Twilight orientation to polarised light in the crepuscular dung beetle Scarabaeus zambesianus.

摘要: The polarisation pattern of skylight offers many arthropods a reference for visual compass orientation. dung beetle Scarabaeus zambesianus starts foraging at around sunset. After locating source fresh droppings, it forms ball and rolls off high speed to escape competition the pile. Using behavioural experiments in field laboratory, we show that is able roll along straight path by using polarised light evening skylight. receptors used detect this cue can be found ommatidia dorsal rim area eye, whose structures differ from regular rest eye. are characterised rhabdoms with microvilli oriented only two orthogonal orientations. Together finding do not twist length rhabdom, indicates photoreceptors sensitive. Large rhabdoms, reflecting tracheal sheath lack screening pigments make eye well adapted detection low levels. fan-shaped arrangement over was previously believed an adaptation analysis, but here argue simply consequence way built.