Neuronal circadian clock protein oscillates similarly in behaviorally rhythmic forager honeybees and in arrhythmic nurses
Taro Fuchikawa, Taro Fuchikawa , Katharina Beer , Charlotte Helfrich-Förster , Guy Bloch
Graduate School of Science, Osaka City University, Japan; Graduate School of Science, Osaka City University, Japan ; Biocenter, University of Würzburg, Germany ; Biocenter, University of Würzburg, Germany ; The A. Silberman Institute of Life Sciences, Hebrew University, Israel
Social insects commonly show remarkable plasticity in behavior and morphology. Both developmental and behavioral plasticities are under strong influence of social interactions within the nest. One remarkable example of such socially-regulated plasticity is in circadian rhythms which is intimately linked to the division of labor. For example, in the honeybee Apis mellifera, nurse bees care for the brood around-the-clock with attenuated circadian rhythms, whereas forager bees that forage outside the nest typically show clear circadian rhythms. Division of labor in honeybees relates to age. thus, a worker bee typically experiences both arrhythmic and rhythmic states throughout her life. However, to date, the mechanisms underlying this natural plasticity in circadian rhythms remain unclear. To clarify the mechanisms underlying the plasticity in circadian rhythms, we first characterized a newly-generated antibody directed against the clock protein PERIOD (PER), of A. mellifera (amPER). Using this specific antibody we provide the most detailed description of the clock network available for any social insect. The neuroanatomical organization of amPER-positive cells in the honeybee brain is overall similar to that in other insects including Drosophila, with main clusters in the dorsal and ventrolateral protocerebrum and the optic lobes. Next, we compared PER expression over the day in arrhythmic nurses and rhythmic foragers collected from free-foraging colonies. We found that the three major clusters of PER-positive cells (putative clock cells) show similarly strong oscillations in the two task groups. These results support and extend earlier evidence that some clock tick in the brain of around the clock active nurses, and suggest that the core circadian clock functions similarly in bees with and without circadian rhythms. Thus, we suggest that the plasticity in circadian rhythms is regulated by circadian clock output pathways.