Genomics and Integrative Analyses of Division of Labor in Honeybee Colonies

Pollen contaminated with a triple-action fungicide induced oxidative stress and reduced longevity though with less impact on lifespan in honey bees from well fed colonies

Experiments were conducted to determine the effects of a triple-action fungicide on bees and whether improved nutrition can ameliorate eventual negative impacts. In cage tests, newly-emerged bees from well fed and from nutritionally-restricted honey bee colonies were fed for five days with pollen from sunflowers that had been sprayed or not with a commercial fungicide containing bixafen, prothioconazole and trifloxystrobin. Bees from well-fed colonies were significantly larger and consumed more uncontaminated pollen. They also exhibited increased glutathione peroxidase activity and higher concentrations of pyridine nucleotides, both of which are involved in antioxidase defense. However, pollen contaminated with fungicide led to an increase in lipoperoxidation, regardless of nutritional status. Bee longevity was reduced by both fungicide contamination of the pollen diet and poor nutritional condition. The fungicide adversely affected bees fed with contaminated pollen, though nutritional supplementation of the bee colonies that reared the bees partially compensated for these effects.

Novel fungicide and neonicotinoid insecticide impair flight behavior in pollen foraging honey bees, Apis mellifera

Bees are often exposed to pesticides affecting physiological functions and molecular mechanisms. Studies showed a potential link between altered expression of energy metabolism related transcripts and increased homing flight time of foragers exposed to pesticides. In this study, we investigated the effects of thiamethoxam and pyraclostrobin on longevity, flight behavior, and expression of transcripts involved in endocrine regulation (hbg-3, buffy, vitellogenin) and energy metabolism (cox5a, cox5b, cox17) using radio frequency identification (RFID) technology and quantitative polymerase chain reaction. Parallel, a laboratory study was conducted investigating whether pesticide exposure alone without the influence of flight activity caused similar expression patterns as in the RFID experiment. No significant effect on survival, homing flight duration, or return rate of exposed bees was detected. The overall time foragers spent outside the hive was significantly reduced post-exposure. Irrespective of the treatment group, a correlation was observed between cox5a, cox5b, cox17 and hbg-3 expression and prolonged homing flight duration. Our results suggest that flight behavior can impact gene expression and exposure to pesticides adversely affects the expression of genes that are important for maintaining optimal flight capacity. Our laboratory-based experiment showed significantly altered expression levels of cox5a, cox6c, and cox17. However, further work is needed to identify transcriptional profiles responsible for prolonged homing flight duration.

Review: Nutritional Needs of Honeybees and Legislation on Apiculture By-Products in Animal Nutrition

Honeybees are some of the smallest farmed animals, and apiculture by-products, e.g., honey, beeswax, propolis, royal jelly, and pollen contribute to animal nutrition. For the effective production of these by-products, the optimal development and nutrient supply of the honeybee is required. Beginning with the development of the mouth and anal pores on the second day of embryonic development, the digestive tract differentiates into the mouth and fore-, mid-, and hindgut during the pupal stage. The various glands within the oral cavity are particularly important, secreting enzymes and substances that are crucial for digestion and hive nutrition, e.g., invertase and royal jelly. Honeybees rely on a specialized caste system, with worker bees collecting nectar, pollen, water, and resin for the nutrition of the entire hive. Macronutrients, including proteins, carbohydrates, and lipids, obtained primarily from pollen and nectar, are essential for the growth and development of larvae and the overall health of the colony. Inadequate nutrient intake can lead to detrimental effects on larval development, prompting cannibalism within the hive. Apiculture by-products possess unique nutritional and therapeutic properties, leading to a growing interest in the use of honey, beeswax, propolis, and pollen as a feed additive. In recent years, the use of apicultural by-products in animal nutrition has been primarily limited to in vivo studies, which have demonstrated various positive impacts on the performance of farm animals. Honey, beeswax, propolis, royal jelly, and pollen are listed feed stuffs according to Regulation (EC) No. 68/2013. However, for animal nutrition there is not any specific legal definition for these products and no legal requirements regarding their ingredients as given for honey or beeswax in European food law.

Nursing Honeybee Behavior and Sensorial-Related Genes Are Altered by Deformed Wing Virus Variant A

Insect behavior is coordinated mainly by smell through the diverse odor-binding proteins (OBP) that allow them to identify and recognize their environment. Sensory information collected through smell is then analyzed and interpreted in the brain, allowing for correct insect functioning. The behavior of honeybees (Apis mellifera L.) can be affected by different pathogens, such as deformed wing virus (DWV). In particular, the DWV variant A (DWV-A) is capable of altering olfactory sensitivity and reducing the gene expression of different OBPs, including those associated with nursing behavior. The DWV is also capable of replicating itself in the sensory lobes of the brain, further compromising the processing of sensory information. This study evaluated the behavioral response of nurse honeybees exposed to a pheromone compound and the alterations in the gene expression of the pre- and post-synaptic neuronal genes neuroxins-1 and neurogilin-1 in the bee heads and OBP proteins in the antennae of nurse bees inoculated with DWV-A. The behavioral response of nurse bees exposed to the larval pheromone compound benzyl alcohol was analyzed using a Y-tube olfactometer. The viral load, the gene expression of OBP5 and OBP11 in antennae, and neuroxins-1 and neurogilin-1 in the bee heads were analyzed via qPCR. High viral loads significantly reduced the ability of 10- and 15-day-old nurse honeybees to choose the correct pheromone compound. Also, the gene expression of OBP5, OBP11, neuroxin-1, and neurogilin-1 in nurse honeybees decreased when they were highly infected with DWV-A. These results suggest that a DWV-A infection can disturb information processing and cause nursing honeybees to reduce their activity inside the hive, altering internal cohesion.

Turnover of strain-level diversity modulates functional traits in the honeybee gut microbiome between nurses and foragers

BACKGROUND

Strain-level diversity is widespread among bacterial species and can expand the functional potential of natural microbial communities. However, to what extent communities undergo consistent shifts in strain composition in response to environmental/host changes is less well understood.

RESULTS

Here, we used shotgun metagenomics to compare the gut microbiota of two behavioral states of the Western honeybee (Apis mellifera), namely nurse and forager bees. While their gut microbiota is composed of the same bacterial species, we detect consistent changes in strain-level composition between nurses and foragers. Single nucleotide variant profiles of predominant bacterial species cluster by behavioral state. Moreover, we identify strain-specific gene content related to nutrient utilization, vitamin biosynthesis, and cell-cell interactions specifically associated with the two behavioral states.

CONCLUSIONS

Our findings show that strain-level diversity in host-associated communities can undergo consistent changes in response to host behavioral changes modulating the functional potential of the community.

Phenotypic dimorphism between honeybee queen and worker is regulated by complicated epigenetic modifications

Phenotypic dimorphism between queens and workers is an important biological characteristic of honeybees that has been the subject of intensive research. The enormous differences in morphology, lifespan, physiology, and behavior between queens and workers are caused by a complicated set of factors. Epigenetic modifications are considered to play an important role in this process. In this study, we analyzed the differences in chromosome interactions and H3K27ac and H3K4me1 modifications between the queens and workers using high-throughput chromosome conformation capture (Hi-C) and Chromatin immunoprecipitation followed by sequencing (ChIP-Seq) technologies. We found that the queens contain more chromosome interactions and more unique H3K27ac modifications than workers; in contrast, workers have more H3K4me1 modifications than queens. Moreover, we identified Map3k15 as a potential caste gene in queen-worker differentiation. Our results suggest that chromosomal conformation and H3K27ac and H3K4me1 modifications are involved in regulating queen-worker differentiation, which reveals that the queen-worker phenotypic dimorphism is regulated by multiple epigenetic modifications.

Non-optimal ambient temperatures aggravate insecticide toxicity and affect honey bees Apis mellifera L. gene regulation

In this study, we conducted a transcriptional analysis of five honey bee genes to examine their functional involvement vis-à-vis ambient temperatures and exposure to imidacloprid. In a 15-day cage experiment, three cohorts of one-day-old sister bees emerged in incubators, were distributed into cages, and maintained at three different temperatures (26 °C, 32 °C, 38 °C). Each cohort was fed a protein patty and three concentrations of imidacloprid-tainted sugar (0 ppb, 5 ppb and 20 ppb) ad libitum. Honey bee mortality, syrup and patty consumption were monitored daily over 15 days. Bees were sampled every three days for a total of five time points. RT-qPCR was used to longitudinally assess gene regulation of Vg, mrjp1, Rsod, AChE-2 and Trx-1 using RNA extracted from whole bee bodies. Kaplan-Meier models show that bees kept at both non-optimal temperatures (26 °C and 38 °C) were more susceptible to imidacloprid, with significantly higher mortality (P < 0.001 and P < 0.01, respectively) compared to the control. At 32 °C, no differences in mortality (P = 0.3) were recorded among treatments. In both imidacloprid treatment groups and the control, the expression of Vg and mrjp1 was significantly downregulated at 26 °C and 38 °C compared to the optimal temperature of 32 °C, indicating major influence of ambient temperature on the regulation of these genes. Within the ambient temperature groups, both imidacloprid treatments exclusively downregulated Vg and mrjp1 at 26 °C. AChE-2 and the poorly characterized Rsod gene were both consistently upregulated at the highest temperature (38 °C) compared to the ideal temperature (32 °C) in all treatment groups. Trx-1 showed no effect to both temperature and imidacloprid treatments and was regulated in an age-related manner. Overall, our results indicate that ambient temperatures amplify imidacloprid toxicity and affect honey bee gene regulation.

Recent Advances and Future Potential of Long Non-Coding RNAs in Insects

Over the last decade, long non-coding RNAs (lncRNAs) have witnessed a steep rise in interest amongst the scientific community. Because of their functional significance in several biological processes, i.e., alternative splicing, epigenetics, cell cycle, dosage compensation, and gene expression regulation, lncRNAs have transformed our understanding of RNA's regulatory potential. However, most knowledge concerning lncRNAs comes from mammals, and our understanding of the potential role of lncRNAs amongst insects remains unclear. Technological advances such as RNA-seq have enabled entomologists to profile several hundred lncRNAs in insect species, although few are functionally studied. This article will review experimentally validated lncRNAs from different insects and the lncRNAs identified via bioinformatic tools. Lastly, we will discuss the existing research challenges and the future of lncRNAs in insects.

Pesticide risk assessment: honeybee workers are not all equal regarding the risk posed by exposure to pesticides

Toxicological studies in honeybees have long shown that a single pesticide dose or concentration does not necessarily induce a single response. Inter-individual differences in pesticide sensitivity and/or the level of exposure (e.g., ingestion of pesticide-contaminated matrices) may explain this variability in risk posed by a pesticide. Therefore, to better inform pesticide risk assessment for honeybees, we studied the risk posed by pesticides to two behavioral castes, nurse, and forager bees, which are largely represented within colonies and which exhibit large differences in their physiological backgrounds. For that purpose, we determined the sensitivity of nurses and foragers to azoxystrobin (fungicide) and sulfoxaflor (insecticide) upon acute or chronic exposure. Azoxystrobin was found to be weakly toxic to both types of bees. However, foragers were more sensitive to sulfoxaflor than nurses upon acute and chronic exposure. This phenomenon was not explained by better sulfoxaflor metabolization in nurses, but rather by differences in body weight (nurses being 1.6 times heavier than foragers). Foragers consistently consumed more sugar syrup than nurses, and this increased consumption was even more pronounced with pesticide-contaminated syrup (at specific concentrations). Altogether, the stronger susceptibility and exposure of foragers to sulfoxaflor contributed to increases of 2 and tenfold for the acute and chronic risk quotients, respectively, compared to nurses. In conclusion, to increase the safety margin and avoid an under-estimation of the risk posed by insecticides to honeybees, we recommend systematically including forager bees in regulatory tests.

Revealing phosphorylation regulatory networks during embryogenesis of honey bee worker and drone (Apis mellifera)

Protein phosphorylation is known to regulate a comprehensive scenario of critical cellular processes. However, phosphorylation-mediated regulatory networks in honey bee embryogenesis are mainly unknown. We identified 6342 phosphosites from 2438 phosphoproteins and predicted 168 kinases in the honey bee embryo. Generally, the worker and drone develop similar phosphoproteome architectures and major phosphorylation events during embryogenesis. In 24 h embryos, protein kinases A play vital roles in regulating cell proliferation and blastoderm formation. At 48–72 h, kinase subfamily dual-specificity tyrosine-regulated kinase, cyclin-dependent kinase (CDK), and induced pathways related to protein synthesis and morphogenesis suggest the centrality to enhance the germ layer development, organogenesis, and dorsal closure. Notably, workers and drones formulated distinct phosphoproteome signatures. For 24 h embryos, the highly phosphorylated serine/threonine-protein kinase minibrain, microtubule-associated serine/threonine-protein kinase 2 (MAST2), and phosphorylation of mitogen-activated protein kinase 3 (MAPK3) at Thr564 in workers, are likely to regulate the late onset of cell proliferation; in contrast, drone embryos enhanced the expression of CDK12, MAPK3, and MAST2 to promote the massive synthesis of proteins and cytoskeleton. In 48 h, the induced serine/threonine-protein kinase and CDK12 in worker embryos signify their roles in the construction of embryonic tissues and organs; however, the highly activated kinases CDK1, raf homolog serine/threonine-protein kinase, and MAST2 in drone embryos may drive the large-scale establishment of tissues and organs. In 72 h, the activated pathways and kinases associated with cell growth and tissue differentiation in worker embryos may promote the configuration of rudimentary organs. However, kinases implicated in cytoskeleton organization in drone embryos may drive the blastokinesis and dorsal closure. Our hitherto most comprehensive phosphoproteome offers a valuable resource for signaling research on phosphorylation dynamics in honey bee embryos.

Behavioral variation across the days and lives of honey bees

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

Silencing of CYP6AS160 in Solenopsis invicta Buren by RNA interference enhances worker susceptibility to fipronil

Cytochrome P450 monooxygenases play a key role in pest resistance to insecticides by detoxification. Four new P450 genes, CYP6AS160, CYP6AS161, CYP4AB73 and CYP4G232 were identified from Solenopsis invicta. CYP6AS160 was highly expressed in the abdomen and its expression could be induced significantly with exposure to fipronil, whereas CYP4AB73 was not highly expressed in the abdomen and its expression could not be significantly induced following exposure to fipronil. Expression levels of CYP6AS160 and CYP4AB73 in workers were significantly higher than that in queens. RNA interference-mediated gene silencing by feeding on double-stranded RNA (dsRNA) found that the levels of this transcript decreased (by maximum to 64.6%) when they fed on CYP6AS160-specific dsRNA. Workers fed dsCYP6AS160 had significantly higher mortality after 24 h of exposure to fipronil compared to controls. Workers fed dsCYP6AS160 had reduced total P450 activity of microsomal preparations toward model substrates p-nitroanisole. However, the knockdown of a non-overexpressed P450 gene, CYP4AB73 did not lead to an increase of mortality or a decrease of total P450 activity. The knockdown effects of CYP6AS160 on worker susceptibility to fipronil, combined with our other findings, indicate that CYP6AS160 is responsible for detoxification of fipronil. Feeding insects dsRNA may be a general strategy to trigger RNA interference and may find applications in entomological research and in the control of insect pests in the field.

Neuropeptides as potential modulators of behavioral transitions in the ant Cataglyphis nodus

Age-related behavioral plasticity is a major prerequisite for the ecological success of insect societies. Although ecological aspects of behavioral flexibility have been targeted in many studies, the underlying intrinsic mechanisms controlling the diverse changes in behavior along the individual life history of social insects are not completely understood. Recently, the neuropeptides allatostatin-A, corazonin, and tachykinin have been associated with the regulation of behavioral transitions in social insects. Here, we investigated changes in brain localization and expression of these neuropeptides following major behavioral transitions in Cataglyphis nodus ants. Our immunohistochemical analyses in the brain revealed that the overall branching pattern of neurons immunoreactive (ir) for the three neuropeptides is largely independent of the behavioral stages. Numerous allatostatin-A- and tachykinin-ir neurons innervate primary sensory neuropils and high-order integration centers of the brain. In contrast, the number of corazonergic neurons is restricted to only four neurons per brain hemisphere with cell bodies located in the pars lateralis and axons extending to the medial protocerebrum and the retrocerebral complex. Most interestingly, the cell-body volumes of these neurons are significantly increased in foragers compared to freshly eclosed ants and interior workers. Quantification of mRNA expression levels revealed a stage-related change in the expression of allatostatin-A and corazonin mRNA in the brain. Given the presence of the neuropeptides in major control centers of the brain and the neurohemal organs, these mRNA-changes strongly suggest an important modulatory role of both neuropeptides in the behavioral maturation of Cataglyphis ants.

Transcriptional identification of differentially expressed genes associated with division of labor in Apis cerana cerana

Workers of Apis cerana cerana undergo an in-hive nursing to outdoor foraging transition, but the genes underlying this age-related transition remain largely unknown. Here, we sequenced the head transcriptomes of its 7-day-old normal nurses, 18- and 22-day-old normal foragers, 7-day-old precocious foragers and 22-day-old over-aged nurses to unravel the genes associated with this transition. Mapping of the sequence reads to Apis mellifera genome showed that the three types of foragers had a greater percentage of reads from annotated exons and intergenic regions, whereas the two types of nurses had a greater percentage of reads from introns. Pair- and group-wise comparisons of the five transcriptomes revealed 59 uniquely expressed genes (18 in nurses and 41 in foragers) and 14 nurse- and 15 forager-upregulated genes. The uniquely expressed genes are usually low-abundance long noncoding RNAs, transcription factors, transcription coactivators, RNA-binding proteins, kinases or phosphatases that are involved in signaling and/or regulation, whereas the nurse- or forager-upregulated genes are often high-abundance downstream genes that directly perform the tasks of nurses or foragers. Taken together, these results suggest that the nurse-forager transition is coordinated by a social signal-triggered epigenetic shift from introns to exons/intergenic regions and the resulting transcriptional shift between the nurse- and forager-associated genes.

Sub-lethal effects of the consumption of Eupatorium buniifolium essential oil in honeybees

When developing new products to be used in honeybee colonies, further than acute toxicity, it is imperative to perform an assessment of risks, including various sublethal effects. The long-term sublethal effects of xenobiotics on honeybees, more specifically of acaricides used in honeybee hives, have been scarcely studied, particularly so in the case of essential oils and their components. In this work, chronic effects of the ingestion of Eupatorium buniifolium (Asteraceae) essential oil were studied on nurse honeybees using laboratory assays. Survival, food consumption, and the effect on the composition of cuticular hydrocarbons (CHC) were assessed. CHC were chosen due to their key role as pheromones involved in honeybee social recognition. While food consumption and survival were not affected by the consumption of the essential oil, CHC amounts and profiles showed dose-dependent changes. All groups of CHC (linear and branched alkanes, alkenes and alkadienes) were altered when honeybees were fed with the highest essential oil dose tested (6000 ppm). The compounds that significantly varied include n-docosane, n-tricosane, n-tetracosane, n-triacontane, n-tritriacontane, 9-tricosene, 7-pentacosene, 9-pentacosene, 9-heptacosene, tritriacontene, pentacosadiene, hentriacontadiene, tritriacontadiene and all methyl alkanes. All of them but pentacosadiene were up-regulated. On the other hand, CHC profiles were similar in healthy and Nosema-infected honeybees when diets included the essential oil at 300 and 3000 ppm. Our results show that the ingestion of an essential oil can impact CHC and that the effect is dose-dependent. Changes in CHC could affect the signaling process mediated by these pheromonal compounds. To our knowledge this is the first report of changes in honeybee cuticular hydrocarbons as a result of essential oil ingestion.

RNA-seq reveals disruption of gene regulation when honey bees are caged and deprived of hive conditions

In this study, we present phenotypic and genetic data characterizing the impact of imidacloprid and caging stress on honey bee Apis mellifera physiological responses and regulation of 45 genes using targeted-RNA seq. The term 'caging stress' characterizes the effects of depriving honey bees of all hive aspects and conditions. Two cohorts of 1 day old sister bees were subjected to different conditions. One cohort was caged and fed different imidacloprid-tainted sugar solutions and the second was marked and introduced back to its natal hive. Physiological bee parameters and diet behavior were monitored daily for caged bees over several weeks. Bee samples from both cohorts were sampled weekly for RNA sequencing and oxidative stress analyses. Imidacloprid induced significant protein damage and post-ingestive aversion responses in caged bees, leading to lower tainted syrup consumption and higher water intake compared with the controls. No differentially expressed genes were observed among caged bees in regards to imidacloprid treatment. However, significant upregulation in antioxidant genes was recorded in caged bees as compared with hive bees, with overwhelming downregulation in all gene categories in caged bees at week 4. We identified two sets of genes that were constantly regulated in caged bees, including Rsod with unknown function in insects that could potentially characterize caging stress in honey bees.

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.

Evolutionary diversity as a catalyst for biological discovery

The tremendous diversity of animal behaviors has inspired generations of scientists from an array of biological disciplines. To complement investigations of ecological and evolutionary factors contributing to behavioral evolution, modern sequencing, gene editing, computational and neuroscience tools now provide a means to discover the proximate mechanisms upon which natural selection acts to generate behavioral diversity. Social behaviors are motivated behaviors that can differ tremendously between closely related species, suggesting phylogenetic plasticity in their underlying biological mechanisms. In addition, convergent evolution has repeatedly given rise to similar forms of social behavior and mating systems in distantly related species. Social behavioral divergence and convergence provides an entry point for understanding the neurogenetic mechanisms contributing to behavioral diversity. We argue that the greatest strides in discovering mechanisms contributing to social behavioral diversity will be achieved through integration of interdisciplinary comparative approaches with modern tools in diverse species systems. We review recent advances and future potential for discovering mechanisms underlying social behavioral variation; highlighting patterns of social behavioral evolution, oxytocin and vasopressin neuropeptide systems, genetic/transcriptional "toolkits," modern experimental tools, and alternative species systems, with particular emphasis on Microtine rodents and Lake Malawi cichlid fishes.

Endocrine disruption and chronic effects of plant protection products in bees: Can we better protect our pollinators?

Exposure to plant protection products (PPPs) is one of the causes for the population decline of pollinators. In addition to direct exposure, pollinators are exposed to PPPs by pollen, nectar and honey that often contain residues of multiple PPPs. While in legislation PPPs are regarded mainly for their acute toxicity in bees, other effects such as neurotoxicity, immunotoxicity, behavioural changes, stress responses and chronic effects that may harm different physiologically and ecologically relevant traits are much less or not regarded. Despite the fact that endocrine disruption by PPPs is among key effects weakening survival and thriving of populations, pollinators have been poorly investigated in this regard. Here we summarize known endocrine disruptive effects of PPPs in bees and compare them to other chronic effects. Endocrine disruption in honey bees comprise negative effects on reproductive success of queens and drones and behavioural transition of nurse bees to foragers. Among identified PPPs are insecticides, including neonicotinoids, fipronil, chlorantraniliprole and azadirachtin. So far, there exists no OECD guideline to investigate possible endocrine effects of PPPs. Admittedly, investigation of effects on reproduction success of queens and drones is rarely possible under laboratory conditions. But the behavioural transition of nurse bees to foragers could be a possible endpoint to analyse endocrine effects of PPPs under laboratory conditions. We identified some genes, including vitellogenin, which regulate this transition and which may be used as biomarkers for endocrine disruptive PPPs. We plea for a better implementation of the adverse outcome pathway concept into bee's research and propose a procedure for extending and complementing current assessments, including OECD guidelines, with additional physiological and molecular endpoints. Consequently, assessing potential endocrine disruption in pollinators should receive much more relevance.

Effects of Field-Realistic Concentrations of Carbendazim on Survival and Physiology in Forager Honey Bees (Hymenoptera: Apidae)

Carbendazim is nowadays widely used to control fungus in various nectariferous crops. Little is known about how honey bees, Apis mellifera L. (Hymenoptera: Apidae), respond to carbendazim exposure. In this study, the effects of field-realistic concentrations of carbendazim (4.516, 0.4516, and 0.04516 ppm) on the survival, biomarker enzyme activity (AChE, GST, CarE, and P450), and four antimicrobial peptide gene expression (hymenoptaecin, defensin, apidaecin, and abaecin) in forager honey bees were evaluated. The forager bees were fed with the pesticides for 10 d. The results showed that the field-realistic concentrations of carbendazim did not affect survival; activities of AChE, GST, and CarE; and expression levels of defensin and abaecin in forager bees. However, 4.516, 0.4516, and 0.04516 ppm of carbendazim all significantly inhibited the expression of hymenoptaecin and apidaecin (P < 0.01), while P450 (7-ethoxycoumarin-O-deethylase) activity was downregulated by 4.516 ppm of carbendazim (P < 0.05). Our results indicate that the field-realistic concentrations of carbendazim may alter the immune response and P450-mediated detoxification of honey bees. Thus, carbendazim should be discreetly used on nectariferous crops during florescence.

Expression Characterization and Localization of the foraging Gene in the Chinese Bee, Apis cerana cerana (Hymenoptera: Apidae)

In social insects, the foraging gene (for) regulates insect age- and task-based foraging behaviors. We studied the expression and localization of the for gene (Acfor) in Apis cerana cerana workers to explore whether the differential regulation of this gene is associated with the behaviors of nurses and foragers. The expression profiles of Acfor in different tissues and at different ages were examined using real-time quantitative reverse transcription polymerase chain reaction. Cellular localization in the brain was detected using in situ hybridization. Acfor transcripts in different ages workers showed that Acfor expression was detected in all the heads of 1- to 30-d-old worker bees. Acfor expression reached a peak at 25 d of age, and then declined with increasing age. The results showed that Acfor gene expression in five tissues was respectively significantly higher in foragers than in nurses. In nurses, the relative expression of Acfor was the highest in the antennae. There was a highly significant difference in expression between antennae, legs, and the other three tissues. In foragers, Acfor expression was the highest in the thorax, which was significantly different from all other tissues. In situ hybridization showed that Acfor was highly expressed in the lamina of the optic lobes, in a central column of Kenyon cells in the mushroom bodies of the brain of workers, and in the antennal lobes. This suggested that Acfor expression affects age-related foraging behavior in Apis cerana cerana, and that it may be related to flight activity.

Nutritional Physiology and Ecology of Honey Bees

Honey bees feed on floral nectar and pollen that they store in their colonies as honey and bee bread. Social division of labor enables the collection of stores of food that are consumed by within-hive bees that convert stored pollen and honey into royal jelly. Royal jelly and other glandular secretions are the primary food of growing larvae and of the queen but are also fed to other colony members. Research clearly shows that bees regulate their intake, like other animals, around specific proportions of macronutrients. This form of regulation is done as individuals and at the colony level by foragers.

Mitochondrial capacity, oxidative damage and hypoxia gene expression are associated with age-related division of labor in honey bee (Apis mellifera L.) workers

During adult life, honey bee workers undergo a succession of behavioral states. Nurse bees perform tasks inside the nest, and when they are about 2-3 weeks old they initiate foraging. This switch is associated with alterations in diet, and with the levels of juvenile hormone and vitellogenin circulating in hemolymph. It is not clear whether this behavioral maturation involves major changes at the cellular level, such as mitochondrial activity and the redox environment in the head, thorax and abdomen. Using high-resolution respirometry, biochemical assays and RT-qPCR, we evaluated the association of these parameters with this behavioral change. We found that tissues from the head and abdomen of nurses have a higher oxidative phosphorylation capacity than those of foragers, while for the thorax we found the opposite situation. As higher mitochondrial activity tends to generate more H₂O₂, and H₂O₂ is known to stabilize HIF-1α, this would be expected to stimulate hypoxia signaling. The positive correlation that we observed between mitochondrial activity and hif-1α gene expression in abdomen and head tissue of nurses would be in line with this hypothesis. Higher expression of antioxidant enzyme genes was observed in foragers, which could explain their low levels of protein carbonylation. No alterations were seen in nitric oxide (NO) levels, suggesting that NO signaling is unlikely to be involved in behavioral maturation. We conclude that the behavioral change seen in honey bee workers is reflected in differential mitochondrial activities and redox parameters, and we consider that this can provide insights into the underlying aging process.

Phosphoproteome Analysis Reveals Phosphorylation Underpinnings in the Brains of Nurse and Forager Honeybees (Apis mellifera)

The honeybee brain is a central organ in regulating wide ranges of honeybee biology, including life transition from nurse to forager bees. Knowledge is still lacking on how protein phosphorylation governs the neural activity to drive the age-specific labor division. The cerebral phosphoproteome of nurse and forager honeybees was characterized using Ti⁴⁺-IMAC phosphopeptide enrichment mass-spectrometry-based proteomics and protein kinases (PKs) were predicted. There were 3,077 phosphosites residing on 3,234 phosphopeptides from 1004 phosphoproteins in the nurse bees. For foragers the numbers were 3,056, 3,110, and 958, respectively. Notably, among the total 231 PKs in honeybee proteome, 179 novel PKs were predicted in the honeybee brain, of which 88 were experimentally identified. Proteins involved in wide scenarios of pathways were phosphorylated depending on age: glycolysis/gluconeogenesis, AGE/RAGE and phosphorylation in nurse bees and metal ion transport, ATP metabolic process and phototransduction in forager bees. These observations suggest that phosphorylation is vital to the tuning of protein activity to regulate cerebral function according to the biological duties as nursing and foraging bees. The data provides valuable information on phosphorylation signaling in the honeybee brain and potentially useful resource to understand the signaling mechanism in honeybee neurobiology and in other social insects as well.

Flight behaviour of honey bee (Apis mellifera) workers is altered by initial infections of the fungal parasite Nosema apis

Honey bees (Apis mellifera) host a wide range of parasites, some being known contributors towards dramatic colony losses as reported over recent years. To counter parasitic threats, honey bees possess effective immune systems. Because immune responses are predicted to cause substantial physiological costs for infected individuals, they are expected to trade off with other life history traits that ultimately affect the performance and fitness of the entire colony. Here, we tested whether the initial onset of an infection negatively impacts the flight behaviour of honey bee workers, which is an energetically demanding behaviour and a key component of foraging activities. To do this, we infected workers with the widespread fungal pathogen Nosema apis, which is recognised and killed by the honey bee immune system. We compared their survival and flight behaviour with non-infected individuals from the same cohort and colony using radio frequency identification tags (RFID). We found that over a time frame of four days post infection, Nosema did not increase mortality but workers quickly altered their flight behaviour and performed more flights of shorter duration. We conclude that parasitic infections influence foraging activities, which could reduce foraging ranges of colonies and impact their ability to provide pollination services.

Proteome Analysis Unravels Mechanism Underling the Embryogenesis of the Honeybee Drone and Its Divergence with the Worker (Apis mellifera lingustica)

The worker and drone bees each contain a separate diploid and haploid genetic makeup, respectively. Mechanisms regulating the embryogenesis of the drone and its mechanistic difference with the worker are still poorly understood. The proteomes of the two embryos at three time-points throughout development were analyzed by applying mass spectrometry-based proteomics. We identified 2788 and 2840 proteins in the worker and drone embryos, respectively. The age-dependent proteome driving the drone embryogenesis generally follows the worker's. The two embryos however evolve a distinct proteome setting to prime their respective embryogenesis. The strongly expressed proteins and pathways related to transcriptional-translational machinery and morphogenesis at 24 h drone embryo relative to the worker, illustrating the earlier occurrence of morphogenesis in the drone than worker. These morphogenesis differences remain through to the middle-late stage in the two embryos. The two embryos employ distinct antioxidant mechanisms coinciding with the temporal-difference organogenesis. The drone embryo's strongly expressed cytoskeletal proteins signify key roles to match its large body size. The RNAi induced knockdown of the ribosomal protein offers evidence for the functional investigation of gene regulating of honeybee embryogenesis. The data significantly expand novel regulatory mechanisms governing the embryogenesis, which is potentially important for honeybee and other insects.

Uncovering the novel characteristics of Asian honey bee, Apis cerana, by whole genome sequencing

Background

The honey bee is an important model system for increasing understanding of molecular and neural mechanisms underlying social behaviors relevant to the agricultural industry and basic science. The western honey bee, Apis mellifera, has served as a model species, and its genome sequence has been published. In contrast, the genome of the Asian honey bee, Apis cerana, has not yet been sequenced. A. cerana has been raised in Asian countries for thousands of years and has brought considerable economic benefits to the apicultural industry. A cerana has divergent biological traits compared to A. mellifera and it has played a key role in maintaining biodiversity in eastern and southern Asia. Here we report the first whole genome sequence of A. cerana.

Results

Using de novo assembly methods, we produced a 238 Mbp draft of the A. cerana genome and generated 10,651 genes. A.cerana-specific genes were analyzed to better understand the novel characteristics of this honey bee species. Seventy-two percent of the A. cerana-specific genes had more than one GO term, and 1,696 enzymes were categorized into 125 pathways. Genes involved in chemoreception and immunity were carefully identified and compared to those from other sequenced insect models. These included 10 gustatory receptors, 119 odorant receptors, 10 ionotropic receptors, and 160 immune-related genes.

Conclusions

This first report of the whole genome sequence of A. cerana provides resources for comparative sociogenomics, especially in the field of social insect communication. These important tools will contribute to a better understanding of the complex behaviors and natural biology of the Asian honey bee and to anticipate its future evolutionary trajectory.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-16-1) contains supplementary material, which is available to authorized users.

Brain GABA and glutamate levels in workers of two ant species (Hymenoptera: Formicidae): interspecific differences and effects of queen presence/absence

Presence of amino acid neurotransmitters gamma-aminobutyric acid (GABA) and glutamate (Glu) in ant brains was reported in very few studies. To learn more about factors influencing GABA and Glu levels in ant brains, we applied high-performance liquid chromatography to measure levels of these compounds in single brains of workers of 2 ant species, Myrmica ruginodis (subfamily Myrmicinae) and Formica polyctena (subfamily Formicinae) taken from queenright/queenless colony fragments and tested in dyadic aggression tests consisting of an encounter with a nestmate, an alien conspecific or a small cricket. Brain glutamate levels were higher than those of GABA in both tested species. Brain GABA levels (in μmol/brain) and GABA : Glu ratio were higher in M. ruginodis (a submissive species) than in F. polyctena (a dominant, aggressive species) in spite of smaller brain weight of M. ruginodis. Brain glutamate levels (in μmol/brain) did not differ between the tested species, which implies that glutamate concentration (in μmol/mg of brain tissue) was higher in M. ruginodis. Queen absence was associated with increased worker brain GABA levels in F. polyctena, but not in M. ruginodis. No significant effects of opponent type were discovered. As GABA agonists enhance friendly social behavior in rodents, we hypothesize that elevated brain GABA levels of orphaned workers of F. polyctena facilitate the adoption of a new queen. This is the first report providing information on GABA and glutamate levels in single ant brains and documenting the effects of queen presence/absence on brain levels of amino acid neurotransmitters in workers of social Hymenoptera.

Highly efficient integration and expression of piggyBac-derived cassettes in the honeybee (Apis mellifera)

Honeybees (Apis mellifera), which are important pollinators of plants, display remarkable individual behaviors that collectively contribute to the organization of a complex society. Advances in dissecting the complex processes of honeybee behavior have been limited in the recent past due to a lack of genetic manipulation tools. These tools are difficult to apply in honeybees because the unit of reproduction is the colony, and many interesting phenotypes are developmentally specified at later stages. Here, we report highly efficient integration and expression of piggyBac-derived cassettes in the honeybee. We demonstrate that 27 and 20% of queens stably transmitted two different expression cassettes to their offspring, which is a 6- to 30-fold increase in efficiency compared with those generally reported in other insect species. This high efficiency implies that an average beekeeping facility with a limited number of colonies can apply this tool. We demonstrated that the cassette stably and efficiently expressed marker genes in progeny under either an artificial or an endogenous promoter. This evidence of efficient expression encourages the use of this system to inhibit gene functions through RNAi in specific tissues and developmental stages by using various promoters. We also showed that the transgenic marker could be used to select transgenic offspring to be employed to facilitate the building of transgenic colonies via the haploid males. We present here the first to our knowledge genetic engineering tool that will efficiently allow for the systematic detection and better understanding of processes underlying the biology of honeybees.

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.

Epigenetic modification of gene expression in honey bees by heterospecific gland secretions

Background

In the honey bee (Apis mellifera), queen and workers have different behavior and reproductive capacity despite possessing the same genome. The primary substance that leads to this differentiation is royal jelly (RJ), which contains a range of proteins, amino acids, vitamins and nucleic acids. MicroRNA (miRNA) has been found to play an important role in regulating the expression of protein-coding genes and cell biology. In this study, we characterized the miRNAs in RJ from two honey bee sister species and determined their possible effect on transcriptome in one species.

Methodology/Principal Findings

We sequenced the miRNAs in RJ either from A. mellifera (RJM) or A. cerana (RJC). We then determined the global transcriptomes of adult A. mellifera developed from larvae fed either with RJM (mRJM) or RJC (mRJC). Finally we analyzed the target genes of those miRNA that are species specific or differentially expressed in the two honey bee species. We show that there were differences in miRNA between RJM and RJC, and that transcriptomes of adult A. mellifera were affected by the two types of RJ. A high proportion (23.3%) of the affected genes were target genes of differential miRNAs.

Conclusion

We show for the first time that there are differences in miRNAs in RJ between A. mellifera and A. cerana. Further, the differences in transcriptomes of bees reared from these two RJs might be related to miRNA differences of the two species. This study provides the first evidence that heterospecific royal jelly can modify gene expression in honey bees through an epigenetic mechanism.

Developmental evolution in social insects: regulatory networks from genes to societies

The evolution and development of complex phenotypes in social insect colonies, such as queen-worker dimorphism or division of labor, can, in our opinion, only be fully understood within an expanded mechanistic framework of Developmental Evolution. Conversely, social insects offer a fertile research area in which fundamental questions of Developmental Evolution can be addressed empirically. We review the concept of gene regulatory networks (GRNs) that aims to fully describe the battery of interacting genomic modules that are differentially expressed during the development of individual organisms. We discuss how distinct types of network models have been used to study different levels of biological organization in social insects, from GRNs to social networks. We propose that these hierarchical networks spanning different organizational levels from genes to societies should be integrated and incorporated into full GRN models to elucidate the evolutionary and developmental mechanisms underlying social insect phenotypes. Finally, we discuss prospects and approaches to achieve such an integration.

New meta-analysis tools reveal common transcriptional regulatory basis for multiple determinants of behavior

A fundamental problem in meta-analysis is how to systematically combine information from multiple statistical tests to rigorously evaluate a single overarching hypothesis. This problem occurs in systems biology when attempting to map genomic attributes to complex phenotypes such as behavior. Behavior and other complex phenotypes are influenced by intrinsic and environmental determinants that act on the transcriptome, but little is known about how these determinants interact at the molecular level. We developed an informatic technique that identifies statistically significant meta-associations between gene expression patterns and transcription factor combinations. Deploying this technique for brain transcriptome profiles from ca. 400 individual bees, we show that diverse determinants of behavior rely on shared combinations of transcription factors. These relationships were revealed only when we considered complex and variable regulatory rules, suggesting that these shared transcription factors are used in distinct ways by different determinants. This regulatory code would have been missed by traditional gene coexpression or cis-regulatory analytic methods. We expect that our meta-analysis tools will be useful for a broad array of problems in systems biology and other fields.

Next-generation small RNA sequencing for microRNAs profiling in Apis mellifera: comparison between nurses and foragers

MicroRNAs (miRNAs) are endogenous small non-coding RNAs regulating gene expression in animals and plants. To find some differentially expressed miRNAs that may be associated with age-dependent behavioural changes in honey bees (Apis mellifera), we applied next-generation high-throughput sequencing technology to detect small RNAs in nurses and foragers. Our results showed that both nurses and foragers had a complicated small RNA population, and the length of small RNAs varied, 22 nucleotides being the predominant length. Combining deep sequencing and bioinformatic analysis, we discovered that nine known miRNAs were significantly different between nurses and foragers (P < 0.01; absolute value of fold-change ≥ 1). Some of their target genes were related to neural function. Moreover, 67 novel miRNAs were identified in nurses and foragers. Ame-miR-31a and ame-miR-13b were further validated using quantitative reverse-transcription PCR assays. The present study provides new information on the miRNA abundance of honey bees, and enhances our understanding of miRNA function in the regulation of honey bee development.

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.

The transcription factor ultraspiracle influences honey bee social behavior and behavior-related gene expression

Behavior is among the most dynamic animal phenotypes, modulated by a variety of internal and external stimuli. Behavioral differences are associated with large-scale changes in gene expression, but little is known about how these changes are regulated. Here we show how a transcription factor (TF), ultraspiracle (usp; the insect homolog of the Retinoid X Receptor), working in complex transcriptional networks, can regulate behavioral plasticity and associated changes in gene expression. We first show that RNAi knockdown of USP in honey bee abdominal fat bodies delayed the transition from working in the hive (primarily “nursing” brood) to foraging outside. We then demonstrate through transcriptomics experiments that USP induced many maturation-related transcriptional changes in the fat bodies by mediating transcriptional responses to juvenile hormone. These maturation-related transcriptional responses to USP occurred without changes in USP's genomic binding sites, as revealed by ChIP–chip. Instead, behaviorally related gene expression is likely determined by combinatorial interactions between USP and other TFs whose cis-regulatory motifs were enriched at USP's binding sites. Many modules of JH– and maturation-related genes were co-regulated in both the fat body and brain, predicting that usp and cofactors influence shared transcriptional networks in both of these maturation-related tissues. Our findings demonstrate how “single gene effects” on behavioral plasticity can involve complex transcriptional networks, in both brain and peripheral tissues.

Animals use behavior as one of the principal means of meeting their basic needs and responding flexibly to changes in their environment. An emerging insight is that changes in behavior are associated with massive changes in gene expression in the brain, but we know relatively little about how these changes are regulated. One important class of gene regulators are transcription factors (TF), proteins that orchestrate the expression of tens to thousands of genes. We discovered that ultraspiracle (USP), a TF previously known primarily for its role in development, regulates behavioral change in the honey bee; and we show that USP causes behaviorally related changes in gene expression by mediating responses to an endocrine regulator, juvenile hormone. We present evidence that these effects on gene expression occur through combinatorial interactions between USP and other TFs, and that these hormonally related transcriptional networks are preserved between two tissues with causal roles in behavioral plasticity: the brain and the fat body, a peripheral nutrient-sensing organ. These results suggest that behavior is subserved by complex interactions between genes and gene networks, occurring both in the brain and in peripheral tissues. More generally our results suggest that molecular systems biology is a promising paradigm by which to understand the mechanistic basis for behavior.

Worker honeybee brain proteome

A large-scale mapping of the worker honeybee brain proteome was achieved by MudPIT. We identified 2742 proteins from forager and nurse honeybee brain samples; 17% of the total proteins were found to be differentially expressed by spectral count sampling statistics and a G-test. Sequences were compared with the EuKaryotic Orthologous Groups (KOG) catalog set using BLASTX and then categorized into the major KOG categories of most similar sequences. According to this categorization, nurse brain showed increased expression of proteins implicated in translation, ribosomal structure, and biogenesis (14.5%) compared with forager (1.8%). Experienced foragers overexpressed proteins involved in energy production and conversion, showing an extensive difference in this set of proteins (17%) in relation to the nurse subcaste (0.6%). Examples of proteins selectively expressed in each subcaste were analyzed. A comparison between these MudPIT experiments and previous 2-DE experiments revealed nine coincident proteins differentially expressed in both methodologies.

Behavior-specific changes in transcriptional modules lead to distinct and predictable neurogenomic states

Using brain transcriptomic profiles from 853 individual honey bees exhibiting 48 distinct behavioral phenotypes in naturalistic contexts, we report that behavior-specific neurogenomic states can be inferred from the coordinated action of transcription factors (TFs) and their predicted target genes. Unsupervised hierarchical clustering of these transcriptomic profiles showed three clusters that correspond to three ecologically important behavioral categories: aggression, maturation, and foraging. To explore the genetic influences potentially regulating these behavior-specific neurogenomic states, we reconstructed a brain transcriptional regulatory network (TRN) model. This brain TRN quantitatively predicts with high accuracy gene expression changes of more than 2,000 genes involved in behavior, even for behavioral phenotypes on which it was not trained, suggesting that there is a core set of TFs that regulates behavior-specific gene expression in the bee brain, and other TFs more specific to particular categories. TFs playing key roles in the TRN include well-known regulators of neural and behavioral plasticity, e.g., Creb, as well as TFs better known in other biological contexts, e.g., NF-κB (immunity). Our results reveal three insights concerning the relationship between genes and behavior. First, distinct behaviors are subserved by distinct neurogenomic states in the brain. Second, the neurogenomic states underlying different behaviors rely upon both shared and distinct transcriptional modules. Third, despite the complexity of the brain, simple linear relationships between TFs and their putative target genes are a surprisingly prominent feature of the networks underlying behavior.

Myosins and DYNLL1/LC8 in the honey bee (Apis mellifera L.) brain

Honey bees have brain structures with specialized and developed systems of communication that account for memory, learning capacity and behavioral organization with a set of genes homologous to vertebrate genes. Many microtubule- and actin-based molecular motors are involved in axonal/dendritic transport. Myosin-Va is present in the honey bee Apis mellifera nervous system of the larvae and adult castes and subcastes. DYNLL1/LC8 and myosin-IIb, -VI and -IXb have also been detected in the adult brain. SNARE proteins, such as CaMKII, clathrin, syntaxin, SNAP25, munc18, synaptophysin and synaptotagmin, are also expressed in the honey bee brain. Honey bee myosin-Va displayed ATP-dependent solubility and was associated with DYNLL1/LC8 and SNARE proteins in the membrane vesicle-enriched fraction. Myosin-Va expression was also decreased after the intracerebral injection of melittin and NMDA. The immunolocalization of myosin-Va and -IV, DYNLL1/LC8, and synaptophysin in mushroom bodies, and optical and antennal lobes was compared with the brain morphology based on Neo-Timm histochemistry and revealed a distinct and punctate distribution. This result suggested that the pattern of localization is associated with neuron function. Therefore, our data indicated that the roles of myosins, DYNLL1/LC8, and SNARE proteins in the nervous and visual systems of honey bees should be further studied under different developmental, caste and behavioral conditions.

Evolution of cooperation and control of cheating in a social microbe

Much of what we know about the evolution of altruism comes from animals. Here, we show that studying a microbe has yielded unique insights, particularly in understanding how social cheaters are controlled. The social stage of Dictylostelium discoideum occurs when the amoebae run out of their bacterial prey and aggregate into a multicellular, motile slug. This slug forms a fruiting body in which about a fifth of cells die to form a stalk that supports the remaining cells as they form hardy dispersal-ready spores. Because this social stage forms from aggregation, it is analogous to a social group, or a chimeric multicellular organism, and is vulnerable to internal conflict. Advances in cell labeling, microscopy, single-gene knockouts, and genomics, as well as the results of decades of study of D. discoideum as a model for development, allow us to explore the genetic basis of social contests and control of cheaters in unprecedented detail. Cheaters are limited from exploiting other clones by high relatedness, kin discrimination, pleiotropy, noble resistance, and lottery-like role assignment. The active nature of these limits is reflected in the elevated rates of change in social genes compared with nonsocial genes. Despite control of cheaters, some conflict is still expressed in chimeras, with slower movement of slugs, slightly decreased investment in stalk compared with spore cells, and differential contributions to stalk and spores. D. discoideum is rapidly becoming a model system of choice for molecular studies of social evolution.