The timing of when we sleep, eat and work is somewhat determined by social cues – when others in our house go to bed, what time our friend can meet for breakfast at the café, and if our boss is at the lab yet. It is also affected by how old we are, and honey bees are much the same. Within the hive there exists a fascinating division of labor. At approximately 2–3 weeks of adult life honey bees work tirelessly inside the hive. At this stage they are on-call, responsible for brood care, ‘nursing’ the younger bees for 24 h a day. Later in adulthood honey bees make a career change. In the final 1–2 weeks of life, bees begin to venture outside the hive to forage for nectar and pollen but they only go out and forage during daylight hours.
The change in overt behavioral patterns, how active animals are throughout the day or night, is also reflected at the cellular level through the cycling of certain genes in clock cells, which are thought to act as pacemakers. Yair Shemesh and colleagues, at The Hebrew University of Jerusalem, recently added to our understanding of how the social environment within the hive sets the daily activity of honey bees with their work published in The Journal of Neuroscience.
The team first asked whether direct contact between the nurse bees and the brood is required to regulate the daily rhythm of clock gene expression within clock cells and second, whether the 24 h active care exhibited by the nurse bees is dependent on direct physical contact with the brood. In three parallel experiments they measured gene expression and behavioral patterns of nurse bees in specific social contexts: nurse aged adults caged on broodless honey comb inside the hive, nurse bees caged on a brood-containing comb outside the hive, and nurse bees caged on a broodless comb outside the hive. These experimental parameters differentiate between the seemingly restrictive age dependent developmental patterns – early nursing and later foraging – of honey bee behavior. By separating the nurse aged adults from the brood and forcing them to function as workers, researchers can ask whether age or social influence determine the honey bees' work status, as nurse or forager.
Shemesh and co-workers found that the nursing bees switched to a daily pattern of behavior soon after release from direct contact with the brood hive, rather than their constant 24 h nursing pattern. This behavioral change was also reflected in changes in clock gene expression. Whereas nurse bees had no or very weak cycling of their clock genes while living in the hive with the brood, after being transferred from the hive to small broodless cages the nurse bees developed a forager-like molecular clock expression pattern.
These results demonstrate the remarkable influence that social context plays at multiple levels from molecular biology to behavior; not only is honey bee nursing activity a reflection of social interactions with the brood but this behavior is revealed at a fundamental level through the cycling of specific genes.