PKA and PKC content in the honey bee central brain differs in genotypic strains with distinct foraging behavior

Social modulation of ageing: mechanisms, ecology, evolution

Human life expectancy increases, but the disease-free part of lifespan (healthspan) and the quality of life in old people may not show the same development. The situation poses considerable challenges to healthcare systems and economies, and calls for new strategies to increase healthspan and for sustainable future approaches to elder care. This call has motivated innovative research on the role of social relationships during ageing. Correlative data from clinical surveys indicate that social contact promotes healthy ageing, and it is time to reveal the causal mechanisms through experimental research. The fruit fly Drosophila melanogaster is a prolific model animal, but insects with more developed social behaviour can be equally instrumental for this research. Here, we discuss the role of social contact in ageing, and identify lines of study where diverse insect models can help uncover the mechanisms that are involved. This article is part of the theme issue 'Ageing and sociality: why, when and how does sociality change ageing patterns?'

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

BACKGROUND

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

RESULTS

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

CONCLUSION

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

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.

Motion cues improve the performance of harnessed bees in a colour learning task

The proboscis extension conditioning (PER) is a successful behavioural paradigm for studying sensory and learning mechanisms in bees. Whilst mainly used with olfactory and tactile stimuli, more recently reliable PER conditioning has been achieved with visual stimuli such as colours and looming stripes. However, the results reported in different studies vary quite strongly, and it remains controversially discussed how to best condition visual PER. It is particularly striking that visual PER leads to more limited performance as compared to visual conditioning of free-flying bees. It could be that visual PER learning is affected by the lack of movement and that the presence of visual motion cues could compensate for it. We tested whether bees would show differences in learning performances when conditioned either with a colour and motion stimulus in combination or with colour alone. Colour acquisition was improved in the presence of the motion stimulus. The result is consistent with the idea that visual learning might be tightly linked to movement in bees, given that they use vision predominantly during flight. Our results further confirm recent findings that successful visual PER conditioning in bees is achievable without obligatorily removing the antennae.

Genetic architecture of a hormonal response to gene knockdown in honey bees

Variation in endocrine signaling is proposed to underlie the evolution and regulation of social life histories, but the genetic architecture of endocrine signaling is still poorly understood. An excellent example of a hormonally influenced set of social traits is found in the honey bee (Apis mellifera): a dynamic and mutually suppressive relationship between juvenile hormone (JH) and the yolk precursor protein vitellogenin (Vg) regulates behavioral maturation and foraging of workers. Several other traits cosegregate with these behavioral phenotypes, comprising the pollen hoarding syndrome (PHS) one of the best-described animal behavioral syndromes. Genotype differences in responsiveness of JH to Vg are a potential mechanistic basis for the PHS. Here, we reduced Vg expression via RNA interference in progeny from a backcross between 2 selected lines of honey bees that differ in JH responsiveness to Vg reduction and measured JH response and ovary size, which represents another key aspect of the PHS. Genetic mapping based on restriction site-associated DNA tag sequencing identified suggestive quantitative trait loci (QTL) for ovary size and JH responsiveness. We confirmed genetic effects on both traits near many QTL that had been identified previously for their effect on various PHS traits. Thus, our results support a role for endocrine control of complex traits at a genetic level. Furthermore, this first example of a genetic map of a hormonal response to gene knockdown in a social insect helps to refine the genetic understanding of complex behaviors and the physiology that may underlie behavioral control in general.

In-depth phosphoproteomic analysis of royal jelly derived from western and eastern honeybee species

The proteins in royal jelly (RJ) play a pivotal role in the nutrition, immune defense, and cast determination of honeybee larvae and have a wide range of pharmacological and health-promoting functions for humans as well. Although the importance of post-translational modifications (PTMs) in protein function is known, investigation of protein phosphorylation of RJ proteins is still very limited. To this end, two complementary phosphopeptide enrichment materials (Ti(4+)-IMAC and TiO2) and high-sensitivity mass spectrometry were applied to establish a detailed phosphoproteome map and to qualitatively and quantitatively compare the phosphoproteomes of RJ produced by Apis mellifera ligustica (Aml) and Apis cerana cerana (Acc). In total, 16 phosphoproteins carrying 67 phosphorylation sites were identified in RJ derived from western bees, and nine proteins phosphorylated on 71 sites were found in RJ produced by eastern honeybees. Of which, eight phosphorylated proteins were common to both RJ samples, and the same motif ([S-x-E]) was extracted, suggesting that the function of major RJ proteins as nutrients and immune agents is evolutionary preserved in both of these honeybee species. All eight overlapping phosphoproteins showed significantly higher abundance in Acc-RJ than in Aml-RJ, and the phosphorylation of Jelleine-II (an antimicrobial peptide, TPFKLSLHL) at S(6) in Acc-RJ had stronger antimicrobial properties than that at T(1) in Aml-RJ even though the overall antimicrobial activity of Jelleine-II was found to decrease after phosphorylation. The differences in phosphosites, peptide abundance, and antimicrobial activity of the phosphorylated RJ proteins indicate that the two major honeybee species employ distinct phosphorylation strategies that align with their different biological characteristics shaped by evolution. The phosphorylation of RJ proteins are potentially driven by the activity of extracellular serine/threonine protein kinase FAM20C-like protein (FAM20C-like) through the [S-x-E] motif, which is supported by evidence that mRNA and protein expression of FAM20C-like protein kinase are both found in the highest level in the hypopharyngeal gland of nurse bees. Our data represent the first comprehensive RJ phosphorylation atlas, recording patterns of phosphorylated RJ protein abundance and antibacterial activity of some RJ proteins in two major managed honeybee species. These data constitute a firm basis for future research to better understand the biological roles of each RJ protein for honeybee biology and human health care.

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

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

The Architecture of the Pollen Hoarding Syndrome in Honey Bees: Implications for Understanding Social Evolution, Behavioral Syndromes, and Selective Breeding

Social evolution has influenced every aspect of contemporary honey bee biology, but the details are difficult to reconstruct. The reproductive ground plan hypothesis of social evolution proposes that central regulators of the gonotropic cycle of solitary insects have been coopted to coordinate social complexity in honey bees, such as the division of labor among workers. The predicted trait associations between reproductive physiology and social behavior have been identified in the context of the pollen hoarding syndrome, a larger suite of interrelated traits. The genetic architecture of this syndrome is characterized by a partially overlapping genetic architecture with several consistent, pleiotropic QTL. Despite these central QTL and an integrated hormonal regulation, separate aspects of the pollen hoarding syndrome may evolve independently due to peripheral QTL and additionally segregating genetic variance. The characterization of the pollen hoarding syndrome has also demonstrated that this syndrome involves many non-behavioral traits, which may be the case for numerous "behavioral" syndromes. Furthermore, the genetic architecture of the pollen hoarding syndrome has implications for breeding programs for improving honey health and other desirable traits: If these traits are comparable to the pollen hoarding syndrome, consistent pleiotropic QTL will enable marker assisted selection, while sufficient additional genetic variation may permit the dissociation of trade-offs for efficient multiple trait selection.

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.

DNA methylation changes elicited by social stimuli in the brains of worker honey bees

Social environments are notoriously multifactorial, yet studies in rodents have suggested that single variables such as maternal care can in fact be disentangled and correlated with specific DNA methylation changes. This study assesses whether non-detrimental social environmental variation in a highly plastic social insect is correlated with epigenomic modifications at the DNA methylation level. Honey bee workers perform tasks such as nursing and foraging in response to the social environment in the hive, in an age-linked but not age-dependent manner. In this study, the methylation levels of 83 cytosine-phosphate-guanosine dinucleotides over eight genomic regions were compared between the brains of age-matched bees performing nursing or foraging tasks. The results reveal more changes correlated with task than with chronological age, and also hive-associated methylation at some sites. One methylation site from a gene encoding Protein Kinase C binding protein 1 was consistently more methylated in foragers than nurses, which is suggested to lead to production of task-specific protein isoforms via alternative splicing. This study illustrates the ability of the neural epigenome to dynamically respond to complex social stimuli.

An immunological role of a PKC alpha binding protein (PICK1) expressed in the hemocytes of the beet armyworm, Spodoptera exigua

Protein kinase C (PKC) regulates various intracellular processes and its activity is tightly controlled by various factors, such as secondary messengers and binding proteins. A cDNA of a PKC alpha binding protein (also called PICK1: protein interacting with C kinase 1) was cloned in hemocytes of the beet armyworm, Spodoptera exigua (Noctuidae: Lepidoptera). It encodes 475 amino acid residues with putative PDZ and BAR domains interacting with other proteins or ligands. The PICK1 gene of S. exigua (Se-PICK1) was expressed in all developmental stages. In the larval stage, it was highly expressed in hemocyte and brain tissues. A quantitative RT-PCR indicated that its expression was significantly up-regulated by a bacterial challenge. RNA interference of Se-PICK1 in the fifth instar larvae with 100ng of a specific double-stranded RNA could effectively knockdown its expression after 48h post-injection in hemocytes. The suppressed expression of Se-PICK1 significantly impaired the larvae of S. exigua to induce hemocyte-spreading behavior and to form hemocyte nodules in response to bacterial infection. This is the first report of an immunological role of PICK1, which has been identified in various insect and mammalian genomes.

Structural and proteomic analyses reveal regional brain differences during honeybee aging

Among insects, learning is particularly well studied in the fruit fly Drosophila melanogaster and the honeybee Apis mellifera. A senescence-dependent decline in classic pavlovian conditioning is demonstrated for both species. To understand how aging affects learning, genetic approaches used with Drosophila can benefit from complementary studies in Apis. Specifically, honeybees have a larger brain size allowing for compartment-specific approaches, and a unique life-history plasticity. They usually perform within-nest tasks early in life (nest bees) and later they collect food (foragers). Senescence of learning performance is a function of the bees' foraging duration but underlying causes are poorly understood. As cognitive aging is commonly associated with structural and biochemical changes in the brain, we hypothesized that brain areas implicated in learning change in synaptic and biochemical composition with increased foraging duration. First, we used synapse-specific immunohistochemistry and proteomics to screen for alterations in the calyx region of the mushroom body, a key structure for memory formation. Using proteomics, we next profiled the central brain, which comprises all higher-order integration centers. We show that, with increased foraging duration, levels of kinases, synaptic- and neuronal growth-related proteins decline in the central brain while the calyx region remains intact both in structure and biochemistry. We suggest that proteome-level changes within major anatomical sites of memory formation other than the calyx region could be central to learning dysfunction. These include large compartments of the central brain, such as the mushroom body's output regions and the antennal lobes. Our data provide novel information toward heterogeneity in the aging insect brain, and demonstrate advantages of the honeybee for invertebrate neurogerontological research.

Characterization of quantitative trait loci for the age of first foraging in honey bee workers

Identifying the basis of quantitative trait loci (QTL) remains challenging for the study of complex traits, such as behavior. The honey bee is a good model combining interesting social behavior with a high recombination rate that facilitates this identification. Several studies have focused on the pollen hoarding syndrome, identifying multiple QTL as the genetic basis of its behavioral components. One component, the age of first foraging, is central for colony organization and four QTL were previously described without identification of their genomic location. Enabled by the honey bee genome project, this study provides data from multiple experiments to scrutinize these QTL, including individual and pooled SNP mapping, sequencing of AFLP markers, and microsatellite genotyping. The combined evidence confirms and localizes two of the previous QTL on chromosome four and five, dismisses the other two, and suggests one novel genomic region on chromosome eleven to influence the age of first foraging. Among the positional candidates the Ank2, PKC, Erk7, and amontillado genes stand out due to corroborating functional evidence. This study thus demonstrates the power of combined, genome-based approaches to enable targeted studies of a manageable set of candidate genes for natural behavioral variation in the important, complex social trait "age of first foraging".

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.

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.

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.

Olfactory memory formation and the influence of reward pathway during appetitive learning by honey bees

Animals possess the ability to assess food quality via taste and via changes in state that occur after ingestion. Here, we investigate the extent to which a honey bee's ability to assess food quality affected the formation of association with an odor stimulus and the retention of olfactory memories associated with reward. We used three different conditioning protocols in which the unconditioned stimulus (food) was delivered as sucrose stimulation to the proboscis (mouthparts), the antennae or to both proboscis and antennae. All means of delivery of the unconditioned stimulus produced robust associative conditioning with an odor. However, the memory of a conditioned odor decayed at a significantly greater rate for subjects experiencing antennal-only stimulation after either multiple- or single-trial conditioning. Finally, to test whether the act of feeding on a reward containing sucrose during conditioning affected olfactory memory formation, we conditioned honey bees to associate an odor with antennal stimulation with sucrose followed by feeding on a water droplet. We observed that a honey bee's ability to recall the conditioned odor was not significantly different from that of subjects conditioned with an antennal-only sucrose stimulus. Our results show that stimulation of the sensory receptors on the proboscis and/or ingestion of the sucrose reward during appetitive olfactory conditioning are necessary for long-term memory formation.

Determination of phosphorylated amino acid residues of Rab8 from Bombyx mori

The Rab family of small GTPases are key regulators of membrane trafficking. Partially purified Rab8 from Bombyx mori (BRab8) was phosphorylated by protein kinase C in mammalian cells in vitro. To determine which of the seven serines and four threonines are phosphorylated, we generated deletion and site-directed mutants of BRab8, inserted them in Escherichia coli, partially purified the encoded fusion proteins by affinity chromatography, and examined their phosphorylation by protein kinase C in vitro. We found that Ser-132 of BRab8 was specifically phosphorylated by protein kinase C. In addition, Western blotting using an antiserum against BRab8 and in-gel staining for phosphorylated proteins revealed that BRab8 is phosphorylated in vivo.

Octopamine influences honey bee foraging preference

Colony condition and differences in individual preferences influence forage type collected by bees. Physiological bases for the changing preferences of individual foragers are just beginning to be examined. Recently, for honey bees octopamine is shown to influence age at onset of foraging and probability of dance for rewards. However, octopamine has not been causally linked with foraging preference in the field. We tested the hypothesis that changes in octopamine may alter forage type (preference hypothesis). We treated identified foragers orally with octopamine or its immediate precursor, tyramine, or sucrose syrup (control). Octopamine-treated foragers switched type of material collected; control bees did not. Tyramine group results were not different from the control group. In addition, sugar concentrations of nectar collected by foragers after octopamine treatment were lower than before treatment, indicating change in preference. In contrast, before and after nectar concentrations for bees in the control group were similar. These results, taken together, support the preference hypothesis.

Octopamine-mediated neuromodulation of insect senses

Octopamine functions as a neuromodulator, neurotransmitter, and neurohormone in insect nervous systems. Octopamine has a prominent role in influencing multiple physiological events: (a) as a neuromodulator, it regulates desensitization of sensory inputs, arousal, initiation, and maintenance of various rhythmic behaviors and complex behaviors such as learning and memory; (b) as a neurotransmitter, it regulates endocrine gland activity; and (c) as a neurohormone, it induces mobilization of lipids and carbohydrates. Octopamine exerts its effects by binding to specific proteins that belong to the superfamily of G protein-coupled receptors and share the structural motif of seven transmembrane domains. The activation of octopamine receptors is coupled with different second messenger pathways depending on species, tissue source, receptor type and cell line used for the expression of cloned receptor. The second messengers include adenosine 3',5'-cyclic monophosphate (cAMP), calcium, diacylglycerol (DAG), and inositol 1,4,5-trisphosphate (IP3). The cAMP activates protein kinase A, calcium and DAG activate protein kinase C, and IP3 mobilizes calcium from intracellular stores. Octopamine-mediated generation of these second messengers is associated with changes in cellular response affecting insect behaviors. The main objective of this review is to discuss significance of octopamine-mediated neuromodulation in insect sensory systems.

The making of a social insect: developmental architectures of social design

We marvel at the social complexity of insects, marked by anatomically and behaviorally distinguishable castes, division of labor and specialization--but how do such systems evolve? Insect societies are composed of individuals, each undergoing its own developmental process and each containing its own genetic information and experiencing its own developmental and experiential environment. Yet societies appear to function as if the colonies themselves are individuals with novel "social genes" and novel social developmental processes. We propose an alternative hypothesis. The origins of complex social behavior, from which insect societies emerge, are derived from ancestral developmental programs. These programs originated in ancient solitary insects and required little evolutionary remodeling. We present evidence from behavioral assays, selective breeding, genetic mapping, functional genomics and endocrinology, and comparative anatomy and physiology. These insights explain how complex social behavior can evolve from heterochronic changes in reproductive signaling systems that govern ubiquitous and ancient relationships between behavior and ovarian development.

Order, disorder, death: lessons from a superorganism

Animal models contribute to the understanding of molecular mechanism of cancer, revealing complex roles of altered cellular-signaling networks and deficient surveillance systems. Analogous pathologies are documented in an unconventional model organism that receives attention in research on systems theory, evolution, and aging. The honeybee (Apis mellifera) colony is an advanced integrative unit, a "superorganism" in which order is controlled via complex signaling cascades and surveillance schemes. A facultatively sterile caste, the workers, regulates patterns of growth, differentiation, homeostasis, and death. Workers differentiate into temporal phenotypes in response to dynamic social cues; chemosensory signals that can translate into dramatic physiological responses, including programmed cell death. Temporal worker forms function together, and effectively identify and terminate abnormal colony members ranging from embryos to adults. As long as this regulatory system is operational at a colony level, the unit survives and propagates. However, if the worker phenotypes that collectively govern order become too few or change into malignant forms that bypass control mechanisms to replicate aberrantly; order is replaced by disorder that ultimately leads to the destruction of the society. In this chapter we describe fundamental properties of honeybee social organization, and explore conditions that lead to states of disorder. Our hope is that this chapter will be an inspirational source for ongoing and future work in the field of cancer research.

Molecular cloning and expression of protein kinase C from Bombyx mori

Two partial cDNA clones (Protein kinase C alpha and Protein kinase C iota), each of which encoded a different member of PKC-protein family, were isolated using RT-PCR from mRNA of Bombyx mori. The full-length cDNAs were isolated using SMART-RACE. The cDNAs were expressed in HepG2 cells and the recombinant proteins were partially purified using an affinity chromatography. Protein kinase C alpha (BPKC alpha) showed a calcium-dependent kinase activity of histones. Whereas protein kinase C iota (BPKC iota) showed a calcium-independent activity. Bisindolyl maleimide I, a PKC inhibitor, inhibited these kinase activities. Furthermore, in vitro BPKC alpha interacted and phosphorylated two proteins expressed in the brain of Bombyx mori: Rab protein, which plays important roles in the vesicle transport in the brain, and bMBD2/3, which is a methyl DNA-binding protein and regulates transcription. These results suggest that these PKCs phosphorylate various substrate proteins and function in the brain of Bombyx mori.

Male behavioural maturation rate responds to selection on pollen hoarding in honeybees

Division of labour in social insect colonies relies on behavioural functional differentiation (specialization) of individuals with similar genomes. However, individual behavioural traits do not evolve independently of each other (behavioural syndromes). A prime example is the suite of behavioural differences in honeybee workers that has evolved in response to bidirectional selection on pollen hoarding of honeybee colonies (pollen-hoarding syndrome). More generally, these differences reflect functional differentiation between nectar and pollen foragers. We demonstrate here that this pollen-hoarding syndrome extends to drones. Similar to what has been shown in workers, drones from the high-pollen-hoarding strain had a higher locomotion activity after emergence, and they initiated flight earlier than did males derived from the low-pollen-hoarding strain, with hybrids intermediate. However, these two behavioural traits were unlinked at the individual level. We also found that social environment (the colony) affects the age at which drones initiate flight. The indirect selection responses of male behaviour suggest that male and worker evolution are not independent and may constrain each other's evolution. Furthermore, we identified three distinct peaks in the probability of flight initiation over the course of the experiment and a decreased phenotypic variability in the 'hybrid' males, contrary to quantitative genetic expectations.

8. The development and evolution of division of labor and foraging specialization in a social insect (Apis mellifera L.)

How does complex social behavior evolve? What are the developmental building blocks of division of labor and specialization, the hallmarks of insect societies? Studies have revealed the developmental origins in the evolution of division of labor and specialization in foraging worker honeybees, the hallmarks of complex insect societies. Selective breeding for a single social trait, the amount of surplus pollen stored in the nest (pollen hoarding) revealed a phenotypic architecture of correlated traits at multiple levels of biological organization in facultatively sterile female worker honeybees. Verification of this phenotypic architecture in "wild-type" bees provided strong support for a "pollen foraging syndrome" that involves increased senso-motor responses, motor activity, associative learning, reproductive status, and rates of behavioral development, as well as foraging behavior. This set of traits guided further research into reproductive regulatory systems that were co-opted by natural selection during the evolution of social behavior. Division of labor, characterized by changes in the tasks performed by bees, as they age, is controlled by hormones linked to ovary development. Foraging specialization on nectar and pollen results also from different reproductive states of bees where nectar foragers engage in pre-reproductive behavior, foraging for nectar for self-maintenance, while pollen foragers perform foraging tasks associated with reproduction and maternal care, collecting protein.

The genetic architecture of sucrose responsiveness in the honeybee (Apis mellifera L.)

One of the best examples of a natural behavioral syndrome is the pollen-hoarding syndrome in honeybees that ties together multiple behavioral phenotypes, ranging from foraging behavior to behavioral ontogeny and learning performance. A central behavioral factor is the bees' responsiveness to sucrose, measured as their proboscis extension reflex. This study examines the genetics of this trait in diploid worker and haploid male honeybees (drones) to learn more about the genetic architecture of the overall behavioral syndrome, using original strains selected for pollen-hoarding behavior. We show that a significant proportion of the phenotypic variability is determined by genotype in males and workers. Second, our data present overwhelming evidence for pleiotropic effects of previously identified quantitative trait loci for foraging behavior (pln-QTL) and epistatic interactions among them. Furthermore, we report on three genomic QTL scans (two reciprocal worker backcrosses and one drone hybrid population) derived from our selection strains. We present at least one significant and two putative new QTL directly affecting the sucrose response of honeybees. Thus, this study demonstrates the modular genetic architecture of behavioral syndromes in general, and elucidates the genetic architecture of the pollen-hoarding behavioral syndrome in particular. Understanding this behavioral syndrome is important for understanding the division of labor in social insects and social evolution itself.

Sociogenomics: social life in molecular terms

Spectacular progress in molecular biology, genome-sequencing projects and genomics makes this an appropriate time to attempt a comprehensive understanding of the molecular basis of social life. Promising results have already been obtained in identifying genes that influence animal social behaviour and genes that are implicated in social evolution. These findings - derived from an eclectic mix of species that show varying levels of sociality - provide the foundation for the integration of molecular biology, genomics, neuroscience, behavioural biology and evolutionary biology that is necessary for this endeavour.

Locomotion and the pollen hoarding behavioral syndrome of the honeybee (Apis mellifera L.)

Honeybees selected for the colony level phenotype of storing large quantities of pollen (pollen hoarding) in the nest exhibit greater walking activity than those selected against pollen hoarding. In this study, we use a simple walking assay to demonstrate that walking activity increases with the proportion of high pollen-hoarding alleles in pure and backcrossed strains of bees (high-strain bees > offspring generated from a high backcross > offspring generated from a low backcross > low-strain bees). The trait is heritable but is not associated with markers linked to three quantitative trait loci (QTL) mapped for their effects on pollen hoarding with demonstrated pleiotropic effects on pollen and nectar foraging and learning behavior. However, locomotion in non-selected bees is correlated with responsiveness to sucrose, a trait that correlates with foraging and learning behavior. We propose that pollen-hoarding behavior involves a syndrome of behavioral traits with complex genetic and regulatory architectures that span sensory sensitivity, foraging behavior, and learning. We propose that locomotor activity is the component of this syndrome and reflects the early maturation of the bees that become pollen foragers.

The genetic architecture of the behavioral ontogeny of foraging in honeybee workers

The initiation of foraging during the life course of honeybee workers is of central interest to understanding the division of labor in social insects, a central theme in sociobiology and behavioral research. It also provides one of the most complex phenotypic traits in biological systems because of the interaction of various external, social, and individual factors. This study reports on a comprehensive investigation of the genetic architecture of the age of foraging initiation in honeybees. It comprises an estimation of genetic variation, the study of candidate loci, and two complementary quantitative trait loci (QTL) maps using two selected, continually bred lines of honeybees. We conclude that considerable genetic variation exists between the selected lines for this central life history component. The study reveals direct pleiotropic and epistatic effects of candidate loci (including previously identified QTL for foraging behavior). Furthermore, two maps of the honeybee genome were constructed from over 400 AFLP markers. Both maps confirm the extraordinary recombinational size of the honeybee genome. On the basis of these maps, we report four new significant QTL and two more suggestive QTL that influence the initiation of foraging.

Phosphorylation of Rab proteins from the brain of Bombyx mori

Rab proteins play fundamental roles in the regulation of membrane traffic. Previously, from the brain of Bombyx mori we isolated two cDNA clones (BRab1 and BRab14), each of which encoded a different member of Rab-protein family and was expressed in Escherichia coli and purified using an affinity chromatography. In this study, one cDNA clone (BRab8) was isolated from a cDNA library from the brain of B. mori. The recombinant protein was expressed in E. coli and purified. Next, the phosphorylations of these three purified BRab proteins were examined, using mammalian protein kinases in vitro. Protein kinase C (PKC) phosphorylated BRab8 and BRab14 proteins. Protein kinase A faintly phosphorylated BRab8 and BRab14 proteins. Calcium/calmodulin-dependent protein kinase faintly phosphorylated BRab8 protein. Next, brains of B. mori were dissected and homogenized. The homogenate showed a calcium-dependent protein kinase activity of BRab8 and BRab14 proteins. So PKC from the brain of B. mori was partially purified by a sequence of chromatographies on DEAE-Cellulofine and affinity chromatography. This PKC phosphorylated BRab8 and BRab14 proteins. These results suggest that the function of Rab proteins in the brain of B. mori is regulated by calcium-dependent protein kinases.

Reproductive ground plan may mediate colony-level selection effects on individual foraging behavior in honey bees

The colony-level phenotype of an insect society emerges from interactions between large numbers of individuals that may differ considerably in their morphology, physiology, and behavior. The proximate and ultimate mechanisms that allow this complex integrated system to form are not fully known, and understanding the evolution of social life strategies is a major topic in systems biology. In solitary insects, behavior, sensory tuning, and reproductive physiology are linked. These associations are controlled in part by pleiotropic networks that organize the sequential expression of phases in the reproductive cycle. Here we explore whether similar associations give rise to different behavioral phenotypes in a eusocial worker caste. We document that the pleiotropic genetic network that controls foraging behavior in functionally sterile honey bee workers (Apis mellifera) has a reproductive component. Associations between behavior, physiology, and sensory tuning in workers with different foraging strategies indicate that the underlying genetic architectures were designed to control a reproductive cycle. Genetic circuits that make up the regulatory "ground plan" of a reproductive strategy may provide powerful building blocks for social life. We suggest that exploitation of this ground plan plays a fundamental role in the evolution of social insect societies.