Function and mechanism of mirror-image ambiguity in bumblebees

This study investigated the function and mechanism underlying a previously documented 'mirror-image ambiguity' (i.e. the mirror image of a pattern is treated as similar to the original stimulus) in foraging bumblebees, Bombus impatiensArtificial flowers were constructed so that the mirror image of a petal configuration was different from the left-right reversal of that configuration. Bees were first trained to discriminate between rewarding and unrewarding artificial flowers that differed only in their configuration of four differently patterned petals. On subsequent choice tests between two empty flowers, the bees chose the rewarding configuration (S+) over the unrewarding one (S-), over the mirror image and over the left-right reversal. In the critical test conditions, the bees failed to choose the mirror image over a novel petal configuration, but they chose the left-right reversal over the novel configuration (78% of the time). A mirror-image mental transformation was ruled out as a mechanism underlying mirror-image ambiguity. The notion that mirror-image ambiguity has general functional significance (e.g. is a by-product of the symmetry of the nervous system) received no support. The results favour a specific mechanism tied to a specific function: a left-right transposition of a floral pattern, which would enable foraging bees to recognize vertically symmetrical flowers that were partially occluded at the time of learning.