Electrophysiological recordings reveal photoreceptor coupling in the dorsal rim areas of honeybee and bumblebee eyes

Many insects rely on skylight polarization patterns to navigate their habitats. To perform this vital task, most insect species have evolved specialized ommatidia in the dorsal rim area (DRA) of their compound eyes that are adapted to detect linearly polarized light in large patches of sky. In this study, we conducted electrophysiological recordings of honeybee ( Apis mellifera ) and bumblebee ( Bombus terrestris ) photoreceptors in the DRA and other regions of the compound eye to map their receptive fields. For both species, we report novel evidence for photoreceptor coupling, i.e., spatial summation, present in the retinal layer of the DRA. We explore spatial summation as a possible, eye-region-specific mechanism to increase the effective size of DRA ommatidia receptive fields; a crucial functional feature of the polarization compass.