Abstract
BackgroundWe have found that the spectral sensitivity of the compound eye in the summer fruit tortrix moth (Adoxophyes orana) differs in laboratory strains originating from different regions of Japan. We have investigated the mechanisms underlying this anomalous spectral sensitivity.MethodsWe applied electrophysiology, light and electron microscopy, opsin gene cloning, mathematical modeling, and behavioral analysis.ResultsThe ERG-determined spectral sensitivity of dark-adapted individuals of all strains peaks around 520 nm. When light-adapted, the spectral sensitivity of the Nagano strain narrows and its peak shifts to 580 nm, while that in other strains remains unchanged. All tested strains appear to be identical in terms of the basic structure of the eye, the pigment migration in response to light- and dark-adaptation, and the molecular structure of long-wavelength absorbing visual pigments. However, the color of the perirhabdomal pigment clearly differs; it is orange in the Nagano strain and purple in the others. The action spectrum of phototaxis appears to be shifted towards longer wavelengths in the Nagano individuals.ConclusionsThe spectral sensitivities of light-adapted eyes can be modeled under the assumption that this screening pigment plays a crucial role in determining the spectral sensitivity. The action spectrum of phototaxis indicates that the change in the eye spectral sensitivity is behaviorally relevant.
Highlights
We have found that the spectral sensitivity of the compound eye in the summer fruit tortrix moth (Adoxophyes orana) differs in laboratory strains originating from different regions of Japan
Similar to the human retina, which separately expresses three color opsins in three types of cone photoreceptor cells, insect compound eyes are typically furnished with three classes of spectral photoreceptors, each expressing the opsin of a short- (S or UV), middle- (M or blue) or long-wavelength (L or green) absorbing visual pigment
Anatomy Electron microscopy of the photoreceptor layer indicated that a single ommatidium of A. orana bears eight photoreceptor cells, R1–8
Summary
We have found that the spectral sensitivity of the compound eye in the summer fruit tortrix moth (Adoxophyes orana) differs in laboratory strains originating from different regions of Japan. Similar to the human retina, which separately expresses three color opsins in three types of cone photoreceptor cells, insect compound eyes are typically furnished with three classes of spectral photoreceptors, each expressing the opsin of a short- (S or UV), middle- (M or blue) or long-wavelength (L or green) absorbing visual pigment. These spectral receptors provide the physiological basis of insect trichromacy [6,7,8]. A Papilio butterfly that expresses three L opsins (L1–3) in addition to one S and one M opsin has tetrachromatic color vision based on the UV, blue, green and red sensitive photoreceptors; the green and red receptors express L2 and L3, respectively [12, 13]
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