Gene regulation supporting sociality shared across lineages and variation in complexity

Across evolutionary lineages, insects vary in social complexity, from those that exhibit extended parental care to those with elaborate divisions of labor. Here, we synthesize the sociogenomic resources from hundreds of species to describe common gene regulatory mechanisms in insects that regulate social organization across phylogeny and levels of social complexity. Different social phenotypes expressed by insects can be linked to the organization of co-expressing gene networks and features of the epigenetic landscape. Insect sociality also stems from processes like the emergence of parental care and the decoupling of ancestral genetic programs. One underexplored avenue is how variation in a group's social environment affects the gene expression of individuals. Additionally, an experimental reduction of gene expression would demonstrate how the activity of specific genes contributes to insect social phenotypes. While tissue specificity provides greater localization of the gene expression underlying social complexity, emerging transcriptomic analysis of insect brains at the cellular level provides even greater resolution to understand the molecular basis of social insect evolution.

Molecular signatures of alternative reproductive strategies in a facultatively social hover wasp

Social insect reproductives and non-reproductives represent ideal models with which to understand the expression and regulation of alternative phenotypes. Most research in this area has focused on the developmental regulation of reproductive phenotypes in obligately social taxa such as honey bees, while relatively few studies have addressed the molecular correlates of reproductive differentiation in species in which the division of reproductive labour is established only in plastic dominance hierarchies. To address this knowledge gap, we generate the first genome for any stenogastrine wasp and analyse brain transcriptomic data for non-reproductives and reproductives of the facultatively social species Liostenogaster flavolineata, a representative of one of the simplest forms of social living. By experimentally manipulating the reproductive 'queues' exhibited by social colonies of this species, we show that reproductive division of labour in this species is associated with transcriptomic signatures that are more subtle and variable than those observed in social taxa in which colony living has become obligate; that variation in gene expression among non-reproductives reflects their investment into foraging effort more than their social rank; and that genes associated with reproductive division of labour overlap to some extent with those underlying division of labour in the separate polistine origin of wasp sociality but only explain a small portion of overall variation in this trait. These results indicate that broad patterns of within-colony transcriptomic differentiation in this species are similar to those in Polistinae but offer little support for the existence of a strongly conserved 'toolkit' for sociality.

Wrestling with Social and Behavioral Genomics: Risks, Potential Benefits, and Ethical Responsibility

In this consensus report by a diverse group of academics who conduct and/or are concerned about social and behavioral genomics (SBG) research, the authors recount the often-ugly history of scientific attempts to understand the genetic contributions to human behaviors and social outcomes. They then describe what the current science-including genomewide association studies and polygenic indexes-can and cannot tell us, as well as its risks and potential benefits. They conclude with a discussion of responsible behavior in the context of SBG research. SBG research that compares individuals within a group according to a "sensitive" phenotype requires extra attention to responsible conduct and to responsible communication about the research and its findings. SBG research (1) on sensitive phenotypes that (2) compares two or more groups defined by (a) race, (b) ethnicity, or (c) genetic ancestry (where genetic ancestry could easily be misunderstood as race or ethnicity) requires a compelling justification to be conducted, funded, or published. All authors agree that this justification at least requires a convincing argument that a study's design could yield scientifically valid results; some authors would additionally require the study to have a socially favorable risk-benefit profile.

Challenging the utility of polygenic scores for social science: Environmental confounding, downward causation, and unknown biology

The sociogenomics revolution is upon us, we are told. Whether revolutionary or not, sociogenomics is poised to flourish given the ease of incorporating polygenic scores (or PGSs) as "genetic propensities" for complex traits into social science research. Pointing to evidence of ubiquitous heritability and the accessibility of genetic data, scholars have argued that social scientists not only have an opportunity but a duty to add PGSs to social science research. Social science research that ignores genetics is, some proponents argue, at best partial and likely scientifically flawed, misleading, and wasteful. Here, I challenge arguments about the value of genetics for social science and with it the claimed necessity of incorporating PGSs into social science models as measures of genetic influences. In so doing, I discuss the impracticability of distinguishing genetic influences from environmental influences because of non-causal gene-environment correlations, especially population stratification, familial confounding, and downward causation. I explain how environmental effects masquerade as genetic influences in PGSs, which undermines their raison d'être as measures of genetic propensity, especially for complex socially contingent behaviors that are the subject of sociogenomics. Additionally, I draw attention to the partial, unknown biology, while highlighting the persistence of an implicit, unavoidable reductionist genes versus environments approach. Leaving sociopolitical and ethical concerns aside, I argue that the potential scientific rewards of adding PGSs to social science are few and greatly overstated and the scientific costs, which include obscuring structural disadvantages and cultural influences, outweigh these meager benefits for most social science applications.

Reconstructing Sociogenomics Research: Dismantling Biological Race and Genetic Essentialism Narratives

We detail the implications of sociogenomics for social determinants research. We focus on education and race because of how early twentieth-century scientific eugenic thinking facilitated a range of racist and eugenic policies, most of which helped justify and pattern racial and educational morbidity and mortality disparities that remain today, and are central to sociological research. Consequently, we detail the implications of sociogenomics research by unpacking key controversies and opportunities in sociogenomics as they pertain to the understanding of racial and educational inequalities. We clarify why race is not a valid biological or genetic construct, the ways that environments powerfully shape genetic influence, and risks linked to this field of research. We argue that sociologists can usefully engage in genetics research, a domain dominated by psychologists and behaviorists who, given their focus on individuals, have mostly not examined the role of history and social structure in shaping genetic influence.

Using Polygenic Scores in Social Science Research: Unraveling Childlessness

Biological, genetic, and socio-demographic factors are all important in explaining reproductive behavior, yet these factors are typically studied in isolation. In this study, we explore an innovative sociogenomic approach, which entails including key socio-demographic (marriage, education, occupation, religion, cohort) and genetic factors related to both behavioral [age at first birth (AFB), number of children ever born (NEB)] and biological fecundity-related outcomes (endometriosis, age at menopause and menarche, polycystic ovary syndrome, azoospermia, testicular dysgenesis syndrome) to explain childlessness. We examine the association of all sets of factors with childlessness as well as the interplay between them. We derive polygenic scores (PGS) from recent genome-wide association studies (GWAS) and apply these in the Health and Retirement Study (N = 10,686) and Wisconsin Longitudinal Study (N = 8,284). Both socio-demographic and genetic factors were associated with childlessness. Whilst socio-demographic factors explain 19-46% in childlessness, the current PGS explains <1% of the variance, and only PGSs from large GWASs are related to childlessness. Our findings also indicate that genetic and socio-demographic factors are not independent, with PGSs for AFB and NEB related to education and age at marriage. The explained variance by polygenic scores on childlessness is limited since it is largely a behavioral trait, with genetic explanations expected to increase somewhat in the future with better-powered GWASs. As genotyping of individuals in social science surveys becomes more prevalent, the method described in this study can be applied to other outcomes.

Effects of the peer metagenomic environment on smoking behavior

Recent scholarship suggests that the genomes of those around us affect our own phenotypes. Much of the empirical evidence for such "metagenomic" effects comes from animal studies, where the socio-genetic environment can be easily manipulated. Among humans, it is more difficult to identify such effects given the nonrandom distribution of genes and environments. Here we leverage the as-if-random distribution of grade-mates' genomes conditional on school-level variation in a nationally representative sample. Specifically, we evaluate whether one's peers' genetic propensity to smoke affects one's own smoking behavior net of one's own genotype. Results show that peer genetic propensity to smoke has a substantial effect on an individual's smoking outcome. This is true not only when the peer group includes direct friends, and therefore where the individual plays an active role in shaping the metagenomic context but also when the peer group includes all grade-mates and thus in cases where the individual does not select the metagenomic environment. We explore these effects further and show that a small minority with high genetic risk to smoke ('bad apples') can greatly affect the smoking behavior of an entire grade. The methodology used in this paper offers a potential solution to many of the challenges inherent in estimating peer effects in nonexperimental settings and can be utilized to study a wide range of outcomes with a genetic basis. On a policy level, our results suggest that efforts to reduce adolescent smoking should take into account metagenomic effects, especially bad apples, within social networks.

Social Status and Gene Regulation: Conservation and Context Dependence in Primates

Current models suggest that low social status affects immune function by increasing inflammation and compromising antiviral defense. While this pattern appears to be somewhat conserved, recent studies argue that the gene regulatory signature of social status also depends on the local environment and the nature of social hierarchies.

The Genome-Wide Study of Human Social Behavior and Its Application in Sociology

Recent years have seen a push for the integration of modern genomic methodologies with sociological inquiry. The inclusion of genomic approaches promises to help address long-standing issues in sociology (e.g., selection effects), as well as open up new avenues for future research. This article reviews the substantive findings of behavior genetic/genomic research, both from the recent past (e.g., twin/adoption studies, candidate gene studies) and from contemporary genomic analyses. The article primarily focuses on modern genomic methods available to sociologists (e.g., polygenic score analysis) and their various applications for answering sociological questions. The article concludes by considering a number of areas to which genomic researchers and sociologists should pay close attention if a consilience between genomic methods and sociological research is to be fully realized.

Draft Genome Assembly and Population Genetics of an Agricultural Pollinator, the Solitary Alkali Bee (Halictidae: Nomia melanderi)

Alkali bees (Nomia melanderi) are solitary relatives of the halictine bees, which have become an important model for the evolution of social behavior, but for which few solitary comparisons exist. These ground-nesting bees defend their developing offspring against pathogens and predators, and thus exhibit some of the key traits that preceded insect sociality. Alkali bees are also efficient native pollinators of alfalfa seed, which is a crop of major economic value in the United States. We sequenced, assembled, and annotated a high-quality draft genome of 299.6 Mbp for this species. Repetitive content makes up more than one-third of this genome, and previously uncharacterized transposable elements are the most abundant type of repetitive DNA. We predicted 10,847 protein coding genes, and identify 479 of these undergoing positive directional selection with the use of population genetic analysis based on low-coverage whole genome sequencing of 19 individuals. We found evidence of recent population bottlenecks, but no significant evidence of population structure. We also identify 45 genes enriched for protein translation and folding, transcriptional regulation, and triglyceride metabolism evolving slower in alkali bees compared to other halictid bees. These resources will be useful for future studies of bee comparative genomics and pollinator health research.

Dominance rank-associated gene expression is widespread, sex-specific, and a precursor to high social status in wild male baboons

In humans and other hierarchical species, social status is tightly linked to variation in health and fitness-related traits. Experimental manipulations of social status in female rhesus macaques suggest that this relationship is partially explained by status effects on immune gene regulation. However, social hierarchies are established and maintained in different ways across species: While some are based on kin-directed nepotism, others emerge from direct physical competition. We investigated how this variation influences the relationship between social status and immune gene regulation in wild baboons, where hierarchies in males are based on fighting ability but female hierarchies are nepotistic. We measured rank-related variation in gene expression levels in adult baboons of both sexes at baseline and in response to ex vivo stimulation with the bacterial endotoxin lipopolysaccharide (LPS). We identified >2,000 rank-associated genes in males, an order of magnitude more than in females. In males, high status predicted increased expression of genes involved in innate immunity and preferential activation of the NF-κB-mediated proinflammatory pathway, a pattern previously associated with low status in female rhesus macaques. Using Mendelian randomization, we reconcile these observations by demonstrating that high status-associated gene expression patterns are precursors, not consequences, of high social status in males, in support of the idea that physiological condition determines who attains high rank. Together, our work provides a test of the relationship between social status and immune gene regulation in wild primates. It also emphasizes the importance of social context in shaping the relationship between social status and immune function.

Genetic analysis of social-class mobility in five longitudinal studies

A summary genetic measure, called a "polygenic score," derived from a genome-wide association study (GWAS) of education can modestly predict a person's educational and economic success. This prediction could signal a biological mechanism: Education-linked genetics could encode characteristics that help people get ahead in life. Alternatively, prediction could reflect social history: People from well-off families might stay well-off for social reasons, and these families might also look alike genetically. A key test to distinguish biological mechanism from social history is if people with higher education polygenic scores tend to climb the social ladder beyond their parents' position. Upward mobility would indicate education-linked genetics encodes characteristics that foster success. We tested if education-linked polygenic scores predicted social mobility in >20,000 individuals in five longitudinal studies in the United States, Britain, and New Zealand. Participants with higher polygenic scores achieved more education and career success and accumulated more wealth. However, they also tended to come from better-off families. In the key test, participants with higher polygenic scores tended to be upwardly mobile compared with their parents. Moreover, in sibling-difference analysis, the sibling with the higher polygenic score was more upwardly mobile. Thus, education GWAS discoveries are not mere correlates of privilege; they influence social mobility within a life. Additional analyses revealed that a mother's polygenic score predicted her child's attainment over and above the child's own polygenic score, suggesting parents' genetics can also affect their children's attainment through environmental pathways. Education GWAS discoveries affect socioeconomic attainment through influence on individuals' family-of-origin environments and their social mobility.

What Can Sociogenomics Learn from Social By Nature? A review of social by nature, by Catherine Bliss

Social by Nature, the recent book by Catherine Bliss on the development and state of the field of sociogenomics, is far from perfect. Yet, this flawed book levies a mixture of erroneous and compelling questions about the state of the field of sociogenomics, many of which we as a field would benefit from considering: How should we bring the environment back in the post-GWAS era? How do the publication and funding incentives of our field influence the evolution of our research agenda? What role should social scientific theory play in motivating our research and interpreting our findings? How can we promote greater diversity in our research community and subjects? And how can we work to better control media and popular narratives of our research? The authors do not attempt to answer all of these questions definitively, but do argue that we as a field must grapple with them seriously to ensure that our ideals and reality as a field are more congruent.

Transcriptomics and neuroanatomy of the clonal raider ant implicate an expanded clade of odorant receptors in chemical communication

A major aim of sociogenomic research is to uncover common principles in the molecular evolution of sociality. This endeavor has been hampered by the small number of specific genes currently known to function in social behavior. Here we provide several lines of evidence suggesting that ants have evolved a large and novel clade of odorant receptor (OR) genes to perceive hydrocarbon-based pheromones, arguably the most important signals in ant communication. This genomic expansion is also mirrored in the ant brain via a corresponding expansion of a specific cluster of glomeruli in the antennal lobe. We show that in the clonal raider ant, hydrocarbon-sensitive basiconic sensilla are found only on the ventral surface of the female antennal club. Correspondingly, nearly all genes in a clade of 180 ORs within the 9-exon subfamily of ORs are expressed exclusively in females and are highly enriched in expression in the ventral half of the antennal club. Furthermore, we found that across species and sexes, the number of 9-exon ORs expressed in antennae is tightly correlated with the number of glomeruli in the antennal lobe region innervated by odorant receptor neurons from basiconic sensilla. Evolutionary analyses show that this clade underwent a striking gene expansion in the ancestors of all ants and slower but continued expansion in extant ant lineages. This evidence suggests that ants have evolved a large clade of genes to support pheromone perception and that gene duplications have played an important role in the molecular evolution of ant communication.

Molecular mechanisms and the conflict between courtship and aggression in three-spined sticklebacks

In nature, animals often face conflicting demands. For example, breeding males must attract a mate but at the same time be ready to defend against rivals. The molecular mechanisms by which the brain resolves behavioural trade-offs are largely unknown. In this study, we compared the brain transcriptional responses of territorial male three-spined sticklebacks to a mating opportunity with a female and to a territorial challenge by a rival male. We focused on the diencephalon and the cerebellum, two regions of the brain implicated in courtship and aggression. There was a set of genes that were differentially expressed in response to both a courtship opportunity and a territorial challenge. Closer inspection of the direction of regulation revealed that genes that were downregulated in response to a courtship opportunity were upregulated in response to a territorial challenge and vice versa. Our study reveals some of the potential molecular mechanisms underlying behavioural trade-offs between sex and aggression, along with a possible solution to the conflict via social context-dependent gene regulation.

Testing the kinship theory of intragenomic conflict in honey bees (Apis mellifera)

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.

Natural variation in brain gene expression profiles of aggressive and nonaggressive individual sticklebacks

Within many species, some individuals are consistently more aggressive than others. We examine whether there are differences in brain gene expression between aggressive versus nonaggressive behavioural types of individuals within a natural population of male three-spined sticklebacks (Gasterosteus aculeatus). We compared gene expression profiles of aggressive male sticklebacks to nonaggressive males in four regions of the brain (brainstem, cerebellum, diencephalon and telencephalon). Relatively few genes were differentially expressed between behavioural types in telencephalon, cerebellum and diencephalon, but hundreds of genes were differentially expressed in brainstem, a brain area involved in detecting threats. Six genes that were differentially expressed in response to a territorial intrusion in a previous study were also differentially expressed between behavioural types in this study, implying primarily non-shared but some shared molecular mechanisms. Our findings offer new insights into the molecular causes and correlates of behavioural plasticity and individual variation in behaviour.

Omic research in termites: an overview and a roadmap

Many recent breakthroughs in our understanding of termite biology have been facilitated by "omics" research. Omic science seeks to collectively catalog, quantify, and characterize pools of biological molecules that translate into structure, function, and life processes of an organism. Biological molecules in this context include genomic DNA, messenger RNA, proteins, and other biochemicals. Other permutations of omics that apply to termites include sociogenomics, which seeks to define social life in molecular terms (e.g., behavior, sociality, physiology, symbiosis, etc.) and digestomics, which seeks to define the collective pool of host and symbiont genes that collaborate to achieve high-efficiency lignocellulose digestion in the termite gut. This review covers a wide spectrum of termite omic studies from the past 15 years. Topics covered include a summary of terminology, the various kinds of omic efforts that have been undertaken, what has been revealed, and to a degree, what the results mean. Although recent omic efforts have contributed to a better understanding of many facets of termite and symbiont biology, and have created important new resources for many species, significant knowledge gaps still remain. Crossing these gaps can best be done by applying new omic resources within multi-dimensional (i.e., functional, translational, and applied) research programs.

The scent of royalty: a p450 gene signals reproductive status in a social insect

Cooperation requires communication; this applies to animals and humans alike. The main communication means differ between taxa and social insects (ants, termites, and some bees and wasps) lack the cognitive abilities of most social vertebrates. Central to the regulation of the reproductive harmony in insect societies is the production of a royalty scent which signals the fertility status of the reproducing queen to the nonreproducing workers. Here, we revealed a central genetic component underlying this hallmark of insect societies in the termite Cryptotermes secundus. Communication between queens and workers relied upon the expression of a gene, Neofem4, which belongs to the cytochrome P450 genes. We inhibited Neofem4 in queens by RNA interference. This resulted in the loss of the royalty scent in queens and the workers behaved as though the queen were absent. The queen's behavior was not generally affected by silencing Neofem4. This suggests that the lack of the royalty scent lead to workers not recognizing her anymore as queen. P450 genes are known to be involved in the production of chemical signals in cockroaches and their expression has been linked to a major fertility regulator, juvenile hormone. This makes P450 genes, both a suitable and available evolutionary substrate in the face of natural selection for production of a queen substance. Our data suggest that in an organism without elaborate cognitive abilities communication has been achieved by the exploitation of a central gene that links the fertility network with the chemical communication pathway. As termites and social Hymenoptera seem to share the same class of compounds in signaling fertility, this role of P450 genes might be more widespread across social insects.

Geographical, environmental and pathophysiological influences on the human blood transcriptome

Gene expression variation provides a read-out of both genetic and environmental influences on gene activity. Geographical, genomic and sociogenomic studies have highlighted how life circumstances of an individual modify the expression of hundreds and in some cases thousands of genes in a co-ordinated manner. This review places such results in the context of a conserved set of 90 transcripts known as Blood Informative Transcripts (BIT) that capture the major conserved components of variation in the peripheral blood transcriptome. Pathophysiological states are also shown to associate with the perturbation of transcript abundance along the major axes. Discussion of false negative rates leads us to argue that simple significance thresholds provide a biased perspective on assessment of differential expression that may cloud the interpretation of studies with small sample sizes.

Molecular evolutionary analyses of insect societies

The social insects live in extraordinarily complex and cohesive societies, where many individuals sacrifice their personal reproduction to become helpers in the colony. Identifying adaptive molecular changes involved in eusocial evolution in insects is important for understanding the mechanisms underlying transitions from solitary to social living, as well as the maintenance and elaboration of social life. Here, we review recent advances made in this area of research in several insect groups: the ants, bees, wasps, and termites. Drawing from whole-genome comparisons, candidate gene approaches, and a genome-scale comparative analysis of protein-coding sequence, we highlight novel insights gained for five major biological processes: chemical signaling, brain development and function, immunity, reproduction, and metabolism and nutrition. Lastly, we make comparisons across these diverse approaches and social insect lineages and discuss potential common themes of eusocial evolution, as well as challenges and prospects for future research in the field.

Towards a molecular definition of worker sterility: differential gene expression and reproductive plasticity in honey bees

We show that differences in the reproductive development of honey bee workers are associated with locus-specific changes to abundance of messenger RNA. Using a cross-fostering field experiment to control for differences related to age and environment, we compared the gene expression profiles of functionally sterile workers (wild-type) and those from a mutant strain in which workers are reproductively active (anarchist). Among the set of three genes that are significantly differentially expressed are two major royal jelly proteins that are up-regulated in wild-type heads. This discovery is consistent with sterile workers synthesizing royal jelly as food for developing brood. Likewise, the relative underexpression of these two royal jellies in anarchist workers is consistent with these workers' characteristic avoidance of alloparental behaviour, in favour of selfish egg-laying. Overall, there is a trend for the most differentially expressed genes to be up-regulated in wild-type workers. This pattern suggests that functional sterility in honey bee workers may generally involve the expression of a suite of genes that effectively 'switch' ovaries off, and that selfish reproduction in honey bee workers, though rare, is the default developmental pathway that results when ovary activation is not suppressed.

Social exploitation of hexamerin: RNAi reveals a major caste-regulatory factor in termites

Lower termites express a unique form of eusocial polyphenism in that totipotent workers can differentiate into either soldier or reproductive caste phenotypes. In this initial effort using RNA interference in termites, we found that two hexamerin genes, Hex-1 and Hex-2, participate in the regulation of caste polyphenism. Our methodology involved a dual gene-silencing approach that used a single short-interfering RNA fragment to silence the two homologous hexamerin genes. We performed validation studies that evaluated effects on nontarget housekeeping genes, silencing of a nonhousekeeping control gene, and effects at the protein level. We found that the two hexamerin proteins, which are inducible by the morphogenetic juvenile hormone and which constitute a significant proportion of total termite protein, suppress juvenile-hormone-dependent worker differentiation to the soldier caste phenotype. This mechanism allows termite colonies to retain high proportions of altruistic worker caste members, thus apparently enhancing colony-inclusive fitness. These findings demonstrate a unique status quo regulatory mechanism for termite worker caste retention and provide an example of previously undescribed preadult developmental/caste-regulatory genes from any social insect.