Molecular evidence implicating low aggression as a sickness behavior in honey bees

Behavior reflects an organism's health status. Many organisms display a generalized suite of behaviors that indicate infection or predict infection susceptibility. We apply this concept to honey bee aggression, a behavior that has been associated with positive health outcomes in previous studies. We sequenced the transcriptomes of the brain, fatbody, and midgut of adult sibling worker bees who developed as pre-adults in relatively high versus low aggression colonies. Previous studies showed that this pre-adult experience impacted both aggressive behavior and resilience to topical pesticide treatments. Our results show that, across all three tissues assessed, variation in aggression is associated with molecular phenotype that broadly characterizes infection and parasitic feeding. In the fatbody, and to a lesser degree the midgut, we find evidence of directional concordance consistent with the hypothesis that low aggression resembles a diseased or parasitized state. However, we find little evidence of overt infection in low aggression individuals. Furthermore, we find little evidence that the brain molecular signature in the current study is enriched for genes modulated by either ephemeral or stable social cues that induce aggression in adults. However, we do find evidence that genes associated with adult behavioral maturation are enriched in the brain our samples, with no clear directional bias.