Influence of gene action across different time scales on behavior

Expression of AmGR10 of the Gustatory Receptor Family in Honey Bee Is Correlated with Nursing Behavior

We investigated the association between the expression of a gene encoding gustatory receptor (G10) and division of labor in the honey bee, Apis mellifera. Among 10 GR genes encoding proteins 15% ~ 99% amino acid identity in the honey bee, we found that AmGR10 with 99% identity is involved in nursing or brood care. Expression of AmGR10 was restricted to organs of the hypopharyngeal gland, brain, and ovary in the nurse bee phase. Members of an extended nursing caste under natural conditions continued to express this gene. RNAi knockdown of AmGR10 accelerated the transition to foraging. Our findings demonstrate that this one gene has profound effects on the division of labor associated with the development and physiology of honeybee society.

Laboratory Assay of Brood Care for Quantitative Analyses of Individual Differences in Honey Bee (Apis mellifera) Affiliative Behavior

Care of offspring is a form of affiliative behavior that is fundamental to studies of animal social behavior. Insects do not figure prominently in this topic because Drosophila melanogaster and other traditional models show little if any paternal or maternal care. However, the eusocial honey bee exhibits cooperative brood care with larvae receiving intense and continuous care from their adult sisters, but this behavior has not been well studied because a robust quantitative assay does not exist. We present a new laboratory assay that enables quantification of group or individual honey bee brood “nursing behavior” toward a queen larva. In addition to validating the assay, we used it to examine the influence of the age of the larva and the genetic background of the adult bees on nursing performance. This new assay also can be used in the future for mechanistic analyses of eusociality and comparative analyses of affilative behavior with other animals.

Trypanosomes Modify the Behavior of Their Insect Hosts: Effects on Locomotion and on the Expression of a Related Gene

Background

As a result of evolution, the biology of triatomines must have been significantly adapted to accommodate trypanosome infection in a complex network of vector-vertebrate-parasite interactions. Arthropod-borne parasites have probably developed mechanisms, largely still unknown, to exploit the vector-vertebrate host interactions to ensure their transmission to suitable hosts. Triatomines exhibit a strong negative phototaxis and nocturnal activity, believed to be important for insect survival against its predators.

Methodology/Principal Findings

In this study we quantified phototaxis and locomotion in starved fifth instar nymphs of Rhodnius prolixus infected with Trypanosoma cruzi or Trypanosoma rangeli. T. cruzi infection did not alter insect phototaxis, but induced an overall 20% decrease in the number of bug locomotory events. Furthermore, the significant differences induced by this parasite were concentrated at the beginning of the scotophase. Conversely, T. rangeli modified both behaviors, as it significantly decreased bug negative phototaxis, while it induced a 23% increase in the number of locomotory events in infected bugs. In this case, the significant effects were observed during the photophase. We also investigated the expression of Rpfor, the triatomine ortholog of the foraging gene known to modulate locomotion in other insects, and found a 4.8 fold increase for T. rangeli infected insects.

Conclusions/Significance

We demonstrated for the first time that trypanosome infection modulates the locomotory activity of the invertebrate host. T. rangeli infection seems to be more broadly effective, as besides affecting the intensity of locomotion this parasite also diminished negative phototaxis and the expression of a behavior-associated gene in the triatomine vector.

The control of Chagas disease, an infection that affects ca. 8 million people in Latin America, is mostly based on vector control activities. Understanding vector biology and how these insects interact with their environment, hosts and pathogens is crucial to improve vector control strategies. The behavior of triatomines has been largely studied, yet few reports have focused on the behavioral effects of the interaction that these insects endure with their natural parasites. Trypanosoma cruzi and Trypanosoma rangeli are two protozoan parasites found naturally infecting Rhodnius species. In this study, we showed for the first time that the locomotory activity of Rhodnius prolixus, a relevant vector of Chagas disease, is affected by trypanosome infection. T. cruzi was found to decrease bug locomotory activity during night hours, while T. rangeli promoted a generally increased insect locomotion. In addition, we searched for the R. prolixus orthologue (Rpfor) of a gene associated with the modulation of insect activity (foraging gene) and found that Rpfor expression was also affected by trypanosome infection.

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

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

Molecular tools and bumble bees: revealing hidden details of ecology and evolution in a model system

Bumble bees are a longstanding model system for studies on behaviour, ecology and evolution, due to their well-studied social lifestyle, invaluable role as wild and managed pollinators, and ubiquity and diversity across temperate ecosystems. Yet despite their importance, many aspects of bumble bee biology have remained enigmatic until the rise of the genetic and, more recently, genomic eras. Here, we review and synthesize new insights into the ecology, evolution and behaviour of bumble bees that have been gained using modern genetic and genomic techniques. Special emphasis is placed on four areas of bumble bee biology: the evolution of eusociality in this group, population-level processes, large-scale evolutionary relationships and patterns, and immunity and resistance to pesticides. We close with a prospective on the future of bumble bee genomics research, as this rapidly advancing field has the potential to further revolutionize our understanding of bumble bees, particularly in regard to adaptation and resilience. Worldwide, many bumble bee populations are in decline. As such, throughout the review, connections are drawn between new molecular insights into bumble bees and our understanding of the causal factors involved in their decline. Ongoing and potential applications to bumble bee management and conservation are also included to demonstrate how genetics- and genomics-enabled research aids in the preservation of this threatened group.

Food searching behaviour of a Lepidoptera pest species is modulated by the foraging gene polymorphism

The extent of damage to crop plants from pest insects depends on the foraging behaviour of the insect's feeding stage. Little is known, however, about the genetic and molecular bases of foraging behaviour in phytophagous pest insects. The foraging gene (for), a candidate gene encoding a PKG-I, has an evolutionarily conserved function in feeding strategies. Until now, for had never been studied in Lepidoptera, which includes major pest species. The cereal stem borer Sesamia nonagrioides is therefore a relevant species within this order with which to study conservation of and polymorphism in the for gene, and its role in foraging - a behavioural trait that is directly associated with plant injuries. Full sequencing of for cDNA in S. nonagrioides revealed a high degree of conservation with other insect taxa. Activation of PKG by a cGMP analogue increased larval foraging activity, measured by how frequently larvae moved between food patches in an actimeter. We found one non-synonymous allelic variation in a natural population that defined two allelic variants. These variants presented significantly different levels of foraging activity, and the behaviour was positively correlated to gene expression levels. Our results show that for gene function is conserved in this species of Lepidoptera, and describe an original case of a single nucleotide polymorphism associated with foraging behaviour variation in a pest insect. By illustrating how variation in this single gene can predict phenotype, this work opens new perspectives into the evolutionary context of insect adaptation to plants, as well as pest management.

Expression of foraging and Gp-9 are associated with social organization in the fire ant Solenopsis invicta

The aim of this study was to investigate levels of expression of two major genes, the odorant binding protein Gp-9 (general protein-9) and foraging, that have been shown to be associated with behavioural polymorphisms in ants. We analysed workers and young nonreproductive queens collected from nests of the monogyne (single reproductive queen per nest) and polygyne (multiple reproductive queens) social forms of Solenopsis invicta. In workers but not young queens, the level of foraging expression was significantly associated with social form and the task performed (ie localization in the nest or foraging area). The level of expression of Gp-9 was also associated with social form and worker localization. In addition there was a higher level of expression of the Gp-9(b) allele compared with the Gp-9(B) allele in the heterozygote workers and the young nonreproductive queens. Finally, in the polygyne colonies the level of expression of foraging was not significantly associated with the Gp-9 genotype for either workers or young nonreproductive queens, suggesting that both genes have independent non-epistatic effects on behaviour in S. invicta.

PKG in honey bees: spatial expression, Amfor gene expression, sucrose responsiveness, and division of labor

Division of labor is a hallmark of social insects. In honey bees, division of labor involves transition of female workers from one task to the next. The most distinct tasks are nursing (providing food for the brood) and foraging (collecting pollen and nectar). The brain mechanisms regulating this form of behavioral plasticity have largely remained elusive. Recently, it was suggested that division of labor is based on nutrition-associated signaling pathways. One highly conserved gene associated with food-related behavior across species is the foraging gene, which encodes a cyclic guanosine monophosphate (cGMP)-dependent protein kinase (PKG). Our analysis of this gene reveals the presence of alternative splicing in the honey bee. One isoform is expressed in the brain. Expression of this isoform is most pronounced in the mushroom bodies, the subesophageal ganglion, and the corpora allata. Division of labor and sucrose responsiveness in honey bees correlate significantly with foraging gene expression in distinct brain regions. Activating PKG selectively increases sucrose responsiveness in nurse bees to the level of foragers, whereas the same treatment does not affect responsiveness to light. These findings demonstrate a direct link between PKG signaling in distinct brain areas and division of labor. Furthermore, they demonstrate that the difference in sensory responsiveness between nurse bees and foragers can be compensated for by activating PKG. Our findings on the function of PKG in regulating specific sensory responsiveness and social organization offer valuable indications for the function of the cGMP/PKG pathway in many other insects and vertebrates.

On-plant selection and genetic analysis of European corn borer (Lepidoptera: Crambidae) behavioral traits: plant abandonment versus plant establishment

Although some studies have investigated how insect behavior could influence resistance evolution to transgenic plants, none have determined if behavioral traits respond to selection pressure and how they may be inherited. We investigated plant establishment and abandonment traits for the European corn borer, Ostrinia nubilalisi (Hübner) (Lepidoptera: Crambidae), by conducting a laboratory selection experiment and quantifying patterns of gene expression. Egg masses with emerging larvae were placed on maize plants and silking individuals were collected every 15 min during a 4-h period to generate a plant abandonment (PA) colony. Plants were dissected 24-72 h later, and larvae were collected for a plant establishment colony. Selection of the PA colony showed an increased propensity to abandon the host plant by the third generation. The propensity for larvae to establish on the plants, however, did not show a significant response until the sixth generation. Quantitative real-time-polymerase chain reaction (qRT-PCR) was used to determine expression profiles for behavior associated genes (foraging and Onslmo). Egg samples from the two selected colonies and nonselected laboratory colony were collected at 0, 24, 48, 72, and 96 h after egg deposition, and first instars were sampled after exposure to maize tissue. Compared with the plant establishment and nonselected laboratory colonies at the 0-h time period, foraging and Onslmo showed higher expression in the PA colony. This is the first study that has specifically selected for these traits over several generations and analyzed behavior-associated genes to elucidate genetic changes.

Identification and characterization of seminal fluid proteins in the Asian tiger mosquito, Aedes albopictus

The Asian tiger mosquito (Aedes albopictus) is an important vector for pathogens that affect human health, including the viruses that cause dengue and Chikungunya fevers. It is also one of the world's fastest-spreading invasive species. For these reasons, it is crucial to identify strategies for controlling the reproduction and spread of this mosquito. During mating, seminal fluid proteins (Sfps) are transferred from male mosquitoes to females, and these Sfps modulate female behavior and physiology in ways that influence reproduction. Despite the importance of Sfps on female reproductive behavior in mosquitoes and other insects, the identity of Sfps in Ae. albopictus has not previously been reported. We used transcriptomics and proteomics to identify 198 Sfps in Ae. albopictus. We discuss possible functions of these Sfps in relation to Ae. albopictus reproduction-related biology. We additionally compare the sequences of these Sfps with proteins (including reported Sfps) in several other species, including Ae. aegypti. While only 72 (36.4%) of Ae. albopictus Sfps have putative orthologs in Ae. aegypti, suggesting low conservation of the complement of Sfps in these species, we find no evidence for an elevated rate of evolution or positive selection in the Sfps that are shared between the two Aedes species, suggesting high sequence conservation of those shared Sfps. Our results provide a foundation for future studies to investigate the roles of individual Sfps on feeding and reproduction in this mosquito. Functional analysis of these Sfps could inform strategies for managing the rate of pathogen transmission by Ae. albopictus.

A sociogenomic perspective on neuroscience in organizational behavior

We critically examine the current biological models of individual organizational behavior, with particular emphasis on the roles of genetics and the brain. We demonstrate how approaches to biology in the organizational sciences assume that biological systems are simultaneously causal and essentially static; that genotypes exert constant effects. In contrast, we present a sociogenomic approach to organizational research, which could provide a meta-theoretical framework for understanding organizational behavior. Sociogenomics is an interactionist approach that derives power from its ability to explain how genes and environment operate. The key insight is that both genes and the environment operate by modifying gene expression. This leads to a conception of genetic and environmental effects that is fundamentally dynamic, rather than the static view of classical biometric approaches. We review biometric research within organizational behavior, and contrast these interpretations with a sociogenomic view. We provide a review of gene expression mechanisms that help explain the dynamism observed in individual organizational behavior, particularly factors associated with gene expression in the brain. Finally, we discuss the ethics of genomic and neuroscientific findings for practicing managers and discuss whether it is possible to practically apply these findings in management.

Social regulation of maternal traits in nest-founding bumble bee (Bombus terrestris) queens

During the nest-founding phase of the bumble bee colony cycle, queens undergo striking changes in maternal care behavior. Early in the founding phase, prior to the emergence of workers in the nest, queens are reproductive and also provision and feed their offspring. However, later in the founding phase, queens reduce their feeding of larvae and become specialized on reproduction. This transition is synchronized with the emergence of workers in the colony, who assume the task of feeding their siblings. Using a social manipulation experiment with the bumble bee Bombus terrestris, we tested the hypothesis that workers regulate the transition from feeding brood to specialization on reproduction in nest-founding bumble bee queens. Consistent with this hypothesis, we found that early-stage nest-founding queens with workers prematurely added to their nests reduce their brood-feeding behavior and increase egg laying, and likewise, late-stage nest-founding queens increase their brood-feeding behavior and decrease egg-laying when workers are removed from their nests. Further, brood-feeding and egg-laying behaviors were negatively correlated. We used Agilent microarrays designed from B. terrestris brain expressed sequenced tags (ESTs) to explore a second hypothesis, that workers alter brain gene expression in nest-founding queens. We found evidence that brain gene expression in nest-founding queens is altered by the presence of workers, with the effect being much stronger in late-stage founding queens. This study provides new insights into how the transition from feeding brood to specialization on reproduction in queen bumble bees is regulated during the nest initiation phase of the colony cycle.

Feminization of pheromone-sensing neurons affects mating decisions in Drosophila males

The response of individual animals to mating signals depends on the sexual identity of the individual and the genetics of the mating targets, which represent the mating social context (social environment). However, how social signals are sensed and integrated during mating decisions remains a mystery. One of the models for understanding mating behaviors in molecular and cellular terms is the male courtship ritual in the fruit fly (Drosophila melanogaster). We have recently shown that a subset of gustatory receptor neurons (GRNs) that are enriched in the male appendages and express the ion channel ppk23 play a major role in the initiation and maintenance of male courtship via the perception of cuticular contact pheromones, and are likely to represent the main chemosensory pathway that influences mating decisions by males. Here we show that genetic feminization of ppk23-expressing GRNs in male flies resulted in a significant increase in male-male sexual attraction without an apparent impact on sexual attraction to females. Furthermore, we show that this increase in male-male sexual attraction is sensory specific, which can be modulated by variable social contexts. Finally, we show that feminization of ppk23-expressing sensory neurons lead to major transcriptional shifts, which may explain the altered interpretation of the social environment by feminized males. Together, these data indicate that the sexual cellular identity of pheromone sensing GRNs plays a major role in how individual flies interpret their social environment in the context of mating decisions.

The genome of the clonal raider ant Cerapachys biroi

Social insects are important models for social evolution and behavior. However, in many species, experimental control over important factors that regulate division of labor, such as genotype and age, is limited. Furthermore, most species have fixed queen and worker castes, making it difficult to establish causality between the molecular mechanisms that underlie reproductive division of labor, the hallmark of insect societies. Here we present the genome of the queenless clonal raider ant Cerapachys biroi, a powerful new study system that does not suffer from these constraints. Using cytology and RAD-seq, we show that C. biroi reproduces via automixis with central fusion and that heterozygosity is lost extremely slowly. As a consequence, nestmates are almost clonally related (r = 0.996). Workers in C. biroi colonies synchronously alternate between reproduction and brood care, and young workers eclose in synchronized cohorts. We show that genes associated with division of labor in other social insects are conserved in C. biroi and dynamically regulated during the colony cycle. With unparalleled experimental control over an individual's genotype and age, and the ability to induce reproduction and brood care, C. biroi has great potential to illuminate the molecular regulation of division of labor.

Examining the role of foraging and malvolio in host-finding behavior in the honey bee parasite, Varroa destructor (Anderson & Trueman)

When a female varroa mite, Varroa destructor (Anderson & Trueman), invades a honey bee brood cell, the physiology rapidly changes from feeding phoretic to reproductive. Changes in foraging and malvolio transcript levels in the brain have been associated with modulated intra-specific food searching behaviors in insects and other invertebrates. Transcription profiles for both genes were examined during and immediately following brood cell invasion to assess their role as potential control elements. Vdfor and Vdmvl transcripts were found in all organs of varroa mites with the highest Vdfor transcript levels in ovary-lyrate organs and the highest Vdmvl in Malpighian tubules. Changes in transcript levels of Vdfor and Vdmvl in synganglia were not associated with the cell invasion process, remaining comparable between early reproductive mites (collected from the pre-capping brood cells) and phoretic mites. However, Vdfor and Vdmvl transcript levels were lowered by 37 and 53%, respectively, in synganglia from reproductive mites compared to early reproductive mites, but not significantly different to levels in synganglia from phoretic mites. On the other hand, in whole body preparations the Vdfor and Vdmvl had significantly higher levels of transcript in reproductive mites compared to phoretic and early reproductive, mainly due to the presence of both transcripts accumulating in the eggs carried by the ovipositing mite. Varroa mites are a critical component for honey bee population decline and finding varroa mite genes associated with brood cell invasion, reproduction, ion balance and other physiological processes will facilitate development of novel control avenues for this honey bee parasite.

Population genomics of the honey bee reveals strong signatures of positive selection on worker traits

Most theories used to explain the evolution of eusociality rest upon two key assumptions: mutations affecting the phenotype of sterile workers evolve by positive selection if the resulting traits benefit fertile kin, and that worker traits provide the primary mechanism allowing social insects to adapt to their environment. Despite the common view that positive selection drives phenotypic evolution of workers, we know very little about the prevalence of positive selection acting on the genomes of eusocial insects. We mapped the footprints of positive selection in Apis mellifera through analysis of 40 individual genomes, allowing us to identify thousands of genes and regulatory sequences with signatures of adaptive evolution over multiple timescales. We found Apoidea- and Apis-specific genes to be enriched for signatures of positive selection, indicating that novel genes play a disproportionately large role in adaptive evolution of eusocial insects. Worker-biased proteins have higher signatures of adaptive evolution relative to queen-biased proteins, supporting the view that worker traits are key to adaptation. We also found genes regulating worker division of labor to be enriched for signs of positive selection. Finally, genes associated with worker behavior based on analysis of brain gene expression were highly enriched for adaptive protein and cis-regulatory evolution. Our study highlights the significant contribution of worker phenotypes to adaptive evolution in social insects, and provides a wealth of knowledge on the loci that influence fitness in honey bees.

Neurogenomics of behavioral plasticity

Across animals, there is remarkable diversity in behavior. Modern genomic approaches have made it possible to identify the molecular underpinnings of varied behavioral phenotypes. By examining species with plastic phenotypes we have begun to understand the dynamic and flexible nature of neural transcriptomes and identified gene modules associated with variation in social and reproductive behaviors in diverse species. Importantly, it is becoming increasingly clear that some candidate genes and gene networks are involved in complex social behaviors across even divergent species, yet few comparative transcriptomics studies have been conducted that examine a specific behavior across species. We discuss the implications of a range of important and insightful studies that have increased our understanding of the neurogenomics of behavioral plasticity. Despite its successes, behavioral genomics has been criticized for its lack of hypotheses and causative insights. We propose here a novel avenue to overcome some of these short-comings by complementing "forward genomics" studies (i.e., from phenotype to behaviorally relevant gene modules) with a "reverse genomics" approach (i.e., manipulating novel gene modules to examine effects on behavior, hormones, and the genome itself) to examine the functional causes and consequences of differential gene expression patterns. We discuss how several established approaches (such as pharmacological manipulations of a novel candidate pathway, fine scale mapping of novel candidate gene expression in the brain, or identifying direct targets of a novel transcription factor of interest) can be used in combination with the analysis of the accompanying neurogenomic responses to reveal unexpected biological processes. The integration of forward and reverse genomics will move the field beyond statistical associations and yield great insights into the neural and molecular control of social behavior and its evolution.

Why control activity? Evolutionary selection pressures affecting the development of physical activity genetic and biological regulation

The literature strongly suggests that daily physical activity is genetically and biologically regulated. Potential identities of the responsible mechanisms are unclear, but little has been written concerning the possible evolutionary selection pressures leading to the development of genetic/biological controls of physical activity. Given the weak relationship between exercise endurance and activity levels and the differential genomic locations associated with the regulation of endurance and activity, it is probable that regulation of endurance and activity evolved separately. This hypothesis paper considers energy expenditures and duration of activity in hunter/gatherers, pretechnology farmers, and modern Western societies and considers the potential of each to selectively influence the development of activity regulation. Food availability is also considered given the known linkage of caloric restriction on physical activity as well as early data relating food oversupply to physical inactivity. Elucidating the selection pressures responsible for the genetic/biological control of activity will allow further consideration of these pressures on activity in today's society, especially the linkages between food and activity. Further, current food abundance is removing the cues for activity that were present for the first 40,000 years of human evolution, and thus future research should investigate the effects of this abundance upon the mechanisms regulating activity.

Interindividual variability in social insects - proximate causes and ultimate consequences

Individuals within social groups often show consistent differences in behaviour across time and context. Such interindividual differences and the evolutionary challenge they present have recently generated considerable interest. Social insects provide some of the most familiar and spectacular examples of social groups with large interindividual differences. Investigating these within-group differences has a long research tradition, and behavioural variability among the workers of a colony is increasingly regarded as fundamental for a key feature of social insects: division of labour. The goal of this review is to illustrate what we know about both the proximate mechanisms underlying behavioural variability among the workers of a colony and its ultimate consequences; and to highlight the many open questions in this research field. We begin by reviewing the literature on mechanisms that potentially introduce, maintain, and adjust the behavioural differentiation among workers. We highlight the fact that so far, most studies have focused on behavioural variability based on genetic variability, provided by e.g. multiple mating of the queen, while other mechanisms that may be responsible for the behavioural differentiation among workers have been largely neglected. These include maturational, nutritional and environmental influences. We further discuss how feedback provided by the social environment and learning and experience of adult workers provides potent and little-explored sources of differentiation. In a second part, we address what is known about the potential benefits and costs of increased behavioural variability within the workers of a colony. We argue that all studies documenting a benefit of variability so far have done so by manipulating genetic variability, and that a direct test of the effect of behavioural variability on colony productivity has yet to be provided. We emphasize that the costs associated with interindividual variability have been largely overlooked, and that a better knowledge of the cost/benefit balance of behavioural variability is crucial for our understanding of the evolution of the mechanisms underlying the social organization of insect societies. We conclude by highlighting what we believe to be promising but little-explored avenues for future research on how within-colony variability has evolved and is maintained. We emphasize the need for comparative studies and point out that, so far, most studies on interindividual variability have focused on variability in individual response thresholds, while the significance of variability in other parameters of individual response, such as probability and intensity of the response, has been largely overlooked. We propose that these parameters have important consequences for the colony response. Much more research is needed to understand if and how interindividual variability is modulated in order to benefit division of labour, homeostasis and ultimately colony fitness in social insects.

Social environment influences performance in a cognitive task in natural variants of the foraging gene

In Drosophila melanogaster, natural genetic variation in the foraging gene affects the foraging behaviour of larval and adult flies, larval reward learning, adult visual learning, and adult aversive training tasks. Sitters (for(s)) are more sedentary and aggregate within food patches whereas rovers (for(R)) have greater movement within and between food patches, suggesting that these natural variants are likely to experience different social environments. We hypothesized that social context would differentially influence rover and sitter behaviour in a cognitive task. We measured adult rover and sitter performance in a classical olfactory training test in groups and alone. All flies were reared in groups, but fly training and testing were done alone and in groups. Sitters trained and tested in a group had significantly higher learning performances compared to sitters trained and tested alone. Rovers performed similarly when trained and tested alone and in a group. In other words, rovers learning ability is independent of group training and testing. This suggests that sitters may be more sensitive to the social context than rovers. These differences in learning performance can be altered by pharmacological manipulations of PKG activity levels, the foraging (for) gene's gene product. Learning and memory is also affected by the type of social interaction (being in a group of the same strain or in a group of a different strain) in rovers, but not in sitters. These results suggest that for mediates social learning and memory in D. melanogaster.

Developmental- and food-dependent foraging transcript levels in the desert locust

Drastic changes in the environment during a lifetime require developmental and physiological flexibility to ensure animal survival. Desert locusts, Schistocerca gregaria, live in an extremely changeable environment, which alternates between periods of rainfall and abundant food and periods of drought and starvation. In order to survive, locusts display an extreme form of phenotypic plasticity that allows them to rapidly cope with these changing conditions by converting from a cryptic solitarious phase to a swarming, voracious gregarious phase. To accomplish this, locusts possess different conserved mediators of phenotypic plasticity. Recently, attention has been drawn to the possible roles of protein kinases in this process. In addition to cyclic AMP-dependent protein kinase (PKA), also cyclic GMP-dependent protein kinase (PKG), which was shown to be involved in changes of food-related behavior in a variety of insects, has been associated with locust phenotypic plasticity. In this article, we study the transcript levels of the S. gregaria orthologue of the foraging gene that encodes a PKG in different food-related, developmental and crowding conditions. Transcript levels of the S. gregaria foraging orthologue are highest in different parts of the gut and differ between isolated and crowd-reared locusts. They change when the availability of food is altered, display a distinct pattern with higher levels after a moult and decrease with age during postembryonic development.

Biogenic amines are associated with worker task but not patriline in the leaf-cutting ant Acromyrmex echinatior

Division of labor among eusocial insect workers is a hallmark of advanced social organization, but its underlying neural mechanisms are not well understood. We investigated whether differences in whole-brain levels of the biogenic amines dopamine (DA), serotonin (5HT), and octopamine (OA) are associated with task specialization and genotype in similarly sized and aged workers of the leaf-cutting ant Acromyrmex echinatior, a polyandrous species in which genotype correlates with worker task specialization. We compared amine levels of foragers and waste management workers to test for an association with worker task, and young in-nest workers across patrilines to test for a genetic influence on brain amine levels. Foragers had higher levels of DA and OA and a higher OA:5HT ratio than waste management workers. Patrilines did not significantly differ in amine levels or their ratios, although patriline affected worker body size, which correlated with amine levels despite the small size range sampled. Levels of all three amines were correlated within individuals in both studies. Among patrilines, mean levels of DA and OA, and OA and 5HT were also correlated. Our results suggest that differences in biogenic amines could regulate worker task specialization, but may be not be significantly affected by genotype.

Vitellogenin underwent subfunctionalization to acquire caste and behavioral specific expression in the harvester ant Pogonomyrmex barbatus

The reproductive ground plan hypothesis (RGPH) proposes that the physiological pathways regulating reproduction were co-opted to regulate worker division of labor. Support for this hypothesis in honeybees is provided by studies demonstrating that the reproductive potential of workers, assessed by the levels of vitellogenin (Vg), is linked to task performance. Interestingly, contrary to honeybees that have a single Vg ortholog and potentially fertile nurses, the genome of the harvester ant Pogonomyrmex barbatus harbors two Vg genes (Pb_Vg1 and Pb_Vg2) and nurses produce infertile trophic eggs. P. barbatus, thus, provides a unique model to investigate whether Vg duplication in ants was followed by subfunctionalization to acquire reproductive and non-reproductive functions and whether Vg reproductive function was co-opted to regulate behavior in sterile workers. To investigate these questions, we compared the expression patterns of P. barbatus Vg genes and analyzed the phylogenetic relationships and molecular evolution of Vg genes in ants. qRT-PCRs revealed that Pb_Vg1 is more highly expressed in queens compared to workers and in nurses compared to foragers. By contrast, the level of expression of Pb_Vg2 was higher in foragers than in nurses and queens. Phylogenetic analyses show that a first duplication of the ancestral Vg gene occurred after the divergence between the poneroid and formicoid clades and subsequent duplications occurred in the lineages leading to Solenopsis invicta, Linepithema humile and Acromyrmex echinatior. The initial duplication resulted in two Vg gene subfamilies preferentially expressed in queens and nurses (subfamily A) or in foraging workers (subfamily B). Finally, molecular evolution analyses show that the subfamily A experienced positive selection, while the subfamily B showed overall relaxation of purifying selection. Our results suggest that in P. barbatus the Vg gene underwent subfunctionalization after duplication to acquire caste- and behavior- specific expression associated with reproductive and non-reproductive functions, supporting the validity of the RGPH in ants.

One of the main features of social insects is the division of labor, whereby queens monopolize reproduction while sterile workers perform all of the tasks related to colony maintenance. The workers usually do so in an age-dependent sequence: young workers tend to nurse the brood inside the nest and older workers are more likely to forage for food. Previous studies revealed that vitellogenin, a yolk protein typically involved in the regulation of reproduction in solitary insects, has been co-opted to regulate division of labor in the honeybee. In this study, we investigate such a role of vitellogenin in another group of social insects: the ants. We first use phylogenetic analyses to reveal the existence of multiple vitellogenin genes in most of the sequenced ant genomes. Then we compare the expression of the two vitellogenin genes (Pb_Vg1 and Pb_Vg2) among queens, nurses and foragers in the seed-harvester ant Pogonomyrmex barbatus. Our results suggest that, after the initial duplication in ants, the vitellogenin genes acquired caste and behavioral specific expression associated with reproductive and non-reproductive nutritionally related functions. This study also shows that ants and bees, despite having evolved sociality independently, have conserved similar mechanisms to regulate division of labor.

ASI regulates satiety quiescence in C. elegans

In Caenorhabditis elegans, satiety quiescence mimics behavioral aspects of satiety and postprandial sleep in mammals. On the basis of calcium-imaging, genetics, and behavioral studies, here we report that a pair of amphid neurons, ASI, is activated by nutrition and regulates worms' behavioral states specifically promoting satiety quiescence; ASI inhibits the switch from quiescence to dwelling (a browsing state) and accelerates the switch from dwelling to quiescence. The canonical TGFβ pathway, whose ligand is released from ASI, regulates satiety quiescence. The mutants of a ligand, a receptor and SMADs in the TGFβ pathway all eat more and show less quiescence than wild-type. The TGFβ receptor in downstream neurons RIM and RIC is sufficient for worms to exhibit satiety quiescence, suggesting neuronal connection from ASI to RIM and RIC is essential for feeding regulation through the TGFβ pathway. ASI also regulates satiety quiescence partly through cGMP signaling; restoring cGMP signaling in ASI rescues the satiety quiescence defect of cGMP signaling mutants. From these results, we propose that TGFβ and cGMP pathways in ASI connect nutritional status to promotion of satiety quiescence, a sleep-like behavioral state.

West Nile virus methyltransferase domain interacts with protein kinase G

Background

The flaviviral nonstructural protein 5 (NS5) is a phosphoprotein, though the precise identities and roles of many specific phosphorylations remain unknown. Protein kinase G (PKG), a cGMP-dependent protein kinase, has previously been shown to phosphorylate dengue virus NS5.

Methods

We used mass spectrometry to specifically identify NS5 phosphosites. Co-immunoprecipitation assays were used to study protein-protein interactions. Effects on viral replication were measured via replicon system and plaque assay titering.

Results

We identified multiple sites in West Nile virus (WNV) NS5 that are phosphorylated during a WNV infection, and showed that the N-terminal methyltransferase domain of WNV NS5 can be specifically phosphorylated by PKG in vitro. Expressing PKG in cell culture led to an enhancement of WNV viral production. We hypothesized this effect on replication could be caused by factors beyond the specific phosphorylations of NS5. Here we show for the first time that PKG is also able to stably interact with a viral substrate, WNV NS5, in cell culture and in vitro. While the mosquito-borne WNV NS5 interacted with PKG, tick-borne Langat virus NS5 did not. The methyltransferase domain of NS5 is able to mediate the interaction between NS5 and PKG, and mutating positive residues in the αE region of the methyltransferase interrupts the interaction. These same mutations completely inhibited WNV replication.

Conclusions

PKG is not required for WNV replication, but does make a stable interaction with NS5. While the consequence of the NS5:PKG interaction when it occurs is unclear, mutational data demonstrates that this interaction occurs in a region of NS5 that is otherwise necessary for replication. Overall, the results identify an interaction between virus and a cellular kinase and suggest a role for a host kinase in enhancing flaviviral replication.

Environment exploration and colonization behavior of the pea aphid associated with the expression of the foraging gene

Aphids respond to specific environmental cues by producing alternative morphs, a phenomenon called polyphenism, but also by modulating their individual behavior even within the same morph. This complex plasticity allows a rapid adaptation of individuals to fluctuating environmental conditions, but the underlying genetic and molecular mechanisms remain largely unknown. The foraging gene is known to be associated with behavior in various species and has been shown to mediate the behavioral shift induced by environmental changes in some insects. In this study, we investigated the function of this gene in the clonal forms of the pea aphid Acyrthosiphon pisum by identifying and cloning cDNA variants, as well as analyzing their expression levels in developmental morphs and behavioral variants. Our results indicate that the expression of foraging changes at key steps of the aphid development. This gene is also highly expressed in sedentary wingless adult morphs reared under crowded conditions, probably just before they start walking and foraging. The cGMP-dependent protein kinase (PKG) enzyme activity measured in the behavioral variants correlates with the level of foraging expression. Altogether, our results suggest that foraging could act to promote the shift from a sedentary to an exploratory behavior, being thus involved in the behavioral plasticity of the pea aphid.

Behavioural syndromes and social insects: personality at multiple levels

Animal personalities or behavioural syndromes are consistent and/or correlated behaviours across two or more situations within a population. Social insect biologists have measured consistent individual variation in behaviour within and across colonies for decades. The goal of this review is to illustrate the ways in which both the study of social insects and of behavioural syndromes has overlapped, and to highlight ways in which both fields can move forward through the synergy of knowledge from each. Here we, (i) review work to date on behavioural syndromes (though not always referred to as such) in social insects, and discuss mechanisms and fitness effects of maintaining individual behavioural variation within and between colonies; (ii) summarise approaches and principles from studies of behavioural syndromes, such as trade-offs, feedback, and statistical methods developed specifically to study behavioural consistencies and correlations, and discuss how they might be applied specifically to the study of social insects; (iii) discuss how the study of social insects can enhance our understanding of behavioural syndromes-research in behavioural syndromes is beginning to explore the role of sociality in maintaining or developing behavioural types, and work on social insects can provide new insights in this area; and (iv) suggest future directions for study, with an emphasis on examining behavioural types at multiple levels of organisation (genes, individuals, colonies, or groups of individuals).

Mosquito protein kinase G phosphorylates flavivirus NS5 and alters flight behavior in Aedes aegypti and Anopheles gambiae

Many arboviral proteins are phosphorylated in infected mammalian cells, but it is unknown if the same phosphorylation events occur when insects are similarly infected. One of the mammalian kinases responsible for phosphorylation, protein kinase G (PKG), has been implicated in the behavior of multiple nonvector insects, but is unstudied in mosquitoes. PKG from Aedes aegypti was cloned, and phosphorylation of specific viral sites was monitored by mass spectrometry from biochemical and cell culture experiments. PKG from Aedes mosquitoes is able to phosphorylate dengue nonstructural protein 5 (NS5) at specific sites in cell culture and cell-free systems and autophosphorylates its own regulatory domain in a cell-free system. Injecting Aedes aegypti and Anopheles gambiae mosquitoes with a pharmacological PKG activator resulted in increased Aedes wing activity during periods of their natural diurnal/crepuscular activity and increased Anopheles nocturnal locomotor/flight activity. Thus, perturbation of the PKG signaling pathway in mosquitoes alters flight behavior. The demonstrated effect of PKG alterations is consistent with a viral PKG substrate triggering increased PKG activity. This increased PKG activity could be the mechanism by which dengue virus increases flight behavior and possibly facilitates transmission. Whether or not PKG is part of the mechanism by which dengue increases flight behavior, this report is the first to show PKG can modulate behavior in hematophagous disease vectors.

Ineffective delivery of diet-derived microRNAs to recipient animal organisms

Cross-kingdom delivery of specific microRNAs to recipient organisms via food ingestion has been reported recently. However, it is unclear if such delivery of microRNAs occurs frequently in animal organisms after typical dietary intake. We found substantial levels of specific microRNAs in diets commonly consumed orally by humans, mice, and honey bees. Yet, after ingestion of fruit replete with plant microRNAs (MIR156a, MIR159a, and MIR169a), a cohort of healthy athletes did not carry detectable plasma levels of those molecules. Similarly, despite consumption of a diet with animal fat replete in endogenous miR-21, negligible expression of miR-21 in plasma or organ tissue was observed in miR-21 -/- recipient mice. Correspondingly, when fed vegetarian diets containing the above plant microRNAs, wild-type recipient mice expressed insignificant levels of these microRNAs. Finally, despite oral uptake of pollen containing these plant microRNAs, negligible delivery of these molecules was observed in recipient honeybees. Therefore, we conclude that horizontal delivery of microRNAs via typical dietary ingestion is neither a robust nor a frequent mechanism to maintain steady-state microRNA levels in a variety of model animal organisms, thus defining the biological limits of these molecules in vivo.

Division of labor is associated with age-independent changes in ovarian activity in Pogonomyrmex californicus harvester ants

An age-independent division of labor can develop in both the reproductive (queen) and non-reproductive (worker) castes of Pogonomyrmex californicus harvester ants, and individuals develop biases for in-nest activities or external foraging. Additionally, ant ovaries normally atrophy in foragers compared to nest-biased workers (nurses). However, it is not clear whether these ovarian changes are due to changes in behavior or age, since foragers are typically older individuals. Here, we clarify this relationship in P. californicus queens and workers by comparing ovarian activity in same-aged ants that exhibit divergent behavioral biases. We found that foraging individuals had significantly reduced ovarian activity compared to their nest-biased counterparts, thereby linking changes in the ants' reproductive system to social task performance rather than to age. The general finding that ovarian physiology is associated with social insect behaviors is consistent with the hypothesis that reproductive physiology may have played an important role in the evolution of social insect behavior.

Transcriptome sequencing and annotation of the predatory mite Metaseiulus occidentalis (Acari: Phytoseiidae): a cautionary tale about possible contamination by prey sequences

Next-generation sequencing was applied to the transcriptome of the phytoseiid Metaseiulus occidentalis to characterize gene expression in all life stages reared under different conditions to optimize the recovery of as many genes as possible. One production and one titration run produced a total of 862,069 reads (average size: 314.87 bp), which generated 255.6 Mbp of sequences on the GS-FLX Titanium sequencing platform. After removal of putative prey sequences 850,543 reads were used in NewBler and PTA assemblies to produce 74,172 non-redundant sequences, including 30,691 contigs and 43,481 singlets with 11,994 contigs consisting of more than 500 bp and 37,278 sequences >300 bp, constituting 48.7 % of all sequences. There were 25,888 hits with the NCBI non-redundant database and 15,376 unique transcripts. There were 26,225 hits with the Ixodes scapularis genome and 6,634 unique transcripts. There were 22,225 hits with the RefSeq of Homo sapiens with 6,465 unique transcripts, and 23,656 hits with the RefSeq of Drosophila melanogaster with 9,216 unique transcripts. Selected ESTs corresponding to genes of interest were analyzed including those related to transposable elements, GPCRs, Sox transcription factors, diapause and foraging behavior, and pesticide resistances. Novel and important genes appear to have been discovered that provide insight into the evolution, biology, and physiology of this important predator of pest mites in agriculture and will be useful in analyzing complete genome sequences of this natural enemy.

cGMP-dependent protein kinase I, the circadian clock, sleep and learning

The second messenger cGMP controls cardiovascular and gastrointestinal homeostasis in mammals. However, its physiological relevance in the nervous system is poorly understood.1 Now, we have reported that the cGMP-dependent protein kinase type I (PRKG1) is implicated in the regulation of the timing and quality of sleep and wakefulness.2Prkg1 mutant mice showed altered distribution of sleep and wakefulness as well as reduction in rapid-eye-movement sleep (REMS) duration and in non-REMS consolidation. Furthermore, the ability to sustain waking episodes was compromised. These observations were also reflected in wheel-running and drinking activity. A decrease in electroencephalogram power in the delta frequency range (1-4 Hz) under baseline conditions was observed, which was normalized after sleep deprivation. Together with the finding that circadian clock amplitude is reduced in Prkg1 mutants these results indicate a decrease of the wake-promoting output of the circadian system affecting sleep. Because quality of sleep might affect learning we tested Prkg1 mutants in several learning tasks and find normal spatial learning but impaired object recognition memory in these animals. Our findings indicate that Prkg1 impinges on circadian rhythms, sleep and distinct aspects of learning.

Barrier immune effectors are maintained during transition from nurse to forager in the honey bee

Foragers facilitate horizontal pathogen transmission in honey bee colonies, yet their systemic immune function wanes during transition to this life stage. In general, the insect immune system can be categorized into mechanisms operating at both the barrier epithelial surfaces and at the systemic level. As proposed by the intergenerational transfer theory of aging, such immunosenescence may result from changes in group resource allocation. Yet, the relative influence of pathogen transmission and resource allocation on immune function in bees from different stages has not been examined in the context of barrier immunity. We find that expression levels of antimicrobial peptides (AMPs) in honey bee barrier epithelia of the digestive tract do not follow a life stage-dependent decrease. In addition, correlation of AMP transcript abundance with microbe levels reveals a number of microbe-associated changes in AMPs levels that are equivalent between nurses and foragers. These results favor a model in which barrier effectors are maintained in foragers as a first line of defense, while systemic immune effectors are dismantled to optimize hive-level resources. These findings have important implications for our understanding of immunosenescence in honey bees and other social insects.

Comparing alternative methods for holding virgin honey bee queens for one week in mailing cages before mating

In beekeeping, queen honey bees are often temporarily kept alive in cages. We determined the survival of newly-emerged virgin honey bee queens every day for seven days in an experiment that simultaneously investigated three factors: queen cage type (wooden three-hole or plastic), attendant workers (present or absent) and food type (sugar candy, honey, or both). Ten queens were tested in each of the 12 combinations. Queens were reared using standard beekeeping methods (Doolittle/grafting) and emerged from their cells into vials held in an incubator at 34C. All 12 combinations gave high survival (90 or 100%) for three days but only one method (wooden cage, with attendants, honey) gave 100% survival to day seven. Factors affecting queen survival were analysed. Across all combinations, attendant bees significantly increased survival (18% vs. 53%, p<0.001). In addition, there was an interaction between food type and cage type (p<0.001) with the honey and plastic cage combination giving reduced survival. An additional group of queens was reared and held for seven days using the best method, and then directly introduced using smoke into queenless nucleus colonies that had been dequeened five days previously. Acceptance was high (80%, 8/10) showing that this combination is also suitable for preparing queens for introduction into colonies. Having a simple method for keeping newly-emerged virgin queens alive in cages for one week and acceptable for introduction into queenless colonies will be useful in honey bee breeding. In particular, it facilitates the screening of many queens for genetic or phenotypic characteristics when only a small proportion meets the desired criteria. These can then be introduced into queenless hives for natural mating or insemination, both of which take place when queens are one week old.