Age-related division of labor in honey bees is associated with plasticity in circadian rhythms. Forager bees that are typically older than 3. weeks of age show strong behavioral and molecular circadian rhythms with higher activity during the day. Younger bees that typically care for (" nurse" ) the brood are active around the clock with similar brain clock gene levels throughout the day. However, nurses that are caged on brood-less combs inside or outside the hive show robust circadian rhythms with higher activity during the day, suggesting that direct contact with the brood mediates the plasticity in the circadian system. The nature of the brood signals affecting the workers' circadian system and the modalities by which they are detected are unknown. Given that the antennae are pivotal sensory organs in bees, we hypothesized that they are involved in mediating the brood influence on the plasticity in circadian rhythms. The flagella of the antennae are densely covered with diverse sensory structures able to detect a wide range of signals. To test our hypothesis, we removed the flagella of nurses and observed their behavior in isolation and in free-foraging colonies. We found that individually-isolated flagella-less bees under constant laboratory conditions show robust circadian rhythms in locomotor activity. In observation hives, flagella-less bees cared for the brood, but were more active during the day. By contrast, sham-treated bees were active around the clock as typical of nurses. Detailed video recordings showed that the brood-tending behavior of flagella-less and sham-treated bees is similar. These observations suggest that the difference in the patterns of brood care activity is not because the flagella-less bees did not contact the brood. Our results suggest that nurses are able to find the brood in the dark environment of the hive without their flagella, perhaps by using other sensory organs. The higher activity of flagella-less bees during the day further suggests that the flagella are involved in mediating the brood signals modulating plasticity in the circadian system.
Bibliographical noteFunding Information:
We thank Alexander Kutovoy, Nadav Yayon and Yafit Brener for assisting in conducting the experiments, Rafi Nir for bee hives management, the Israeli Science Foundation (ISF, grant number 1662/11 to GB), and the Israel-US Binational Science Foundation (BSF, grant 2007-465 to GB) for financial support, and two anonymous reviewers for their comments on earlier version of this manuscript.
- Apis mellifera
- Circadian rhythm
- Division of labor