A Method for Measuring the Surface Features of the Firefly (Coleoptera: Lampyridae) Compound Eye

Al Marshad, H; Corless, A; Copeland, J; Moiseff, A

ABSTRACT: An inexpensive miniature stage goniometer compatible with a conventional optical microscope was developed to study the size and distribution of ommatidia facets across the compound eye of fireflies (Coleoptera: Lampyridae). The goniometer device was used to take sequential overlapping images of the hemispherical surface along longitudinal great-circle arcs of each eye of Photinus carolinus firefly and Photuris sp. males and females. Images covering the entire eye required 7 great circle scans at increments of 26° rotation. Using the multiple images, we minimized distortions associated with imaging a spherical surface in 2 dimensions and measured surface features with an error of <1.5%. A polar plot provided a consistent display format to relate facet area with location on the surface of the eye. We tested the functionality of the goniometer on a small number of male and female fireflies. It enabled us to make accurate measurements of surface features and address whether there is sexual dimorphism in firefly eyes. Within our limited sample, our results indicated that male eyes were larger than female eyes. In both firefly species the difference between the two sexes in the eye surface area was found statistically significant (P< 0.0001, unpaired Mests). Male and female eyes also exhibited regional variation in facet area. We hypothesize that the sexual dimorphism and regional variation of firefly eye reflect functional and behavioral capabilities.