Division Of Labor In Honey Bees Research Articles

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

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.

Effects of microRNA-305 knockdown on brain gene expression associated with division of labor in honey bee colonies (Apis mellifera).

Division of labor in honey bee colonies is based on the behavioral maturation of adult workers that involves a transition from working in the hive to foraging. This behavioral maturation is associated with distinct task-related transcriptomic profiles in the brain and abdominal fat body that are related to multiple regulatory factors including juvenile hormone (JH) and queen mandibular pheromone (QMP). A prominent physiological feature associated with behavioral maturation is a loss of abdominal lipid mass as bees transition to foraging. We used transcriptomic and physiological analyses to study whether microRNAs (miRNAs) are involved in the regulation of division of labor. We first identified two miRNAs that showed patterns of expression associated with behavioral maturation, ame-miR-305-5p and ame-miR-375-3p. We then downregulated the expression of these two miRNAs with sequence-specific antagomirs. Neither ame-miR-305-5p nor ame-miR-375-3p knockdown in the abdomen affected abdominal lipid mass on their own. Similarly, knockdown of ame-miR-305-5p in combination with JH or QMP also did not affect lipid mass. By contrast, ame-miR-305-5p knockdown in the abdomen caused substantial changes in gene expression in the brain. Brain gene expression changes included genes encoding transcription factors previously implicated in behavioral maturation. The results of these functional genomic experiments extend previous correlative associations of microRNAs with honey bee division of labor and point to specific roles for ame-miR-305-5p.

INSIGHTS OF CASTE DETERMINATIONS IN SOCIAL INSECTS

Eusocial insects display caste structures in which reproductive ability is possessed by a single or a few queens while all other colony members act as workers. In social insects like ants, bees, and termites, vital physiological processes are regulated at the colony scale. Females in social insects have at least one reproductive caste and one nonreproductive caste; many termites have at least two male castes. The castes have considerable anatomical, physiological, and behavioural differences in higher social insects. Organismal systems, such as pheromone sensing, hormone signaling, and brain signaling pathways, are deployed in novel circumstances to impact nestmate and colony behaviours due to physiological decentralization over evolutionary time. Significant morphogenesis with region-specific cellular proliferation and degradation occurs during soldier development through two moulting via a presoldier stage in termite. JH action has been developed, in which a high JH titer causes soldier differentiation and a low JH titer causes alate differentiation. A monogamous pair of primary reproductives (one king and one queen) generated from alates normally establishes termite colonies (winged adults). The nymph-alate pathway (sexual pathway) or the worker pathway differentiates larvae in Reticulitermes termites (neuter pathway). Haplo-diploid sex determination controls the first developmental transition, in which unfertilized (haploid) embryos become males and fertilized (diploid) embryos become females in the case of Cataglyphis ant genus. The queen’s mandibular gland secretion, a mix of fatty acids and aromatic chemicals, is critical for maintaining the reproductive division of labour in honeybees (Apis mellifera), suppressing ovary growth in workers. Besides this, the brood produced by the queen also inhibits ovary development in workers by emitting two pheromones: the brood pheromone (BP), mainly composed of esters, and the highly volatile E-b-ocimene.

Levels and activity of cyclic guanosine monophosphate-dependent protein kinase in nurse and forager honeybees.

Age-dependent division of labour in honeybees was shown to be connected to sensory response thresholds. Foragers show a higher gustatory responsiveness than nurse bees. It is generally assumed that nutrition-related signalling pathways underlie this behavioural plasticity. Here, one important candidate gene is the foraging gene, which encodes a cyclic guanosine monophosphate-dependent protein kinase (PKG). Several roles of members of this enzyme family were analysed in vertebrates. They own functions in important processes such as growth, secretion and neuronal adaptation. Honeybee foraging messenger RNA expression is upregulated in the brain of foragers. In vivo activation of PKG can modulate gustatory responsiveness. We present for the first time PKG protein level and activity data in the context of social behaviour and feeding. Protein level was significantly higher in brains of foragers than in those of nurse bees, substantiating the role of PKG in behavioural plasticity. However, enzyme activity did not differ between behavioural roles. The mediation of feeding status appears independent of PKG signalling. Neither PKG content nor enzyme activity differed between starved and satiated individuals. We suggest that even though nutrition-related pathways are surely involved in controlling behavioural plasticity, which involves changes in PKG signalling, mediation of satiety itself is independent of PKG.

Sucrose response thresholds of honey bee (Apis mellifera) foragers are not modulated by brood ester pheromone

Abstract Division of labor is a hallmark of eusocial insects and their ecological success can be attributed to it. Honey bee division of labor proceeds along a stereotypical ontogenetic path based on age, modulated by various internal and external stimuli. Brood pheromone is a major social pheromone of the honey bee that has been shown to affect honey bee division of labor. It elicits several physiological and behavioral responses; notably, regulating the timing of the switch from performing in-hive tasks to the initiation of foraging. Additionally, brood pheromone affects future foraging choice. In honey bees, sucrose response threshold is a physiological correlate of age of first foraging and foraging choice. Brood pheromone has been shown to modulate sucrose response threshold in young bees, but its effects on sucrose response thresholds of bees in advanced behavioral states (foragers) are not known. In this study we examined the sucrose response thresholds of two different task groups, foragers (pollen and non-pollen) and non-foraging bees, in response to honey bee brood pheromone. Sucrose response thresholds were not significantly different between brood pheromone treatment and controls among both non-pollen and pollen foragers. However, the sucrose response threshold of non-foraging bees was significantly higher in the brood pheromone treatment group than in the control group. The switch to foraging task is considered a terminal one, with honey bee lifespan being determined at least partially by risks and stress accompanying foraging. Our results indicate that foragers are physiologically resistant to brood pheromone priming of sucrose response thresholds.

Comparative transcriptome analysis of Apis mellifera antennae of workers performing different tasks.

Honey bee is a social insect. Its colony is mainly coordinated by the chemical signals such as pheromones produced by queen or brood. Correspondingly, the worker bee developed numerous complicated olfactory sensilla in antennae for detection of these colony chemical signals and nectar/pollen signals in foraging. With the normal development of new emerged workers, young adults (nurse bee) worked in colony at the first 2-3weeks and then followed by the foraging activity outside of the hive, which give rise to great change of the surrounding chemical signals. However, the olfactory adaption mechanism of worker bee in these processes of behavioral development is still unclear. In this study, we conducted a comprehensive and quantitative analysis of gene expression in Apis mellifera antenna of newly emerged workers, nurses and foragers using transcriptome analysis. Meanwhile, we constructed experimental colonies to collect age-matched samples, which were used to determine whether task is the principal determinant of differential expression. RNA sequencing and quantitative real-time polymerase chain reaction revealed that 6 and 14 genes were closely associated with nurse and forager behaviors, respectively. Furthermore, a broad dynamic range of chemosensory gene families and candidate odorant degrading enzymes were analyzed at different behavior statuses. We firstly reported genes associated with nursing/foraging behavior from antennae and the variations of expression of genes belonging to various olfactory gene families at different development stages. These results not only could contribute to elucidating the relationship between olfactory and behavior-related changes, but also provide a new perspective into the molecular mechanism underlying honey bee division of labor.

Complex patterns of differential expression in candidate master regulatory genes for social behavior in honey bees

Division of labor (DOL) in the social insects is one of nature’s most derived examples of phenotypic plasticity. Here, we explore the regulatory genomics of DOL in honey bees using RNA-Seq between nurses and foragers for eight tissues. We begin to test the hypothesis that caste-specific gene expression may be controlled in a manner analogous to how sex-specific gene expression is controlled. Specifically, we look for candidate master caste regulators that could play a role in controlling caste-specific gene expression analogous to the role played by double sex in sex-specific gene expression. We make significant first steps towards testing this hypothesis by showing that only a small number of regulatory genes show widespread differential expression across many tissues and are thus candidates for genes that could coordinate widespread patterns of gene expression in response to endocrine signals responsive to social needs. Two strong candidates are kruppel homolog-1 and double sex. Double sex, in particular, has previously been associated with sex linked phenotypic plasticity in other insects and is a promising candidate for future work. In addition to testing this primary hypothesis, we also show that the control of DOL has a complex genetic basis such that the same regulatory genes are used repeatedly in different tissues at the same caste transition in an independent manner. We further show that most regulatory genes only show differential expression in a single tissue. Overall, this study suggests candidate genes for the key regulators of social behavior in honey bees.

From honeybees to robots and back: division of labour based on partitioning social inhibition

In this paper, a distributed adaptive partitioning algorithm inspired by division of labor in honeybees is investigated for its applicability in a swarm of underwater robots in one hand and is qualitatively compared with the behavior of honeybee colonies on the other hand. The algorithm, partitioning social inhibition (PSI), is based on local interactions and uses a simple logic inspired from age-polyethism and task allocation in honeybee colonies. The algorithm is analyzed in simulation and is successfully applied here to partition a swarm of underwater robots into groups demonstrating its adaptivity to changes and applicability in real world systems. In a turn towards the inspiration origins of the algorithm, three honeybee colonies are then studied for age-polyethism behaviors and the results are contrasted with a simulated swarm running the PSI algorithm. Similar effects are detected in both the biological and simulated swarms suggesting biological plausibility of the mechanisms employed by the artificial system.

Birth weight and sucrose responsiveness predict cognitive skills of honeybee foragers

Honeybees, Apis mellifera , can differ considerably in their birth weights but the consequences of these weight differences for behaviour are unknown. I investigated how these birth weight differences affected their cognitive skills when the bees reached foraging age. Individual sucrose responsiveness measured by the proboscis extension response is a strong determinant of appetitive olfactory learning performance in honeybees. Most of the observed learning differences between individuals or between genetic bee strains correlate with differences in their sucrose responsiveness. My second aim was therefore to investigate whether the sucrose responsiveness of newly emerged bees could predict the learning behaviour of the bees 3 weeks later. Both birth weight and sucrose responsiveness measured at emergence could predict olfactory learning scores as demonstrated by significant positive correlations. Heavy bees and bees with high sucrose responsiveness later learned better than lighter individuals or bees with lower responsiveness to sucrose at emergence. These results demonstrate for the first time a fundamental relationship between sensory responsiveness and morphology at emergence and later cognitive skills in insects. Because sensory responsiveness is closely linked to division of labour in honeybees, differences in weight and sucrose responsiveness at emergence might be involved in regulating division of labour. ► I studied the relationship of birth weight, sensitivity and learning in honeybees. ► Heavy newly emerged bees learned better in later life than lighter bees. ► Sucrose-sensitive bees learned better at foraging age than insensitive bees.

Individual-level patterns of division of labor in honeybees highlight flexibility in colony-level developmental mechanisms

Honeybee division of labor (DOL) has become a model system for exploring the genetic basis of complex traits and phenotypic plasticity. Although many highly informative behavioral studies have been conducted on this topic (both at the cohort and individual levels), most studies have focused on a few behavioral acts, such as the age of first foraging. Few studies have recorded large numbers of relatively complete individual-level patterns of DOL. Such fine-scale patterns would lay the foundation for rigorous molecular analyses of this phenomenon and allow us to differentiate between competing mechanistic models of DOL. Here, we record over 100 individual-level DOL patterns of bees living under natural conditions. We found that the transitions between castes (polyphenism states) are often gradual, with bees being in multiple castes at once. This is contrary to the traditional view that changes are abrupt. We also found that bees often skip castes, a key prediction of a recent model of DOL. We further confirm variation in the rate at which bees pass through castes and the age of first foraging. Taken together, these results greatly improve our understanding of this model system and allow for a strong revision of current models of honeybee DOL.

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.

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.

TaskSelSim: a model of the self-organization of the division of labour in honeybees

We here describe a novel multi-agent model of the decentralized task selection process in honeybee colonies. The model is based on individual behavioural programs represented as hierarchical finite state automatons. We successfully simulated empirical experiments (with real honeybees) using the model. We shed more light on task specialization and polyethism in honeybees by modelling the heterogeneous environment that emerges over time inside the colony and by considering the changing differences in stimuli strength in each small area of the hive. Our simulation experiments presented here investigate the model's reaction to changing values in crucial model parameters and investigate the stability of the predicted colony behaviours.

Within-nest temporal polyethism in the honey bee

A well-regulated division of labor has been one of the core adaptations leading to the success of the social insects. Honeybee division of labor has been classically viewed as a sequence of age-related changes in task performance. Kolmes questioned this view arguing that his studies did not support the existence of any age-related within-nest specialization. To resolve this controversy, Kolmes and Seeley conducted a joint study with mixed results. They found support for a cell cleaning caste, but diverged on whether their results supported distinct nursing and middle age castes. In this paper, I follow up on their work to resolve the question of caste number in within-nest honey bees. To determine whether nurses (typically aged 4–12 days) and middle-aged bees (aged 12–20 days) have distinct task repertoires, I conducted focal animal observations on a large number of workers in both age groups working within the same nests at the same time. The results support their being two castes of within-nest bees. Young bees specialized on brood care tasks, while middle-aged bees specialized on nectar processing and nest maintenance. Middle-aged bees were observed caring for brood in less than 1% of the observations. Moreover, both castes exhibited movement patterns that correspond to the traditional view that nurses stay within the broodnest, while middle-aged bees move around a great deal in search of work throughout the nest. A review of studies conducted since the debate of Seeley and Kolmes supports the reliability of these results. This work has relevance for proximate models of temporal polyethism, as it is often assumed by such models that there is only one within-nest caste in the honeybee.

The foraging gene, behavioral plasticity, and honeybee division of labor

In recent years, the honeybee has emerged as an excellent model for molecular and genetic studies of complex social behaviors. By using the global gene expression methods as well as the candidate gene approach, it is now possible to link the function of genes to social behaviors. In this paper, I discuss the findings about one such gene, foraging, a cGMP-dependent protein kinase. The involvement of this gene in regulating division of labor is discussed on two independent, but not mutually exclusive levels; the possible mechanisms for PKG action in regulating behavioral transitions associated with honeybee division of labor, and its possible involvement in the evolution of division of labor in bees.

Worker nutrition and division of labour in honeybees

We determined whether there is an association between nutritional state (as indicated by stored abdominal lipid amounts) and division of labour in the honeybee, Apis mellifera. We found that foragers (typically older bees) had lower lipid amounts than did nurses (typically young bees). Results from experimental colonies that contained nurses and foragers of the same age showed that the lipid decline in foragers was not attributable to age. Analysis of bees with different amounts of foraging experience revealed little effect of the act of foraging on lipid stores. Lipid levels were low even on the first day of foraging, suggesting that the decline in stored lipid precedes the onset of foraging. We also found that bees that revert from foraging to nursing did not regain their lipid stores, indicating that high lipid stores are not required to sustain brood care behaviour. This demonstration of a robust association between reduced lipid stores and the transition to foraging suggests that worker nutritional state may be involved in the regulation of division of labour in honeybee colonies.

CGMP-dependent changes in phototaxis: a possible role for the foraging gene in honey bee division of labor.

Division of labor in honey bee colonies is influenced by the foraging gene (Amfor), which encodes a cGMP-dependent protein kinase (PKG). Amfor upregulation in the bee brain is associated with the age-related transition from working in the hive to foraging for food outside, and cGMP treatment (which increases PKG activity) causes precocious foraging. We present two lines of evidence in support of the hypothesis that Amfor affects division of labor by modulating phototaxis. We first show that a subset of worker bees involved in the removal of corpses from the hive had forager-like brain levels of Amfor brain expression despite being middle aged; age-matched food-handlers, who do not leave the hive to perform their job, had low levels of Amfor expression. This finding suggests that occupations that involve working outside the hive are associated with high levels of Amfor in brain. Secondly, foragers were much more positively phototactic than hive bees in a laboratory assay, and cGMP treatment caused a precocious onset of positive phototaxis. The cGMP effect was not due to a general increase in behavioral activity; cGMP treatment had no effect on locomotor activity under either constant darkness or a light:dark regime. The cGMP effect also was not due to changes in circadian rhythmicity; cGMP treatment had no effect on age at onset of locomotor circadian rhythmicity or the period of rhythmicity. The effects of Amfor on phototaxis are not related to peripheral processing; electroretinogram analysis revealed no effect of cGMP treatment on photoreceptor activity and no differences between untreated hive bees and foragers. The cAMP/PKA pathway does not appear to be playing a similar role to cGMP/PKG in the honey bee; cAMP treatment did not affect phototaxis and gene expression analysis revealed task-related differences only for the gene encoding the regulatory subunit, but not the catalytic subunit, of PKA. Our findings implicate one neural process associated with honey bee division of labor that can be affected by naturally occurring changes in the expression of AMFOR:

Juvenile hormone and circadian locomotor activity in the honey bee Apis mellifera

Age-related division of labor in honeybees is associated with plasticity in circadian rhythms. Young nest bees care for brood around the clock with no circadian rhythms while older foragers have strong circadian rhythms that are used for sun compass navigation and for timing visits to flowers. Since juvenile hormone (JH) is involved in the coordination of physiological and behavioral processes underlying age-related division of labor in honey bees, we tested the hypothesis that JH influences the ontogeny of circadian rhythms and other clock parameters in young worker bees. Treatments with the JH analog methoprene or allatectomy did not influence the onset of rhythmicity, overall locomotor activity, or the free-running period of rhythmic locomotor behavior. There were, however, significant differences in the onset of rhythmicity, overall locomotor activity, and longevity between bees from different source colonies, suggesting that there is significant genetic variation for these traits. Our results suggest that JH does not coordinate all aspects of division of labor in bees and that coordination of task performance with circadian rhythms is probably mediated by other regulatory systems.

Social Inhibition and the Regulation of Temporal Polyethism in Honey Bees

Honey bee division of labor is characterized by temporal polyethism, in which young workers remain in the hive and perform tasks there, whereas old workers perform more risky outside tasks, mainly foraging. We present a model of honey bee division of labor based on (1) an intrinsic process of behavioral development and (2) inhibition of development through social interactions among the workers in a colony. The model shows that these two processes can explain the main features of honey bee temporal polyethism: the correlation between age and task performance; the age at which a worker first forages and how this age varies among hives; the balanced allocation of workers to hive tasks and foraging; the recovery of a colony from demographic perturbations; and the differentiation of workers into different behavioral roles. The model provides a baseline picture of individual and colony behavior that can serve as the basis for studies of more fine-grained regulation of division of labor.

Octopamine influences division of labor in honey bee colonies.

Forager honey bees have higher brain levels of octopamine than do bees tending larvae in the hive. To test the hypothesis that octopamine influences honey bee division of labor we treated bees orally with octopamine or its immediate precursor tyramine and determined whether these treatments increased the probability of initiating foraging. Octopamine treatment significantly elevated levels of octopamine in the brain and caused a significant dose-dependent increase in the number of new foragers. This effect was seen for precocious foragers in single-cohort colonies and foragers in larger colonies with more typical age demographies. Tyramine treatment did not increase the number of new foragers, suggesting that octopamine was exerting a specific effect. Octopamine treatment was effective only when given to bees old enough to forage, i.e., older than 4 days of age. Treatment when bees were 1-3 days of age did not cause a significant increase in the number of new foragers when the bees reached the minimal foraging age. These results demonstrate that octopamine influences division of labor in honey bee colonies. We speculate that octopamine is acting in this context as a neuromodulator.