The hive bee to forager transition in honeybee colonies: the double repressor hypothesis

Immune-related gene expression in nurse honey bees (Apis mellifera) exposed to synthetic acaricides

The mite Varroa destructor is an ectoparasite affecting honey bees worldwide. Synthetic acaricides have been among the principal tools available to beekeepers for its control, although several studies have shown its negative effects on honey bee physiology. Recent research suggests that those molecules strongly impact on immune signaling cascades and cellular immunity. In the present work, LC(50) in six-day-old bees were determined for the following acaricides: tau-fluvalinate, flumethrin, amitraz and coumaphos. According to this obtained value, a group of individuals was treated with each acaricide and then processed for qPCR analysis. Transcript levels for genes encoding antimicrobial peptides and immune-related proteins were assessed. Flumethrin increased the expression of hymenoptaecin when comparing treated and control bees. Significant differences were recorded between coumaphos and flumethrin treatments, while the first one reduced the expression of hymenoptaecin and abaecin, the last one up-regulated their expressions. No significant statistically changes were recorded in the expression levels of vitellogenin, lysozyme or glucose dehydrogenase among bees treated with acaricides and control bees. This work constitutes the first report, under laboratory conditions, about induction of immune related genes in response to synthetic miticides.

Experience, corpulence and decision making in ant foraging

Social groups are structured by the decisions of their members. Social insects typically divide labour: some decide to stay in the nest while others forage for the colony. Two sources of information individuals may use when deciding whether to forage are their own experience of recent task performance and their own physiology, e.g. fat reserves (corpulence). The former is primarily personal information; the latter may give an indication of the food reserves of the whole colony. These factors are hard to separate because typically leaner individuals are also more experienced foragers. We designed an experiment to determine whether foraging specialisation is physiological or experience based (or both). We invented a system of automatic doors controlled by radio-tag information to manipulate task access and decouple these two sources of information. Our results show that when information from corpulence and recent experience conflict, ants behave only in accordance with their corpulence. However, among ants physiologically inclined to forage (less corpulent ants), recent experience of success positively influenced their propensity to forage again. Hence, foraging is organised via long-term physiological differences among individuals resulting in a relatively stable response threshold distribution, with fine-tuning provided by short-term learning processes. Through these simple rules, colonies can organise their foraging effort both robustly and flexibly.

Understanding the relationship between brain gene expression and social behavior: lessons from the honey bee

Behavior is a complex phenotype that is plastic and evolutionarily labile. The advent of genomics has revolutionized the field of behavioral genetics by providing tools to quantify the dynamic nature of brain gene expression in relation to behavioral output. The honey bee Apis mellifera provides an excellent platform for investigating the relationship between brain gene expression and behavior given both the remarkable behavioral repertoire expressed by members of its intricate society and the degree to which behavior is influenced by heredity and the social environment. Here, we review a linked series of studies that assayed changes in honey bee brain transcriptomes associated with natural and experimentally induced changes in behavioral state. These experiments demonstrate that brain gene expression is closely linked with behavior, that changes in brain gene expression mediate changes in behavior, and that the association between specific genes and behavior exists over multiple timescales, from physiological to evolutionary.

Transcriptome comparison between honey bee queen- and worker-destined larvae

Caste differentiation in the female honey bee is one of the most intriguing polyphenism phenomena. This developmental switch depends on the differential expression of entire suites of the genes involved in the larval fate between the queens and workers. In this study, we compared the transcriptome differences between full-sister queen- (QL) and worker-destined larvae (WL) using high-throughput RNA-Seq. QL and WL at fourth (L4) and fifth instar (L5) were used to prepare four libraries and to generate 50,191,699 (QL4), 57,628,541 (WL4), 56,613,619 (QL5), and 58,626,829 (WL5) usable reads, which were assembled into groups of 7,952, 7,993, 7,971, and 8,023 genes, respectively. The transcriptome changes were investigated using the DEGs Package (DEGseq), which resulted in more than 4,500 differentially expressed genes (DEGs) between the castes. Eight of the DEGs were verified by quantitative real-time RT-PCR (qRT-PCR), and the results supported our sequencing data. All of the DEGs were analysed using Web Gene Ontology Annotation Plot (WEGO) and then mapped using the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. These results suggest that over 70% of the DEGs in each instar were more highly expressed in QL than in WL, possibly suggesting that the QL genes had higher transcriptional activity than the WL genes during differentiation. The same gene set is active (but differentially expressed) in both castes, which in turn result in dimorphic females. The L4 stage is a very active gene expression period for both QL and WL before their pupal stage. The activity of the mTOR (a target of rapamycin) encoding gene in the mTOR signalling pathway is higher in QL4 than in WL4, and this difference was no longer present by the L5 feeding stage. The genes down-stream of mTOR maintained this change at the L5 stage. These results could contribute to an in-depth study of the candidate genes during honey bee caste differentiation and improve our current understanding of the polyphenism phenomenon in insects.

Genetics of reproduction and regulation of honeybee (Apis mellifera L.) social behavior

Honeybees form complex societies with a division of labor for reproduction, nutrition, nest construction and maintenance, and defense. How does it evolve? Tasks performed by worker honeybees are distributed in time and space. There is no central control over behavior and there is no central genome on which selection can act and effect adaptive change. For 22 years, we have been addressing these questions by selecting on a single social trait associated with nutrition: the amount of surplus pollen (a source of protein) that is stored in the combs of the nest. Forty-two generations of selection have revealed changes at biological levels extending from the society down to the level of the gene. We show how we constructed this vertical understanding of social evolution using behavioral and anatomical analyses, physiology, genetic mapping, and gene knockdowns. We map out the phenotypic and genetic architectures of food storage and foraging behavior and show how they are linked through broad epistasis and pleiotropy affecting a reproductive regulatory network that influences foraging behavior. This is remarkable because worker honeybees have reduced reproductive organs and are normally sterile; however, the reproductive regulatory network has been co-opted for behavioral division of labor.

A vitellogenin polyserine cleavage site: highly disordered conformation protected from proteolysis by phosphorylation

Vitellogenin (Vg) is an egg-yolk precursor protein in most oviparous species. In honeybee (Apis mellifera), the protein (AmVg) also affects social behavior and life-span plasticity. Despite its manifold functions, the AmVg molecule remains poorly understood. The subject of our structure-oriented AmVg study is its polyserine tract - a little-investigated repetitive protein segment mostly found in insects. We previously reported that AmVg is tissue specifically cleaved in the vicinity of this tract. Here, we show that, despite its potential for an open, disordered structure, AmVg is unexpectedly resistant to trypsin/chymotrypsin digestion at the tract. Our findings suggest that multiple phosphorylation plays a role in this resilience. Sequence variation is highly pronounced at the polyserine region in insect Vgs. We demonstrate that sequence differences in this region can lead to structural variation, as NMR and circular dichroism (CD) evidence assign different conformational propensities to polyserine peptides from the honeybee and the jewel wasp Nasonia vitripennis; the former is extended and disordered and the latter more compact and helical. CD analysis of the polyserine region of bumblebee Bombus ignitus and wasp Pimpla nipponica supports a random coil structure in these species. The spectroscopic results strengthen our model of the AmVg polyserine tract as a flexible domain linker shielded by phosphorylation.

Gustatory perception and fat body energy metabolism are jointly affected by vitellogenin and juvenile hormone in honey bees

Honey bees (Apis mellifera) provide a system for studying social and food-related behavior. A caste of workers performs age-related tasks: young bees (nurses) usually feed the brood and other adult bees inside the nest, while older bees (foragers) forage outside for pollen, a protein/lipid source, or nectar, a carbohydrate source. The workers' transition from nursing to foraging and their foraging preferences correlate with differences in gustatory perception, metabolic gene expression, and endocrine physiology including the endocrine factors vitellogenin (Vg) and juvenile hormone (JH). However, the understanding of connections among social behavior, energy metabolism, and endocrine factors is incomplete. We used RNA interference (RNAi) to perturb the gene network of Vg and JH to learn more about these connections through effects on gustation, gene transcripts, and physiology. The RNAi perturbation was achieved by single and double knockdown of the genes ultraspiracle (usp) and vg, which encode a putative JH receptor and Vg, respectively. The double knockdown enhanced gustatory perception and elevated hemolymph glucose, trehalose, and JH. We also observed transcriptional responses in insulin like peptide 1 (ilp1), the adipokinetic hormone receptor (AKHR), and cGMP-dependent protein kinase (PKG, or "foraging gene" Amfor). Our study demonstrates that the Vg-JH regulatory module controls changes in carbohydrate metabolism, but not lipid metabolism, when worker bees shift from nursing to foraging. The module is also placed upstream of ilp1, AKHR, and PKG for the first time. As insulin, adipokinetic hormone (AKH), and PKG pathways influence metabolism and gustation in many animals, we propose that honey bees have conserved pathways in carbohydrate metabolism and conserved connections between energy metabolism and gustatory perception. Thus, perhaps the bee can make general contributions to the understanding of food-related behavior and metabolic disorders.

Worker division of labor and endocrine physiology are associated in the harvester ant, Pogonomyrmex californicus

In Pogonomyrmex californicus harvester ants, an age-associated division of labor occurs in the worker caste, in which young workers perform in-nest tasks and older workers forage for food. Here, we tested whether this behavioral division is age based or age flexible, and whether it coincides with differential expression of systemic hormones with known roles in behavioral regulation. Whole-body content of juvenile hormone (JH) and ecdysteroids was determined in workers from (1) age-typical colonies, in which a typical age structure is maintained and workers transition across behaviors naturally, and (2) single-cohort colonies, which are entirely composed of same-aged workers, facilitating the establishment of age-independent division of labor. Foragers from both colony types had higher JH and lower ecdysteroid content than workers performing in-nest tasks, suggesting that age is not the sole determinant of worker behavior. This association between hormone content and behavior of P. californicus workers is similar to that previously observed in founding queens of this species. Because these hormones are key regulators of development and reproductive behavior, our data are consistent with the reproductive ground plan hypothesis (RGPH), which posits that the reproductive regulatory mechanisms of solitary ancestors were co-opted to regulate worker behavior.

Genes associated with honey bee behavioral maturation affect clock-dependent and -independent aspects of daily rhythmic activity in fruit flies

Background

In the honey bee, the age-related and socially regulated transition of workers from in-hive task performance (e.g., caring for young) to foraging (provisioning the hive) is associated with changes in many behaviors including the 24-hour pattern of rhythmic activity. We have previously shown that the hive-bee to forager transition is associated with extensive changes in brain gene expression. In this study, we test the possible function of a subset of these genes in daily rhythmic activity pattern using neural-targeted RNA interference (RNAi) of an orthologous gene set in Drosophila melanogaster.

Principal Findings

Of 10 genes tested, knockdown of six affected some aspect of locomotor activity under a 12 h∶12 h light:dark regime (LD). Inos affected anticipatory activity preceding lights-off, suggesting a possible clock-dependent function. BM-40-SPARC, U2af50 and fax affected peak activity at dawn without affecting anticipation or overall inactivity (proportion of 15-min intervals without activity), suggesting that these effects may depend on the day-night light cycle. CAH1 affected overall inactivity. The remaining gene, abl, affected peak activity levels but was not clearly time-of-day-specific. No gene tested affected length of period or strength of rhythmicity in constant dark (DD), suggesting that these genes do not act in the core clock.

Significance

Taking advantage of Drosophila molecular genetic tools, our study provides an important step in understanding the large set of gene expression changes that occur in the honey bee transition from hive bee to forager. We show that orthologs of many of these genes influence locomotor activity in Drosophila, possibly through both clock-dependent and -independent pathways. Our results support the importance of both circadian clock and direct environmental stimuli (apart from entrainment) in shaping the bee’s 24-hour pattern of activity. Our study also outlines a new approach to dissecting complex behavior in a social animal.

Physiological variation as a mechanism for developmental caste-biasing in a facultatively eusocial sweat bee

Social castes of eusocial insects may have arisen through an evolutionary modification of an ancestral reproductive ground plan, such that some adults emerge from development physiologically primed to specialize on reproduction (queens) and others on maternal care expressed as allo-maternal behaviour (workers). This hypothesis predicts that variation in reproductive physiology should emerge from ontogeny and underlie division of labour. To test these predictions, we identified physiological links to division of labour in a facultatively eusocial sweat bee, Megalopta genalis. Queens are larger, have larger ovaries and have higher vitellogenin titres than workers. We then compared queens and workers with their solitary counterparts-solitary reproductive females and dispersing nest foundresses-to investigate physiological variation as a factor in caste evolution. Within dyads, body size and ovary development were the best predictors of behavioural class. Queens and dispersers are larger, with larger ovaries than their solitary counterparts. Finally, we raised bees in social isolation to investigate the influence of ontogeny on physiological variation. Body size and ovary development among isolated females were highly variable, and linked to differences in vitellogenin titres. As these are key physiological predictors of social caste, our results provide evidence for developmental caste-biasing in a facultatively eusocial bee.

Mechanisms of stable lipid loss in a social insect

Worker honey bees undergo a socially regulated, highly stable lipid loss as part of their behavioral maturation. We used large-scale transcriptomic and proteomic experiments, physiological experiments and RNA interference to explore the mechanistic basis for this lipid loss. Lipid loss was associated with thousands of gene expression changes in abdominal fat bodies. Many of these genes were also regulated in young bees by nutrition during an initial period of lipid gain. Surprisingly, in older bees, which is when maximum lipid loss occurs, diet played less of a role in regulating fat body gene expression for components of evolutionarily conserved nutrition-related endocrine systems involving insulin and juvenile hormone signaling. By contrast, fat body gene expression in older bees was regulated more strongly by evolutionarily novel regulatory factors, queen mandibular pheromone (a honey bee-specific social signal) and vitellogenin (a conserved yolk protein that has evolved novel, maturation-related functions in the bee), independent of nutrition. These results demonstrate that conserved molecular pathways can be manipulated to achieve stable lipid loss through evolutionarily novel regulatory processes.

Nosema spp. parasitization decreases the effectiveness of acaricide strips (Apivar(®) ) in treating varroosis of honey bee (Apis mellifera iberiensis) colonies

Given the key role played by honey bees in almost all terrestrial ecosystems, maintaining bee populations in adequate sanitary conditions is crucial for these essential pollinators to continue their work. From the beginning of the 21st century, beekeepers have reported a progressive increase in the overwintering mortality of honey bee colonies worldwide. Despite the failure to reach a consensus regarding the cause of this phenomenon, pathogens are thought to be strongly implicated. In the present work, we provide evidence of the negative effects of colony parasitization by Nosema spp. - primarily by N. ceranae- on the effectiveness of acaricide strips to treat Varroa destructor. The effectiveness of the Varroa mite strip treatment (Apivar(®) ) was greater in colonies in which Nosema spp. parasitization had been controlled. Several studies report that infection by Nosema spp. may affect the behaviour of worker bees. As the effectiveness of Varroa strip treatment depends on bees contacting the strips and their subsequent interaction within the colony, such behavioural and social alterations could interfere with the treatment and allow more severe effects to develop in the colonies infected by Nosema. These results should be considered when assessing acaricide treatments in field conditions due to the high prevalence of both pathogens worldwide.

Regulation of behaviorally associated gene networks in worker honey bee ovaries

Several lines of evidence support genetic links between ovary size and division of labor in worker honey bees. However, it is largely unknown how ovaries influence behavior. To address this question, we first performed transcriptional profiling on worker ovaries from two genotypes that differ in social behavior and ovary size. Then, we contrasted the differentially expressed ovarian genes with six sets of available brain transcriptomes. Finally, we probed behavior-related candidate gene networks in wild-type ovaries of different sizes. We found differential expression in 2151 ovarian transcripts in these artificially selected honey bee strains, corresponding to approximately 20.3% of the predicted gene set of honey bees. Differences in gene expression overlapped significantly with changes in the brain transcriptomes. Differentially expressed genes were associated with neural signal transmission (tyramine receptor, TYR) and ecdysteroid signaling; two independently tested nuclear hormone receptors (HR46 and ftz-f1) were also significantly correlated with ovary size in wild-type bees. We suggest that the correspondence between ovary and brain transcriptomes identified here indicates systemic regulatory networks among hormones (juvenile hormone and ecdysteroids), pheromones (queen mandibular pheromone), reproductive organs and nervous tissues in worker honey bees. Furthermore, robust correlations between ovary size and neuraland endocrine response genes are consistent with the hypothesized roles of the ovaries in honey bee behavioral regulation.

The effect of induced queen replacement on Nosema spp. infection in honey bee (Apis mellifera iberiensis) colonies

Microsporidiosis of adult honeybees caused by Nosema apis and Nosema ceranae is a common worldwide disease with negative impacts on colony strength and productivity. Few options are available to control the disease at present. The role of the queen in bee population renewal and the replacement of bee losses due to Nosema infection is vital to maintain colony homeostasis. Younger queens have a greater egg laying potential and they produce a greater proportion of uninfected newly eclosed bees to compensate for adult bee losses; hence, a field study was performed to determine the effect of induced queen replacement on Nosema infection in honey bee colonies, focusing on colony strength and honey production. In addition, the impact of long-term Nosema infection of a colony on the ovaries and ventriculus of the queen was evaluated. Queen replacement resulted in a remarkable decrease in the rates of Nosema infection, comparable with that induced by fumagillin treatment. However, detrimental effects on the overall colony state were observed due to the combined effects of stressors such as the queenless condition, lack of brood and high infection rates. The ovaries and ventriculi of queens in infected colonies revealed no signs of Nosema infection and there were no lesions in ovarioles or epithelial ventricular cells.

Comparison of within hive sampling and seasonal activity of Nosema ceranae in honey bee colonies

Nosema ceranae is a microsporidian parasite of the European honey bee, Apis mellifera, that is found worldwide and in multiple Apis spp.; however, little is known about the effects of N. ceranae on A. mellifera. Previous studies using spore counts suggest that there is no longer a seasonal cycle for N. ceranae and that it is found year round with little variation in infection intensity among months. Our goal was to determine whether infection levels differ in bees collected from different areas of the hive and if there may be seasonal differences in N. ceranae infections. A multiplex species-specific real-time PCR assay was used for the detection and quantification of N. ceranae. Colonies were sampled monthly from September 2009-2010 by collecting workers from honey supers, the fringe of the brood nest, and the brood nest. We found that all bees sampled were infected with N. ceranae and that there was no significant difference in infection levels among the different groups of bees sampled (P=0.74). However, significant differences in colony infection levels were found at different times of the year (P<0.01) with the highest levels in April-June and lower levels in the fall and winter. While our study was only performed for one year, it sheds light on the fact that there may be a seasonality to N. ceranae infections. Being able to predict future N. ceranae infections can be used to better advise beekeepers on N. ceranae management.

The worker honeybee fat body proteome is extensively remodeled preceding a major life-history transition

Honeybee workers are essentially sterile female helpers that make up the majority of individuals in a colony. Workers display a marked change in physiology when they transition from in-nest tasks to foraging. Recent technological advances have made it possible to unravel the metabolic modifications associated with this transition. Previous studies have revealed extensive remodeling of brain, thorax, and hypopharyngeal gland biochemistry. However, data on changes in the abdomen is scarce. To narrow this gap we investigated the proteomic composition of abdominal tissue in the days typically preceding the onset of foraging in honeybee workers.

In order to get a broader representation of possible protein dynamics, we used workers of two genotypes with differences in the age at which they initiate foraging. This approach was combined with RNA interference-mediated downregulation of an insulin/insulin-like signaling component that is central to foraging behavior, the insulin receptor substrate (irs), and with measurements of glucose and lipid levels.

Our data provide new insight into the molecular underpinnings of phenotypic plasticity in the honeybee, invoke parallels with vertebrate metabolism, and support an integrated and irs-dependent association of carbohydrate and lipid metabolism with the transition from in-nest tasks to foraging.

Honey bee PTEN--description, developmental knockdown, and tissue-specific expression of splice-variants correlated with alternative social phenotypes

Background

Phosphatase and TENsin (PTEN) homolog is a negative regulator that takes part in IIS (insulin/insulin-like signaling) and Egfr (epidermal growth factor receptor) activation in Drosophila melanogaster. IIS and Egfr signaling events are also involved in the developmental process of queen and worker differentiation in honey bees (Apis mellifera). Here, we characterized the bee PTEN gene homologue for the first time and begin to explore its potential function during bee development and adult life.

Results

Honey bee PTEN is alternatively spliced, resulting in three splice variants. Next, we show that the expression of PTEN can be down-regulated by RNA interference (RNAi) in the larval stage, when female caste fate is determined. Relative to controls, we observed that RNAi efficacy is dependent on the amount of PTEN dsRNA that is delivered to larvae. For larvae fed queen or worker diets containing a high amount of PTEN dsRNA, PTEN knockdown was significant at a whole-body level but lethal. A lower dosage did not result in a significant gene down-regulation. Finally, we compared same-aged adult workers with different behavior: nursing vs. foraging. We show that between nurses and foragers, PTEN isoforms were differentially expressed within brain, ovary and fat body tissues. All isoforms were expressed at higher levels in the brain and ovaries of the foragers. In fat body, isoform B was expressed at higher level in the nurse bees.

Conclusion

Our results suggest that PTEN plays a central role during growth and development in queen- and worker-destined honey bees. In adult workers, moreover, tissue-specific patterns of PTEN isoform expression are correlated with differences in complex division of labor between same-aged individuals. Therefore, we propose that knowledge on the roles of IIS and Egfr activity in developmental and behavioral control may increase through studies of how PTEN functions can impact bee social phenotypes.

Insulin-like peptide genes in honey bee fat body respond differently to manipulation of social behavioral physiology

Nutrient sensitive insulin-like peptides (ILPs) have profound effects on invertebrate metabolism, nutrient storage, fertility and aging. Many insects transcribe ILPs in specialized neurosecretory cells at changing levels correlated with life history. However, the major site of insect metabolism and nutrient storage is not the brain, but rather the fat body, where functions of ILP expression are rarely studied and poorly understood. Fat body is analogous to mammalian liver and adipose tissue, with nutrient stores that often correlate with behavior. We used the honey bee (Apis mellifera), an insect with complex behavior, to test whether ILP genes in fat body respond to experimentally induced changes of behavioral physiology. Honey bee fat body influences endocrine state and behavior by secreting the yolk protein precursor vitellogenin (Vg), which suppresses lipophilic juvenile hormone and social foraging behavior. In a two-factorial experiment, we used RNA interference (RNAi)-mediated vg gene knockdown and amino acid nutrient enrichment of hemolymph (blood) to perturb this regulatory module. We document factor-specific changes in fat body ilp1 and ilp2 mRNA, the bee's ILP-encoding genes, and confirm that our protocol affects social behavior. We show that ilp1 and ilp2 are regulated independently and differently and diverge in their specific expression-localization between fat body oenocyte and trophocyte cells. Insect ilp functions may be better understood by broadening research to account for expression in fat body and not only brain.

Social context, stress, and plasticity of aging

Positive social contact is an important factor in healthy aging, but our understanding of how social interactions influence senescence is incomplete. As life expectancy continues to increase because of reduced death rates among elderly, the beneficial role of social relationships is emerging as a cross-cutting theme in research on aging and healthspan. There is a need to improve knowledge on how behavior shapes, and is shaped by, the social environment, as well as needs to identify and study biological mechanisms that can translate differences in the social aspects of behavioral efforts, relationships, and stress reactivity (the general physiological and behavioral response-pattern to harmful, dangerous or unpleasant situations) into variation in aging. Honey bees (Apis mellifera) provide a genetic model in sociobiology, behavioral neuroscience, and gerontology that is uniquely sensitive to social exchange. Different behavioral contact between these social insects can shorten or extend lifespan more than 10-fold, and some aspects of their senescence are reversed by social cues that trigger aged individuals to express youthful repertoires of behavior. Here, I summarize how variation in social interactions contributes to this plasticity of aging and explain how beneficial and detrimental roles of social relationships can be traced from environmental and biological effects on honey bee physiology and behavior, to the expression of recovery-related plasticity, stress reactivity, and survival during old age. This system provides intriguing opportunities for research on aging.

Nutritional regulation of division of labor in honey bees: toward a systems biology perspective

Organisms adapt their behavior and physiology to environmental conditions through processes of phenotypic plasticity. In one well-studied example, the division of labor among worker honey bees involves a stereotyped yet plastic pattern of behavioral and physiological maturation. Early in life, workers perform brood care and other in-hive tasks and have large internal nutrient stores; later in life, they forage for nectar and pollen outside the hive and have small nutrient stores. The pace of maturation depends on colony conditions, and the environmental, physiological, and genomic mechanisms by which this occurs are being actively investigated. Here we review current knowledge of the mechanisms by which a key environmental variable, nutritional status, influences worker honey bee division of labor. These studies demonstrate that changes in individual nutritional status and conserved food-related molecular and hormonal pathways regulate the age at which individual bees begin to forage. We then outline ways in which systems biology approaches, enabled by the sequencing of the honey bee genome, will allow researchers to gain deeper insight into nutritional regulation of honey bee behavior, and phenotypic plasticity in general.

Comparative endocrinology of aging and longevity regulation

Hormones regulate growth, development, metabolism, and other complex processes in multicellular animals. For many years it has been suggested that hormones may also influence the rate of the aging process. Aging is a multifactorial process that causes biological systems to break down and cease to function in adult organisms as time passes, eventually leading to death. The exact underlying causes of the aging process remain a topic for debate, and clues that may shed light on these causes are eagerly sought after. In the last two decades, gene mutations that result in delayed aging and extended longevity have been discovered, and many of the affected genes have been components of endocrine signaling pathways. In this review we summarize the current knowledge on the roles of endocrine signaling in the regulation of aging and longevity in various animals. We begin by discussing the notion that conserved systems, including endocrine signaling pathways, "regulate" the aging process. Findings from the major model organisms: worms, flies, and rodents, are then outlined. Unique lessons from studies of non-traditional models: bees, salmon, and naked mole rats, are also discussed. Finally, we summarize the endocrinology of aging in humans, including changes in hormone levels with age, and the involvement of hormones in aging-related diseases. The most well studied and widely conserved endocrine pathway that affects aging is the insulin/insulin-like growth factor system. Mutations in genes of this pathway increase the lifespan of worms, flies, and mice. Population genetic evidence also suggests this pathway's involvement in human aging. Other hormones including steroids have been linked to aging only in a subset of the models studied. Because of the value of comparative studies, it is suggested that the aging field could benefit from adoption of additional model organisms.

Surgically increased ovarian mass in the honey bee confirms link between reproductive physiology and worker behavior

Honey bee (Apis mellifera L.) workers are essentially sterile females that are used to study how complex social behavior develops. Workers perform nest tasks, like nursing larvae, prior to field tasks, like foraging. Despite worker sterility, this behavioral progression correlates with ovary size: workers with larger ovaries (many ovary filaments) start foraging at younger ages on average. It is untested, however, whether the correlation confers a causal relationship between ovary size and behavioral development. Here, we successfully grafted supernumerary ovaries into worker bees to produce an artificial increase in the amount of ovary tissue. We next measured fat body mRNA levels for the yolk precursor gene vitellogenin, which influences honey bee behavioral development and can correlate with ovary size. Vitellogenin was equally expressed in surgical controls and bees with supernumerary ovaries, leading us to predict that these groups would be characterized by equal behavior. Contrary to our prediction, bees with supernumerary ovaries showed accelerated behavioral development compared to surgical controls, which behaved like reference bees that were not treated surgically. To explore this result we monitored fat body expression levels of a putative ecdysteroid-response gene, HR46, which is genetically linked to ovary size in workers. Our data establish that social insect worker behavior can be directly influenced by ovaries, and that HR46 expression changes with ovary size independent of vitellogenin.

Mars is close to venus--female reproductive proteins are expressed in the fat body and reproductive tract of honey bee (Apis mellifera L.) drones

Vitellogenin (Vg) and lipophorin (Lp) are lipoproteins which play important roles in female reproductive physiology of insects. Both are actively taken up by growing oocytes and especially Vg and its receptor are considered as female-specifically expressed. The finding that the fat body of in honey bee (Apis mellifera) drones synthesizes Vg and is present in hemolymph has long been viewed as a curiosity. The recent paradigm change concerning the role played by Vg in honey bee life history, especially social division of labor, has now led us to investigate whether a physiological constellation similar to that seen in female reproduction may also be represented in the male sex. By means of Western blot analysis we could show that both Vg and Lp are present in the reproductive tract of adult drones, including the accessory (mucus) glands, but apparently are not secreted. Furthermore, we analyzed the transcript levels of the genes encoding these proteins (vg and lp), as well as their putative receptors (Amvgr and Amlpr) in fat body and accessory glands. Whereas lp, vg and Amlpr transcript levels decreased with age in both tissues, Amvgr mRNA levels increased with age in fat body. To our knowledge this is the first report that vitellogenin and its receptor are co-expressed in the reproductive system of a male insect. We interpret these findings as a cross-sexual transfer of a social physiological trait, associated with the rewiring of the juvenile hormone/vitellogenin circuitry that occurred in the female sex of honey bees.

Genotype effect on regulation of behaviour by vitellogenin supports reproductive origin of honeybee foraging bias

In honeybee colonies, food collection is performed by a group of mostly sterile females called workers. After an initial nest phase, workers begin foraging for nectar and pollen, but tend to bias their collection towards one or the other. The foraging choice of honeybees is influenced by vitellogenin (vg), an egg-yolk precursor protein that is expressed although workers typically do not lay eggs. The forager reproductive ground plan hypothesis (RGPH) proposes an evolutionary path in which the behavioural bias toward collecting nectar or pollen on foraging trips is influenced by variation in reproductive physiology, such as hormone levels and vg gene expression. Recently, the connections between vg and foraging behaviour were challenged by Oldroyd and Beekman (2008), who concluded from their study that the ovary, and especially vg, played no role in foraging behaviour of bees. We address their challenge directly by manipulating vg expression by RNA interference- (RNAi) mediated gene knockdown in two honeybee genotypes with different foraging behaviour and reproductive physiology. We show that the effect of vg on the food-loading decisions of the workers occurs only in the genotype where timing of foraging onset (by age) is also sensitive to vg levels. In the second genotype, changing vg levels do not affect foraging onset or bias. The effect of vg on workers' age at foraging onset is explained by the well-supported double repressor hypothesis (DHR), which describes a mutually inhibitory relationship between vg and juvenile hormone (JH) - an endocrine factor that influences development, reproduction, and behaviour in many insects. These results support the RGPH and demonstrate how it intersects with an established mechanism of honeybee behavioural control.

The developmental genetics and physiology of honeybee societies

Eusocial animal societies, as diverse as those found in the ants, bees, wasps, shrimp and naked mole-rats, are structured around one or few reproductive females. The remaining females are helpers called 'workers' that are mostly sterile. A paradigm in studies of eusociality is that worker sterility is a key to societal functions because advanced sociality cannot be achieved when there is conflict over reproduction. Yet, traits such as sensory responsiveness, foraging and hoarding behaviour that change between female reproductive life stages also vary between workers. This variation is central to worker division of labour, a complex social trait believed to be instrumental for the ecological success of animal societies. Thus, we took a step back from established views on worker sterility and societal functions, and hypothesized that division of labour can be better understood if adaptive variation in worker behaviour is seen as emerging from pre-existing mechanisms associated with female reproduction. In exploring this reproductive ground plan hypothesis (RGPH) in honeybee workers, we established that variation in foraging division of labour correlates with ovary size and is affected by expression changes in vitellogenin, an egg yolk protein precursor. Here, we explain and reconcile the RGPH with data on honeybee sensory sensitivity, genomic mapping, transcript and endocrine profiling, and link our discussion with Ihle et al. (2010, this issue, pp. xx-xx). The findings bring together mechanistic and evolutionary explanations of honeybee worker behaviour. This essay suggests that a broader view on worker reproductive traits can increase the understanding of animal social behaviour.

The curious case of aging plasticity in honey bees

As in all advanced insect societies, colony-organization in honey bees emerges through a structured division of labor between essentially sterile helpers called workers. Worker bees are sisters that conduct all social tasks except for egg-laying, for example nursing brood and foraging for food. Curiously, aging progresses slowly in workers that engage in nursing and even slower when bees postpone nursing during unfavorable periods. We, therefore, seek to understand how senescence can emerge as a function of social task performance. The alternative utilization of a common yolk precursor protein (vitellogenin) in nursing and somatic maintenance can link behavior and aging plasticity in worker bees. Beneficial effects of vitellogenin may also be mediated by inhibitory action on juvenile hormone and insulin-like signaling.

Division of labor in honeybees: form, function, and proximate mechanisms

Honeybees exhibit two patterns of organization of work. In the spring and summer, division of labor is used to maximize growth rate and resource accumulation, while during the winter, worker survivorship through the poor season is paramount, and bees become generalists. This work proposes new organismal and proximate level conceptual models for these phenomena. The first half of the paper presents a push–pull model for temporal polyethism. Members of the nursing caste are proposed to be pushed from their caste by the development of workers behind them in the temporal caste sequence, while middle-aged bees are pulled from their caste via interactions with the caste ahead of them. The model is, hence, an amalgamation of previous models, in particular, the social inhibition and foraging for work models. The second half of the paper presents a model for the proximate basis of temporal polyethism. Temporal castes exhibit specialized physiology and switch caste when it is adaptive at the colony level. The model proposes that caste-specific physiology is dependent on mutually reinforcing positive feedback mechanisms that lock a bee into a particular behavioral phase. Releasing mechanisms that relate colony level information are then hypothesized to disrupt particular components of the priming mechanisms to trigger endocrinological cascades that lead to the next temporal caste. Priming and releasing mechanisms for the nursing caste are mapped out that are consistent with current experimental results. Less information-rich, but plausible, mechanisms for the middle-aged and foraging castes are also presented.

PDK1 and HR46 gene homologs tie social behavior to ovary signals

The genetic basis of division of labor in social insects is a central question in evolutionary and behavioral biology. The honey bee is a model for studying evolutionary behavioral genetics because of its well characterized age-correlated division of labor. After an initial period of within-nest tasks, 2–3 week-old worker bees begin foraging outside the nest. Individuals often specialize by biasing their foraging efforts toward collecting pollen or nectar. Efforts to explain the origins of foraging specialization suggest that division of labor between nectar and pollen foraging specialists is influenced by genes with effects on reproductive physiology. Quantitative trait loci (QTL) mapping of foraging behavior also reveals candidate genes for reproductive traits. Here, we address the linkage of reproductive anatomy to behavior, using backcross QTL analysis, behavioral and anatomical phenotyping, candidate gene expression studies, and backcross confirmation of gene-to-anatomical trait associations. Our data show for the first time that the activity of two positional candidate genes for behavior, PDK1 and HR46, have direct genetic relationships to ovary size, a central reproductive trait that correlates with the nectar and pollen foraging bias of workers. These findings implicate two genes that were not known previously to influence complex social behavior. Also, they outline how selection may have acted on gene networks that affect reproductive resource allocation and behavior to facilitate the evolution of social foraging in honey bees.

Insect vitellogenin/lipophorin receptors: molecular structures, role in oogenesis, and regulatory mechanisms

Insect vitellogenin and lipophorin receptors (VgRs/LpRs) belong to the low-density lipoprotein receptor (LDLR) gene superfamily and play a critical role in oocyte development by mediating endocytosis of the major yolk protein precursors Vg and Lp, respectively. Precursor Vg and Lp are synthesized, in the majority of insects, extraovarially in the fat body and are internalized by competent oocytes through membrane-bound receptors (i.e., VgRs and LpRs, respectively). Structural analysis reveals that insect VgRs/LpRs and all other LDLR family receptors share a group of five structural domains: clusters of cysteine-rich repeats constituting the ligand-binding domain (LBD), epidermal growth factor (EGF)-precursor homology domain that mediates the acid-dependent dissociation of ligands, an O-linked sugar domain of unknown function, a transmembrane domain anchoring the receptor in the plasma membrane, and a cytoplasmic domain that mediates the clustering of the receptor into the coated pits. The sequence analysis indicates that insect VgRs harbor two LBDs with five repeats in the first and eight repeats in the second domain as compared to LpRs which have a single 8-repeat LBD. Moreover, the cytoplasmic domain of all insect VgRs contains a LI internalization signal instead of the NPXY motif found in LpRs and in the majority of other LDLR family receptors. The exception is that of Solenopsis invicta VgR, which also contains an NPXY motif in addition to LI signal. Cockroach VgRs still harbor another motif, NPTF, which is also believed to be a functional internalization signal. The expression studies clearly demonstrate that insect VgRs are ovary-bound receptors of the LDLR family as compared to LpRs, which are transcribed in a wide range of tissues including ovary, fat body, midgut, brain, testis, Malpighian tubules, and muscles. VgR/LpR mRNA and the protein were detected in the germarium, suggesting that the genes involved in receptor-endocytotic machinery are specifically expressed long before they are functionally required.

The buzz on fly neuronal remodeling

Hormone-dependent rewiring of axons and dendrites is a conserved feature of nervous system development and plasticity. During metamorphosis in insects, steroid hormones (the ecdysteroids) and terpenoid hormones (the juvenile hormones) regulate extensive remodeling of the nervous system. These changes retool the nervous system for new behavioral and physiological functions that are required for the adult stage of the life cycle. In honey bees and other highly social insects, hormones also regulate behavioral changes and neuronal plasticity associated with transitions between social caste roles. This review focuses on recent work in fruit flies and honey bees that reveals hormonal and molecular mechanisms underlying metamorphic and caste-dependent neuronal remodeling, with specific emphasis on the role of Krüppel homolog 1.

Sensory response system of social behavior tied to female reproductive traits

BACKGROUND

Honey bees display a complex set of anatomical, physiological, and behavioral traits that correlate with the colony storage of surplus pollen (pollen hoarding). We hypothesize that the association of these traits is a result of pleiotropy in a gene signaling network that was co-opted by natural selection to function in worker division of labor and foraging specialization. By acting on the gene network, selection can change a suite of traits, including stimulus/response relationships that affect individual foraging behavior and alter the colony level trait of pollen hoarding. The 'pollen-hoarding syndrome' of honey bees is the best documented syndrome of insect social organization. It can be exemplified as a link between reproductive anatomy (ovary size), physiology (yolk protein level), and foraging behavior in honey bee strains selected for pollen hoarding, a colony level trait. The syndrome gave rise to the forager-Reproductive Ground Plan Hypothesis (RGPH), which proposes that the regulatory control of foraging onset and foraging preference toward nectar or pollen was derived from a reproductive signaling network. This view was recently challenged. To resolve the controversy, we tested the associations between reproductive anatomy, physiology, and stimulus/response relationships of behavior in wild-type honey bees.

METHODOLOGY/PRINCIPAL FINDINGS

Central to the stimulus/response relationships of honey bee foraging behavior and pollen hoarding is the behavioral trait of sensory sensitivity to sucrose (an important sugar in nectar). To test the linkage of reproductive traits and sensory response systems of social behavior, we measured sucrose responsiveness with the proboscis extension response (PER) assay and quantified ovary size and vitellogenin (yolk precursor) gene expression in 6-7-day-old bees by counting ovarioles (ovary filaments) and by using semiquantitative real time RT-PCR. We show that bees with larger ovaries (more ovarioles) are characterized by higher levels of vitellogenin mRNA expression and are more responsive to sucrose solutions, a trait that is central to division of labor and foraging specialization.

CONCLUSIONS/SIGNIFICANCE

Our results establish that in wild-type honey bees, ovary size and vitellogenin mRNA level covary with the sucrose sensory response system, an important component of foraging behavior. This finding validates links between reproductive physiology and behavioral-trait associations of the pollen-hoarding syndrome of honey bees, and supports the forager-RGPH. Our data address a current evolutionary debate, and represent the first direct demonstration of the links between reproductive anatomy, physiology, and behavioral response systems that are central to the control of complex social behavior in insects.

Genetic and genomic analyses of the division of labour in insect societies

Division of labour--individuals specializing in different activities--features prominently in the spectacular success of the social insects. Until recently, genetic and genomic analyses of division of labour were limited to just a few species. However, research on an ever-increasing number of species has provided new insight, from which we highlight two results. First, heritable influences on division of labour are more pervasive than previously imagined. Second, different forms of division of labour, in lineages in which eusociality has arisen independently, have evolved through changes in the regulation of highly conserved molecular pathways associated with several basic life-history traits, including nutrition, metabolism and reproduction.

Evolution and mechanisms of long life and high fertility in queen honey bees

Honey bees (Apis mellifera) are eusocial insects that exhibit striking caste-specific differences in longevity. Queen honey bees live on average 1-2 years whereas workers live on average 15-38 days in the summer and 150-200 days in the winter. Previous studies of senescence in the honey bee have focused on establishing the importance of extrinsic mortality factors (predation, weather) and behavior (nursing and foraging) in worker bee longevity. However, few studies have tried to elucidate the mechanisms that allow queen honey bees to achieve their long lifespan without sacrificing fecundity. Here, we review both types of studies and emphasize the importance of understanding both proximate and ultimate causes of the unusual life history of honey bee queens.

Expression analysis of putative vitellogenin and lipophorin receptors in honey bee (Apis mellifera L.) queens and workers

Two members of the low density lipoprotein receptor (LDLR) family were identified as putative orthologs for a vitellogenin receptor (Amvgr) and a lipophorin receptor (Amlpr) in the Apis mellifera genome. Both receptor sequences have the structural motifs characteristic of LDLR family members and show a high degree of similarity with sequences of other insects. RT-PCR analysis of Amvgr and Amlpr expression detected the presence of both transcripts in different tissues of adult female (ovary, fat body, midgut, head and specifically hypopharyngeal gland), as well as in embryos. In the head RNA samples we found two variant forms of AmLpR: a full length one and a shorter one lacking 29 amino acids in the O-linked sugar domain. In ovaries the expression levels of the two honey bee LDLR members showed opposing trends: whereas Amvgr expression was upregulated as the ovaries became activated, Amlpr transcript levels gradually declined. In situ hybridization analysis performed on ovaries detected Amvgr mRNA exclusively in germ line cells and corroborated the qPCR results showing an increase in Amvgr gene expression concomitant with follicle growth.

RNAi-mediated silencing of vitellogenin gene function turns honeybee (Apis mellifera) workers into extremely precocious foragers

The switch from within-hive activities to foraging behavior is a major transition in the life cycle of a honeybee (Apis mellifera) worker. A prominent regulatory role in this switch has long been attributed to juvenile hormone (JH), but recent evidence also points to the yolk precursor protein vitellogenin as a major player in behavioral development. In the present study, we injected vitellogenin double-stranded RNA (dsVg) into newly emerged worker bees of Africanized genetic origin and introduced them together with controls into observation hives to record flight behavior. RNA interference-mediated silencing of vitellogenin gene function shifted the onset of long-duration flights (>10 min) to earlier in life (by 3-4 days) when compared with sham and untreated control bees. In fact, dsVg bees were observed conducting such flights extremely precociously, when only 3 days old. Short-duration flights (<10 min), which bees usually perform for orientation and cleaning, were not affected. Additionally, we found that the JH titer in dsVg bees collected after 7 days was not significantly different from the controls. The finding that depletion of the vitellogenin titer can drive young bees to become extremely precocious foragers could imply that vitellogenin is the primary switch signal. At this young age, downregulation of vitellogenin gene activity apparently had little effect on the JH titer. As this unexpected finding stands in contrast with previous results on the vitellogenin/JH interaction at a later age, when bees normally become foragers, we propose a three-step sequence in the constellation of physiological parameters underlying behavioral development.

Ageing in a eusocial insect: molecular and physiological characteristics of life span plasticity in the honey bee

Commonly held views assume that ageing, or senescence, represents an inevitable, passive, and random decline in function that is strongly linked to chronological age. In recent years, genetic intervention of life span regulating pathways, for example, in Drosophila as well as case studies in non-classical animal models, have provided compelling evidence to challenge these views.Rather than comprehensively revisiting studies on the established genetic model systems of ageing, we here focus on an alternative model organism with a wild type (unselected genotype) characterized by a unique diversity in longevity - the honey bee.Honey bee (Apis mellifera) life span varies from a few weeks to more than 2 years. This plasticity is largely controlled by environmental factors. Thereby, although individuals are closely related genetically, distinct life histories can emerge as a function of social environmental change.Another remarkable feature of the honey bee is the occurrence of reverted behavioural ontogeny in the worker (female helper) caste. This behavioural peculiarity is associated with alterations in somatic maintenance functions that are indicative of reverted senescence. Thus, although intraspecific variation in organismal life span is not uncommon, the honey bee holds great promise for gaining insights into regulatory pathways that can shape the time-course of ageing by delaying, halting or even reversing processes of senescence. These aspects provide the setting of our review.We will highlight comparative findings from Drosophila melanogaster and Caenorhabditis elegans in particular, and focus on knowledge spanning from molecular- to behavioural-senescence to elucidate how the honey bee can contribute to novel insights into regulatory mechanisms that underlie plasticity and robustness or irreversibility in ageing.

Aging and demographic plasticity in response to experimental age structures in honeybees (Apis mellifera L)

Honeybee colonies are highly integrated functional units characterized by a pronounced division of labor. Division of labor among workers is mainly age-based, with younger individuals focusing on in-hive tasks and older workers performing the more hazardous foraging activities. Thus, experimental disruption of the age composition of the worker hive population is expected to have profound consequences for colony function. Adaptive demography theory predicts that the natural hive age composition represents a colony-level adaptation and thus results in optimal hive performance. Alternatively, the hive age composition may be an epiphenomenon, resulting from individual life history optimization. We addressed these predictions by comparing individual worker longevity and brood production in hives that were composed of a single age cohort, two distinct age cohorts, and hives that had a continuous, natural age distribution. Four experimental replicates showed that colonies with a natural age composition did not consistently have a higher life expectancy and/or brood production than the single cohort or double cohort hives. Instead, a complex interplay of age structure, environmental conditions, colony size, brood production, and individual mortality emerged. A general trade-off between worker life expectancy and colony productivity was apparent, and the transition from in-hive tasks to foraging was the most significant predictor of worker lifespan irrespective of the colony age structure. We conclude that the natural age structure of honeybee hives is not a colony-level adaptation. Furthermore, our results show that honeybees exhibit pronounced demographic plasticity in addition to behavioral plasticity to react to demographic disturbances of their societies.

Aging and reproduction in social insects--a mini-review

Perennial social insects are characterized by the extraordinarily long lifespan of their reproductive females, which may be tens or hundreds of times larger than that of non-social insects of similar body size and also greatly surpasses that of conspecific non-reproductives. Evolutionary theories of aging explain this phenomenon from the low extrinsic mortality queens experience once they have successfully established their colony. The aim of our review is to summarize recent findings on the ultimate and proximate causes of increased queen longevity in social insects, in particular ants and honey bees. While progress is being made in elucidating the interrelations between the vitellogenin, juvenile hormone, fecundity, and senescence, we feel that the explanation for the comparatively short lifespan of queens in multi-queen societies is as yet not satisfactory and needs further attention, both concerning its proximate and ultimate basis.

The gene vitellogenin has multiple coordinating effects on social organization

Temporal division of labor and foraging specialization are key characteristics of honeybee social organization. Worker honeybees (Apis mellifera) initiate foraging for food around their third week of life and often specialize in collecting pollen or nectar before they die. Variation in these fundamental social traits correlates with variation in worker reproductive physiology. However, the genetic and hormonal mechanisms that mediate the control of social organization are not understood and remain a central question in social insect biology. Here we demonstrate that a yolk precursor gene, vitellogenin, affects a complex suite of social traits. Vitellogenin is a major reproductive protein in insects in general and a proposed endocrine factor in honeybees. We show by use of RNA interference (RNAi) that vitellogenin gene activity paces onset of foraging behavior, primes bees for specialized foraging tasks, and influences worker longevity. These findings support the view that the worker specializations that characterize hymenopteran sociality evolved through co-option of reproductive regulatory pathways. Further, they demonstrate for the first time how coordinated control of multiple social life-history traits can originate via the pleiotropic effects of a single gene that affects multiple physiological processes.

Animals that live in groups often specialize in different tasks, creating a division of labor. One extreme example can be seen in honeybees, in which most tasks are performed by thousands of worker females that are essentially sterile helpers. Workers start out as nurse bees that care for larvae in the nest. Later they embark on foraging trips, specializing in either pollen or nectar collection, and continue to forage until they die. The age when workers initiate foraging and the tendency to collect pollen or nectar have been linked to a rudimentary reproductive physiology in which the protein vitellogenin appears to play a central role. Vitellogenin is normally used to produce egg yolk, but it may affect behavior and lifespan in workers. We tested this hypothesis by knocking down the vitellogenin gene of worker bees. Workers with suppressed vitellogenin levels foraged earlier, preferred nectar, and lived shorter lives. Thus, vitellogenin has multiple effects on honeybee social organization. By using gene knockdown to understand insect social behavior, our study supports the view that social life in bees evolved by co-opting genes involved in reproduction.

vitellogenin gene activity paces onset of foraging behavior in worker bees, demonstrating how coordinated control of multiple social life-history traits can originate via the pleiotropic effects of a single gene.

Cognitive aging is linked to social role in honey bees (Apis mellifera)

Aging is associated with cognitive impairment in numerous animal species. Across taxa, decline in learning performance is linked to chronological age. The honey bee (Apis mellifera), in contrast, offers an opportunity to study such aspects of aging largely independent of age per se. This is because foraging onset can be decoupled from chronological age, although workers typically first perform tasks inside the nest and later forage outside the hive. Further, early phases of foraging are characterized by growth of specific brain neuropiles, whereas late phases of the forager life-stage are accompanied by accelerated rates of physiological senescence. Yet, it is unclear if these patterns of senescence include cognitive function. The flexibility of worker ontogeny, however, suggests that the bee can become an attractive model for studies of plasticity in cognitive aging that ultimately may lead to insight into mechanisms that govern age-related cognitive decline. To address this potential, we studied effects of honey bee chronological age and of social role on sensory sensitivity and associative olfactory learning performance. Our results show a decline in olfactory acquisition performance that is linked to social role, but not to chronological age. This decline occurs only in foragers with long foraging duration, but at the same time the foragers show less generalization of odors, which is indicative of more precise learning. Foragers that are reversed from foraging to nest tasks, furthermore, do not show deficits in olfactory acquisition. These results point to complex effects of aging on associative learning in honey bees.