Abstract
When honeybees are presented with a colour discrimination task, they tend to choose swiftly and accurately when objects are presented in the ventral part of their frontal visual field. In contrast, poor performance is observed when objects appear in the dorsal part. Here we investigate if this asymmetry is caused by fixed search patterns or if bees can use alternative search mechanisms such as spatial attention, which allows flexible focusing on different areas of the visual field. We asked individual honeybees to choose an orange rewarded target among blue distractors. Target and distractors were presented in the ventral visual field, the dorsal field or both. Bees presented with targets in the ventral visual field consistently had the highest search efficiency, with rapid decisions, high accuracy and direct flight paths. In contrast, search performance for dorsally located targets was inaccurate and slow at the beginning of the test phase, but bees increased their search performance significantly after a few learning trials: they found the target faster, made fewer errors and flew in a straight line towards the target. However, bees needed thrice as long to improve the search for a dorsally located target when the target's position changed randomly between the ventral and the dorsal visual field. We propose that honeybees form expectations of the location of the target's appearance and adapt their search strategy accordingly. Different possible mechanisms of this behavioural adaptation are discussed.
Highlights
When honeybees search for targets presented on a vertical plane, they show a distinct spatial asymmetry in colour and pattern learning between the ventral and the dorsal half of their frontal visual field
This is found in the eye of the honeybee drone, where the dorsal area is adapted to queen detection by increasing visual acuity and sensitivity, which is partly achieved by enlarged facet diameters and a reduction of the interommatidial angles (Menzel et al, 1991; Seidl, 1982; Streinzer et al, 2013; van Praagh et al, 1980)
Such regional specialisation in eye optics is not found in the worker honeybee, where the interommatidial angles and facet diameters are similar in the frontal visual field 30° below and above the horizontal plane (Seidl, 1982)
Summary
When honeybees search for targets presented on a vertical plane, they show a distinct spatial asymmetry in colour and pattern learning between the ventral and the dorsal half of their frontal visual field They learn a target when its defining features are perceived by the ventro-frontal area of the eye, but are less accurate when the crucial features of the target appear in the dorso-frontal area (Baumgärtner, 1928; Chittka et al, 1988; Giurfa et al, 1999; Lehrer, 1999; Morawetz & Spaethe, 2012; Wehner, 1972). The data hint at differences in neuronal processing between these two eye regions and correspond with the behavioural evidence of a dorso-ventral differentiation (Baumgärtner, 1928; Chittka et al, 1988; Giurfa et al, 1999; Lehrer, 1999; Morawetz & Spaethe, 2012; Wehner, 1972)
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