Project description:BACKGROUND: Social insects, such as honey bees, use molecular, physiological and behavioral responses to combat pathogens and parasites. The honey bee genome contains all of the canonical insect immune response pathways, and several studies have demonstrated that pathogens can activate expression of immune effectors. Honey bees also use behavioral responses, termed social immunity, to collectively defend their hives from pathogens and parasites. These responses include hygienic behavior (where workers remove diseased brood) and allo-grooming (where workers remove ectoparasites from nestmates). We have previously demonstrated that immunostimulation causes changes in the cuticular hydrocarbon profiles of workers, which results in altered worker-worker social interactions. Thus, cuticular hydrocarbons may enable workers to identify sick nestmates, and adjust their behavior in response. Here, we test the specificity of behavioral, chemical and genomic responses to immunostimulation by challenging workers with a panel of different immune stimulants (saline, Sephadex beads and Gram-negative bacteria E. coli). RESULTS: While only bacteria-injected bees elicited altered behavioral responses from healthy nestmates compared to controls, all treatments resulted in significant changes in cuticular hydrocarbon profiles. Immunostimulation caused significant changes in expression of hundreds of genes, the majority of which have not been identified as members of the canonical immune response pathways. Furthermore, several new candidate genes that may play a role in cuticular hydrocarbon biosynthesis were identified. Finally, we identified common genes regulated by pathogen challenge in honey bees and other insects, suggesting that immune responses are conserved at the molecular level. CONCLUSIONS: These studies suggest that honey bee genomic responses to immunostimulation are substantially broader than expected, and may mediate the behavioral changes associated with social immunity by orchestrating changes in chemical signaling.
Project description:We studied behavioral, brain transcriptomic and epigenetic responses of honey bees to social challenge. Bees were exposed to two intruders at different intervals. The initial exposure caused two behavioral effects at the individual level: an increase in the intensity of aggression toward a second intruder at 30 and 60 minutes, and an increased probability of responding aggressively toward a second intruder that persisted for two hours. The shorter-lived response was associated with one pattern of gene expression in the mushroom bodies, highlighted by genes related to cytoskeleton remodeling. The longer-lived response was associated with a different pattern; highlighted by genes related to hormones, stress response and transcription factors. Histone profiling revealed few changes in chromatin accessibility in response to social challenge; most differentially expressed genes were “ready” to be activated. These results demonstrate how biological embedding of a social challenge involves changes in the neurogenomic state to influence future behavior.
Project description:DNA methylation is an important chromatin modification that is necessary for the structural integrity and proper regulation of the genome for many species. Despite its conservation across the tree of life, little is known about its contribution to complex traits. Reports that differences in DNA methylation between castes in closely related Hymenopteran insects (ants, bees and wasps) contributes to social behaviors has generated hypotheses on the role of DNA methylation in governing social behavior. However, social behavior has evolved multiple times across insecta, and a common role of DNA methylation in social behavior remains outstanding. Using phylogenetic comparative methods we sought to better understand patterns of DNA methylation and social behavior across insects. DNA methylation can be found in social and solitary insects from all orders, except Diptera (flies), which suggests a shared loss of DNA methylation within this order. The lack of DNA methylation is reflected in the absence of the maintenance and de novo DNA methyltransferases (DNMT) 1 and 3, respectively. Interestingly, DNA methylation is found in species without DNMT3. DNA methylation and social behavior (social/solitary) or with division of labor (caste+/caste–) for 123 insect species analyzed from 11 orders are not evolutionary dependent, which is further supported by sequencing of DNA methylomes from 40 species.
Project description:We studied behavioral, brain transcriptomic and epigenetic responses of honey bees to social challenge. Bees were exposed to two intruders at different intervals. The initial exposure caused two behavioral effects at the individual level: an increase in the intensity of aggression toward a second intruder at 30 and 60 minutes, and an increased probability of responding aggressively toward a second intruder that persisted for two hours. The shorter-lived response was associated with one pattern of gene expression in the mushroom bodies, highlighted by genes related to cytoskeleton remodeling. The longer-lived response was associated with a different pattern; highlighted by genes related to hormones, stress response and transcription factors. Histone profiling revealed few changes in chromatin accessibility in response to social challenge; most differentially expressed genes were “ready” to be activated. These results demonstrate how biological embedding of a social challenge involves changes in the neurogenomic state to influence future behavior.
Project description:The timing and amplitude of reproductive effort are central life history variables for all organisms. In social insects, reproductive effort is collectively controlled at the colony level but little is known about the mechanisms that determine how much colonies invest in reproduction. As part of their female reproductive investment, honey bee colonies raise multiple new queens by feeding royal jelly to female larvae. Artificial selection for commercial royal jelly production in China has generated over the past 40 years a stock of royal jelly bees that raises an order of magnitude more queens and provisions each queen with >3x more royal jelly than unselected stock. Here we establish in a reciprocal cross-fostering experiment that this dramatic shift in social phenotype is due to changes in the nurse bees that care for the brood. We demonstrate higher electrophysiological responsiveness to brood pheromones in royal jelly bees than in unselected bees. Comparing the antennal proteome of unselected and royal jelly bees, we identify proteins involved in chemosensation and energy metabolism as candidates for the observed differences. We confirm several candidates, most prominently OBP16 and CSP4, with quantitative differences of corresponding mRNA levels and functional binding assays between the brood pheromones and the chemosensory proteins. Furthermore, we complement analyses of brood volatiles and electrophysiological recordings with behavioral attraction assays to confirm the presumed biological function of one newly discovered and two existing larval pheromones. Together, these findings help our understanding of pheromonal communication in honey bees and explain how sensory changes in nurse honey bees as alloparental caregivers have evolved in response to artificial selection, leading to a profound shift in colony-level resource allocation to sexual reproduction.
Project description:Honey bees move through a series of in-hive tasks (“nursing”) to outside tasks (“foraging”) that coincident with an intense increase in metabolic activity. Social context can cause worker bees to speed up, or slow down this process and foragers may revert back to their earlier in hive tasks accompanied by reversion to earlier physiological states. To determine if the transcriptional profile of forager bees can revert, or if the effects of flight on gene expression are irreversible, we used whole-genome microarrays. Brain tissue and flight muscle exhibited independent patterns of expression during behavioral transitions, with patterns of expression in the brain reflecting both age and behavior, while flight muscle exhibited primarily age-related patterns of expression. Our data suggest that the transition from little to no flight (nurse) to intense flight (forager), rather than the amount of flight has a major effect on gene expression. Following behavioral reversion there was a partial reversion in gene expression but some aspects of forager expression patterns, such as those for genes involved in immune function, remained. These data suggest an epigenetic control and energy balance role in honey bee functional senescence.
Project description:Experimental infection of (2 days old) adult honey bee workers (30 bees per replicates, 3 replicates per treatments, from 3 different colonies (one colony per cage for each treatment)) with 10^9 genome equivalent of Black Queen Cell Virus (BQCV) in 10µl of sugar solution and/or 10^5 fresh Nosema ceranae spores (control bees were given a similar bee extract in PBS, without pathogen). Bees were kept in cages of 30 bees in incubator (30°C/50%RH). At day 13 p.i., bees were flash frozen, and stored at -80°C. Brain mRNA profiles of 15 old bees were generated by deep sequencing, in triplicates except for bees infected by both Nosema ceranae and Black Queen Cell Virus (duplicates)
Project description:Experimental infection of (2 days old) adult honey bee workers (30 bees per replicates, 3 replicates per treatments, from 3 different colonies (one colony per cage for each treatment)) with 10^9 genome equivalent of Black Queen Cell Virus (BQCV) in 10µl of sugar solution and/or 10^5 fresh Nosema ceranae spores (control bees were given a similar bee extract in PBS, without pathogen). Bees were kept in cages of 30 bees in incubator (30°C/50%RH). At day 13 p.i., bees were flash frozen, and stored at -80°C.
Project description:Responses to social cues, such as pheromones, can be modified by genotype, physiology, or environmental context. Honey bee queens produce a pheromone (queen mandibular pheromone; QMP) which regulates many aspects of worker bee behavior and physiology. Forager honey bees are less responsive to QMP than young nurse bees engaged in brood care, suggesting that physiological changes associated with behavioral maturation may modulate response to this pheromone. Since cGMP is a major regulator of behavioral maturation in honey bee workers, we examined its role in modulating worker responses to QMP. Treatment with a cGMP analog, 8-Br-cGMP, resulted in significant reductions in both behavioral and physiological responses to QMP in young caged workers. Treatment significantly reduced attraction to QMP (the retinue response) and inhibited the QMP-mediated increase in vitellogenin levels in the fat bodies of worker bees. Genome-wide analysis of brain gene expression patterns demonstrated that cGMP has a larger effect on expression levels than QMP, and that QMP has specific effects in the presence of cGMP, suggesting that some responses to QMP may be dependent on an individual beesM-^R physiological state. Several functional gene categories were significantly differentially expressed, including genes involved in regulating GTPase activity, phototransduction, immunity, and carboxylic acid transmembrane transporter activity. Overall, our data suggest that cGMP-mediated processes play a large role in modulating responses to queen pheromone in honey bees, at the behavioral, physiological and molecular levels.