Hormonal and Genetic Control of Behavioral Integration in Honey Bee Colonies

Gut microbiota influences onset of foraging-related behavior but not physiological hallmarks of division of labor in honeybees

Gut microbes can impact cognition and behavior, but whether they regulate the division of labor in animal societies is unknown. We addressed this question using honeybees since they exhibit division of labor between nurses and foragers and because their gut microbiota can be manipulated. Using automated behavioral tracking and controlling for co-housing effects, we show that gut microbes influence the age at which bees start expressing foraging-like behaviors in the laboratory but have no effects on the time spent in a foraging arena and number of foraging trips. Moreover, the gut microbiota did not influence hallmarks of behavioral maturation such as body weight, cuticular hydrocarbon profile, hypopharyngeal gland size, gene expression, and the proportion of bees maturing into foragers. Overall, this study shows that the honeybee gut microbiota plays a role in controlling the onset of foraging-related behavior without permanent consequences on colony-level division of labor and several physiological hallmarks of behavioral maturation.

IMPORTANCE

The honeybee is emerging as a model system for studying gut microbiota-host interactions. Previous studies reported gut microbiota effects on multiple worker bee phenotypes, all of which change during behavioral maturation-the transition from nursing to foraging. We tested whether the documented effects may stem from an effect of the microbiota on behavioral maturation. The gut microbiota only subtly affected maturation: it accelerated the onset of foraging without affecting the overall proportion of foragers or their average output. We also found no effect of the microbiota on host weight, cuticular hydrocarbon (CHC) profile, hypopharyngeal gland size, and the expression of behavioral maturation-related genes. These results are inconsistent with previous studies reporting effects of the gut microbiota on bee weight and CHC profile. Our experiments revealed that co-housed bees tend to converge in behavior and physiology, suggesting that spurious associations may emerge when rearing environments are not replicated sufficiently or accounted for analytically.

Advancing ecotoxicity assessment: Leveraging pre-trained model for bee toxicity and compound degradability prediction

The prediction of ecological toxicity plays an increasingly important role in modern society. However, the existing models often suffer from poor performance and limited predictive capabilities. In this study, we propose a novel approach for ecological toxicity assessment based on pre-trained models. By leveraging pre-training techniques and graph neural network models, we establish a highperformance predictive model. Furthermore, we incorporate a variational autoencoder to optimize the model, enabling simultaneous discrimination of toxicity to bees and molecular degradability. Additionally, despite the low similarity between the endogenous hormones in bees and the compounds in our dataset, our model confidently predicts that these hormones are non-toxic to bees, which further strengthens the credibility and accuracy of our model. We also discovered the negative correlation between the degradation and bee toxicity of compounds. In summary, this study presents an ecological toxicity assessment model with outstanding performance. The proposed model accurately predicts the toxicity of chemicals to bees and their degradability capabilities, offering valuable technical support to relevant fields.

The honeybee microbiota and its impact on health and disease

Honeybees (Apis mellifera) are key pollinators that support global agriculture and are long-established models for developmental and behavioural research. Recently, they have emerged as models for studying gut microbial communities. Earlier research established that hindguts of adult worker bees harbour a conserved set of host-restricted bacterial species, each showing extensive strain variation. These bacteria can be cultured axenically and introduced to gnotobiotic hosts, and some have basic genetic tools available. In this Review, we explore the most recent research showing how the microbiota establishes itself in the gut and impacts bee biology and health. Microbiota members occupy specific niches within the gut where they interact with each other and the host. They engage in cross-feeding and antagonistic interactions, which likely contribute to the stability of the community and prevent pathogen invasion. An intact gut microbiota provides protection against diverse pathogens and parasites and contributes to the processing of refractory components of the pollen coat and dietary toxins. Absence or disruption of the microbiota results in altered expression of genes that underlie immunity, metabolism, behaviour and development. In the field, such disruption by agrochemicals may negatively impact bees. These findings demonstrate a key developmental and protective role of the microbiota, with broad implications for bee health.

Gut microbiota contribute to variations in honey bee foraging intensity

Gut microbiomes are increasingly recognized for mediating diverse biological aspects of their hosts, including complex behavioral phenotypes. Although many studies have reported that experimental disruptions to the gut microbial community result in atypical host behavior, studies that address how gut microbes contribute to adaptive behavioral trait variation are rare. Eusocial insects represent a powerful model to test this, because of their simple gut microbiota and complex division of labor characterized by colony-level variation in behavioral phenotypes. Although previous studies report correlational differences in gut microbial community associated with division of labor, here, we provide evidence that gut microbes play a causal role in defining differences in foraging behavior between European honey bees (Apis mellifera). We found that gut microbial community structure differed between hive-based nurse bees and bees that leave the hive to forage for floral resources. These differences were associated with variation in the abundance of individual microbes, including Bifidobacterium asteroides, Bombilactobacillus mellis, and Lactobacillus melliventris. Manipulations of colony demography and individual foraging experience suggested that differences in gut microbial community composition were associated with task experience. Moreover, single-microbe inoculations with B. asteroides, B. mellis, and L. melliventris caused effects on foraging intensity. These results demonstrate that gut microbes contribute to division of labor in a social insect, and support a role of gut microbes in modulating host behavioral trait variation.

Analyzing Gut Microbial Community in Varroa destructor-Infested Western Honeybee (Apis mellifera)

The western honeybee Apis mellifera L., a vital crop pollinator and producer of honey and royal jelly, faces numerous threats including diseases, chemicals, and mite infestations, causing widespread concern. While extensive research has explored the link between gut microbiota and their hosts. However, the impact of Varroa destructor infestation remains understudied. In this study, we employed massive parallel amplicon sequencing assays to examine the diversity and structure of gut microbial communities in adult bee groups, comparing healthy (NG) and Varroa-infested (VG) samples. Additionally, we analyzed Varroa-infested hives to assess the whole body of larvae. Our results indicated a notable prevalence of the genus Bombella in larvae and the genera Gillamella, unidentified Lactobacillaceae, and Snodgrassella in adult bees. However, no statistically significant difference was observed between NG and VG. Furthermore, our PICRUSt analysis demonstrated distinct KEGG classification patterns between larval and adult bee groups, with larvae displaying a higher abundance of genes involved in cofactor and vitamin production. Notably, despite the complex nature of the honeybee bacterial community, methanogens were found to be present in low abundance in the honeybee microbiota.

Spontaneous and information-induced bursting activities in honeybee hives

Social entrainment is important for functioning of beehive organization. By analyzing a dataset of approximately 1000 honeybees (Apis mellifera) tracked in 5 trials, we discovered that honeybees exhibit synchronized activity (bursting behavior) in their locomotion. These bursts occurred spontaneously, potentially as a result of intrinsic bee interactions. The empirical data and simulations demonstrate that physical contact is one of the mechanisms for these bursts. We found that a subset of honeybees within a hive which become active before the peak of each burst, and we refer to these bees as "pioneer bees." Pioneer bees are not selected randomly, but rather, are linked to foraging behavior and waggle dancing, which may help spread external information in the hive. By using transfer entropy, we found that information flows from pioneer bees to non-pioneer bees, which suggest that the bursting behavior is caused by foraging behavior and spreading the information through the hive and promoting integrated group behavior among individuals.

Developmental biomechanics and age polyethism in leaf-cutter ants

Many social insects display age polyethism: young workers stay inside the nest, and only older workers forage. This behavioural transition is accompanied by genetic and physiological changes, but the mechanistic origin of it remains unclear. To investigate if the mechanical demands on the musculoskeletal system effectively prevent young workers from foraging, we studied the biomechanical development of the bite apparatus in Atta vollenweideri leaf-cutter ants. Fully matured foragers generated peak in vivo bite forces of around 100 mN, more than one order of magnitude in excess of those measured for freshly eclosed callows of the same size. This change in bite force was accompanied by a sixfold increase in the volume of the mandible closer muscle, and by a substantial increase of the flexural rigidity of the head capsule, driven by a significant increase in both average thickness and indentation modulus of the head capsule cuticle. Consequently, callows lack the muscle force capacity required for leaf-cutting, and their head capsule is so compliant that large muscle forces would be likely to cause damaging deformations. On the basis of these results, we speculate that continued biomechanical development post eclosion may be a key factor underlying age polyethism, wherever foraging is associated with substantial mechanical demands.

Changes in gut microbiota and metabolism associated with phenotypic plasticity in the honey bee Apis mellifera

Honey bees exhibit an elaborate social structure based in part on an age-related division of labor. Young workers perform tasks inside the hive, while older workers forage outside the hive, tasks associated with distinct diets and metabolism. Critical to colony fitness, the work force can respond rapidly to changes in the environment or colony demography and assume emergency tasks, resulting in young foragers or old nurses. We hypothesized that both task and age affect the gut microbiota consistent with changes to host diet and physiology. We performed two experiments inducing precocious foragers and reverted nurses, then quantified tissue-specific gut microbiota and host metabolic state associated with nutrition, immunity and oxidative stress. In the precocious forager experiment, both age and ontogeny explained differences in midgut and ileum microbiota, but host gene expression was best explained by an interaction of these factors. Precocious foragers were nutritionally deficient, and incurred higher levels of oxidative damage relative to age-matched nurses. In the oldest workers, reverted nurses, the oxidative damage associated with age and past foraging was compensated by high Vitellogenin expression, which exceeded that of young nurses. Host-microbial interactions were evident throughout the dataset, highlighted by an age-based increase of Gilliamella abundance and diversity concurrent with increased carbonyl accumulation and CuZnSOD expression. The results in general contribute to an understanding of ecological succession of the worker gut microbiota, defining the species-level transition from nurse to forager.

Behavioral variation across the days and lives of honey bees

In honey bee colonies, workers generally change tasks with age (from brood care, to nest work, to foraging). While these trends are well established, our understanding of how individuals distribute tasks during a day, and how individuals differ in their lifetime behavioral trajectories, is limited. Here, we use automated tracking to obtain long-term data on 4,100+ bees tracked continuously at 3 Hz, across an entire summer, and use behavioral metrics to compare behavior at different timescales. Considering single days, we describe how bees differ in space use, detection, and movement. Analyzing the behavior exhibited across their entire lives, we find consistent inter-individual differences in the movement characteristics of individuals. Bees also differ in how quickly they transition through behavioral space to ultimately become foragers, with fast-transitioning bees living the shortest lives. Our analysis framework provides a quantitative approach to describe individual behavioral variation within a colony from single days to entire lifetimes.

Bumblebees with the socially transmitted microbiome: A novel model organism for gut microbiota research

Eusocial bumble and honey bees are important pollinators for global ecology and the agricultural economy. Although both the bumble and honey bees possess similar and host-restricted gut microbiota, they differ in aspects of morphology, autonomy, physiology, behavior, and life cycle. The social bee gut bacteria exhibit host specificity that is likely a result of long-term co-evolution. The unique life cycle of bumblebees is key for the acquisition and development of their gut microbiota, and affects the strain-level diversity of the core bacterial species. Studies on bumblebee gut bacteria show that they retain less functional capacity for carbohydrate metabolism compared with that of the honeybee. We discuss the potential roles of the bumblebee gut microbiota against pathogenic threats and the application of host-specific probiotics for bumblebees. Given the advantages of the bumblebee microbiome, including the simple structure and host specificity, and the ease of manipulating bumblebee colonies, we propose that bumblebees may provide a valuable system for understanding the general principles of host-microbe interactions, gut-brain axis, and vertical transmission.

Individual experience influences reconstruction of division of labour under colony disturbance in a queenless ant species

BACKGROUND

Division of labour (DOL) is ubiquitous across biological hierarchies. In eusocial insects, DOL is often characterized by age-related task allocation, but workers can flexibly change their tasks, allowing for DOL reconstruction in fluctuating environments. Behavioural change driven by individual experience is regarded as a key to understanding this task flexibility. However, experimental evidence for the influence of individual experience is remains sparse. Here we tested the effect of individual experience on task choice in the queenless ponerine ant, Diacamma cf. indicum from Japan.

RESULTS

We confirmed that both nurses and foragers shifted to vacant tasks when the colony composition was biased to one or the other. We also found that nurses which are induced to forage readily revert to nursing when reintroduced into balanced colonies. In contrast, foragers which are induced to revert to nursing very rarely return to a foraging role, even 19 days post reintroduction to their original colony.

CONCLUSIONS

Taken together, our results suggest that individual experience decreases the response threshold of original foragers, as they continue to be specialist nurses in a disturbed colony. However, original nurses do not appear strongly affected by having forager experience and revert to being nurses. Therefore, while individual experience does have an effect, other factors, such as reproductive ability, are clearly required to understand DOL maintenance in fluctuating environments.

Context-dependent influence of threat on honey bee social network dynamics and brain gene expression

Adverse social experience affects social structure by modifying the behavior of individuals, but the relationship between an individual's behavioral state and its response to adversity is poorly understood. We leveraged naturally occurring division of labor in honey bees and studied the biological embedding of environmental threat using laboratory assays and automated behavioral tracking of whole colonies. Guard bees showed low intrinsic levels of sociability compared with foragers and nurse bees, but large increases in sociability following exposure to a threat. Threat experience also modified the expression of caregiving-related genes in a brain region called the mushroom bodies. These results demonstrate that the biological embedding of environmental experience depends on an individual's societal role and, in turn, affects its future sociability.

Antibiotics Alter the Expression of Genes Related to Behavioral Development in Honey Bees (Hymenoptera: Apidae)

Honey bees, as many species of social insects, display a division of labor among colony members based on behavioral specializations related to age. Adult worker honey bees perform a series of tasks in the hive when they are young (such as brood care or nursing) and at ca. 2-3 wk of age, shift to foraging for nectar and pollen outside the hive. The transition to foraging involves changes in metabolism and neuroendocrine activities. These changes are associated with a suite of developmental genes. It was recently demonstrated that antibiotics influence behavioral development by accelerating or delaying the onset of foraging depending on timing of antibiotic exposure. To understand the mechanisms of these changes, we conducted a study on the effects of antibiotics on expression of candidate genes known to regulate behavioral development. We demonstrate a delay in the typical changes in gene expression over the lifetime of the individuals that were exposed to antibiotics during immature stage and adulthood. Additionally, we show an acceleration in the typical changes in gene expression on individuals that were expose to antibiotics only during immature stage. These results show that timing of antibiotic exposure alter the typical regulation of behavioral development by metabolic and neuroendocrine processes.

Investigating the Foraging, Guarding and Drifting Behaviors of Commercial Bombus terrestris

Social insects have high levels of cooperation and division of labor. In bumble bees this is partly size-based, with larger bees performing tasks outside the nest and smaller bees remaining inside, although bumble bees still display considerable behavioral plasticity. The level of specialization in tasks outside the colony, including foraging, guarding and drifting (entering a foreign colony), is currently unknown for bumble bees. This study aimed to assess division of labor between outside tasks and the degree of specialization in foraging, guarding, and switching colonies in commercially reared bumble bees placed in the field. Nine factory-bought Bombus terrestris colonies were placed on three farms in Sussex, UK, between June and August 2015. Forty workers from each colony were radio-tagged and a reader on the colony entrance recorded the date, time and bee ID as they passed. The length and frequency of foraging trips and guarding behavior were calculated, and drifting recorded. The mean (±SD) length of foraging trips was 45 ± 36 min, and the mean number of foraging trips per day was 7.75 ± 7.71. Low levels of specialization in guarding or foraging behavior were found; however, some bees appeared to guard more frequently than others, and twenty bees were categorized as guards. Five bees appeared to exhibit repeated "stealing" behavior, which may have been a specialist task. The division of labor between tasks was not size-based. It is concluded that commercial bumble bees are flexible in performing outside nest tasks and may have diverse foraging strategies including intra-specific nest robbing.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10905-021-09790-0.

Cuticle melanization and the expression of immune-related genes in the honeybee Apis mellifera (Hymenoptera: Apidae) adult workers

The global decline of bee populations has several factors, including pathogens, which need overcome the insect defenses such as the physical barriers, the body cuticle and peritrophic matrix (primary defenses), as well as the secondary defenses with antimicrobial peptides (AMPs) and the enzyme lysozyme. The regulation of immune defenses according to the infection risks raises questions about the immunity of social bees due to their exposition to different pathogens pressures during the adult lifespan and tasks performed. This study evaluated the primary (body cuticle melanization, peritrophic matrix and cpr14 expression) and secondary (AMPs and lysozyme expression) defenses of the honeybee Apis mellifera workers according to the age and tasks. The expression of malvolio was used to detect precocious forage tasks outside the colony. Forager workers have higher amount of cuticular melanization in the body cuticle than nurse, but not when the age effect is retired, indicating the gradual acquisition of this compound in the integument of adult bees. The relative value of chitin in the peritrophic matrix and cpr14 mRNA are similar in all bees evaluated, suggesting that these components of primary defenses do not change according to the task and age. Differential expression of genes for AMPs in workers performing different tasks, within the same age group, indicates that the behavior stimulates expression of genes related to secondary immune defense. The expression of malvolio gene, accelerating the change in workers behavior, and those related to immune defense suggest the investment in secondary defense mechanisms when the primary defense of the body cuticle is not yet completed.

A Machine Learning Approach to Study Demographic Alterations in Honeybee Colonies Using SDS-PAGE Fingerprinting

Honeybees, as social insects, live in highly organised colonies where tasks reflect the age of individuals. As is widely known, in this context, emergent properties arise from interactions between them. The accelerated maturation of nurses into foragers, stimulated by many negative factors, may disrupt this complex equilibrium. This complexity needs a paradigm shift: from the study of a single stressor to the study of the effects exerted by multiple stressors on colony homeostasis. The aim of this research is, therefore, to study colony population disturbances by discriminating overaged nurses from proper aged nurses and precocious foragers from proper aged foragers using SDS-PAGE patterns of haemolymph proteins and a machine-learning algorithm. The KNN (K Nearest Neighbours) model fitted on the forager dataset showed remarkably good performances (accuracy 0.93, sensitivity 0.88, specificity 1.00) in discriminating precocious foragers from proper aged ones. The main strength of this innovative approach lies in the possibility of it being deployed as a preventive tool. Depopulation is an elusive syndrome in bee pathology and early detection with the method described could shed more light on the phenomenon. In addition, it enables countermeasures to revert this vicious circle.

Ant behavioral maturation is mediated by a stochastic transition between two fundamental states

The remarkable ecological success of social insects is often attributed to their advanced division of labor, which is closely associated with temporal polyethism in which workers transition between different tasks as they age. Young nurses are typically found deep within the nest where they tend to the queen and the brood, whereas older foragers are found near the entrance and outside the nest.^1-3 However, the individual-level maturation dynamics remain poorly understood because following individuals over relevant timescales is difficult; hence, previous experimental studies used same-age cohort designs.^4-15 To address this, we used an automated tracking system to follow >500 individuals over >100 days and constructed networks of physical contacts to provide a continuous measure of worker social maturity. These analyses revealed that most workers occupied one of two steady states, namely a low-maturity nurse state and a high-maturity forager state, with the remaining workers rapidly transitioning between these states. There was considerable variation in the age at transition, and, surprisingly, the transition probability was age independent. This suggests that the transition is largely stochastic rather than a hard-wired age-dependent physiological change. Despite the variation in timing, the transition dynamics were highly stereotyped. Transitioning workers moved from the nurse to the forager state according to an S-shaped trajectory, and only began foraging after completing the transition. Stochastic switching, which occurs in many other biological systems, may provide ant colonies with robustness to extrinsic perturbations by allowing the colony to decouple its division of labor from its demography.

Expressions of conventional vitellogenin and vitellogenin-like A in worker brains are associated with a nursing task in a ponerine ant

In eusocial insect colonies, non-reproductive workers often perform different tasks. Tasks of an individual worker are shifted depending on various factors, e.g., age and colony demography. Although a vitellogenin (Vg) gene play regulatory roles in both reproductive and non-reproductive division of labours in a honeybee, it has been shown that the insect Vg underwent multiple gene duplications and sub-functionalisation, especially in apical ant lineages. The regulatory roles of duplicated Vgs were suggested to change evolutionarily among ants, whereas such roles in phylogenetically basal ants remain unclear. Here, we examined the expression patterns of conventional Vg (CVg), Vg-like A, Vg-like B and Vg-like C, as well as Vg receptor, during the task shift in an age-dependent manner and under experimental manipulation of colony demography in a primitive ant Diacamma sp. Expressions of CVg and Vg-like A in a brain were associated with a nursing task. It is suggested that associations of brain expressions of these Vgs with worker tasks were acquired in the basal ant lineage, and that such Vg functions could have sub-functionalised in the derived ant lineage.

Forager age and foraging state, but not cumulative foraging activity, affect biogenic amine receptor gene expression in the honeybee mushroom bodies

Foraging behavior is crucial for the development of a honeybee colony. Biogenic amines are key mediators of learning and the transition from in-hive tasks to foraging. Foragers vary considerably in their behavior, but whether and how this behavioral diversity depends on biogenic amines is not yet well understood. For example, forager age, cumulative foraging activity or foraging state may all be linked to biogenic amine signaling. Furthermore, expression levels may fluctuate depending on daytime. We tested if these intrinsic and extrinsic factors are linked to biogenic amine signaling by quantifying the expression of octopamine, dopamine and tyramine receptor genes in the mushroom bodies, important tissues for learning and memory. We found that older foragers had a significantly higher expression of Amdop1, Amdop2, AmoctαR1, and AmoctβR1 compared to younger foragers, whereas Amtar1 showed the opposite pattern. Surprisingly, our measures of cumulative foraging activity were not related to the expression of the same receptor genes in the mushroom bodies. Furthermore, we trained foragers to collect sucrose solution at a specific time of day and tested if the foraging state of time-trained foragers affected receptor gene expression. Bees engaged in foraging had a higher expression of Amdop1 and AmoctβR3/4 than inactive foragers. Finally, the expression of Amdop1, Amdop3, AmoctαR1, and Amtar1 also varied with daytime. Our results show that receptor gene expression in forager mushroom bodies is complex and depends on both intrinsic and extrinsic factors.

Post-embryonic Development of the Circadian Clock Seems to Correlate With Social Life Style in Bees

Social life style can influence many aspects of an animal’s daily life, but it has not yet been clarified, whether development of the circadian clock in social and solitary living bees differs. In a comparative study, with the social honey bee, Apis mellifera, and the solitary mason bee, Osmia bicornis, we now found indications for a differentially timed clock development in social and solitary bees. Newly emerged solitary bees showed rhythmic locomotion right away and the number of neurons in the brain that produce the clock component pigment-dispersing factor (PDF) did not change during aging of the adult solitary bee. Honey bees on the other hand, showed no circadian locomotion directly after emergence and the neuronal clock network continued to grow after emergence. Social bees appear to emerge at an early developmental stage at which the circadian clock is still immature, but bees are already able to fulfill in-hive tasks.

The sensitivity of a honeybee colony to worker mortality depends on season and resource availability

Background

Honeybees have extraordinary phenotypic plasticity in their senescence rate, making them a fascinating model system for the evolution of aging. Seasonal variation in senescence and extrinsic mortality results in a tenfold increase in worker life expectancy in winter as compared to summer. To understand the evolution of this remarkable pattern of aging, we must understand how individual longevity scales up to effects on the entire colony. In addition, threats to the health of honey bees and other social insects are typically measured at the individual level. To predict the effects of environmental change on social insect populations, we must understand how individual effects impact colony performance. We develop a matrix model of colony demographics to ask how worker age-dependent and age-independent mortality affect colony fitness and how these effects differ by seasonal conditions.

Results

We find that there are seasonal differences in honeybee colony elasticity to both senescent and extrinsic worker mortality. Colonies are most elastic to extrinsic (age-independent) nurse and forager mortality during periods of higher extrinsic mortality and resource availability but most elastic to age-dependent mortality during periods of lower extrinsic mortality and lower resource availability.

Conclusions

These results suggest that seasonal changes in the strength of selection on worker senescence partly explain the observed pattern of seasonal differences in worker aging in honey bees. More broadly, these results extend our understanding of the role of extrinsic mortality in the evolution of senescence to social animals and improve our ability to model the effects of environmental change on social insect populations of economic or conservation concern.

Honey bee virus causes context-dependent changes in host social behavior

Anthropogenic changes create evolutionarily novel environments that present opportunities for emerging diseases, potentially changing the balance between host and pathogen. Honey bees provide essential pollination services, but intensification and globalization of honey bee management has coincided with increased pathogen pressure, primarily due to a parasitic mite/virus complex. Here, we investigated how honey bee individual and group phenotypes are altered by a virus of concern, Israeli acute paralysis virus (IAPV). Using automated and manual behavioral monitoring of IAPV-inoculated individuals, we find evidence for pathogen manipulation of worker behavior by IAPV, and reveal that this effect depends on social context; that is, within versus between colony interactions. Experimental inoculation reduced social contacts between honey bee colony members, suggesting an adaptive host social immune response to diminish transmission. Parallel analyses with double-stranded RNA (dsRNA)-immunostimulated bees revealed these behaviors are part of a generalized social immune defensive response. Conversely, inoculated bees presented to groups of bees from other colonies experienced reduced aggression compared with dsRNA-immunostimulated bees, facilitating entry into susceptible colonies. This reduction was associated with a shift in cuticular hydrocarbons, the chemical signatures used by bees to discriminate colony members from intruders. These responses were specific to IAPV infection, suggestive of pathogen manipulation of the host. Emerging bee pathogens may thus shape host phenotypes to increase transmission, a strategy especially well-suited to the unnaturally high colony densities of modern apiculture. These findings demonstrate how anthropogenic changes could affect arms races between human-managed hosts and their pathogens to potentially affect global food security.

Revising the Superorganism: An Organizational Approach to Complex Eusociality

Eusociality is broadly defined as: colonies consisting of overlapping generations, cooperative brood care, and a reproductive division of labor where sterile (or non-reproductive) workers help the reproductive members. Colonies of many complex eusocial insect species (e.g., ants, bees, termites) exhibit traits, at the collective level, that are more analogous to biological individuals rather than to groups. Indeed, due to this, colonies of the most complex species are typically a unit of selection, which has led many authors to once again apply the concept of the superorganism to eusocial insects. However, unlike Wheeler, who originally employed the concept from a physiological and evolutionary perspective, today the superorganism is typically understood only from an evolutionary perspective, using group selection. This is because of the widely held view that eusocial colonies are self-organized systems. According to this view, even the most complex eusocial systems can be explained by appealing to a set of local interactions between parts of an initially disordered system (i.e., self-organization), without the need of any hierarchical control. In this paper, we challenge the mainstream view that hierarchical control and regulation does not occur, or is not necessary, in complex eusocial colonies. Using a case study of honey bees (Apis mellifera), we develop an alternative to the self-organization approach that focuses on the hierarchical nature of the organization of complex eusocial systems—that we refer to as the hierarchical-organizational approach. In addition, we analyze how colonies of eusocial insects show a complex set of interactions between the different organisms that bring forth a new cohesive collective organization, and how in turn the constitutive entities of this collective organization are transformed in this process. This paper argues that an inter-identity (namely the superorganism) emerges at the collective level in complex eusocial colonies, such as honey bees, due to the hierarchically organized network of interactions within the colony.

lncRNA profile of Apis mellifera and its possible role in behavioural transition from nurses to foragers

BACKGROUND

The behavioural transition from nurses to foragers in honey bees is known to be affected by intrinsic and extrinsic factors, including colony demography, hormone levels, brain chemistry and structure, and gene expression in the brain. However, the molecular mechanism underlying this behavioural transition of honey bees is still obscure.

RESULTS

Through RNA sequencing, we performed a comprehensive analysis of lncRNAs and mRNAs in honey bee nurses and foragers. Nurses and foragers from both typical colonies and single-cohort colonies were used to prepare six libraries to generate 49 to 100 million clear reads per sample. We obtained 6863 novel lncRNAs, 1480 differentially expressed lncRNAs between nurses and foragers, and 9308 mRNAs. Consistent with previous studies, lncRNAs showed features distinct from mRNAs, such as shorter lengths, lower exon numbers, and lower expression levels compared to mRNAs. Bioinformatic analysis showed that differentially expressed genes were mostly involved in the regulation of sensory-related events, such as olfactory receptor activity and odorant binding, and enriched Wnt and FoxO signaling pathways. Moreover, we found that lncRNAs TCONS_00356023, TCONS_00357367, TCONS_00159909 and mRNAs dop1, Kr-h1 and HR38 may play important roles in behavioural transition in honey bees.

CONCLUSION

This study characterized the expression profile of lncRNAs in nurses and foragers and provided a framework for further study of the role of lncRNAs in honey bee behavioural transition.

Oxytocin/vasopressin-like peptide inotocin regulates cuticular hydrocarbon synthesis and water balancing in ants

Inotocin, the oxytocin/vasopressin-like peptide, is widely conserved in arthropods; however, little is known about its molecular function. Here, we show that, in ants, the expression levels of inotocin and its receptor are correlated with the age of workers and their behavior. We also demonstrate that inotocin signaling is involved in desiccation resistance by regulating the synthesis of cuticular hydrocarbons. We propose that the up-regulation of inotocin and its receptor as workers age and switch tasks from nursing to foraging is a key physiological adaption to survive drier environments outside of the nest.

Oxytocin/vasopressin-like peptides are important regulators of physiology and social behavior in vertebrates. However, the function of inotocin, the homologous peptide in arthropods, remains largely unknown. Here, we show that the level of expression of inotocin and inotocin receptor are correlated with task allocation in the ant Camponotus fellah. Both genes are up-regulated when workers age and switch tasks from nursing to foraging. in situ hybridization revealed that inotocin receptor is specifically expressed in oenocytes, which are specialized cells synthesizing cuticular hydrocarbons which function as desiccation barriers in insects and for social recognition in ants. dsRNA injection targeting inotocin receptor, together with pharmacological treatments using three identified antagonists blocking inotocin signaling, revealed that inotocin signaling regulates the expression of cytochrome P450 4G1 (CYP4G1) and the synthesis of cuticular hydrocarbons, which play an important role in desiccation resistance once workers initiate foraging.

The cuticular hydrocarbon profiles of honey bee workers develop via a socially-modulated innate process

Large social insect colonies exhibit a remarkable ability for recognizing group members via colony-specific cuticular pheromonal signatures. Previous work suggested that in some ant species, colony-specific pheromonal profiles are generated through a mechanism involving the transfer and homogenization of cuticular hydrocarbons (CHCs) across members of the colony. However, how colony-specific chemical profiles are generated in other social insect clades remains mostly unknown. Here we show that in the honey bee (Apis mellifera), the colony-specific CHC profile completes its maturation in foragers via a sequence of stereotypic age-dependent quantitative and qualitative chemical transitions, which are driven by environmentally-sensitive intrinsic biosynthetic pathways. Therefore, the CHC profiles of individual honey bees are not likely produced through homogenization and transfer mechanisms, but instead mature in association with age-dependent division of labor. Furthermore, non-nestmate rejection behaviors seem to be contextually restricted to behavioral interactions between entering foragers and guards at the hive entrance.

Honey bees are social insects that live in large groups called colonies, within structures known as hives. The young adult bees stay within the hive to build nests and care for the young, while the older bees leave the hive to forage for food. Honey bees store food and other valuable resources in their hives, so they are often targeted by predators, parasites and ‘robber’ bees from other colonies. Therefore, it is important for bees to determine whether individuals trying to enter the nest are group members or intruders.

While it is known that social insects use blends of waxy chemicals called cuticular hydrocarbons to identify group members at the entrance to the colony, it is not clear how members of the same colony acquire a similar blend of cuticular hydrocarbons. Some previous work suggested that in some ant species (which are also social insects), colony members exchange cuticular hydrocarbons with each other so that all members of the colony are covered with a similar blend of chemicals. However, it was not known whether honey bees also share cuticular hydrocarbons between colony members in order to identify members of a hive.

Vernier et al. used chemical, molecular and behavioral approaches to study the cuticular hydrocarbons found on honey bees. The results show that, rather than exchanging chemicals with other members of their colony, individual bees make their own blends of cuticular hydrocarbons. As a bee ages it makes different blends of cuticular hydrocarbons, and by the time it starts to leave the hive to forage it makes a blend that is specific to the colony it belongs to. The production of this final blend is influenced by the environment within the hive.

Thus, the findings of Vernier et al. indicate that honey bees guarding the entrance to a hive can only identify non-colony-member forager bees as intruders, rather than any non-colony-member bee that happens upon the hive entrance. Honey bees play an essential role in pollinating many crop plants so understanding how these insects maintain their social groups may help to improve agriculture in the future. Furthermore, this work may aid our understanding of how other social insects interact in a variety of biological situations.

Sequence and structural properties of circular RNAs in the brain of nurse and forager honeybees (Apis mellifera)

Background

The honeybee (Apis mellifera) represents a model organism for social insects displaying behavioral plasticity. This is reflected by an age-dependent task allocation. The most protruding tasks are performed by young nurse bees and older forager bees that take care of the brood inside the hive and collect food from outside the hive, respectively. The molecular mechanism leading to the transition from nurse bees to foragers is currently under intense research. Circular RNAs, however, were not considered in this context so far. As of today, this group of non-coding RNAs was only known to exist in two other insects, Drosophila melanogaster and Bombyx mori. Here we complement the state of circular RNA research with the first characterization in a social insect.

Results

We identified numerous circular RNAs in the brain of A. mellifera nurse bees and forager bees using RNA-Seq with exonuclease enrichment. Presence and circularity were verified for the most abundant representatives. Back-splicing in honeybee occurs further towards the end of transcripts and in transcripts with a high number of exons. The occurrence of circularized exons is correlated with length and CpG-content of their flanking introns. The latter coincides with increased DNA-methylation in the respective loci. For two prominent circular RNAs the abundance in worker bee brains was quantified in TaqMan assays. In line with previous findings of circular RNAs in Drosophila, circAmrsmep2 accumulates with increasing age of the insect. In contrast, the levels of circAmrad appear age-independent and correlate with the bee’s task. Its parental gene is related to amnesia-resistant memory.

Conclusions

We provide the first characterization of circRNAs in a social insect. Many of the RNAs identified here show homologies to circular RNAs found in Drosophila and Bombyx, indicating that circular RNAs are a common feature among insects. We find that exon circularization is correlated to DNA-methylation at the flanking introns. The levels of circAmrad suggest a task-dependent abundance that is decoupled from age. Moreover, a GO term analysis shows an enrichment of task-related functions. We conclude that circular RNAs could be relevant for task allocation in honeybee and should be investigated further in this context.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5402-6) contains supplementary material, which is available to authorized users.

Genetic accommodation and the role of ancestral plasticity in the evolution of insect eusociality

For over a century, biologists have proposed a role for phenotypic plasticity in evolution, providing an avenue for adaptation in addition to 'mutation-first' models of evolutionary change. According to the various versions of this idea, the ability of organisms to respond adaptively to their environment through phenotypic plasticity may lead to novel phenotypes that can be screened by natural selection. If these initially environmentally induced phenotypes increase fitness, then genetic accommodation can lead to allele frequency change, influencing the expression of those phenotypes. Despite the long history of 'plasticity-first' models, the importance of genetic accommodation in shaping evolutionary change has remained controversial - it is neither fully embraced nor completely discarded by most evolutionary biologists. We suggest that the lack of acceptance of genetic accommodation in some cases is related to a lack of information on its molecular mechanisms. However, recent reports of epigenetic transgenerational inheritance now provide a plausible mechanism through which genetic accommodation may act, and we review this research here. We also discuss current evidence supporting a role for genetic accommodation in the evolution of eusociality in social insects, which have long been models for studying the influence of the environment on phenotypic variation, and may be particularly good models for testing hypotheses related to genetic accommodation. Finally, we introduce 'eusocial engineering', a method by which novel social phenotypes are first induced by environmental modification and then studied mechanistically to understand how environmentally induced plasticity may lead to heritable changes in social behavior. We believe the time is right to incorporate genetic accommodation into models of the evolution of complex traits, armed with new molecular tools and a better understanding of non-genetic heritable elements.

Honey bees as models for gut microbiota research

The gut microbiota of the honey bee (Apis mellifera) offers several advantages as an experimental system for addressing how gut communities affect their hosts and for exploring the processes that determine gut community composition and dynamics. A small number of bacterial species dominate the honey bee gut community. These species are restricted to bee guts and can be grown axenically and genetically manipulated. Large numbers of microbiota-free hosts can be economically reared and then inoculated with single isolates or defined communities to examine colonization patterns and effects on host phenotypes. Honey bees have been studied extensively, due to their importance as agricultural pollinators and as models for sociality. Because of this history of bee research, the physiology, development, and behavior of honey bees is relatively well understood, and established behavioral and phenotypic assays are available. To date, studies on the honey bee gut microbiota show that it affects host nutrition, weight gain, endocrine signaling, immune function, and pathogen resistance, while perturbation of the microbiota can lead to reduced host fitness. As in humans, the microbiota is concentrated in the distal part of the gut, where it contributes to digestion and fermentation of plant cell wall components. Much like the human gut microbiota, many bee gut bacteria are specific to the bee gut and can be directly transmitted between individuals through social interaction. Although simpler than the human gut microbiota, the bee gut community presents opportunities to understand the processes that govern the assembly of specialized gut communities as well as the routes through which gut communities impact host biology.

Methoprene does not affect juvenile hormone titers in honey bee (Apis mellifera) workers

Methoprene, a juvenile hormone (JH) analog, is a widely used insecticide that also accelerates behavioral development in honey bees (Apis mellifera). JH regulates the transition from nursing to foraging in adult worker bees, and treatment with JH or methoprene have both been shown to induce precocious foraging. To determine how methoprene changes honey bee behavior, we compared JH titers of methoprene-treated and untreated bees. Behavioral observations confirmed that methoprene treatment significantly increased the number of precocious foragers in 3 out of 4 colonies. In only 1 out of 4 colonies, however, was there a significant difference in JH titers between the methoprene-treated and control bees. Further, in all 4 colonies, there was no significant differences in JH titers between precocious and normal-aged foragers. These results suggest that methoprene did not directly affect the endogenous JH secreted by corpora allata. Because methoprene caused early foraging without changing workers' JH titers, we conclude that methoprene most likely acts directly on the JH receptors as a substitute for JH.

Automated monitoring of behavior reveals bursty interaction patterns and rapid spreading dynamics in honeybee social networks

Social networks mediate the spread of information and disease. The dynamics of spreading depends, among other factors, on the distribution of times between successive contacts in the network. Heavy-tailed (bursty) time distributions are characteristic of human communication networks, including face-to-face contacts and electronic communication via mobile phone calls, email, and internet communities. Burstiness has been cited as a possible cause for slow spreading in these networks relative to a randomized reference network. However, it is not known whether burstiness is an epiphenomenon of human-specific patterns of communication. Moreover, theory predicts that fast, bursty communication networks should also exist. Here, we present a high-throughput technology for automated monitoring of social interactions of individual honeybees and the analysis of a rich and detailed dataset consisting of more than 1.2 million interactions in five honeybee colonies. We find that bees, like humans, also interact in bursts but that spreading is significantly faster than in a randomized reference network and remains so even after an experimental demographic perturbation. Thus, while burstiness may be an intrinsic property of social interactions, it does not always inhibit spreading in real-world communication networks. We anticipate that these results will inform future models of large-scale social organization and information and disease transmission, and may impact health management of threatened honeybee populations.

Disentangling metabolic functions of bacteria in the honey bee gut

It is presently unclear how much individual community members contribute to the overall metabolic output of a gut microbiota. To address this question, we used the honey bee, which harbors a relatively simple and remarkably conserved gut microbiota with striking parallels to the mammalian system and importance for bee health. Using untargeted metabolomics, we profiled metabolic changes in gnotobiotic bees that were colonized with the complete microbiota reconstituted from cultured strains. We then determined the contribution of individual community members in mono-colonized bees and recapitulated our findings using in vitro cultures. Our results show that the honey bee gut microbiota utilizes a wide range of pollen-derived substrates, including flavonoids and outer pollen wall components, suggesting a key role for degradation of recalcitrant secondary plant metabolites and pollen digestion. In turn, multiple species were responsible for the accumulation of organic acids and aromatic compound degradation intermediates. Moreover, a specific gut symbiont, Bifidobacterium asteroides, stimulated the production of host hormones known to impact bee development. While we found evidence for cross-feeding interactions, approximately 80% of the identified metabolic changes were also observed in mono-colonized bees, with Lactobacilli being responsible for the largest share of the metabolic output. These results show that, despite prolonged evolutionary associations, honey bee gut bacteria can independently establish and metabolize a wide range of compounds in the gut. Our study reveals diverse bacterial functions that are likely to contribute to bee health and provide fundamental insights into how metabolic activities are partitioned within gut communities.

Methyl farnesoate epoxidase (mfe) gene expression and juvenile hormone titers in the life cycle of a highly eusocial stingless bee, Melipona scutellaris

In social insects, juvenile hormone (JH) has acquired novel functions related to caste determination and division of labor among workers, and this is best evidenced in the honey bee. In contrast to honey bees, stingless bees are a much more diverse group of highly eusocial bees, and the genus Melipona has long called special attention due to a proposed genetic mechanism of caste determination. Here, we examined methyl farnesoate epoxidase (mfe) gene expression, encoding an enzyme relevant for the final step in JH biosynthesis, and measured the hemolymph JH titers for all life cycle stages of Melipona scutellaris queens and workers. We confirmed that mfe is exclusively expressed in the corpora allata. The JH titer is high in the second larval instar, drops in the third, and rises again as the larvae enter metamorphosis. During the pupal stage, mfe expression is initialy elevated, but then gradually drops to low levels before adult emergence. No variation was, however, seen in the JH titer. In adult virgin queens, mfe expression and the JH titer are significantly elevated, possibly associated with their reproductive potential. For workers we found that JH titers are lower in foragers than in nurse bees, while mfe expression did not differ. Stingless bees are, thus, distinct from honey bee workers, suggesting that they have maintained the ancestral gonadotropic function for JH. Hence, the physiological circuitries underlying a highly eusocial life style may be variable, even within a monophyletic clade such as the corbiculate bees.

Effects of age and nutritional state on the expression of gustatory receptors in the honeybee (Apis mellifera)

Gustatory receptors (Grs) expressed in insect taste neurons signal the presence of carbohydrates, sugar alcohols, CO₂, bitter compounds and oviposition stimulants. The honeybee (Apis mellifera) has one of the smallest Gr gene sets (12 Gr genes) of any insect whose genome has been sequenced. Honeybees live in eusocial colonies with a division of labour and perform age-dependent behavioural tasks, primarily food collection. Here, we used RT-qPCR to quantify Gr mRNA in honeybees at two ages (newly-emerged and foraging-age adults) to examine the relationship between age-related physiology and expression of Gr genes. We measured the Gr mRNAs in the taste organs and also the brain and gut. The mRNA of all Gr genes was detected in all tissues analysed but showed plasticity in relative expression across tissues and in relation to age. Overall, Gr gene expression was higher in the taste organs than in the internal tissues but did not show an overall age-dependent difference. In contrast Gr gene expression in brain was generally higher in foragers, which may indicate greater reliance on internal nutrient sensing. Expression of the candidate sugar receptors AmGr1, AmGr2 and AmGr3 in forager brain was affected by the types of sugars bees fed on. The levels of expression in the brain were greater for AmGr1 but lower for AmGr2 and AmGr3 when bees were fed with glucose and fructose compared with sucrose. Additionally, AmGr3 mRNA was increased in starved bees compared to bees provided ad libitum sucrose. Thus, expression of these Grs in forager brain reflects both the satiety state of the bee (AmGr3) and the type of sugar on which the bee has fed.

Contextual organismality: Beyond pattern to process in the emergence of organisms

Biologists have taken the concept of organism largely for granted. However, advances in the study of chimerism, symbiosis, bacterial‐eukaryote associations, and microbial behavior have prompted a redefinition of organisms as biological entities exhibiting low conflict and high cooperation among their parts. This expanded view identifies organisms in evolutionary time. However, the ecological processes, mechanisms, and traits that drive the formation of organisms remain poorly understood. Recognizing that organismality can be context dependent, we advocate elucidating the ecological contexts under which entities do or do not act as organisms. Here we develop a “contextual organismality” framework and provide examples of entities, such as honey bee colonies, tumors, and bacterial swarms, that can act as organisms under specific life history, resource, or other ecological circumstances. We suggest that context dependence may be a stepping stone to the development of increased organismal unification, as the most integrated biological entities generally show little context dependence. Recognizing that organismality is contextual can identify common patterns and testable hypotheses across different entities. The contextual organismality framework can illuminate timeless as well as pressing issues in biology, including topics as disparate as cancer emergence, genomic conflict, evolution of symbiosis, and the role of the microbiota in impacting host phenotype.

Larval Exposure to the Juvenile Hormone Analog Pyriproxyfen Disrupts Acceptance of and Social Behavior Performance in Adult Honeybees

BACKGROUND

Juvenile hormone (JH) plays an important role in honeybee development and the regulation of age-related division of labor. However, honeybees can be exposed to insect growth regulators (IGRs), such as JH analogs developed for insect pest and vector control. Although their side effects as endocrine disruptors on honeybee larval or adult stages have been studied, little is known about the subsequent effects on adults of a sublethal larval exposure. We therefore studied the impact of the JH analog pyriproxyfen on larvae and resulting adults within a colony under semi-field conditions by combining recent laboratory larval tests with chemical analysis and behavioral observations. Oral and chronic larval exposure at cumulative doses of 23 or 57 ng per larva were tested.

RESULTS

Pyriproxyfen-treated bees emerged earlier than control bees and the highest dose led to a significant rate of malformed adults (atrophied wings). Young pyriproxyfen-treated bees were more frequently rejected by nestmates from the colony, inducing a shorter life span. This could be linked to differences in cuticular hydrocarbon (CHC) profiles between control and pyriproxyfen-treated bees. Finally, pyriproxyfen-treated bees exhibited fewer social behaviors (ventilation, brood care, contacts with nestmates or food stocks) than control bees.

CONCLUSION

Larval exposure to sublethal doses of pyriproxyfen affected several life history traits of the honeybees. Our results especially showed changes in social integration (acceptance by nestmates and social behaviors performance) that could potentially affect population growth and balance of the colony.

Changes in the Gene Expression Profiles of the Hypopharyngeal Gland of Worker Honeybees in Association with Worker Behavior and Hormonal Factors

The hypopharyngeal glands (HPGs) of worker honeybees undergo physiological changes along with the age-dependent role change from nursing to foraging: nurse bee HPGs secrete mainly major royal jelly proteins, whereas forager HPGs secrete mainly α-glucosidase III, which converts the sucrose in the nectar into glucose and fructose. We previously identified two other genes, Apis mellifera buffy (Ambuffy) and Apis mellifera matrix metalloproteinase 1 (AmMMP1), with enriched expression in nurse bee and forager HPGs, respectively. In the present study, to clarify the molecular mechanisms that coordinate HPG physiology with worker behavior, we first analyzed whether Ambuffy, AmMMP1, mrjp2 (a gene encoding one of major royal jelly protein isoforms), and Hbg3 (a gene encoding α-glucosidase III) expression, is associated with worker behavior in 'single-cohort colonies' where workers of almost the same age perform different tasks. Expression of these genes correlated with the worker’s role, while controlling for age, indicating their regulation associated with the worker’s behavior. Associated gene expression suggested the possible involvement of some hormonal factors in its regulation. We therefore examined the relationship between ecdysone- and juvenile hormone (JH)-signaling, and the expression profiles of these ‘indicator’ genes (nurse bee HPG-selective genes: mrjp2 and Ambuffy, and forager HPG-selective genes: Hbg3 and AmMMP1). Expression of both ecdysone-regulated genes (ecdysone receptor, mushroom body large type Kenyon cell specific protein-1, and E74) and JH-regulated genes (Methoprene tolerant and Krüppel homolog 1) was higher in the forager HPGs than in the nurse bee HPGs, suggesting the possible roles of ecdysone- and JH-regulated genes in worker HPGs. Furthermore, 20-hydroxyecdysone-treatment repressed both nurse bee- and forager-selective gene expression, whereas methoprene-treatment enhanced the expression of forager-selective genes and repressed nurse bee-selective genes in the HPGs. Our findings suggest that both ecdysone- and JH-signaling cooperatively regulate the physiological state of the HPGs in association with the worker’s behavior.

Effects of the juvenile hormone analogue methoprene on rate of behavioural development, foraging performance and navigation in honey bees (Apis mellifera)

Worker honey bees change roles as they age as part of a hormonally regulated process of behavioural development that ends with a specialised foraging phase. The rate of behavioural development is highly plastic and responsive to changes in colony condition such that forager losses, disease or nutritional stresses accelerate behavioural development and cause an early onset of foraging in workers. It is not clear to what degree the behavioural development of workers can be accelerated without there being a cost in terms of reduced foraging performance. Here, we compared the foraging performance of bees induced to accelerate their behavioural development by treatment with the juvenile hormone analogue methoprene with that of controls that developed at a normal rate. Methoprene treatment accelerated the onset of both flight and foraging behaviour in workers, but it also reduced foraging span, the total time spent foraging and the number of completed foraging trips. Methoprene treatment did not alter performance in a short-range navigation task, however. These data indicate a limitation to the physiological plasticity of bees, and a trade off between forager performance and the speed at which bees begin foraging. Chronic stressors will be expected to reduce the mean age of the foraging force, and therefore also reduce the efficiency of the foraging force. This interaction may explain why honey bee colonies react to sustained stressors with non-linear population decline.

Social modulation of stress reactivity and learning in young worker honey bees

Alarm pheromone and its major component isopentylacetate induce stress-like responses in forager honey bees, impairing their ability to associate odors with a food reward. We investigated whether isopentylacetate exposure decreases appetitive learning also in young worker bees. While isopentylacetate-induced learning deficits were observed in guards and foragers collected from a queen-right colony, learning impairments resulting from exposure to this pheromone could not be detected in bees cleaning cells. As cell cleaners are generally among the youngest workers in the colony, effects of isopentylacetate on learning behavior were examined further using bees of known age. Adult workers were maintained under laboratory conditions from the time of adult emergence. Fifty percent of the bees were exposed to queen mandibular pheromone during this period, whereas control bees were not exposed to this pheromone. Isopentylacetate-induced learning impairments were apparent in young (less than one week old) controls, but not in bees of the same age exposed to queen mandibular pheromone. This study reveals young worker bees can exhibit a stress-like response to alarm pheromone, but isopentylacetate-induced learning impairments in young bees are suppressed by queen mandibular pheromone. While isopentylacetate exposure reduced responses during associative learning (acquisition), it did not affect one-hour memory retrieval.

Division of labour in honey bees: age- and task-related changes in the expression of octopamine receptor genes

The honey bee (Apis mellifera L.) has developed into an important ethological model organism for social behaviour and behavioural plasticity. Bees perform a complex age-dependent division of labour with the most pronounced behavioural differences occurring between in-hive bees and foragers. Whereas nurse bees, for example, stay inside the hive and provide the larvae with food, foragers leave the hive to collect pollen and nectar for the entire colony. The biogenic amine octopamine appears to play a major role in division of labour but the molecular mechanisms involved are unknown. We here investigated the role of two characterized octopamine receptors in honey bee division of labour. AmOctαR1 codes for a Ca(2+) -linked octopamine receptor. AmOctβR3/4 codes for a cyclic adenosine monophosphate-coupled octopamine receptor. Messenger RNA expression of AmOctαR1 in different brain neuropils correlates with social task, whereas expression of AmOctβR3/4 changes with age rather than with social role per se. Our results for the first time link the regulatory role of octopamine in division of labour to specific receptors and brain regions. They are an important step forward in our understanding of complex behavioural organization in social groups.

Aversive conditioning in honey bees (Apis mellifera anatolica): a comparison of drones and workers

Honey bees provide a model system to elucidate the relationship between sociality and complex behaviors within the same species, as females (workers) are highly social and males (drones) are more solitary. We report on aversive learning studies in drone and worker honey bees (Apis mellifera anatolica) in escape, punishment and discriminative punishment situations. In all three experiments, a newly developed electric shock avoidance assay was used. The comparisons of expected and observed responses were performed with conventional statistical methods and a systematic randomization modeling approach called object oriented modeling. The escape experiment consisted of two measurements recorded in a master-yoked paradigm: frequency of response and latency to respond following administration of shock. Master individuals could terminate an unavoidable shock triggered by a decrementing 30 s timer by crossing the shuttlebox centerline following shock activation. Across all groups, there was large individual response variation. When assessing group response frequency and latency, master subjects performed better than yoked subjects for both workers and drones. In the punishment experiment, individuals were shocked upon entering the shock portion of a bilaterally wired shuttlebox. The shock portion was spatially static and unsignalled. Only workers effectively avoided the shock. The discriminative punishment experiment repeated the punishment experiment but included a counterbalanced blue and yellow background signal and the side of shock was manipulated. Drones correctly responded less than workers when shock was paired with blue. However, when shock was paired with yellow there was no observable difference between drones and workers.

Activity-dependent gene expression in honey bee mushroom bodies in response to orientation flight

The natural history of adult worker honey bees (Apis mellifera) provides an opportunity to study the molecular basis of learning in an ecological context. Foragers must learn to navigate between the hive and floral locations that may be up to miles away. Young pre-foragers prepare for this task by performing orientation flights near the hive, during which they begin to learn navigational cues such as the appearance of the hive, the position of landmarks, and the movement of the sun. Despite well-described spatial learning and navigation behavior, there is currently limited information on the neural basis of insect spatial learning. We found that Egr, an insect homolog of Egr-1, is rapidly and transiently upregulated in the mushroom bodies in response to orientation. This result is the first example of an Egr-1 homolog acting as a learning-related immediate-early gene in an insect and also demonstrates that honey bee orientation uses a molecular mechanism that is known to be involved in many other forms of learning. This transcriptional response occurred both in naïve bees and in foragers induced to re-orient. Further experiments suggest that visual environmental novelty, rather than exercise or memorization of specific visual cues, acts as the stimulus for Egr upregulation. Our results implicate the mushroom bodies in spatial learning and emphasize the deep conservation of Egr-related pathways in experience-dependent plasticity.