Signals from the brood modulate the sleep of brood tending bumblebee workers

Sleep is ubiquitous in vertebrates and invertebrates, and its chronic lost is typically associated with reduced performance, health, or survival. Nevertheless, some animals can give up sleep in order to increase survival or mating opportunities. We studied the interplay between sleep and brood care in the social bumblebee Bombus terrestris. We first used video recording and detailed behavioral analyses to confirm that the bumblebee shows the essential behavioral characteristics of sleep. Based on these analyses we next used immobility bouts of >5' as proxy for sleep in automatic activity monitoring records, and found that sleep is severely reduced in the presence of larvae that require feeding or pupae that are not fed. Reduced sleep was correlated with wax pot building, which is a behavior typical to nest founding mother queens. Sleep was also reduced in the presence of empty cocoons, but this effect was transient and reduced with time. This observation that is consistent with the presence of a sleep modulating pheromonal signal. These results provide the first evidence for brood modulation of sleep in an insect, and are consistent with the hypothesis that plasticity in sleep can evolve as a mechanism to improve care for dependent juveniles.