The Dual Function of Orchid Bee Ocelli as Revealed by X-Ray Microtomography.
Visually guided flight control in the rainforest is arguably one of the most complex insect behaviors: illumination varies dramatically depending on location [1], and the densely cluttered environment blocks out most of the sky [2]. What visual information do insects sample for flight control in this habitat? To begin answering this question, we determined the visual fields of the ocelli-thought to play a role in attitude stabilization of some flying insects [3-5]-of an orchid bee, Euglossa imperialis. High-resolution 3D models of the ocellar system from X-ray microtomography were used for optical ray tracing simulations. Surprisingly, these showed that each ocellus possesses two distinct visual fields-a focused monocular visual field suitable for detecting features elevated above the horizon and therefore assisting with flight stabilization [3-5] and, unlike other ocelli investigated to date [4, 6, 7], a large trinocular fronto-dorsal visual field shared by all ocelli. Histological analyses show that photoreceptors have similar orientations within each ocellus and are likely to be sensitive to polarized light, as in some other hymenopterans [7, 8]. We also found that the average receptor orientation is offset between the ocelli, each having different axes of polarization sensitivity relative to the head. Unlike the eyes of any other insect described to date, this ocellar system meets the requirements of a true polarization analyzer [9, 10]. The ocelli of E. imperialis could provide sensitive compass information for navigation in the rainforest and, additionally, provide cues for visual discrimination or flight control.
Department of Biology, Lund University, Lund 223 62, Sweden. Electronic address: gavin.taylor@biol.lu.se.
Gavin J
GJ
Taylor
Research School of Biology, Australian National University, Canberra, ACT, 2601, Australia.
Willi
W
Ribi
Department of Clinical Sciences, Lund University, Lund 223 62, Sweden.
Martin
M
Bech
Diamond Light Source, Didcot OX11 0QX, UK.
Andrew J
AJ
Bodey
Diamond Light Source, Didcot OX11 0QX, UK.
Christoph
C
Rau
Nelson Mandela Metropolitan University, Port Elizabeth 6011, South Africa.
Axel
A
Steuwer
Department of Biology, Lund University, Lund 223 62, Sweden.
Eric J
EJ
Warrant
Department of Biology, Lund University, Lund 223 62, Sweden. Electronic address: emily.baird@biol.lu.se.
Emily
E
Baird
D000818:Animals; D001516:Bees / Q000166:cytology / Q000502:physiology* / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D017956:Photoreceptor Cells, Invertebrate / Q000166:cytology* / Q000648:ultrastructure; D014794:Visual Fields; D055114:X-Ray Microtomography
Euglossa imperialis; X-ray microCT; polarization sensitivity; rainforest; ray tracing; retina; synchrotron; vision