Anatomical and physiological evidence for polarisation vision in the nocturnal bee Megalopta genalis

Abstract

The presence of a specialised dorsal rim area with an ability to detect the e-vector orientation of polarised light is shown for the first time in a nocturnal hymenopteran. The dorsal rim area of the halictid bee Megalopta genalis features a number of characteristic anatomical specialisations including an increased rhabdom diameter and a lack of primary screening pigments. Optically, these specialisations result in wide spatial receptive fields (Ap = 14°), a common adaptation found in the dorsal rim areas of insects used to filter out interfering effects (i.e. clouds) from the sky. In this specialised eye region all nine photoreceptors contribute their microvilli to the entire length of the ommatidia. These orthogonally directed microvilli are anatomically arranged in an almost linear, anterior-posterior orientation. Intracellular recordings within the dorsal rim area show very high polarisation sensitivity and a sensitivity peak within the ultraviolet part of the spectrum.

Extreme polarization sensitivity in the retina of the corn borer moth Ostrinia

“…Their PS exceeds the highest values ever measured in any arthropod species (e.g. PS>21 in the DRA of the bee Megalopta) (Greiner et al, 2007; review in Stowasser and Buschbeck, 2012), except for the case of the fly DRA cells R7marg and R8marg, which produce hyperpolarising responses to polarised stimuli in the non-preferred direction (Hardie, 1984;Weir et al, 2016). In the fly DRA, the high PS is, however, possible due to filtering in a tiered rhabdom and electrical interactions between the two photoreceptors in a polarisation-opponent pair (Weir et al, 2016).…”

Haze, clouds and limited sky visibility: polarotactic orientation of crickets under difficult stimulus conditions

“…For small stimuli, which tend to produce weak irradiances at the eye, the number of ommatidia delivering reliable information is therefore considerably reduced. In Megalopta genalis, a nocturnal bee featuring a DRA with corneal structures similar to those of the honey bee, angular sensitivity functions of photoreceptors are much broader (average half-width ~13.8°) probably due to the 6-7 times wider diameter of the rhabdom (Greiner et al, 2007).…”

Ocellar adaptations for dim light vision in a nocturnal bee

“…It is not known whether these broad sensitivity profiles represent a true physiological response or whether they are an artefact of the recording process. Polarisation sensitivity (PS) was assessed by measuring intensityresponse functions to flashes of white light taken with a linear polarising filter in the light path oriented to a position deemed to give maximal response (⌽ max ), and again with the filter rotated by 90deg (⌽ min ) (Greiner et al, 2007). PS is given by 10  , where  is the difference (in log units) between the half-maximum responses of the two intensity-response functions (arrows in Fig.6).…”