Absence of eye shine and tapetum in the heterogeneous eye of Anthocharis butterflies (Pieridae)

Insect eyes are composed of spectrally heterogeneous ommatidia, typically with three different types. The ommatidial heterogeneity in butterflies can be identified non-invasively by the colorful eye shine, the reflection from the tapetal mirror located at the proximal end of the ommatidia, which can be observed by epi-illumination microscopy. Since the color of eye shine is determined by the spectral properties of the ommatidia, it has been tentatively related to color vision. In the course of a survey of ommatidial heterogeneity in butterflies, we found that members of the pierid genus Anthocharis lack the eye shine. We therefore carried out anatomy of the eye of the yellow tip, Anthocharis scolymus, and correlated it with the absence of the tapetum. The butterfly tapetum is a remnant of the ancestral moth tapetum, a trait that has been completely lost in the papilionids and also, as now appears, in the genus Anthocharis. Anatomical investigations also revealed that, considering rhabdom shape, peri-rhabdomal pigment clusters and autofluorescence, the ommatidia can be divided in at least two different types, which are randomly distributed in the retina.