Colony volatiles and substrate-borne vibrations entrain circadian rhythms and are potential mediators of social synchronization in honey bee colonies

Internal circadian clocks organize animal behavior and physiology and are entrained by ecologically-relevant external time-givers such as light and temperature cycles. In the highly social honey bee, social time-givers are important and can override photic entrainment, but the cues mediating social synchronization are unknown. Here we tested whether substrate-borne vibrations and hive volatiles can mediate social synchronization in honey bees. We first placed newly-emerged worker bees on the same or on a different substrate on which we placed cages with foragers entrained to ambient day- night cycles, while minimizing transfer of volatiles between cages. In the second experiment, we exposed young bees to constant airflow coming from either a free-foraging colony or a similar size control hive containing only empty combs, while minimizing transfer of substrate-borne vibrations between cages. After five days, we individually isolated each focal bee in an individual cage in an environmental chamber, and monitored locomotor activity. We repeated each experiment five times, each trail with bees from a different source colony, monitoring a total of more than 1000 bees representing diverse genotypes. We found that bees placed on the same substrate as foragers showed a stronger phase coherence; and in 3 of 5 trials their phase was more similar to that of foragers, compared to bees placed on a different substrate. In the second experiment, bees exposed to air from a colony showed a stronger phase coherence, and in 4 out of 5 trial their phase was more similar to that of foragers, compared to control bees exposed to air from an empty hive. These findings lend credence to the hypothesis that surrogates of activity such as substrate-borne vibrations, and volatile cues entrain circadian rhythms in natural free-foraging honey bee colonies.