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, which are adapted to detect linearly polarized light in large patches of the sky. In this study, we conducted electrophysiological recordings of ultraviolet-sensitive photoreceptors in the DRA and other regions of the compound eyes in honeybees ( Apis mellifera ) and bumblebees ( Bombus terrestris ) to map their receptive fields (RFs). For both species, we report novel evidence for photoreceptor coupling, i.e. spatial summation, recorded in the retinal layer of the DRA. We explore spatial summation as a possible mechanism to increase the effective size of DRA ommatidia RFs, a crucial functional feature of the polarization compass.