Influence of gene action across different time scales on behavior

Behavioral and genetic correlates of heterogeneity in learning performance in individual honeybees, Apis mellifera

Learning an olfactory discrimination task leads to heterogeneous results in honeybees with some bees performing very well and others at low rates. Here we investigated this behavioral heterogeneity and asked whether it was associated with particular gene expression patterns in the bee's brain. Bees were individually conditioned using a sequential conditioning protocol involving several phases of olfactory learning and retention tests. A cumulative score was used to differentiate the tested bees into high and low performers. The rate of CS+ odor learning was found to correlate most strongly with a cumulative performance score extracted from all learning and retention tests. Microarray analysis of gene expression in the mushroom body area of the brains of these bees identified a number of differentially expressed genes between high and low performers. These genes are associated with diverse biological functions, such as neurotransmission, memory formation, cargo trafficking and development.

Genomic characterization, phylogenetic and expression analysis of foraging gene in Apis mellifera

The genomic characterization of the foraging gene and its expression analysis are required to better understand the behavior of honey bees (Apis mellifera). The present study performed a genome-wide characterization of the foraging gene, analyzing its physicochemical properties, phylogenetic features, and expression. An in silico analysis was carried out to characterize the foraging gene and the motifs and conserved domains of the encoded protein to predict its physicochemical properties. Moreover, a phylogenetic analysis of the foraging gene was performed in different species using MEGAX. The relative expression of the foraging gene was determined using qRT-PCR in two groups of forager bee samples (incoming and outgoing bees) during two seasons (five times per day). In addition, the queen effect was evaluated in another experiment. The results revealed that foraging gene expression and bee traffic were influenced by the interaction of season and daytime. The daily foraging traffic and transcription level of the foraging gene were the same in both seasons. The traffic of bees and the transcription abundance of the foraging gene were the highest in the middle and at the end of the day in the first and second seasons, respectively. Furthermore, the mRNA expression of the foraging gene was relatively higher in incoming bees than in outgoing bees. The queen also had a significant effect on the outgoing bees. We conclude that gene-environment interactions affect the foraging behavior of bees through the modulation of the foraging gene transcription.

Unique spatially and temporary-regulated/sex-specific expression of a long ncRNA, Nb-1, suggesting its pleiotropic functions associated with honey bee lifecycle

Honey bees are social insects, and each colony member has unique morphological and physiological traits associated with their social tasks. Previously, we identified a long non-coding RNA from honey bees, termed Nb-1, whose expression in the brain decreases associated with the age-polyethism of workers and is detected in some neurosecretory cells and octopaminergic neurons, suggesting its role in the regulation of worker labor transition. Herein, we investigated its spatially and temporary-regulated/sex-specific expression. Nb-1 was expressed as an abundant maternal RNA during oogenesis and embryogenesis in both sexes. In addition, Nb-1 was expressed preferentially in the proliferating neuroblasts of the mushroom bodies (a higher-order center of the insect brain) in the pupal brains, suggesting its role in embryogenesis and mushroom body development. On the contrary, Nb-1 was expressed in a drone-specific manner in the pupal and adult retina, suggesting its role in the drone visual development and/or sense. Subcellular localization of Nb-1 in the brain during development differed depending on the cell type. Considering that Nb-1 is conserved only in Apidae, our findings suggest that Nb-1 potentially has pleiotropic functions in the expression of multiple developmental, behavioral, and physiological traits, which are closely associated with the honey bee lifecycle.

Feedforward and feedback mechanisms cooperatively regulate rapid experience-dependent response adaptation in a single thermosensory neuron type

Sensory adaptation allows neurons to adjust their sensitivity and responses based on recent experience. The mechanisms that mediate continuous adaptation to stimulus history over seconds- to hours-long timescales, and whether these mechanisms can operate within a single sensory neuron type, are unclear. The single pair of AFD thermosensory neurons in Caenorhabditis elegans exhibits experience-dependent plasticity in their temperature response thresholds on both minutes- and hours-long timescales upon a temperature upshift. While long-term response adaptation requires changes in gene expression in AFD, the mechanisms driving rapid response plasticity are unknown. Here, we show that rapid thermosensory response adaptation in AFD is mediated via cGMP and calcium-dependent feedforward and feedback mechanisms operating at the level of primary thermotransduction. We find that either of two thermosensor receptor guanylyl cyclases (rGCs) alone is sufficient to drive rapid adaptation, but that each rGC drives adaptation at different rates. rGC-driven adaptation is mediated in part via phosphorylation of their intracellular domains, and calcium-dependent feedback regulation of basal cGMP levels via a neuronal calcium sensor protein. In turn, cGMP levels feedforward via cGMP-dependent protein kinases to phosphorylate a specific subunit of the cGMP-gated thermotransduction channel to further regulate rapid adaptation. Our results identify multiple molecular pathways that act in AFD to ensure rapid adaptation to a temperature change and indicate that the deployment of both transcriptional and nontranscriptional mechanisms within a single sensory neuron type can contribute to continuous sensory adaptation.

Gut microbiota contribute to variations in honey bee foraging intensity

Gut microbiomes are increasingly recognized for mediating diverse biological aspects of their hosts, including complex behavioral phenotypes. Although many studies have reported that experimental disruptions to the gut microbial community result in atypical host behavior, studies that address how gut microbes contribute to adaptive behavioral trait variation are rare. Eusocial insects represent a powerful model to test this, because of their simple gut microbiota and complex division of labor characterized by colony-level variation in behavioral phenotypes. Although previous studies report correlational differences in gut microbial community associated with division of labor, here, we provide evidence that gut microbes play a causal role in defining differences in foraging behavior between European honey bees (Apis mellifera). We found that gut microbial community structure differed between hive-based nurse bees and bees that leave the hive to forage for floral resources. These differences were associated with variation in the abundance of individual microbes, including Bifidobacterium asteroides, Bombilactobacillus mellis, and Lactobacillus melliventris. Manipulations of colony demography and individual foraging experience suggested that differences in gut microbial community composition were associated with task experience. Moreover, single-microbe inoculations with B. asteroides, B. mellis, and L. melliventris caused effects on foraging intensity. These results demonstrate that gut microbes contribute to division of labor in a social insect, and support a role of gut microbes in modulating host behavioral trait variation.

Feedforward and feedback mechanisms cooperatively regulate rapid experience-dependent response adaptation in a single thermosensory neuron type

Sensory adaptation allows neurons to adjust their sensitivity and responses based on recent experience. The mechanisms that mediate continuous adaptation to stimulus history over seconds to hours long timescales, and whether these mechanisms can operate within a single sensory neuron type, are unclear. The single pair of AFD thermosensory neurons in C. elegans exhibits experience-dependent plasticity in their temperature response thresholds on both minutes- and hours-long timescales upon a temperature upshift. While long-term response adaptation requires changes in gene expression in AFD, the mechanisms driving rapid response plasticity are unknown. Here, we show that rapid thermosensory response adaptation in AFD is mediated via cGMP and calcium-dependent feedforward and feedback mechanisms operating at the level of primary thermotransduction. We find that either of two thermosensor receptor guanylyl cyclases (rGCs) alone is sufficient to drive rapid adaptation, but that each rGC drives adaptation at different rates. rGC-driven adaptation is mediated in part via phosphorylation of their intracellular domains, and calcium-dependent feedback regulation of basal cGMP levels via a neuronal calcium sensor protein. In turn, cGMP levels feedforward via cGMP-dependent protein kinases to phosphorylate a specific subunit of the cGMP-gated thermotransduction channel to further regulate rapid adaptation. Our results identify multiple molecular pathways that act in AFD to ensure rapid adaptation to a temperature change, and indicate that the deployment of both transcriptional and non-transcriptional mechanisms within a single sensory neuron type can contribute to continuous sensory adaptation.

Labor division of worker ants can be controlled by insulin synthesis targeted through miR-279c-5p in Solenopsis invicta (Hymenoptera: Formicidae)

BACKGROUND

In social insects, the labor division of workers is ubiquitous and controlled by genetic and environmental factors. However, how they modulate this coordinately remains poorly understood.

RESULTS

We report miR-279c-5p participation in insulin synthesis and behavioral transition by negatively regulating Rab8A in Solenopsis invicta. Eusocial specific miR-279c-5p is age-associated and highly expressed in nurse workers, and localized in the cytoplasm of neurons, where it is partly co-localized with its target, Rab8A. We determined that miR-279c-5p agomir suppressed Rab8A expression in forager workers, consequently decreasing insulin content, resulting in the behavioral shift to 'nurse-like' behaviors, while the decrease in miR-279c-5p increased Rab8A expression and increased insulin content in nurse workers, leading to the behavioral shift to 'foraging-like' behaviors. Moreover, insulin could rescue the 'foraging behavior' induced by feeding miR-279c-5p to nurse workers. The overexpression and suppression of miR-279c-5p in vivo caused an obvious behavioral transition between foragers and nurses, and insulin synthesis was affected by miR-279c-5p by regulating the direct target Rab8A.

CONCLUSION

We first report that miR-279c-5p is a novel regulator that promotes labor division by negatively regulating the target gene Rab8A by controlling insulin production in ants. This miRNA-mediated mechanism is significant for understanding the behavioral plasticity of social insects between complex factors and potentially provides new targets for controlling red imported fire ants. © 2023 Society of Chemical Industry.

Task-specific odorant receptor expression in worker antennae indicates that sensory filters regulate division of labor in ants

Division of labor (DOL) is a characteristic trait of insect societies, where tasks are generally performed by specialized individuals. Inside workers focus on brood or nest care, while others take risks by foraging outside. Theory proposes that workers have different thresholds to perform certain tasks when confronted with task-related stimuli, leading to specialization and consequently DOL. Workers are presumed to vary in their response to task-related cues rather than in how they perceive such information. Here, we test the hypothesis that DOL instead stems from workers varying in their efficiency to detect stimuli of specific tasks. We use transcriptomics to measure mRNA expression levels in the antennae and brain of nurses and foragers of the ant Temnothorax longispinosus. We find seven times as many genes to be differentially expressed between behavioral phenotypes in the antennae compared to the brain. Moreover, half of all odorant receptors are differentially expressed, with an overrepresentation of the 9-exon gene family upregulated in the antennae of nurses. Nurses and foragers thus apparently differ in the perception of their olfactory environment and task-related signals. Our study supports the hypothesis that antennal sensory filters predispose workers to specialize in specific tasks.

Causal Genetic Loci for a Motivated Behavior Spectrum Harbor Psychiatric Risk Genes

Behavioral diversity is critical for population fitness. Individual differences in risk-taking are observed across species, but underlying genetic mechanisms and conservation are largely unknown. We examined dark avoidance in larval zebrafish, a motivated behavior reflecting an approach-avoidance conflict. Brain-wide calcium imaging revealed significant neural activity differences between approach-inclined versus avoidance-inclined individuals. We used a population of ∼6,000 to perform the first genome-wide association study (GWAS) in zebrafish, which identified 34 genomic regions harboring many genes that are involved in synaptic transmission and human psychiatric diseases. We used CRISPR to study several causal genes: serotonin receptor-1b ( htr1b ), nitric oxide synthase-1 ( nos1 ), and stress-induced phosphoprotein-1 ( stip1 ). We further identified 52 conserved elements containing 66 GWAS significant variants. One encoded an exonic regulatory element that influenced tissue-specific nos1 expression. Together, these findings reveal new genetic loci and establish a powerful, scalable animal system to probe mechanisms underlying motivation, a critical dimension of psychiatric diseases.

Age and Task Modulate Olfactory Sensitivity in the Florida Carpenter Ant Camponotus floridanus

Age-related changes in behavior and sensory perception have been observed in a wide variety of animal species. In ants and other eusocial insects, workers often progress through an ordered sequence of olfactory-driven behavioral tasks. Notably, these behaviors are plastic, and workers adapt and rapidly switch tasks in response to changing environmental conditions. In the Florida carpenter ant, smaller minors typically perform most of the work needed to maintain the colony, while the larger majors are specialized for nest defense and rarely engage in these routine tasks. Here, we investigate the effects of age and task group on olfactory responses to a series of odorant blends in minor and major worker castes. Consistent with their respective roles within the colony, we observed significant age-associated shifts in the olfactory responses of minors as they transitioned between behavioral states, whereas the responses of majors remained consistently low regardless of age. Furthermore, we have identified a unitary compound, 3-methylindole, which elicited significantly higher responses and behavioral aversion in minor nurses than in similarly aged foragers suggesting that this compound may play an important role in brood care. Taken together, our results suggest that age- and task-associated shifts in olfactory physiology may play a critical role in the social organization of ant colonies.

Transcriptomic effects of the foraging gene shed light on pathways of pleiotropy and plasticity

Genes are often pleiotropic and plastic in their expression, features which increase and diversify the functionality of the genome. The foraging (for) gene in Drosophila melanogaster is highly pleiotropic and a long-standing model for studying individual differences in behavior and plasticity from ethological, evolutionary, and genetic perspectives. Its pleiotropy is known to be linked to its complex molecular structure; however, the downstream pathways and interactors remain mostly elusive. To uncover these pathways and interactors and gain a better understanding of how pleiotropy and plasticity are achieved at the molecular level, we explore the effects of different for alleles on gene expression at baseline and in response to 4 h of food deprivation, using RNA sequencing analysis in different Drosophila larval tissues. The results show tissue-specific transcriptomic dynamics influenced by for allelic variation and food deprivation, as well as genotype by treatment interactions. Differentially expressed genes yielded pathways linked to previously described for phenotypes and several potentially novel phenotypes. Together, these findings provide putative genes and pathways through which for might regulate its varied phenotypes in a pleiotropic, plastic, and gene-structure-dependent manner.

Age and Task Modulate Olfactory Sensitivity in the Florida Carpenter Ant Camponotus floridanus

Age-related changes in behavior and sensory perception have been observed in a wide variety of animal species. In ants and other eusocial insects, workers often progress through an ordered sequence of olfactory-driven behavioral tasks. Notably, these behaviors are plastic, and workers adapt and rapidly switch tasks in response to changing environmental conditions. In the Florida carpenter ant, smaller minors typically perform most of the work needed to maintain the colony while the larger majors are specialized for nest defense and rarely engage in these routine tasks. Here, we investigate the effects of age and task group on olfactory responses to a series of odorant blends in minor and major worker castes. Consistent with their respective roles within the colony, we observed significant age-associated shifts in the olfactory responses of minors as they transitioned between behavioral states, whereas the responses of majors remained consistently low regardless of age. Furthermore, we identified a unitary compound, 3-methylindole, which elicited significantly higher responses and behavioral aversion in minor nurses than in similarly aged foragers suggesting that this compound may play an important role in brood care. Taken together, our results suggest that age- and task-associated shifts in olfactory physiology may play a critical role in the social organization of ant colonies.

Simple Summary

Florida carpenter ants ( Camponotus floridanus ) live in colonies comprised of thousands of workers. The smallest workers, known as minors, engage in routine tasks such as nursing and foraging while the largest workers, known as majors, are thought to be soldiers specialized for defending the nest. How ant colonies allocate their workforce to address the dynamic and ever-changing needs of the colonies remains an open question in the field, but current evidence suggests that ant social behavior likely results from a combination of genetic/epigenetic, physiological, and systems-level processes. Here, we extend these studies by investigating the role of olfactory sensitivity in regulating ant behavior. Minor workers exhibited significant shifts in olfactory sensitivity and odor coding as they aged and switched tasks. The olfactory sensitivity of majors, however, remained relatively stable as they aged. From these studies, we also identified a single compound, 3-methylindole, which elicited significantly higher olfactory responses and aversive behavior in nurses compared to foragers, suggesting that this chemical may have a role in brood care. Overall, these studies support the hypothesis that changes in olfactory sensitivity play an important role in regulating social behavior in ants.

Developmental biomechanics and age polyethism in leaf-cutter ants

Many social insects display age polyethism: young workers stay inside the nest, and only older workers forage. This behavioural transition is accompanied by genetic and physiological changes, but the mechanistic origin of it remains unclear. To investigate if the mechanical demands on the musculoskeletal system effectively prevent young workers from foraging, we studied the biomechanical development of the bite apparatus in Atta vollenweideri leaf-cutter ants. Fully matured foragers generated peak in vivo bite forces of around 100 mN, more than one order of magnitude in excess of those measured for freshly eclosed callows of the same size. This change in bite force was accompanied by a sixfold increase in the volume of the mandible closer muscle, and by a substantial increase of the flexural rigidity of the head capsule, driven by a significant increase in both average thickness and indentation modulus of the head capsule cuticle. Consequently, callows lack the muscle force capacity required for leaf-cutting, and their head capsule is so compliant that large muscle forces would be likely to cause damaging deformations. On the basis of these results, we speculate that continued biomechanical development post eclosion may be a key factor underlying age polyethism, wherever foraging is associated with substantial mechanical demands.

Evolutionary dynamics of mushroom body Kenyon cell types in hymenopteran brains from multifunctional type to functionally specialized types

Evolutionary dynamics of diversification of brain neuronal cell types that have underlain behavioral evolution remain largely unknown. Here, we compared transcriptomes and functions of Kenyon cell (KC) types that compose the mushroom bodies between the honey bee and sawfly, a primitive hymenopteran insect whose KCs likely have the ancestral properties. Transcriptome analyses show that the sawfly KC type shares some of the gene expression profile with each honey bee KC type, although unique gene expression profiles have also been acquired in each honey bee KC type. In addition, functional analysis of two sawfly genes suggested that the functions in learning and memory of the ancestral KC type were heterogeneously inherited among the KC types in the honey bee. Our findings strongly suggest that the functional evolution of KCs in Hymenoptera involved two previously hypothesized processes for evolution of cell function: functional segregation and divergence.

Unraveling the phenotypic and genomic background of behavioral plasticity and temperament in North American Angus cattle

BACKGROUND

Longitudinal records of temperament can be used for assessing behavioral plasticity, such as aptness to learn, memorize, or change behavioral responses based on affective state. In this study, we evaluated the phenotypic and genomic background of North American Angus cow temperament measured throughout their lifetime around the weaning season, including the development of a new indicator trait termed docility-based learning and behavioral plasticity. The analyses included 273,695 and 153,898 records for yearling (YT) and cow at weaning (CT) temperament, respectively, 723,248 animals in the pedigree, and 8784 genotyped animals. Both YT and CT were measured when the animal was loading into/exiting the chute. Moreover, CT was measured around the time in which the cow was separated from her calf. A random regression model fitting a first-order Legendre orthogonal polynomial was used to model the covariance structure of temperament and to assess the learning and behavioral plasticity (i.e., slope of the regression) of individual cows. This study provides, for the first time, a longitudinal perspective of the genetic and genomic mechanisms underlying temperament, learning, and behavioral plasticity in beef cattle.

RESULTS

CT measured across years is heritable (0.38-0.53). Positive and strong genetic correlations (0.91-1.00) were observed among all CT age-group pairs and between CT and YT (0.84). Over 90% of the candidate genes identified overlapped among CT age-groups and the estimated effect of genomic markers located within important candidate genes changed over time. A small but significant genetic component was observed for learning and behavioral plasticity (heritability = 0.02 ± 0.002). Various candidate genes were identified, revealing the polygenic nature of the traits evaluated. The pathways and candidate genes identified are associated with steroid and glucocorticoid hormones, development delay, cognitive development, and behavioral changes in cattle and other species.

CONCLUSIONS

Cow temperament is highly heritable and repeatable. The changes in temperament can be genetically improved by selecting animals with favorable learning and behavioral plasticity (i.e., habituation). Furthermore, the environment explains a large part of the variation in learning and behavioral plasticity, leading to opportunities to also improve the overall temperament by refining management practices. Moreover, behavioral plasticity offers opportunities to improve the long-term animal and handler welfare through habituation.

Major royal jelly proteins influence the neurobiological regulation of the division of labor among honey bee workers

Age-based division of labor among workers is a fundamental life-history trait of many social insects, including the Western honey bee, Apis mellifera L. Extensive studies of the causation of the most pronounced transition from performing tasks in the nest to outside foraging indicate hormonal regulation of complex physiological changes. However, the proximate neurobiological mechanisms that cause the behavioral repertoire to change are still not understood and require novel approaches to be fully characterized. Thus, we established the first comprehensive monoclonal antibody microarray in honey bees with 16,320 antibodies to directly identify proteins in the brain that regulate the transition to foraging. Major royal jelly protein (MRJP) 1 and MRJP3 were identified as potential protein effectors and further investigated. A series of experimental manipulations of the workers' behavioral transition led to changes in MRJP1 and MRJP3 quantities in accordance with their presumed functional role. Injection of MRJPs into the brain resulted in increased task-reversal from foraging to nursing and decreased task-progression from nursing to foraging, while the latter was increased by injection with MRJP antibodies. Finally, down-regulation of MRJP1 and MRJP3 expression via RNAi injection into the brain increased the transition from in-hive nursing to outside foraging, confirming a causal role of these two proteins in the proximate regulation of behavior and life-history of honey bee workers. Interaction partners of MRJP1 and MRJP3 in the honey bee brain included other regulators of honey bee behavior and life history. Thus, our transformative methodological advancement of proteome analysis in honey bees reveals novel regulators of honey bee behavior, extends our understanding of the functional pleiotropy of MRJPs, and supports a general nutrition-based model of the regulation of the age-based division of labor in honey bees.

Global characterization of gene expression in the brain of starved immature Rhodnius prolixus

BACKGROUND

Rhodnius prolixus is a vector of Chagas disease and has become a model organism to study physiology, behavior, and pathogen interaction. The publication of its genome allowed initiating a process of comparative characterization of the gene expression profiles of diverse organs exposed to varying conditions. Brain processes control the expression of behavior and, as such, mediate immediate adjustment to a changing environment, allowing organisms to maximize their chances to survive and reproduce. The expression of fundamental behavioral processes like feeding requires fine control in triatomines because they obtain their blood meals from potential predators. Therefore, the characterization of gene expression profiles of key components modulating behavior in brain processes, like those of neuropeptide precursors and their receptors, seems fundamental. Here we study global gene expression profiles in the brain of starved R. prolixus fifth instar nymphs by means of RNA sequencing (RNA-Seq).

RESULTS

The expression of neuromodulatory genes such as those of precursors of neuropeptides, neurohormones, and their receptors; as well as the enzymes involved in the biosynthesis and processing of neuropeptides and biogenic amines were fully characterized. Other important gene targets such as neurotransmitter receptors, nuclear receptors, clock genes, sensory receptors, and takeouts genes were identified and their gene expression analyzed.

CONCLUSION

We propose that the set of neuromodulatory-related genes highly expressed in the brain of starved R. prolixus nymphs deserves functional characterization to allow the subsequent development of tools targeting them for bug control. As the brain is a complex structure that presents functionally specialized areas, future studies should focus on characterizing gene expression profiles in target areas, e.g. mushroom bodies, to complement our current knowledge.

The for gene as one of the drivers of foraging variations in a parasitic wasp

Foraging behaviours encompass strategies to locate resources and to exploit them. In many taxa, these behaviours are driven by a major gene called for, but the mechanisms of gene regulation vary between species. In the parasitoid wasp Venturia canescens, sexual and asexual populations coexist in sympatry but differ in life-history traits, physiology and behaviours, which could impact their foraging strategies. Here, we explored the molecular bases underpinning divergence in behaviours by testing two mutually nonexclusive hypotheses: first, the divergence in the for gene correlates with differences in foraging strategies, and second, the latter rely on a divergence in whole-genome expression. Using comparative genomics, we showed that the for gene was conserved across insects considering both sequence and gene model complexity. Polymorphism analysis did not support the occurrence of two allelic variants diverging across the two populations, yet the asexual population exhibited less polymorphism than the sexual population. Sexual and asexual transcriptomes split sharply, with 10.9% differentially expressed genes, but these were not enriched in behaviour-related genes. We showed that the for gene was more highly expressed in asexual female heads than in sexual heads and that those differences correlate with divergence in foraging behaviours in our experiment given that asexuals explored the environment more and exploited more host patches. Overall, these results suggested that fine tuning of for gene expression between populations may have led to distinct foraging behaviours. We hypothesized that reproductive polymorphism and coexistence in sympatry of sexual and asexual populations specialized to different ecological niches via divergent optima on phenotypic traits could imply adaptation through different expression patterns of the for gene and at many other loci throughout the genome.

Mblk-1/E93, an ecdysone related-transcription factor, targets synaptic plasticity-related genes in the honey bee mushroom bodies

Among hymenopteran insects, aculeate species such as bees, ants, and wasps have enlarged and morphologically elaborate mushroom bodies (MBs), a higher-order brain center in the insect, implying their relationship with the advanced behavioral traits of aculeate species. The molecular bases leading to the acquisition of complicated MB functions, however, remains unclear. We previously reported the constitutive and MB-preferential expression of an ecdysone-signaling related transcription factor, Mblk-1/E93, in the honey bee brain. Here, we searched for target genes of Mblk-1 in the worker honey bee MBs using chromatin immunoprecipitation sequence analyses and found that Mblk-1 targets several genes involved in synaptic plasticity, learning, and memory abilities. We also demonstrated that Mblk-1 expression is self-regulated via Mblk-1-binding sites, which are located upstream of Mblk-1. Furthermore, we showed that the number of the Mblk-1-binding motif located upstream of Mblk-1 homologs increased associated with evolution of hymenopteran insects. Our findings suggest that Mblk-1, which has been focused on as a developmental gene transiently induced by ecdysone, has acquired a novel expression pattern to play a role in synaptic plasticity in honey bee MBs, raising a possibility that molecular evolution of Mblk-1 may have partly contributed to the elaboration of MB function in insects.

Role of the foraging gene in worker behavioral transition in the red imported fire ant, Solenopsis invicta (Hymenoptera: Formicidae)

BACKGROUND

Worker division of labor is predominant in social insects. The foraging (for) gene, which encodes cGMP-dependent protein kinase (PKG), has been implicated in the regulation of behavioral transitions in honeybees, but information regarding its function in other social insects is scarce.

RESULTS

We investigated the role of the for (Sifor) gene in the red imported fire ant, Solenopsis invicta, and found that Sifor and PKG exhibited different expression patterns in different castes, body sizes, ages and tissues of fire ants, especially in foragers and nurses. Foragers displayed greater locomotor activity but showed no preference for larval or adult odors, whereas nurses showed lesser locomotor activity but had a strong preference for larval odors. We found that the expression of Sifor was significantly higher in the heads of foragers (compared to nurses). RNA interference-mediated Sifor knockdown in foraging workers induced behavioral transition of foragers toward the nurse phenotype characterized by reduced locomotor activity and a stronger preference for larval odors. By contrast, treating nurses with 8-Br-cGMP, an activator of PKG, resulted in behavioral transition toward the forager phenotype characterized by higher locomotor activity but reduced preference for larval odors.

CONCLUSION

Our results suggest that Sifor plays a critical role in the behavioral transition between foragers and nurses of workers, which may be a promising target for RNAi-based management of worker caste organization in S. invicta. © 2022 Society of Chemical Industry.

The foraging Gene Is Involved in the Presence of Wings and Explorative Behaviours in Parthenogenetic Females of the Aphid Myzus persicae

The foraging gene (for) encodes for a cyclic guanosine monophosphate (cGMP)-dependent protein kinase involved in behavioural plasticity in aphids and in other insects. In this paper, we analysed the complete for sequence in eight clones of the peach potato aphid Myzus persicae, reporting the presence of nonsense and frameshift mutations in three studied clones characterized by a reduced number of winged females and by the absence of exploratory behaviours. Quantitative PCR experiments evidenced similar results in clones possessing for genes with a conserved coding sequence, but low expression levels. The comparison of the for transcriptional level in Myzus persicae persicae and Myzus persicae nicotianae showed very different expression in the two studied M. p. nicotianae clones so that our data did not support a previous hypothesis suggesting that a differential for expression was related to ecological specialization of M. p. nicotianae. In view of its role in both the dispersal of winged females and exploratory behaviours, the screening of the for sequences could be useful for predicting invasions of cultivated areas by peach potato aphids.

Adolescent high-fructose corn syrup consumption leads to dysfunction in adult affective behaviors and mesolimbic proteins in male Sprague-Dawley rats

Adolescence is a critical period of development, during which the brain undergoes rapid maturation. Problematically, adolescents are the top consumers of high fructose corn syrup (HFCS) sweetened beverages and snacks, which may have neurodevelopmental consequences. While HFCS consumption has been linked to an increased likelihood of obesity and other physical health impairments, the link between HFCS and persistent behavioral changes is not yet fully established. The present study aimed to assess whether adolescent HFCS consumption could lead to alterations in adult behaviors and protein expression, following cessation. Adolescent HFCS-exposure contributed to deficits in learning and motivation on an effort-related T-Maze procedure, as well as increased immobility time in the forced swim paradigm during adulthood. Molecularly, protracted decreases in accumbal dopamine D1 and D2 receptors and protein kinase G (PKG), as well as increases in tyrosine hydroxylase and GluA2 receptor subunits, were observed following HFCS-exposure. Taken together, these data suggest that adolescent HFCS-consumption leads to protracted dysfunction in affective behaviors and alterations in accumbal proteins which persist following cessation of HFCS-consumption.

Foraging gene expression patterns in queens, workers, and males in a eusocial insect

Reproductive division of labour is based on biased expression of complementary parental behaviours, brood production (egg-laying) by queens and brood care (in particular, brood-provisioning) by workers. In many social insect species, queens provision brood when establishing colonies at the beginning of a breeding season and reproductive division of labour begins with the emergence of workers. In many social insect species, the expression of foraging (for) mRNA is associated with the intensity of foraging behaviour and therefore brood-provisioning. However, only two studies have compared queen and worker for expression levels and neither accounted for transcript splice variation. In this study, we compare the expression level of the for-α transcript variant across four life stages of the queen caste, two behavioural groups of workers, and males of a eusocial sweat bee Lasioglossum laevissimum (Smith, 1853). Foundresses collected prior to the onset of the foraging season and males had the highest for-α expression levels. All active (post-hibernatory) queens and workers had similar for-α expression levels independent of behaviour. These results suggest that the for gene in L. laevissimum acts as a primer before foraging activity and that caste-specific expression patterns correlate with the timing of foraging activity in queens and workers.

Independent variations in genome-wide expression, alternative splicing, and DNA methylation in brain tissues among castes of the buff-tailed bumblebee, Bombus terrestris

Caste differentiation in social hymenopterans is an intriguing example of phenotypic plasticity. However, the co-ordination among gene regulatory factors to mediate caste differentiation remains inconclusive. In this study, we determined the role of gene regulation and related epigenetic processes in pre-imaginal caste differentiation in the primitively eusocial bumblebee Bombus terrestris. By combining RNA-Seq data from Illumina and PacBio and accurately quantifying methylation at whole-genomic base pair resolution, we found that queens, workers, and drones mainly differentiate in gene expression but not in alternative splicing and DNA methylation. Gynes are the most distinct with the lowest global level of whole-genomic methylation and with the largest number of caste-specific transcripts and alternative splicing events. By contrast, workers exhibit few uniquely expressed or alternatively spliced genes. Moreover, several genes involved in hormone and neurotransmitter metabolism are related to caste differentiation, whereas several neuropeptides are linked with sex differentiation. Despite little genome-wide association among differential gene expression, splicing, and differential DNA methylation, the overlapped gene ontology (GO) terms point to nutrition-related activity. Therefore, variations in gene regulation correlate with the behavioral differences among castes and highlight the specialization of toolkit genes in bumblebee gynes at the beginning of the adult stage.

The Foraging Gene, a New Environmental Adaptation Player Involved in Xenobiotic Detoxification

Foraging is vital for animals, especially for food. In Drosophila melanogaster, this behavior is controlled by the foraging gene (for) which encodes a cyclic guanosine monophosphate (cGMP)-dependent protein kinase (PKG). In wild populations of Drosophila, rover individuals that exhibit long foraging trails and sitter individuals that exhibit short ones coexist and are characterized by high and low levels of PKG activity, respectively. We, therefore, postulated that rover flies are more exposed to environmental stresses, including xenobiotics contamination, than sitter flies. We then tested whether these flies differed in their ability to cope with xenobiotics by exposing them to insecticides from different chemical families. We performed toxicological tests and measured the activity and expression levels of different classes of detoxification enzymes. We have shown that a link exists between the for gene and certain cytochrome P450-dependent activities and that the expression of the insecticide-metabolizing cytochrome P450 Cyp6a2 is controlled by the for gene. An unsuspected regulatory pathway of P450s expression involving the for gene in Drosophila is revealed and we demonstrate its involvement in adaptation to chemicals in the environment. This work can serve as a basis for reconsidering adaptation to xenobiotics in light of the behavior of species, including humans.

The foraging gene as a modulator of division of labour in social insects

The social ants, bees, wasps, and termites include some of the most ecologically-successful groups of animal species. Their dominance in most terrestrial environments is attributed to their social lifestyle, which enable their colonies to exploit environmental resources with remarkable efficiency. One key attribute of social insect colonies is the division of labour that emerges among the sterile workers, which represent the majority of colony members. Studies of the mechanisms that drive division of labour systems across diverse social species have provided fundamental insights into the developmental, physiological, molecular, and genomic processes that regulate sociality, and the possible genetic routes that may have led to its evolution from a solitary ancestor. Here we specifically discuss the conserved role of the foraging gene, which encodes a cGMP-dependent protein kinase (PKG). Originally identified as a behaviourally polymorphic gene that drives alternative foraging strategies in the fruit fly Drosophila melanogaster, changes in foraging expression and kinase activity were later shown to play a key role in the division of labour in diverse social insect species as well. In particular, foraging appears to regulate worker transitions between behavioural tasks and specific behavioural traits associated with morphological castes. Although the specific neuroethological role of foraging in the insect brain remains mostly unknown, studies in genetically tractable insect species indicate that PKG signalling plays a conserved role in the neuronal plasticity of sensory, cognitive and motor functions, which underlie behaviours relevant to division of labour, including appetitive learning, aggression, stress response, phototaxis, and the response to pheromones.

Learning about quantitative genetics from Marla Sokolowski

Marla Sokolowski is a true pioneer in behavioral genetics, having made the first molecular delineation of a naturally occurring behavioral polymorphism in her work on the foraging locus in Drosophila melanogaster. The gene was subsequently found to be responsible for behavioral variants and types in many other species, both invertebrate and mammal (human). The path to get there is a paradigmatic example of how to use the power of genetic analysis, including some rather esoteric techniques, to zero in on a gene and delineate its molecular identity and its pleiotropic roles.

The Drosophila melanogaster foraging gene affects social networks

Drosophila melanogaster displays social behaviors including courtship, mating, aggression, and group foraging. Recent studies employed social network analyses (SNAs) to show that D. melanogaster strains differ in their group behavior, suggesting that genes influence social network phenotypes. Aside from genes associated with sensory function, few studies address the genetic underpinnings of these networks. The foraging gene (for) is a well-established example of a pleiotropic gene that regulates multiple behavioral phenotypes and their plasticity. In D. melanogaster, there are two naturally occurring alleles of for called rover and sitter that differ in their larval and adult food-search behavior as well as other behavioral phenotypes. Here, we hypothesize that for affects behavioral elements required to form social networks and the social networks themselves. These effects are evident when we manipulate gene dosage. We found that flies of the rover and sitter strains exhibit differences in duration, frequency, and reciprocity of pairwise interactions, and they form social networks with differences in assortativity and global efficiency. Consistent with other adult phenotypes influenced by for, rover-sitter heterozygotes show intermediate patterns of dominance in many of these characteristics. Multiple generations of backcrossing a rover allele into a sitter strain showed that many but not all of these rover-sitter differences may be attributed to allelic variation at for. Our findings reveal the significant role that for plays in affecting social network properties and their behavioral elements in Drosophila melanogaster.

Women in science: a son's perspective

I am often asked how our mother inspired my sister Moriah and me to want to become scientists. She never directly suggested we should go down that path. Instead, she shared the aspects of the natural world, that she loved, with us while keeping the non-science aspects of her job separate from our lives at home. Now, I have learned that her perspective provides insights that spark innovative discoveries, some of which challenged the status quo. Her passion for research has allowed her to pursue what she believes to be worth studying. Her personality and collaborative nature allow her to be teased at home, facilitate a room of diverse opinions, and command a hall of hundreds of people. Her respect for those around her is inspiring. My mom's trust in her trainees and collaborators allows her to answer questions that could fundamentally not be answered had she pigeonholed herself to a single field. She managed to accomplish everything while being nothing other than my mom to me, and I am so glad that I am growing into a person who can truly appreciate the woman she is to everyone else.

The foraging gene affects alcohol sensitivity, metabolism and memory in Drosophila

The genetic basis of alcohol use disorder (AUD) is complex. Understanding how natural genetic variation contributes to alcohol phenotypes can help us identify and understand the genetic basis of AUD. Recently, a single nucleotide polymorphism in the human foraging (for) gene ortholog, Protein Kinase cGMP-Dependent 1 (PRKG1), was found to be associated with stress-induced risk for alcohol abuse. However, the mechanistic role that PRKG1 plays in AUD is not well understood. We use natural variation in the Drosophila for gene to describe how variation of cGMP-dependent protein kinase (PKG) activity modifies ethanol-induced phenotypes. We found that variation in for affects ethanol-induced increases in locomotion and memory of the appetitive properties of ethanol intoxication. Further, these differences may stem from the ability to metabolize ethanol. Together, this data suggests that natural variation in PKG modulates cue reactivity for alcohol, and thus could influence alcohol cravings by differentially modulating metabolic and behavioral sensitivities to alcohol.

(Epi)Genetic Mechanisms Underlying the Evolutionary Success of Eusocial Insects

Eusocial insects, such as bees, ants, and wasps of the Hymenoptera and termites of the Blattodea, are able to generate remarkable diversity in morphology and behavior despite being genetically uniform within a colony. Most eusocial insect species display caste structures in which reproductive ability is possessed by a single or a few queens while all other colony members act as workers. However, in some species, caste structure is somewhat plastic, and individuals may switch from one caste or behavioral phenotype to another in response to certain environmental cues. As different castes normally share a common genetic background, it is believed that much of this observed within-colony diversity results from transcriptional differences between individuals. This suggests that epigenetic mechanisms, featured by modified gene expression without changing genes themselves, may play an important role in eusocial insects. Indeed, epigenetic mechanisms such as DNA methylation, histone modifications and non-coding RNAs, have been shown to influence eusocial insects in multiple aspects, along with typical genetic regulation. This review summarizes the most recent findings regarding such mechanisms and their diverse roles in eusocial insects.

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.

Gene expression and epigenetics reveal species-specific mechanisms acting upon common molecular pathways in the evolution of task division in bees

A striking feature of advanced insect societies is the existence of workers that forgo reproduction. Two broad types of workers exist in eusocial bees: nurses who care for their young siblings and the queen, and foragers who guard the nest and forage for food. Comparisons between these two worker subcastes have been performed in honeybees, but data from other bees are scarce. To understand whether similar molecular mechanisms are involved in nurse-forager differences across distinct species, we compared gene expression and DNA methylation profiles between nurses and foragers of the buff-tailed bumblebee Bombus terrestris and the stingless bee Tetragonisca angustula. These datasets were then compared to previous findings from honeybees. Our analyses revealed that although the expression pattern of genes is often species-specific, many of the biological processes and molecular pathways involved are common. Moreover, the correlation between gene expression and DNA methylation was dependent on the nucleotide context, and non-CG methylation appeared to be a relevant factor in the behavioral changes of the workers. In summary, task specialization in worker bees is characterized by a plastic and mosaic molecular pattern, with species-specific mechanisms acting upon broad common pathways across species.

Insecticides cause transcriptional alterations of endocrine related genes in the brain of honey bee foragers

Bees are exposed to endocrine active insecticides. Here we assessed expressional alteration of marker genes indicative of endocrine effects in the brain of honey bees. We exposed foragers to chlorpyrifos, cypermethrin and thiacloprid and assessed the expression of genes after exposure for 24 h, 48 h and 72 h. Chlorpyrifos caused the strongest expressional changes at 24 h characterized by induction of vitellogenin, major royal jelly protein (mrjp) 2 and 3, insulin-like peptide (ilp1), alpha-glucosidase (hbg3) and sima, and down-regulation of buffy. Cypermethrin caused minor induction of mrjp1, mrjp2, mmp1 and ilp1. The sima transcript showed down-regulation at 48 h and up-regulation at 72 h. Exposure to thiacloprid caused down-regulation of vitellogenin, mrjp1 and sima at 24 h, and hbg3 at 72 h, as well as induction of ilp1 at 48 h. The buffy transcript was down-regulated at 24 h and up-regulated at 48 h. Despite compound-specific expression patterns, each insecticide altered the expression of some of the suggested endocrine system related genes. Our study suggests that expressional changes of genes prominently expressed in nurse or forager bees, including down-regulation of buffy and mrjps and up-regulation of hbg3 and ilp1 may serve as indicators for endocrine activity of insecticides in foragers.

Automated measurement of long-term bower behaviors in Lake Malawi cichlids using depth sensing and action recognition

In the wild, behaviors are often expressed over long time periods in complex and dynamic environments, and many behaviors include direct interaction with the environment itself. However, measuring behavior in naturalistic settings is difficult, and this has limited progress in understanding the mechanisms underlying many naturally evolved behaviors that are critical for survival and reproduction. Here we describe an automated system for measuring long-term bower construction behaviors in Lake Malawi cichlid fishes, in which males use their mouths to sculpt sand into large species-specific structures for courtship and mating. We integrate two orthogonal methods, depth sensing and action recognition, to simultaneously track the developing bower structure and the thousands of individual sand manipulation behaviors performed throughout construction. By registering these two data streams, we show that behaviors can be topographically mapped onto a dynamic 3D sand surface through time. The system runs reliably in multiple species, across many aquariums simultaneously, and for up to weeks at a time. Using this system, we show strong differences in construction behavior and bower form that reflect species differences in nature, and we gain new insights into spatial, temporal, social dimensions of bower construction, feeding, and quivering behaviors. Taken together, our work highlights how low-cost tools can automatically quantify behavior in naturalistic and social environments over long timescales in the lab.

Behavior-related gene regulatory networks: A new level of organization in the brain

Neuronal networks are the standard heuristic model today for describing brain activity associated with animal behavior. Recent studies have revealed an extensive role for a completely distinct layer of networked activities in the brain-the gene regulatory network (GRN)-that orchestrates expression levels of hundreds to thousands of genes in a behavior-related manner. We examine emerging insights into the relationships between these two types of networks and discuss their interplay in spatial as well as temporal dimensions, across multiple scales of organization. We discuss properties expected of behavior-related GRNs by drawing inspiration from the rich literature on GRNs related to animal development, comparing and contrasting these two broad classes of GRNs as they relate to their respective phenotypic manifestations. Developmental GRNs also represent a third layer of network biology, playing out over a third timescale, which is believed to play a crucial mediatory role between neuronal networks and behavioral GRNs. We end with a special emphasis on social behavior, discuss whether unique GRN organization and cis-regulatory architecture underlies this special class of behavior, and review literature that suggests an affirmative answer.

C. elegans episodic swimming is driven by multifractal kinetics

Fractal scaling is a common property of temporal change in various modes of animal behavior. The molecular mechanisms of fractal scaling in animal behaviors remain largely unexplored. The nematode C. elegans alternates between swimming and resting states in a liquid solution. Here, we report that C. elegans episodic swimming is characterized by scale-free kinetics with long-range temporal correlation and local temporal clusterization, namely consistent with multifractal kinetics. Residence times in actively-moving and inactive states were distributed in a power law-based scale-free manner. Multifractal analysis showed that temporal correlation and temporal clusterization were distinct between the actively-moving state and the inactive state. These results indicate that C. elegans episodic swimming is driven by transition between two behavioral states, in which each of two transition kinetics follows distinct multifractal kinetics. We found that a conserved behavioral modulator, cyclic GMP dependent kinase (PKG) may regulate the multifractal kinetics underlying an animal behavior. Our combinatorial analysis approach involving molecular genetics and kinetics provides a platform for the molecular dissection of the fractal nature of physiological and behavioral phenomena.

Genetic Underpinnings of Host Manipulation by Ophiocordyceps as Revealed by Comparative Transcriptomics

Ant-infecting Ophiocordyceps fungi are globally distributed, host manipulating, specialist parasites that drive aberrant behaviors in infected ants, at a lethal cost to the host. An apparent increase in activity and wandering behaviors precedes a final summiting and biting behavior onto vegetation, which positions the manipulated ant in a site beneficial for fungal growth and transmission. We investigated the genetic underpinnings of host manipulation by: (i) producing a high-quality hybrid assembly and annotation of the Ophiocordyceps camponoti-floridani genome, (ii) conducting laboratory infections coupled with RNAseq of O. camponoti-floridani and its host, Camponotus floridanus, and (iii) comparing these data to RNAseq data of Ophiocordyceps kimflemingiae and Camponotus castaneus as a powerful method to identify gene expression patterns that suggest shared behavioral manipulation mechanisms across Ophiocordyceps-ant species interactions. We propose differentially expressed genes tied to ant neurobiology, odor response, circadian rhythms, and foraging behavior may result by activity of putative fungal effectors such as enterotoxins, aflatrem, and mechanisms disrupting feeding behaviors in the ant.

Transcriptome analysis of a social caterpillar, Drepana arcuata: De novo assembly, functional annotation and developmental analysis

The masked birch caterpillar, Drepana arcuata, provides an excellent opportunity to study mechanisms mediating developmental changes in social behaviour. Larvae transition from being social to solitary during the 3^rd instar, concomitant with shifts in their use of acoustic communication. In this study we characterize the transcriptome of D. arcuata to initiate sociogenomic research of this lepidopteran insect. We assembled and annotated the combined larval transcriptome of “social” early and “solitary” late instars using next generation Illumina sequencing, and used this transcriptome to conduct differential gene expression analysis of the two behavioural phenotypes. A total of 211,012,294 reads generated by RNA sequencing were assembled into 231,348 transcripts and 116,079 unigenes for the functional annotation of the transcriptome. Expression analysis revealed 3300 transcripts that were differentially expressed between early and late instars, with a large proportion associated with development and metabolic processes. We independently validated differential expression patterns of selected transcripts using RT-qPCR. The expression profiles of social and solitary larvae revealed differentially expressed transcripts coding for gene products that have been previously reported to influence social behaviour in other insects (e.g. cGMP- and cAMP- dependent kinases, and bioamine receptors). This study provides the first transcriptomic resources for a lepidopteran species belonging to the superfamily Drepanoidea, and gives insight into genetic factors mediating grouping behaviour in insects.

Functional genomics of parental care of insects

Parental care was likely the first step most lineages made towards sociality. However, the molecular mechanisms that generate parental care are not broadly characterized. Insects are important as an evolutionary independent group from classic models of parental care, such as, house mice. They provide an opportunity to test the generality of our understanding. With this review, I survey the functional genomics of parental care of insects, summarize several recent advances in the broader framework for studying and understanding parental care, and finish with suggested priorities for further research. Although there are too few studies to draw definitive conclusions, I argue that natural selection appears to be rewiring existing gene networks to produce parental care, that the epigenetic mechanisms influencing parental care are not well understood, and, as an interesting early consensus, that genes strongly associated with carer/offspring interactions appear biased towards proteins that are secreted. I summarize the studies that have functionally validate candidate genes and highlight the increasing need to perform this work. I finish with arguments for both conceptual and practical changes moving forward. I argue that future work can increase the use of predictive frameworks, broaden its definition of conservation of mechanism to gene networks rather than single genes, and increase the use of more established comparative methods. I further highlight the practical considerations of standardizing analyses and reporting, increasing the sampling of both carers and offspring, better characterizing gene regulatory networks, better characterizing taxonomically restricted genes and any consistent role they have underpinning parental care, and using factorial designs to disentangle the influence of multiple variables on the expression of parental care.

Co-existing locomotory activity and gene expression profiles in a kissing-bug vector of Chagas disease

The triatomine bug Rhodnius prolixus is a main vector of Chagas disease, which affects several million people in Latin-America. These nocturnal insects spend most of their locomotory activity during the first hours of the scotophase searching for suitable hosts. In this study we used multivariate analysis to characterize spontaneous locomotory activity profiles presented by 5th instar nymphs. In addition, we investigated whether sex and the expression of the foraging (Rpfor) gene could modulate this behavioral trait. Hierarchical Clustering and Redundancy Analyses detected individuals with distinct locomotory profiles. In addition to a great variation in locomotory intensity, we found that a proportion of nymphs walked during unusual time intervals. Locomotory activity profiles were mostly affected by the cumulative activity expressed by the nymphs. These effects promoted by cumulative activity were in turn influenced by nymph sex. Sex and the Rpfor expression had a significant influence on the profiles, as well as in the levels of total activity. In conclusion, the locomotory profiles evinced by the multivariate analyses suggest the co-existence of different foraging strategies in bugs. Additionally, we report sex-specific effects on the locomotion patterns of 5th instar R. prolixus, which are apparently modulated by the differential expression of the Rpfor gene.

The physiology of movement

Movement, from foraging to migration, is known to be under the influence of the environment. The translation of environmental cues to individual movement decision making is determined by an individual's internal state and anticipated to balance costs and benefits. General body condition, metabolic and hormonal physiology mechanistically underpin this internal state. These physiological determinants are tightly, and often genetically linked with each other and hence central to a mechanistic understanding of movement. We here synthesise the available evidence of the physiological drivers and signatures of movement and review (1) how physiological state as measured in its most coarse way by body condition correlates with movement decisions during foraging, migration and dispersal, (2) how hormonal changes underlie changes in these movement strategies and (3) how these can be linked to molecular pathways. We reveale that a high body condition facilitates the efficiency of routine foraging, dispersal and migration. Dispersal decision making is, however, in some cases stimulated by a decreased individual condition. Many of the biotic and abiotic stressors that induce movement initiate a physiological cascade in vertebrates through the production of stress hormones. Movement is therefore associated with hormone levels in vertebrates but also insects, often in interaction with factors related to body or social condition. The underlying molecular and physiological mechanisms are currently studied in few model species, and show -in congruence with our insights on the role of body condition- a central role of energy metabolism during glycolysis, and the coupling with timing processes during migration. Molecular insights into the physiological basis of movement remain, however, highly refractory. We finalise this review with a critical reflection on the importance of these physiological feedbacks for a better mechanistic understanding of movement and its effects on ecological dynamics at all levels of biological organization.

Rhythms in Foraging Behavior and Expression Patterns of the Foraging Gene in Solenopsis invicta (Hymenoptera: Formicidae) in relation to Photoperiod

The foraging gene (for) is associated with foraging and other associated behaviors in social insect species. Photoperiod is known to entrain the rhythmic biological functions of ants; however, how photoperiod might influence the intensity and duration of foraging, and the expression of for, remains unexplored. This study determined the correlation between rhythm in foraging behavior and expression of the foraging gene (Sifor) mRNA in red imported fire ant, Solenopsis invicta Buren. Foragers were exposed to three photoperiod conditions (12:12 [L:D], 24:0 [L:D], and 0:24 [L:D]) in the laboratory and foraging activities were recorded using a video-computer recording system. Sifor expression in the foragers was tested using real-time reverse-transcription quantitative PCR. Results revealed that foraging activity rhythm and Sifor expression profile were unimodal under all three photoperiod conditions. Levels of foraging activity were associated with photoperiodic modification, a stable phase difference between the onset of activity and the onset of gene expression was discovered. Light-dark transients stimulated foraging activity in 12:12 (L:D). There were significant daily oscillations (amplitude of 0.21 ± 0.08 for 12:12 [L:D], 0.12 ± 0.02 for 24:0 [L:D], and 0.09 ± 0.01 for 0:24 [L:D]) in the expression of Sifor. A positive relationship (r = 0.5903, P < 0.01) was found between the expression level of Sifor and foraging activity, which indicated that Sifor is linked to some extent to foraging behavior. Our results demonstrated that foragers could adjust the rhythms in foraging behavior according to light-dark cycle and suggested that Sifor may play an important role in the response of S. invicta to photoperiod.

Social inhibition maintains adaptivity and consensus of honeybees foraging in dynamic environments

To effectively forage in natural environments, organisms must adapt to changes in the quality and yield of food sources across multiple timescales. Individuals foraging in groups act based on both their private observations and the opinions of their neighbours. How do these information sources interact in changing environments? We address this problem in the context of honeybee colonies whose inhibitory social interactions promote adaptivity and consensus needed for effective foraging. Individual and social interactions within a mathematical model of collective decisions shape the nutrition yield of a group foraging from feeders with temporally switching quality. Social interactions improve foraging from a single feeder if temporal switching is fast or feeder quality is low. When the colony chooses from multiple feeders, the most beneficial form of social interaction is direct switching, whereby bees flip the opinion of nest-mates foraging at lower-yielding feeders. Model linearization shows that effective social interactions increase the fraction of the colony at the correct feeder (consensus) and the rate at which bees reach that feeder (adaptivity). Our mathematical framework allows us to compare a suite of social inhibition mechanisms, suggesting experimental protocols for revealing effective colony foraging strategies in dynamic environments.

A Multiscale Review of Behavioral Variation in Collective Foraging Behavior in Honey Bees

The emergence of collective behavior from local interactions is a widespread phenomenon in social groups. Previous models of collective behavior have largely overlooked the impact of variation among individuals within the group on collective dynamics. Honey bees (Apis mellifera) provide an excellent model system for exploring the role of individual differences in collective behavior due to their high levels of individual variation and experimental tractability. In this review, we explore the causes and consequences of individual variation in behavior for honey bee foraging across multiple scales of organization. We summarize what is currently known about the genetic, developmental, and neurophysiological causes of individual differences in learning and memory among honey bees, as well as the consequences of this variation for collective foraging behavior and colony fitness. We conclude with suggesting promising future directions for exploration of the genetic and physiological underpinnings of individual differences in behavior in this model system.

Genetics in the Honey Bee: Achievements and Prospects toward the Functional Analysis of Molecular and Neural Mechanisms Underlying Social Behaviors

The European honey bee is a model organism for studying social behaviors. Comprehensive analyses focusing on the differential expression profiles of genes between the brains of nurse bees and foragers, or in the mushroom bodies—the brain structure related to learning and memory, and multimodal sensory integration—has identified candidate genes related to honey bee behaviors. Despite accumulating knowledge on the expression profiles of genes related to honey bee behaviors, it remains unclear whether these genes actually regulate social behaviors in the honey bee, in part because of the scarcity of genetic manipulation methods available for application to the honey bee. In this review, we describe the genetic methods applied to studies of the honey bee, ranging from classical forward genetics to recently developed gene modification methods using transposon and CRISPR/Cas9. We then discuss future functional analyses using these genetic methods targeting genes identified by the preceding research. Because no particular genes or neurons unique to social insects have been found yet, further exploration of candidate genes/neurons correlated with sociality through comprehensive analyses of mushroom bodies in the aculeate species can provide intriguing targets for functional analyses, as well as insight into the molecular and neural bases underlying social behaviors.