A Transferrable Change in Preferences of Floral Patterns by Bumblebees through Reward Reversal

This study examines the use behavioral transfer across perceptually similar stimuli in bumblebees (Bombus impatiens) and addresses whether foraging judgments about a floral stimulus can change in a way that contradicts direct previous experience with that stimulus. Twenty bees from each of four colonies underwent discrimination training of stimuli placed in a radial maze. Bees were trained to discriminate between two corresponding object and photograph pairs of artificial flowers, where one object and its corresponding photo were rewarding, while another object and its corresponding photo were unrewarding. Following discrimination training, one stimulus from each pair (either the object or the photo) was removed. The predictive reward values of the remaining stimuli were either switched for one group or stayed the same for another. Subsequent testing on the removed stimuli revealed foraging preferences to shift based on experience with the other stimulus in the group. For instance, bees treated a previously unrewarding object as rewarding after learning that the corresponding photograph had become rewarding. Foraging decisions depend not only on previous experience with stimuli, but also category membership.

Anatomical Changes in Rudbeckia hirta L. during Transition to Flowering

Histological and histochemical examination of floral initiation was conducted to determine the pattern of flowering in Rudbeckia hirta, a long-day (LD) plant. Plants were grown under 8-hour short days (SDs) until they had 14 to 16 expanded leaves. Half of the group of plants was moved to LD conditions consisting of natural daylength plus a 4-hour night interruption. Rudbeckia hirta had a pattern of differentiation in flowering similar to that reported in species requiring one inductive day for initiation. Rudbeckia hirta required 8 LDs for evocation and 18 LDs for completion of initiation. Involucral bracts initiated after 18 LDs, after which the receptacle enlarged and was capped by a meristematic mantle of cells signaling the start of development. Floret primordia did not initiate, even after 20 LDs. Increases in pyronin staining were observed in actively dividing cells of the procambium, leaf primordium, and corpus of the vegetative meristems. After 8 LDs, the pith rib meristem stained darkly, a result indicating the arrival of the floral stimulus. An increase in pyronin staining was also observed in the meristematic mantle covering the receptacle after 18 LDs, a result indicating increased RNA levels.