification and, in a few cases, sexual signalling. The use of polarization vision for sky compass orientation has received particular attention. Scattering of sunlight by air molecules generates a pattern of skylight polarization, which insects can use, just like the sun itself, as a visual celestial compass. Polarized skylight is detected by specialized ommatidia in the so-called dorsal rim area of the eye. In this eye region, ommatidial photoreceptors have highly aligned rhodopsin-bearing microvilli, resulting in high polarization sensitivity. Photoreceptors are homochromatic and occur in each ommatidium as sets of receptors with orthogonal microvillar orientations. Antagonistic input from these photoreceptors likely results in polarization-opponency in neurons of the polarization vision pathway in the brain. Studies in locusts, monarch butterflies, and a few other species have shown that convergence of signals from both eyes occurs in the central complex, a group of midline-spanning neuropils in the brain. Here, bilateral integration results in a compass-like topographic representation of zenithal E-vectors, which may be used as a frame of reference for spatial memory, path integration, and other spatial tasks. Integration of other celestial cues, such as the sky chromatic contrast, occurs at central stages of the polarization vision system, presumably to increase the robustness of the sky compass signal.