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The past decade of social insect research has seen rapid development in automated behavioral tracking and molecular profiling of the nervous system, two distinct but complementary lines of inquiry into phenotypic variation across individuals, colonies, populations, and species. These experimental strategies have developed largely in parallel, as automated tracking generates a continuous stream of behavioral data, while, in contrast, 'omics-based profiling provides a single 'snapshot' of the brain. Better integration of these approaches applied to studying variation in social behavior will reveal the underlying genetic and neurobiological mechanisms that shape the evolution and diversification of social life. In this review, we discuss relevant advances in both fields and propose new strategies to better elucidate the molecular and behavioral innovations that generate social life., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Comparative genomic studies of social insects suggest that changes in gene regulation are associated with evolutionary transitions in social behavior, but the activity of predicted regulatory regions has not been tested empirically. We used self-transcribing active regulatory region sequencing, a high-throughput enhancer discovery tool, to identify and measure the activity of enhancers in the socially variable sweat bee, Lasioglossum albipes. We identified over 36,000 enhancers in the L. albipes genome from 3 social and 3 solitary populations. Many enhancers were identified in only a subset of L. albipes populations, revealing rapid divergence in regulatory regions within this species. Population-specific enhancers were often proximal to the same genes across populations, suggesting compensatory gains and losses of regulatory regions may preserve gene activity. We also identified 1,182 enhancers with significant differences in activity between social and solitary populations, some of which are conserved regulatory regions across species of bees. These results indicate that social trait variation in L. albipes is associated with the fine-tuning of ancient enhancers as well as lineage-specific regulatory changes. Combining enhancer activity with population genetic data revealed variants associated with differences in enhancer activity and identified a subset of differential enhancers with signatures of selection associated with social behavior. Together, these results provide the first empirical map of enhancers in a socially flexible bee and highlight links between cis-regulatory variation and the evolution of social behavior., Competing Interests: Conflict of Interest The authors have no conflict of interest to declare., (© The Author(s) 2024. Published by Oxford University Press on behalf of Society for Molecular Biology and Evolution.)

Season length and its associated variables can influence the expression of social behaviours, including the occurrence of eusociality in insects. Eusociality can vary widely across environmental gradients, both within and between different species. Numerous theoretical models have been developed to examine the life history traits that underlie the emergence and maintenance of eusociality, yet the impact of seasonality on this process is largely uncharacterized. Here, we present a theoretical model that incorporates season length and offspring development time into a single, individual-focused model to examine how these factors can shape the costs and benefits of social living. We find that longer season lengths and faster brood development times are sufficient to favour the emergence and maintenance of a social strategy, while shorter seasons favour a solitary one. We also identify a range of season lengths where social and solitary strategies can coexist. Moreover, our theoretical predictions are well matched to the natural history and behaviour of two flexibly eusocial bee species, suggesting that our model can make realistic predictions about the evolution of different social strategies. Broadly, this work reveals the crucial role that environmental conditions can have in shaping social behaviour and its evolution and it underscores the need for further models that explicitly incorporate such variation to study the evolutionary trajectories of eusociality.

Natural variation can provide important insights into the genetic and environmental factors that shape social behaviour and its evolution. The sweat bee, Lasioglossum baleicum, is a socially flexible bee capable of producing both solitary and eusocial nests. We demonstrate that within a single nesting aggregation, soil temperatures are a strong predictor of the social structure of nests. Sites with warmer temperatures in the spring have a higher frequency of social nests than cooler sites, perhaps because warmer temperatures provide a longer reproductive window for those nests. To identify the molecular correlates of this behavioural variation, we generated a de novo genome assembly for L. baleicum, and we used transcriptomic profiling to compare adults and developing offspring from eusocial and solitary nests. We find that adult, reproductive females have similar expression profiles regardless of social structure in the nest, but that there are strong differences between reproductive females and workers from social nests. We also find substantial differences in the transcriptomic profiles of stage-matched pupae from warmer, social-biased sites compared to cooler, solitary-biased sites. These transcriptional differences are strongly predictive of adult reproductive state, suggesting that the developmental environment may set the stage for adult behaviours in L. baleicum. Together, our results help to characterize the molecular mechanisms shaping variation in social behaviour and highlight a potential role of environmental tuning during development as a factor shaping adult behaviour and physiology in this socially flexible bee., (© 2023 The Authors. Molecular Ecology published by John Wiley & Sons Ltd.)

1. Significant advances in computational ethology have allowed the quantification of behaviour in unprecedented detail. Tracking animals in social groups, however, remains challenging as most existing methods can either capture pose or robustly retain individual identity over time but not both. 2. To capture finely resolved behaviours while maintaining individual identity, we built NAPS (NAPS is ArUco Plus SLEAP), a hybrid tracking framework that combines state-of-the-art, deep learning-based methods for pose estimation (SLEAP) with unique markers for identity persistence (ArUco). We show that this framework allows the exploration of the social dynamics of the common eastern bumblebee ( Bombus impatiens ). 3. We provide a stand-alone Python package for implementing this framework along with detailed documentation to allow for easy utilization and expansion. We show that NAPS can scale to long timescale experiments at a high frame rate and that it enables the investigation of detailed behavioural variation within individuals in a group. 4. Expanding the toolkit for capturing the constituent behaviours of social groups is essential for understanding the structure and dynamics of social networks. NAPS provides a key tool for capturing these behaviours and can provide critical data for understanding how individual variation influences collective dynamics., Competing Interests: CONFLIC T OF INTEREST STATEMENT The authors have no conflict of interest to declare.

Here, we reveal an unanticipated role of the blood-brain barrier (BBB) in regulating complex social behavior in ants. Using scRNA-seq, we find localization in the BBB of a key hormone-degrading enzyme called juvenile hormone esterase (Jhe), and we show that this localization governs the level of juvenile hormone (JH3) entering the brain. Manipulation of the Jhe level reprograms the brain transcriptome between ant castes. Although ant Jhe is retained and functions intracellularly within the BBB, we show that Drosophila Jhe is naturally extracellular. Heterologous expression of ant Jhe into the Drosophila BBB alters behavior in fly to mimic what is seen in ants. Most strikingly, manipulation of Jhe levels in ants reprograms complex behavior between worker castes. Our study thus uncovers a remarkable, potentially conserved role of the BBB serving as a molecular gatekeeper for a neurohormonal pathway that regulates social behavior., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Sweat bees have repeatedly gained and lost eusociality, a transition from individual to group reproduction. Here we generate chromosome-length genome assemblies for 17 species and identify genomic signatures of evolutionary trade-offs associated with transitions between social and solitary living. Both young genes and regulatory regions show enrichment for these molecular patterns. We also identify loci that show evidence of complementary signals of positive and relaxed selection linked specifically to the convergent gains and losses of eusociality in sweat bees. This includes two pleiotropic proteins that bind and transport juvenile hormone (JH)-a key regulator of insect development and reproduction. We find that one of these proteins is primarily expressed in subperineurial glial cells that form the insect blood-brain barrier and that brain levels of JH vary by sociality. Our findings are consistent with a role of JH in modulating social behaviour and suggest that eusocial evolution was facilitated by alteration of the proteins that bind and transport JH, revealing how an ancestral developmental hormone may have been co-opted during one of life's major transitions. More broadly, our results highlight how evolutionary trade-offs have structured the molecular basis of eusociality in these bees and demonstrate how both directional selection and release from constraint can shape trait evolution., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

Social isolation, particularly in early life, leads to deleterious physiological and behavioral outcomes. Here, we leverage new high-throughput tools to comprehensively investigate the impact of isolation in the bumblebee, Bombus impatiens, from behavioral, molecular, and neuroanatomical perspectives. We reared newly emerged bumblebees in complete isolation, in small groups, or in their natal colony, and then analyzed their behaviors while alone or paired with another bee. We find that when alone, individuals of each rearing condition show distinct behavioral signatures. When paired with a conspecific, bees reared in small groups or in the natal colony express similar behavioral profiles. Isolated bees, however, showed increased social interactions. To identify the neurobiological correlates of these differences, we quantified brain gene expression and measured the volumes of key brain regions for a subset of individuals from each rearing condition. Overall, we find that isolation increases social interactions and disrupts gene expression and brain development. Limited social experience in small groups is sufficient to preserve typical patterns of brain development and social behavior., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Low doses of dopamine D 1 agonists improve working memory-related behavior, but high doses eliminate the improvement, thus yielding an 'inverted-U' dose-response curve. This dose-dependency also occurs at the single neuron level in the prefrontal cortex where the cellular basis of working memory is represented. Because signaling mechanisms are unclear, we examined this process at the neuron population level. Two D 1 agonists (2-methyldihydrexidine and CY208,243) having different signaling bias were tested in rats performing a spatial working memory-related T-maze task. 2-Methyldihydrexidine is slightly bias toward D 1 -mediated β-arrestin-related signaling as it is a full agonist at adenylate cyclase and a super-agonist at β-arrestin recruitment, whereas CY208,243 is slightly bias toward D 1 -mediated cAMP signaling as it has relatively high intrinsic activity at adenylate cyclase, but is a partial agonist at β-arrestin recruitment. Both compounds had the expected inverted U dose-dependency in modulating prefrontal neuronal activities, albeit with important differences. Although CY208,243 was superior in improving the strength of neuronal outcome sensitivity to the working memory-related choice behavior in the T-maze, 2-methyldihydrexidine better reduced neuron-to-neuron variation. Interestingly, at the neuron population level, both drugs affected the percentage, uniformity, and ensemble strength of neuronal sensitivity in a complicated dose-dependent fashion, but the overall effect suggested higher efficiency and potency of 2-methyldihydrexidine compared to CY208,243. The differences between 2-methyldihydrexidine and CY208,243 may be related to their specific D 1 signaling. These results suggest that D 1 -related dose-dependent regulation of working memory can be modified differentially by functionally selective ligands, theoretically increasing the balance between desired and undesired effects., Competing Interests: RM has interests in issued and pending patents related to dopamine D1 receptor mechanisms that constitute a conflict of interest for which there is University oversight. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Yang, Kocher, Lewis and Mailman.)

The desire to understand how the brain generates and patterns behavior has driven rapid methodological innovation in tools to quantify natural animal behavior. While advances in deep learning and computer vision have enabled markerless pose estimation in individual animals, extending these to multiple animals presents unique challenges for studies of social behaviors or animals in their natural environments. Here we present Social LEAP Estimates Animal Poses (SLEAP), a machine learning system for multi-animal pose tracking. This system enables versatile workflows for data labeling, model training and inference on previously unseen data. SLEAP features an accessible graphical user interface, a standardized data model, a reproducible configuration system, over 30 model architectures, two approaches to part grouping and two approaches to identity tracking. We applied SLEAP to seven datasets across flies, bees, mice and gerbils to systematically evaluate each approach and architecture, and we compare it with other existing approaches. SLEAP achieves greater accuracy and speeds of more than 800 frames per second, with latencies of less than 3.5 ms at full 1,024 × 1,024 image resolution. This makes SLEAP usable for real-time applications, which we demonstrate by controlling the behavior of one animal on the basis of the tracking and detection of social interactions with another animal., (© 2022. The Author(s).)

Background: Despite the presence of multiple classification systems for discoid meniscus, no system has yet to demonstrate utility in predicting the need for meniscal repair. The purpose of this study was to correlate characteristics associated with meniscal repair and propose a model that can inform preoperative planning and initial counseling of surgical plans and expectations., Methods: Medical and operative records of 434 knees with lateral discoid meniscus in children and adolescents treated between 1991 and 2016 were reviewed retrospectively to determine the surgical procedure performed (saucerization with or without meniscal repair), discoid meniscal morphology and stability, and location and type of any associated tear. Univariate associations between discoid meniscal characteristics and surgery type were calculated and a logistic regression model of surgery type was generated., Results: In univariate models, unstable menisci (93%, or 179/204, P<0.001) and menisci with tears extending peripherally (75%, or 85/204, P<0.001) were more likely to receive surgery with repair. In isolation, instability demonstrated 89% sensitivity and 94% specificity in predicting surgery with repair. A logistic regression model including stability, tear, and their interaction (stability×tear) showed that that the odds of unstable lateral discoid menisci receiving surgery with repair was 114 times higher than stable menisci (P<0.001) while lateral discoid menisci with peripherally extending tears had 6.4 times higher odds of receiving repair than those that had an isolated central tear (P<0.001)., Conclusion: Stability and tear location of lateral discoid menisci were associated with surgical treatment in univariate and logistic regression models. The proposed classification system, in which menisci are classified by stability [Stable (S0), Unstable (S1), morphology (Incomplete (M0), Complete (M1))], and tear [No tear (T0), Central tear, isolated (T1), or Central tear, peripheral extension (T2)], is easily remembered and predicts surgical repair for discoid menisci. This scheme can serve to inform preoperative planning and initial counseling of primary surgical management and postoperative expectations. Subsequent research should develop a system that predicts meniscal survival and patient outcomes following the index operation., Level of Evidence: Level III., Competing Interests: The authors declare no conflicts of interest., (Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.)

Background: Medial discoid meniscus (MDM) is an exceedingly rare anatomic abnormality that presents similarly to other meniscal pathologies. Symptomatic MDM is typically managed arthroscopically with mixed short-term and long-term outcomes, although the existing knowledge about MDM is limited. The purpose of this study was to describe the presentation and surgical treatment of MDM in pediatric and adolescent patients., Methods: Medical records of 12 knees with MDM in 8 pediatric and adolescent patients treated between 1991 and 2016 were reviewed retrospectively for patient characteristics, clinical manifestations, radiographic findings, operative techniques, and surgical outcomes., Results: Of the 446 knees diagnosed arthroscopically with discoid menisci, lateral discoid meniscus was noted in 434 knees (97.3%) and MDM was present in 12 knees (2.7%). The MDM series included 8 patients of mean age 13.8 years (range: 7.8 to 19.8), of which 5 were males (63%), and 4 (50%) had bilateral involvement. Of the 11 knees with available clinical records, all cases presented symptomatically (pain, mechanical symptoms); 10 (91%) had concurrent physical exam findings. On intraoperative examination, discoid morphologies were described as complete in 4/8 knees (50%) or incomplete in 4/8 (50%), with associated instability in 6/12 (50%). Meniscal tears were reported in 9 cases (75%)-primarily, horizontal cleavage tears. Saucerization was performed in 11 knees (92%), with medial meniscal repair in 7 (58%), when indicated. Retear of the medial meniscus occurred in 4/11 knees (36%) at a mean of 25.8 months postoperation; 2 knees required revisions. One knee developed arthrofibrosis and underwent arthroscopic lysis of adhesions., Conclusions: MDM is a rare diagnosis, representing 3% of all discoid menisci, with a nonspecific clinical manifestation. Operative management of symptomatic MDM typically involves saucerization and meniscal repair, when indicated, for concurrent tears. Symptom resolution is common short-term, but long-term outcomes include recurrent meniscal tears. Subsequent observational studies are important to evaluate long-term outcomes, such as arthritic changes, with the advancement of arthroscopic techniques for meniscal preservation., Level of Evidence: Level IV-retrospective case series., Competing Interests: The authors declare no conflicts of interest., (Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.)

Background: Discoid meniscus is a congenital variant typically affecting the lateral meniscus of the knee. Historically, surgical intervention when symptomatic consisted of total meniscectomy; however, after degenerative changes were observed, current treatments now focus on rim preservation with arthroscopic saucerization and meniscal repair for instability, when indicated. The purpose of our study was to examine long-term patient-reported outcomes of lateral discoid meniscus (LDM) treated with meniscal-preserving techniques., Methods: Ninety-eight patients treated arthroscopically for LDM at a single institution at a minimum of 15 years ago were retrospectively identified and contacted by mailers and telephone to participate. Subjective functional outcomes and patient satisfaction data were collected using a questionnaire that included the validated International Knee Documentation Committee Subjective Knee Evaluation Form, Lysholm Score, Marx Activity Rating Scale, Tegner Activity Score, and Western Ontario and McMaster University Osteoarthritis Index Osteoarthritis Index. Patient and surgical characteristics and patient-reported outcomes were summarized by mean and SD, median and interquartile range (interquartile range), or frequency and percent, as appropriate., Results: Of the 46 patients contacted (response rate of 46/98 eligible), 25 (54%) completed the questionnaires. The mean (±SD) age at initial surgery was 10.8 (±3.4) and 30.3 (±3.7) years at final follow-up. The mean (±SD) follow-up time from initial surgery was 19.5 (±2.8) years (range, 16 to 27). Patient-reported outcomes included: International Knee Documentation Committee 77.4±17.2, Lysholm 78.6±21, Western Ontario and McMaster University Osteoarthritis Index 7.6±11.3, Tegner Activity 7 (of 10), and Marx Activity Rating Scale 8 (of 10). Eleven (44%) cases underwent subsequent LDM-related surgery on the ipsilateral knee(s). There were no cases of total knee replacement., Conclusions: Overall, patient-reported outcomes were favorable at a minimum of 15-year follow-up after rim-preserving saucerization of LDM. While two thirds of patients were satisfied with their surgical outcomes, nearly half of patients underwent revision saucerization with or without meniscal repair. Subsequent long-term follow-up studies with objective outcome measures are important to further elucidate the natural history of LDM and understand how rim-preserving procedures may prevent the development of degenerative processes., Level of Evidence: Level IV-case series, prognostic study., Competing Interests: The authors declare no conflicts of interest., (Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.)

Background: Discoid meniscus is a congenital variant, typically involving the lateral meniscus, that comprises a spectrum of meniscal shapes and degrees of instability in an estimated 1% to 15% of the population. The purpose of this study was to describe the clinical and operative course of a large cohort of children and adolescents patients with symptomatic lateral discoid meniscus., Methods: Medical records of 470 knees with symptomatic lateral discoid meniscus in 401 patients ages 18 years or younger diagnosed at a single institution between 1991 and 2016 were reviewed retrospectively for patient characteristics, treatment course (nonoperative and/or operative), and complications. Surgical reports were reviewed in the operative group., Results: The series included 401 patients of mean age 11.6 years (range: 1 mo-18.9 y), of which 222 (55%) were female, and 69 (17%) had bilateral involvement. Of 470 knees, 83 (18%) were initially managed nonoperatively. Of these, 32 knees (39%) failed nonoperative management and were converted to surgical treatment at a median of 7.9 months (interquartile range: 4.0-15.1). In total, 419 knees were managed surgically with saucerization (partial meniscectomy) with or without meniscal repair/stabilization; 84 knees (20%) required at least one concurrent nonmeniscal procedure. Discoid meniscus tears were reported in 264/419 knees (63%) intraoperatively; horizontal cleavage tears were most common. Reoperation was required for 66/379 cases (17%) with clinical follow-up, at a median of 19.6 months (range: 9.2-34.9) after index saucerization; 60/379 cases (16%) had ongoing pain and/or mechanical symptoms at final follow-up., Conclusion: With a failure rate of 39% (32/83 knees), nonoperative management for discoid lateral meniscus frequently convert to surgical treatment. During surgery, meniscus tearing and instability are common and should be anticipated. Postoperatively, 33% (126/379) of knees with clinical follow-up underwent either reoperation, or had ongoing symptoms of the knee at final follow-up. Discoid mensical retear is the most common complication (94%, 62/66) prompting repeat surgery, and should be discussed with families before the index operation., Level of Evidence: Level IV-descriptive case series., Competing Interests: The authors declare no conflicts of interest., (Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.)

The evolutionary origins of eusociality represent increases in complexity from individual to caste-based, group reproduction. These behavioural transitions have been hypothesized to go hand in hand with an increased ability to regulate when and where genes are expressed. Bees have convergently evolved eusociality up to five times, providing a framework to test this hypothesis. To examine potential links between putative gene regulatory elements and social evolution, we compare alignable, non-coding sequences in 11 diverse bee species, encompassing three independent origins of reproductive division of labour and two elaborations of eusocial complexity. We find that rates of evolution in a number of non-coding sequences correlate with key social transitions in bees. Interestingly, while we find little evidence for convergent rate changes associated with independent origins of social behaviour, a number of molecular pathways exhibit convergent rate changes in conjunction with subsequent elaborations of social organization. We also present evidence that many novel non-coding regions may have been recruited alongside the origin of sociality in corbiculate bees; these loci could represent gene regulatory elements associated with division of labour within this group. Thus, our findings are consistent with the hypothesis that gene regulatory innovations are associated with the evolution of eusociality and illustrate how a thorough examination of both coding and non-coding sequence can provide a more complete understanding of the molecular mechanisms underlying behavioural evolution. This article is part of the theme issue 'Convergent evolution in the genomics era: new insights and directions'.

The emergence of eusociality represents a major evolutionary transition from solitary to group reproduction. The most commonly studied eusocial species, honey bees and ants, represent the behavioral extremes of social evolution but lack close relatives that are non-social. Unlike these species, the halictid bee Lasioglossum albipes produces both solitary and eusocial nests and this intraspecific variation has a genetic basis. Here, we identify genetic variants associated with this polymorphism, including one located in the intron of syntaxin 1a (syx1a), a gene that mediates synaptic vesicle release. We show that this variant can alter gene expression in a pattern consistent with differences between social and solitary bees. Surprisingly, syx1a and several other genes associated with sociality in L. albipes have also been implicated in autism spectrum disorder in humans. Thus, genes underlying behavioral variation in L. albipes may also shape social behaviors across a wide range of taxa, including humans.

Social interactions can facilitate transmission of microbes between individuals, reducing variation in gut communities within social groups. Thus, the evolution of social behaviours and symbiont community composition have the potential to be tightly linked. We explored this connection by characterizing the diversity of bacteria associated with both eusocial and solitary bee species within the behaviourally variable family Halictidae using 16S amplicon sequencing. Contrary to expectations, we found few differences in bacterial abundance or variation between social forms; most halictid species appear to share similar gut bacterial communities. However, several strains of Sodalis, a genus described as a symbiont in a variety of insects but yet to be characterized in bees, differ in abundance between eusocial and solitary bees. Phylogenetic reconstructions based on whole-genome alignments indicate that Sodalis has independently colonized halictids at least three times. These strains appear to be mutually exclusive within individual bees, although they are not host-species-specific and no signatures of vertical transmission were observed, suggesting that Sodalis strains compete for access to hosts. The symbiosis between halictids and Sodalis therefore appears to be in its early stages., Competing Interests: We declare we have no competing interests.

Bee viral ecology is a fascinating emerging area of research: viruses exert a range of effects on their hosts, exacerbate impacts of other environmental stressors, and, importantly, are readily shared across multiple bee species in a community. However, our understanding of bee viral communities is limited, as it is primarily derived from studies of North American and European Apis mellifera populations. Here, we examined viruses in populations of A. mellifera and 11 other bee species from 9 countries, across 4 continents and Oceania. We developed a novel pipeline to rapidly and inexpensively screen for bee viruses. This pipeline includes purification of encapsulated RNA/DNA viruses, sequence-independent amplification, high throughput sequencing, integrated assembly of contigs, and filtering to identify contigs specifically corresponding to viral sequences. We identified sequences for (+)ssRNA, (-)ssRNA, dsRNA, and ssDNA viruses. Overall, we found 127 contigs corresponding to novel viruses (i.e. previously not observed in bees), with 27 represented by >0.1% of the reads in a given sample, and 7 contained an RdRp or replicase sequence which could be used for robust phylogenetic analysis. This study provides a sequence-independent pipeline for viral metagenomics analysis, and greatly expands our understanding of the diversity of viruses found in bee communities.

The original version of the Article contained incorrect citation information in reference 67. The reference should read "Russell, A. L., Morrison, S. J., Moschonas, E. H. & Papaj, D. R. Patterns of pollen and nectar foraging specialization by bumblebees over multiple timescales using RFID. Sci. Rep. 7, 1-13 (2017)." This error has now been corrected in the PDF and HTML versions of the Article.

Individuals in social insect colonies cooperate to perform collective work. While colonies often respond to changing environmental conditions by flexibly reallocating workers to different tasks, the factors determining which workers switch and why are not well understood. Here, we use an automated tracking system to continuously monitor nest behavior and foraging activity of uniquely identified workers from entire bumble bee (Bombus impatiens) colonies foraging in a natural outdoor environment. We show that most foraging is performed by a small number of workers and that the intensity and distribution of foraging is actively regulated at the colony level in response to forager removal. By analyzing worker nest behavior before and after forager removal, we show that spatial fidelity of workers within the nest generates uneven interaction with relevant localized information sources, and predicts which workers initiate foraging after disturbance. Our results highlight the importance of spatial fidelity for structuring information flow and regulating collective behavior in social insect colonies.

Social animals must communicate to define group membership and coordinate social organization. For social insects, communication is predominantly mediated through chemical signals, and as social complexity increases, so does the requirement for a greater diversity of signals. This relationship is particularly true for advanced eusocial insects, including ants, bees, and wasps, whose chemical communication systems have been well-characterized. However, we know surprisingly little about how these communication systems evolve during the transition between solitary and group living. Here, we demonstrate that the sensory systems associated with signal perception are evolutionarily labile. In particular, we show that differences in signal production and perception are tightly associated with changes in social behavior in halictid bees. Our results suggest that social species require a greater investment in communication than their solitary counterparts and that species that have reverted from eusociality to solitary living have repeatedly reduced investment in these potentially costly sensory perception systems., Competing Interests: The authors declare no conflict of interest.

Changes in gene regulation that underlie phenotypic evolution can be encoded directly in the DNA sequence or mediated by chromatin modifications such as DNA methylation. It has been hypothesized that the evolution of eusocial division of labor is associated with enhanced gene regulatory potential, which may include expansions in DNA methylation in the genomes of Hymenoptera (bees, ants, wasps, and sawflies). Recently, this hypothesis garnered support from analyses of a commonly used metric to estimate DNA methylation in silico, CpG content. Here, we test this hypothesis using direct, nucleotide-level measures of DNA methylation across nine species of Hymenoptera. In doing so, we generated new DNA methylomes for three species of interest, including one solitary and one facultatively eusocial halictid bee and a sawfly. We demonstrate that the strength of correlation between CpG content and DNA methylation varies widely among hymenopteran taxa, highlighting shortcomings in the utility of CpG content as a proxy for DNA methylation in comparative studies of taxa with sparse DNA methylomes. We observed strikingly high levels of DNA methylation in the sawfly relative to other investigated hymenopterans. Analyses of molecular evolution suggest the relatively distinct sawfly DNA methylome may be associated with positive selection on functional DNMT3 domains. Sawflies are an outgroup to all ants, bees, and wasps, and no sawfly species are eusocial. We find no evidence that either global expansions or variation within individual ortholog groups in DNA methylation are consistently associated with the evolution of social behavior., (© The Author 2017. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.)

Sexual reproduction brings genes from two parents (matrigenes and patrigenes) together into one individual. These genes, despite being unrelated, should show nearly perfect cooperation because each gains equally through the production of offspring. However, an individual's matrigenes and patrigenes can have different probabilities of being present in other relatives, so kin selection could act on them differently. Such intragenomic conflict could be implemented by partial or complete silencing (imprinting) of an allele by one of the parents. Evidence supporting this theory is seen in offspring-mother interactions, with patrigenes favoring acquisition of more of the mother's resources if some of the costs fall on half-siblings who do not share the patrigene. The kinship theory of intragenomic conflict is little tested in other contexts, but it predicts that matrigene-patrigene conflict may be rife in social insects. We tested the hypothesis that honey bee worker reproduction is promoted more by patrigenes than matrigenes by comparing across nine reciprocal crosses of two distinct genetic stocks. As predicted, hybrid workers show reproductive trait characteristics of their paternal stock, (indicating enhanced activity of the patrigenes on these traits), greater patrigenic than matrigenic expression, and significantly increased patrigenic-biased expression in reproductive workers. These results support both the general prediction that matrigene-patrigene conflict occurs in social insects and the specific prediction that honey bee worker reproduction is driven more by patrigenes. The success of these predictions suggests that intragenomic conflict may occur in many contexts where matrigenes and patrigenes have different relatednesses to affected kin.

The evolution of eusociality is one of the major transitions in evolution, but the underlying genomic changes are unknown. We compared the genomes of 10 bee species that vary in social complexity, representing multiple independent transitions in social evolution, and report three major findings. First, many important genes show evidence of neutral evolution as a consequence of relaxed selection with increasing social complexity. Second, there is no single road map to eusociality; independent evolutionary transitions in sociality have independent genetic underpinnings. Third, though clearly independent in detail, these transitions do have similar general features, including an increase in constrained protein evolution accompanied by increases in the potential for gene regulation and decreases in diversity and abundance of transposable elements. Eusociality may arise through different mechanisms each time, but would likely always involve an increase in the complexity of gene networks., (Copyright © 2015, American Association for the Advancement of Science.)

Parent-specific gene expression (PSGE) is little known outside of mammals and plants. PSGE occurs when the expression level of a gene depends on whether an allele was inherited from the mother or the father. Kin selection theory predicts that there should be extensive PSGE in social insects because social insect parents can gain inclusive fitness benefits by silencing parental alleles in female offspring. We searched for evidence of PSGE in honey bees using transcriptomes from reciprocal crosses between European and Africanized strains. We found 46 transcripts with significant parent-of-origin effects on gene expression, many of which overexpressed the maternal allele. Interestingly, we also found a large proportion of genes showing a bias toward maternal alleles in only one of the reciprocal crosses. These results indicate that PSGE may occur in social insects. The nonreciprocal effects could be largely driven by hybrid incompatibility between these strains. Future work will help to determine if these are indeed parent-of-origin effects that can modulate inclusive fitness benefits., (Copyright © 2015 Kocher et al.)

Social insect colonies can be seen as a distinct form of biological organisation because they function as superorganisms. Understanding how natural selection acts on the emergence and maintenance of these colonies remains a major question in evolutionary biology and ecology. Here, we explore this by using multi-type branching processes to calculate the basic reproductive ratios and the extinction probabilities for solitary vs. eusocial reproductive strategies. We find that eusociality, albeit being hugely successful once established, is generally less stable than solitary reproduction unless large demographic advantages of eusociality arise for small colony sizes. We also demonstrate how such demographic constraints can be overcome by the presence of ecological niches that strongly favour eusociality. Our results characterise the risk-return trade-offs between solitary and eusocial reproduction, and help to explain why eusociality is taxonomically rare: eusociality is a high-risk, high-reward strategy, whereas solitary reproduction is more conservative., (© 2014 John Wiley & Sons Ltd/CNRS.)

Eusociality is taxonomically rare, yet associated with great ecological success. Surprisingly, studies of environmental conditions favouring eusociality are often contradictory. Harsh conditions associated with increasing altitude and latitude seem to favour increased sociality in bumblebees and ants, but the reverse pattern is found in halictid bees and polistine wasps. Here, we compare the life histories and distributions of populations of 176 species of Hymenoptera from the Swiss Alps. We show that differences in altitudinal distributions and development times among social forms can explain these contrasting patterns: highly social taxa develop more quickly than intermediate social taxa, and are thus able to complete the reproductive cycle in shorter seasons at higher elevations. This dual impact of altitude and development time on sociality illustrates that ecological constraints can elicit dynamic shifts in behaviour, and helps explain the complex distribution of sociality across ecological gradients., (© 2014 The Author(s) Published by the Royal Society. All rights reserved.)

Background: Taxa that harbor natural phenotypic variation are ideal for ecological genomic approaches aimed at understanding how the interplay between genetic and environmental factors can lead to the evolution of complex traits. Lasioglossum albipes is a polymorphic halictid bee that expresses variation in social behavior among populations, and common-garden experiments have suggested that this variation is likely to have a genetic component., Results: We present the L. albipes genome assembly to characterize the genetic and ecological factors associated with the evolution of social behavior. The de novo assembly is comparable to other published social insect genomes, with an N50 scaffold length of 602 kb. Gene families unique to L. albipes are associated with integrin-mediated signaling and DNA-binding domains, and several appear to be expanded in this species, including the glutathione-s-transferases and the inositol monophosphatases. L. albipes has an intact DNA methylation system, and in silico analyses suggest that methylation occurs primarily in exons. Comparisons to other insect genomes indicate that genes associated with metabolism and nucleotide binding undergo accelerated evolution in the halictid lineage. Whole-genome resequencing data from one solitary and one social L. albipes female identify six genes that appear to be rapidly diverging between social forms, including a putative odorant receptor and a cuticular protein., Conclusions: L. albipes represents a novel genetic model system for understanding the evolution of social behavior. It represents the first published genome sequence of a primitively social insect, thereby facilitating comparative genomic studies across the Hymenoptera as a whole.

Several lines of evidence support genetic links between ovary size and division of labor in worker honey bees. However, it is largely unknown how ovaries influence behavior. To address this question, we first performed transcriptional profiling on worker ovaries from two genotypes that differ in social behavior and ovary size. Then, we contrasted the differentially expressed ovarian genes with six sets of available brain transcriptomes. Finally, we probed behavior-related candidate gene networks in wild-type ovaries of different sizes. We found differential expression in 2151 ovarian transcripts in these artificially selected honey bee strains, corresponding to approximately 20.3% of the predicted gene set of honey bees. Differences in gene expression overlapped significantly with changes in the brain transcriptomes. Differentially expressed genes were associated with neural signal transmission (tyramine receptor, TYR) and ecdysteroid signaling; two independently tested nuclear hormone receptors (HR46 and ftz-f1) were also significantly correlated with ovary size in wild-type bees. We suggest that the correspondence between ovary and brain transcriptomes identified here indicates systemic regulatory networks among hormones (juvenile hormone and ecdysteroids), pheromones (queen mandibular pheromone), reproductive organs and nervous tissues in worker honey bees. Furthermore, robust correlations between ovary size and neuraland endocrine response genes are consistent with the hypothesized roles of the ovaries in honey bee behavioral regulation.

While chemical communication regulates individual behavior in a wide variety of species, these communication systems are most elaborated in insect societies. In these complex systems, pheromones produced by the reproductive individuals (queens) are critical in establishing and maintaining dominant reproductive status over hundreds to thousands of workers. The proximate and ultimate mechanisms by which these intricate pheromone communication systems evolved are largely unknown, though there has been much debate over whether queen pheromones function as a control mechanism or as an honest signal facilitating cooperation. Here, we summarize results from recent studies in honey bees, bumble bees, wasps, ants and termites. We further discuss evolutionary mechanisms by which queen pheromone communication systems may have evolved. Overall, these studies suggest that queen-worker pheromone communication is a multi-component, labile dialog between the castes, rather than a simple, fixed signal-response system. We also discuss future approaches that can shed light on the proximate and ultimate mechanisms that underlie these complex systems by focusing on the development of increasingly sophisticated genomic tools and their potential applications to examine the molecular mechanisms that regulate pheromone production and perception.

Honeybee workers are essentially sterile female helpers that make up the majority of individuals in a colony. Workers display a marked change in physiology when they transition from in-nest tasks to foraging. Recent technological advances have made it possible to unravel the metabolic modifications associated with this transition. Previous studies have revealed extensive remodeling of brain, thorax, and hypopharyngeal gland biochemistry. However, data on changes in the abdomen is scarce. To narrow this gap we investigated the proteomic composition of abdominal tissue in the days typically preceding the onset of foraging in honeybee workers. In order to get a broader representation of possible protein dynamics, we used workers of two genotypes with differences in the age at which they initiate foraging. This approach was combined with RNA interference-mediated downregulation of an insulin/insulin-like signaling component that is central to foraging behavior, the insulin receptor substrate (irs), and with measurements of glucose and lipid levels. Our data provide new insight into the molecular underpinnings of phenotypic plasticity in the honeybee, invoke parallels with vertebrate metabolism, and support an integrated and irs-dependent association of carbohydrate and lipid metabolism with the transition from in-nest tasks to foraging.

Mating is fundamental to most organisms, although the physiological and transcriptional changes associated with this process have been largely characterized only in Drosophila melanogaster. In this study, we use honey bees as a model system because their queens undergo massive and permanent physiological and behavioural changes following mating. Previous studies have identified changes associated with the transition from a virgin queen to a fully mated, egg-laying queen. Here, we further uncouple the mating process to examine the effects of natural mating vs. instrumental insemination and saline vs. semen insemination. We observed effects on flight behaviour, vitellogenin expression and significant overlap in transcriptional profiles between our study and analogous studies in D. melanogaster, suggesting that some post-mating mechanisms are conserved across insect orders.

Background: Variation in individual behavior within social groups can affect the fitness of the group as well as the individual, and can be caused by a combination of genetic and environmental factors. However, the molecular factors associated with individual variation in social behavior remain relatively unexplored. We used honey bees (Apis mellifera) as a model to examine differences in socially-regulated behavior among individual workers, and used transcriptional profiling to determine if specific gene expression patterns are associated with these individual differences. In honey bees, the reproductive queen produces a pheromonal signal that regulates many aspects of worker behavior and physiology and maintains colony organization., Methodology/principal Findings: Here, we demonstrate that there is substantial natural variation in individual worker attraction to queen pheromone (QMP). Furthermore, worker attraction is negatively correlated with ovariole number-a trait associated with reproductive potential in workers. We identified transcriptional differences in the adult brain associated with individual worker attraction to QMP, and identified hundreds of transcripts that are organized into statistically-correlated gene networks and associated with this response., Conclusions/significance: Our studies demonstrate that there is substantial variation in worker attraction to QMP among individuals, and that this variation is linked with specific differences in physiology and brain gene expression patterns. This variation in individual response thresholds may reveal underlying variation in queen-worker reproductive conflict, and may mediate colony function and productivity by creating variation in individual task performance.

The mandibular glands of queen honeybees produce a pheromone that modulates many aspects of worker honeybee physiology and behavior and is critical for colony social organization. The exact chemical blend produced by the queen differs between virgin and mated, laying queens. Here, we investigate the role of mating and reproductive state on queen pheromone production and worker responses. Virgin queens, naturally mated queens, and queens instrumentally inseminated with either semen or saline were collected 2 days after mating or insemination. Naturally mated queens had the most activated ovaries and the most distinct chemical profile in their mandibular glands. Instrumentally inseminated queens were intermediate between virgins and naturally mated queens for both ovary activation and chemical profiles. There were no significant differences between semen- and saline-inseminated queens. Workers were preferentially attracted to the mandibular gland extracts from queens with significantly more activated ovaries. These studies suggest that the queen pheromone blend is modulated by the reproductive status of the queens, and workers can detect these subtle differences and are more responsive to queens with higher reproductive potential. Furthermore, it appears as if insemination substance does not strongly affect physiological characteristics of honeybee queens 2 days after insemination, suggesting that the insemination process or volume is responsible for stimulating these early postmating changes in honeybee queens.

Background: The molecular mechanisms underlying the post-mating behavioral and physiological transitions undergone by females have not been explored in great detail. Honey bees represent an excellent model system in which to address these questions because they exhibit a range of "mating states," with two extremes (virgins and egg-laying, mated queens) that differ dramatically in their behavior, pheromone profiles, and physiology. We used an incompletely-mated mating-state to understand the molecular processes that underlie the transition from a virgin to a mated, egg-laying queen. We used same-aged virgins, queens that mated once but did not initiate egg-laying, and queens that mated once and initiated egg-laying., Results: Differences in the behavior and physiology among groups correlated with the underlying variance observed in the top 50 predictive genes in the brains and the ovaries. These changes were correlated with either a behaviorally-associated pattern or a physiologically-associated pattern. Overall, these results suggest that the brains and the ovaries of queens are uncoupled or follow different timescales; the initiation of mating triggers immediate changes in the ovaries, while changes in the brain may require additional stimuli or take a longer time to complete. Comparison of our results to previous studies of post-mating changes in Drosophila melanogaster identified common biological processes affected by mating, including stress response and alternative-splicing pathways. Comparison with microarray data sets related to worker behavior revealed no obvious correlation between genes regulated by mating and genes regulated by behavior/physiology in workers., Conclusion: Studying the underlying molecular mechanisms of post-mating changes in honey bee queens will not only give us insight into how molecular mechanisms regulate physiological and behavioral changes, but they may also lead to important insights into the evolution of social behavior. Post-mating changes in gene regulation in the brains and ovaries of honey bee queens appear to be triggered by different stimuli and may occur on different timescales, potentially allowing changes in the brains and the ovaries to be uncoupled.