Novel methodology for localizing and studying the insect dorsal rim area morphology in 2D and 3D

Abstract

1.Polarized light-based navigation in insects is facilitated by a specialised polarisation-sensitive part of the eye known as the dorsal rim area (DRA). Existing methods to study the anatomy of the DRA are in most cases destructive and very time consuming. Here, we present a novel method that allows for DRA localization using 3D volumetric images acquired through micro-computed tomography in combination with 2D photographs. We used the method on size polymorphic buff-tailed bumblebees, Bombus terrestris. We found that the size of the DRA can be easily acquired from photographs of the dorsal part of the eye. An allometric analysis of the size of the DRA in relation to body size in B. terrestris showed that the DRA region increases with body size but not at the same rate. Using our method, we localised the DRA in a 3D volume rendering of the eye using 2D photos localization of an individuals DRA onto the volumetric image stack of the head allowed for individual-level descriptions of the ommatidial structures (lens, crystalline cones, rhabdoms) to be performed on three different eye regions (DRA, non-DRA, proximate to DRA). The only feature distinctly unique to the DRA ommatidia was the smaller dimension of crystalline cones in comparison to other regions. Using our novel methodology we provide the first individual-level description of DRA ommatidial features and a comparison of how the DRA area varies with body size in bumblebees.