Behavioral rhythmicity, age, division of labor and period expression in the honey bee brain

Young adult honey bees work inside the beehive "nursing" brood around the c lock with no circadian rhythms; older bees forage for nectar and pollen out side with strong circadian rhythms. Previous research has shown that the de velopment of an endogenous rhythm of activity is also seen in the laborator y in a constant environment. Newly emerging bees maintained in isolation ar e typically arrhythmic during the first few days of adult life and develop strong circadian rhythms by about a few days of age. In addition, average d aily levels of period (per) mRNA in the brain are higher in foragers or for ager-age bees (> 21 days of age) relative to young nest bees (similar to 7 days of age). The authors used social manipulations to uncouple behavioral rhythmicity, age, and task to determine the relationship between these fact ors and per. There was no obligate link between average daily levels of per brain mRNA and either behavioral rhythmicity or age. There also were no di fferences in per brain mRNA levels between nurse bees and foragers in socia l environments that promote precocious or reversed behavioral development. Nurses and other hive-age bees can have high or low levels of per mRNA leve ls in the brain, depending on the social environment, while foragers and fo raging-age bees always have high levels. These findings suggest a link betw een honey bee foraging behavior and per up-regulation. Results also suggest task-related differences in the amplitude of per mRNA oscillation in the b rain, with foragers having larger diurnal fluctuation in per than nurses, r egardless of age. Taken together, these results suggest that social factors may exert potent influences on the regulation of clock genes.