Multiple observations motivate investigation into the epigenetics of this response. Once disturbed, they develop a state of aggressive vigilance against other potential threats and exhibit heightened responses to future intrusions. When faced with a territorial intruder, bees protect their colony with defensive behavior such as biting and stinging. This reaction to stress exists in many animal model systems, including honey bees.
For example, acute stress, including exposure to social stressors, can lead to a transient state of increased aggression. Many DNA methylation differences that occurred in association with the expression of aggression in real time also exist between Africanized bees and European bees, suggesting an evolutionarily conserved role for epigenetic regulation in aggressive behavior.Įxperiences produce molecular responses in the brain that exert long-term influences on behavior, affecting the way individuals or groups respond to future circumstances. These differences increased in number a few hours after the initial exposure and overlap with previously reported aggression-associated genes and neurobiologically relevant transcription factor binding sites. There were DNA methylation differences in the brain associated with response to an intruder. Lastly, we identified individually statistically suggestive CpGs that as a group were significantly associated with differentially expressed genes underlying aggressive behavior and also co-localize with binding sites of transcription factors involved in neuroplasticity or neurodevelopment. Additionally, there was a significant overlap of differential methylation with previously published epigenetic differences that distinguish aggressive Africanized and gentle European honey bees, suggesting an evolutionarily conserved use of brain DNA methylation in the regulation of aggression.
Differential methylation occurred at genes involved in neural plasticity, chromatin remodeling and hormone signaling. For clusters of CpGs, we report four genomic regions differentially methylated between aggressive and control bees at the 5-min time point, and 50 regions differentially methylated at the120-minute time point following intruder exposure. Eighteen individual CpG sites showed significant difference between aggressive and control bees 120 min post stimulus. There were DNA methylation differences between aggressive and control bees for individual cytosine-guanine dinucleotides (CpGs) across the genome.
We sampled five minutes and two hours after stimulus exposure to examine the effect of time on epigenetic profiles of aggression. We investigated whether threat-induced aggression altered DNA methylation profiles in the honey bee brain in response to a behavioral stimulus (aggression-provoking intruder bee or inert control). A previous study reported DNA methylation differences between aggressive Africanized and gentle European honey bees. DNA methylation is stably maintained over time, but also reversible in response to specific environmental conditions, and may thus be a neuromolecular regulator of both of these processes. Aggression is influenced by individual variation in temperament as well as behavioral plasticity in response to adversity.
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