Spectral characteristics and regionalization of the eye of the satyrid Bicyclus anynana

Abstract

The ommatidial characteristics of the eyes of many insects are non-uniform (Stavenga, 1992). The retinal heterogeneity has been investigated in the satyrid Bicyclus anynana by in vivo microspectrophotometry of the eye shine from individual ommatidia. The ommatidial reflectances fall into two classes. The reflectance of the first, yellow-green (YG) class has a main band peaking at 570 nm (width ca 50 nm) and a subsidiary band in the violet; the second, red (R) class has a broad band from 580 to 680 nm. All ommatidia in the dorsal part of the eye belong to the YG-class. The ommatidia of the ventral part of the eye belong to either the YG- or the R-class. The density of the R-class is highest in the downward-looking area. The eye shine is maximal in the dark-adapted eye, but it rapidly decreases upon illumination with bright light, due to migration of pigment granules towards the light guiding rhabdom. The time constant of this pupil mechanism is in the order of a few seconds. The reflectance also exhibits distinct spectral changes due to changes in the content of the visual pigments in the rhabdom. This phenomenon allows studying the decay and renewal of visual pigment in vivo