Microarray analysis of time-trained honey bees: insights into forager time-keeping mechanisms

Honey bees, Apis mellifera, have a time sense (Zeitgedächtnis) which allows them to adjust their foraging behavior based on previous experience of when food sources are available. Many flowers have nectar secretion rhythms in which the food is provided for pollinators only during certain restricted, but consistent, time windows. In addition, bees will specialize on single food sources including those with time-restricted availability, creating a situation where different foragers will be active at different times of day. In this study, each colony of bees was trained to collect sucrose solution at artificial feeders at two different times of day, one in the morning and the other in the late afternoon. To separate circadian activity states from time-training, both groups of bees were collected at both times of day --"active and inactive"-- during the stereotypical anticipation phase just prior to the onset of the training time, and during the time when they were not trained. Microarray analysis revealed that hundreds of genes were differentially expressed in the brain based on time of day or activity state. Relatively few genes differed between the morning vs. afternoon trained groups, suggesting a common state of arousal is somehow coupled to the circadian clock to time foraging activity. Surprisingly, some clock genes, such as period, appear to be changing in expression due to training time, rather than time of day.