Microbial transmission in the social microbiome and host health and disease

Although social interactions are known to drive pathogen transmission, the contributions of socially transmissible host-associated mutualists and commensals to host health and disease remain poorly explored. We use the concept of the social microbiome-the microbial metacommunity of a social network of hosts-to analyze the implications of social microbial transmission for host health and disease. We investigate the contributions of socially transmissible microbes to both eco-evolutionary microbiome community processes (colonization resistance, the evolution of virulence, and reactions to ecological disturbance) and microbial transmission-based processes (transmission of microbes with metabolic and immune effects, inter-specific transmission, transmission of antibiotic-resistant microbes, and transmission of viruses). We consider the implications of social microbial transmission for communicable and non-communicable diseases and evaluate the importance of a socially transmissible component underlying canonically non-communicable diseases. The social transmission of mutualists and commensals may play a significant, under-appreciated role in the social determinants of health and may act as a hidden force in social evolution.

Coupled information networks drive honeybee (Apis mellifera) collective foraging

Collective behaviour by eusocial insect colonies is typically achieved through multiple communication networks that produce complex behaviour at the group level but often appear to provide redundant or even competing information. A classic example occurs in honeybee (Apis mellifera) colonies, where both the dance communication system and robust scent-based mechanisms contribute to the allocation of a colony's workforce by regulating the flow of experienced foragers among known food sources. Here we analysed social connectivity patterns during the reactivation of experienced foragers to familiar feeding sites to show that these social information pathways are not simply multiple means to achieve the same end but intersect to play complementary roles in guiding forager behaviour. Using artificial feeding stations, we mimicked a natural scenario in which two forager groups were simultaneously collecting from distinct patches containing different flowering species. We then observed the reactivation of these groups at their familiar feeding sites after interrupting their foraging. Social network analysis revealed that temporarily unemployed individuals interacted more often and for longer with foragers that advertised a familiar versus unfamiliar foraging site. Due to such resource-based assortative mixing, network-based diffusion analysis estimated that reactivation events primarily resulted from interactions among bees that had been trained to the same feeding station and less so from different-feeder interactions. Both scent- and dance-based interactions strongly contributed to reactivation decisions. However, each bout of dance-following had an especially strong effect on a follower's likelihood of reactivation, particularly when dances indicated locations familiar to followers. Our findings illustrate how honeybee foragers can alter their social connectivity in ways that are likely to enhance collective outcomes by enabling foragers to rapidly access up-to-date information about familiar foraging sites. In addition, our results highlight how reliance on multiple communication mechanisms enables social insect workers to utilise flexible information-use strategies that are robust to variation in the availability of social information.

A qualitative study exploring the social contagion of attitudes and uptake of COVID-19 vaccinations

Vaccination attitudes and uptake can spread within social networks. This study aims to understand the perceived social contagion mechanisms of vaccination uptake in the context of COVID-19 pandemic. Eleven semi-structured interviews were conducted following a purposive sampling of three hesitant, three anti- COVID-19 vaccine and five pro- COVID-19 vaccine (27% females). Thematic Analysis suggested two general themes reflecting the type of contagion: 1) information contagion and 2) behavior contagion. Transcending these themes was the notion of ownership of choice/decision. Almost all participants used the media and experts as the main source of information regarding vaccination. They influenced - and they were being influenced by - friends and family members with whom they share similar traits and attitudes and have a close relationship of trust and intimacy. Also, being exposed to positive attitudes and beliefs toward vaccination and COVID-19 vaccines, enhanced vaccination behaviors. However, the vaccination decision-making process was not perceived as a passive process - there was ownership over the decisions made. This study highlights the perceived mechanisms of social contagion. It also suggests that the meaning individuals pose on their social world is crucial on their decision-making. Policymakers are advised to consider including social networks of individuals and trusted sources (i.e. healthcare providers) when delivering interventions or educational campaigns on vaccinations.

Social learning mechanisms shape transmission pathways through replicate local social networks of wild birds

The emergence and spread of novel behaviours via social learning can lead to rapid population-level changes whereby the social connections between individuals shape information flow. However, behaviours can spread via different mechanisms and little is known about how information flow depends on the underlying learning rule individuals employ. Here, comparing four different learning mechanisms, we simulated behavioural spread on replicate empirical social networks of wild great tits and explored the relationship between individual sociality and the order of behavioural acquisition. Our results reveal that, for learning rules dependent on the sum and strength of social connections to informed individuals, social connectivity was related to the order of acquisition, with individuals with increased social connectivity and reduced social clustering adopting new behaviours faster. However, when behavioural adoption depends on the ratio of an individuals' social connections to informed versus uninformed individuals, social connectivity was not related to the order of acquisition. Finally, we show how specific learning mechanisms may limit behavioural spread within networks. These findings have important implications for understanding whether and how behaviours are likely to spread across social systems, the relationship between individuals' sociality and behavioural acquisition, and therefore for the costs and benefits of sociality.

Visual attention across cultures: Similarities and differences in child development and maternal attention styles

Previous cross-cultural research has described two different attention styles: a holistic style, characterized by context-sensitive processing, generally associated with interdependent cultural contexts, and an analytic style, a higher focus on salient objects, generally found in independent cultural contexts. Though a general assumption in the field is that attention styles are gradually socialized in culture-specific interactions in childhood, empirical evidence for the proximal mechanisms underlying this development is scarce. This study aimed to document the emergence of cross-cultural differences in attention styles in three cultural contexts differing in social orientations, namely in urban middle-class families from Münster, Germany (i.e., more independent context), and Kyoto, Japan, and Indigenous-heritage families from Cotacachi, Ecuador (i.e., more interdependent contexts). Furthermore, to test the assumption that caregivers' attention guidance is one of the forces driving differential development, we investigated how caregivers guide children's attention. In total, 270 children between 4 and 9 years of age and their mothers participated in three tasks: an eye-tracking task, a picture description task and a forced-choice recognition task. Results indicate a mixed pattern of findings: While some tasks revealed the expected cultural differences, namely a higher object focus in Münster compared to Kyoto and Cotacachi, others did not. Regarding caregivers' attention guidance, we found that mothers in Münster more strongly emphasized the focal object than mothers in Kyoto and Cotacachi. The results are discussed in terms of culture-specific developmental trajectories and the generalizability of attentional processes across tasks and cultural contexts. RESEARCH HIGHLIGHTS: We investigated visual attention styles in 4- to 9-year-old children and their mothers from urban Germany, urban Japan, and rural Ecuador in three different tasks. Special emphasis lied on mothers' verbal attention guidance toward their children as a proximal mechanism underlying the emergence of culture-specific attention styles. Mothers from urban Germany guided their children's attention in more analytic ways than mothers from urban Japan and rural Ecuador. The relevance of verbal attention guidance in the development of culture-specific attention styles has been demonstrated beyond the East-West dichotomy.

The social origins of obesity within and across generations

We propose a model for obesity development that traces a considerable part of its origins to the social domain (mainly different forms of prolonged social adversity), both within and across generations, working in tandem with a genetic predisposition. To facilitate overview of social pathways, we place particular focus on three areas that form a cascading sequence: (A) social adversity within the family (parents having a low education, a low social position, poverty and financial insecurity; offspring being exposed to gestational stress, unmet social and emotional needs, abuse, maltreatment and other negative life events, social deprivation and relationship discord); (B) increasing levels of insecurity, negative emotions, chronic stress, and a disruption of energy homeostasis; and (C) weight gain and obesity, eliciting further social stress and weight stigma in both generations. Social adversity, when combined with genetic predisposition, thereby substantially contributes to highly effective transmission of obesity from parents to offspring, as well as to obesity development within current generations. Prevention efforts may benefit from mitigating multiple types of social adversity in individuals, families, and communities, notably poverty and financial strain, and by improving education levels.

Social genetic effects for drug use disorder among spouses

AIMS

Preclinical and human studies suggest that a social partner's genotype may be associated with addiction-related outcomes. This study measured whether spousal genetic makeup is associated with risk of developing drug use disorder (DUD) during marriage and whether the risk associated with a spouse's genotype could be disentangled from potentially confounding rearing environmental effects.

DESIGN

Univariable and multivariable logistic regression analyses.

SETTING

Sweden.

PARTICIPANTS

Men and women born between 1960 and 1990 and in opposite-sex first marriages before age 35 (n = 294 748 couples).

MEASUREMENTS

Outcome was DUD diagnosis (inclusive of opioids, sedatives/hypnotics/anxiolytics, cocaine, cannabis, amphetamine and other psychostimulants, hallucinogens, other drugs of abuse and combinations thereof) obtained from legal, medical and pharmacy registries. The focal predictor was family genetic risk scores for DUD (FGRS-DUD), which were inferred from diagnoses in first- through fifth-degree relatives and weighted by degree of genetic sharing. FGRS-DUD were calculated separately for each partner in a couple.

FINDINGS

Marriage to a spouse with a high FGRS-DUD was associated with increased risk of developing DUD during marriage, OR_males  = 1.68 (95% CI = 1.50, 1.88) and OR_females  = 1.35 (1.16, 1.56), above and beyond the risk associated with one's own FGRS-DUD. The risk associated with a spouse's FGRS-DUD remained statistically significant after covarying for parental education. As indicated by a series of null interaction effects, there was no evidence that the risk associated with a spouse's FGRS-DUD differed depending on whether the spouse was DUD-affected, probands' probable contact with in-laws and whether the spouse was raised by his/her biological parents or in another home.

CONCLUSIONS

There is relatively robust evidence that a person's risk for developing drug use disorder is associated with the genetic makeup of the person's spouse.

Emotions and virality: Social transmission of political messages on Twitter

Drawing on previous literature that valence and arousal constitute the fundamental properties of emotions and that emotional content is a determinant of social transmission, this study examines the role of valence and arousal in the social transmission of politicians' messages on Twitter. For over 3,000 tweets from five Austrian party leaders, the discrete emotion that the message intended to elicit in its recipients was captured by human coders and then classified on its valence (positive or negative) and arousal (low or high). We examined the effects of valence and arousal on the retweet probability of messages. Results indicate that tweets eliciting a negative (vs. positive) valence decreased retweet probability, whereas tweets eliciting a high (vs. low) arousal increased retweet probability. The present research replicates previous findings that arousal constitutes a determinant of social transmission but extends this mechanism to the realm of political communication on Twitter. Moreover, in contrast to the frequently mentioned negativity bias, positive emotions increased the likelihood of a message being shared in this study.

Socially Transferred Stress Experience Modulates Social Affective Behaviors in Rats

Social communication of affective states between individuals, as well as actual experiences, influences their internal states and behaviors. Although prior stress experiences promote empathy-like behaviors, it remains unclear whether the social transmission of stress events modulates these behaviors. Here, we provide evidence that transferred stress experiences from cage mates modulate socioaffective approach-avoidance behaviors in rats. Male Wistar-Imamichi rats were assigned to one of five experimental groups (Control (n = 15); no shock with shocked cage mates (n = 15); low (0.1 mA, n = 15), middle (0.5 mA, n = 14), and high shock (1.0 mA, n = 14)). Except for the naïve and housed with stressed mate groups, rats received two foot-shocks (5 s for each). The next day, the subjects were allowed to explore two unfamiliar conspecifics; one was a naïve, while the other was a distressed conspecific that received two foot-shocks (1.0 mA, 5 s) immediately before the test. Rats that were housed with stressed mates, as well as those that experienced a higher intensity of foot-shocks, were more likely to approach, while naïve rats avoided, a distressed conspecific. These results suggest that socially transferred stress shifts socioaffective response styles from avoidance to approach toward a stressed conspecific in rats.

Higher-order sequences of vocal mimicry performed by male Albert's lyrebirds are socially transmitted and enhance acoustic contrast

Most studies of acoustic communication focus on short units of vocalization such as songs, yet these units are often hierarchically organized into higher-order sequences and, outside human language, little is known about the drivers of sequence structure. Here, we investigate the organization, transmission and function of vocal sequences sung by male Albert's lyrebirds (Menura alberti), a species renowned for vocal imitations of other species. We quantified the organization of mimetic units into sequences, and examined the extent to which these sequences are repeated within and between individuals and shared among populations. We found that individual males organized their mimetic units into stereotyped sequences. Sequence structures were shared within and to a lesser extent among populations, implying that sequences were socially transmitted. Across the entire species range, mimetic units were sung with immediate variety and a high acoustic contrast between consecutive units, suggesting that sequence structure is a means to enhance receiver perceptions of repertoire complexity. Our results provide evidence that higher-order sequences of vocalizations can be socially transmitted, and that the order of vocal units can be functionally significant. We conclude that, to fully understand vocal behaviours, we must study both the individual vocal units and their higher-order temporal organization.

Counterintuitive Pseudoscience Propagates by Exploiting the Mind's Communication Evaluation Mechanisms

Epidemiological models of culture posit that the prevalence of a belief depends in part on the fit between that belief and intuitions generated by the mind's reliably developing architecture. Application of such models to pseudoscience suggests that one route via which these beliefs gain widespread appeal stems from their compatibility with these intuitions. For example, anti-vaccination beliefs are readily adopted because they cohere with intuitions about the threat of contagion. However, other varieties of popular pseudoscience such as astrology and parapsychology contain content that violates intuitions held about objects and people. Here, we propose a pathway by which "counterintuitive pseudoscience" may spread and receive endorsement. Drawing on recent empirical evidence, we suggest that counterintuitive pseudoscience triggers the mind's communication evaluation mechanisms. These mechanisms are hypothesized to quarantine epistemically-suspect information including counterintuitive pseudoscientific concepts. As a consequence, these beliefs may not immediately update conflicting intuitions and may be largely restricted from influencing behavior. Nonetheless, counterintuitive pseudoscientific concepts, when in combination with intuitively appealing content, may differentially draw attention and memory. People may also be motivated to seek further information about these concepts, including by asking others, in an attempt to reconcile them with prior beliefs. This in turn promotes the re-transmission of these ideas. We discuss how, during this information-search, support for counterintuitive pseudoscience may come from deference to apparently authoritative sources, reasoned arguments, and the functional outcomes of these beliefs. Ultimately, these factors promote the cultural success of counterintuitive pseudoscience but explicit endorsement of these concepts may not entail tacit commitment.

Recognising the key role of individual recognition in social networks

Many aspects of sociality rely on individuals recognising one another. Understanding how, when, and if individuals recognise others can yield insights into the foundations of social relationships and behaviours. Through synthesising individual recognition research in different sensory and social domains, and doing so across various related social contexts, we propose that a social network perspective can help to uncover how individual recognition may vary across different settings, species, and populations. Specifically, combining individual recognition with social networks has unrecognised potential for determining the level and relative importance of individual recognition complexity. This will provide insights not only on the ecology and evolution of individual recognition itself, but also on social structure, social transmission, and social interactions such as cooperation.

The modularity of a social group does not affect the transmission speed of a novel, socially learned behaviour, or the formation of local variants

The structure of a group is critical in determining how a socially learnt behaviour will spread. Predictions from theoretical models indicate that specific parameters of social structure differentially influence social transmission. Modularity describes how the structure of a group or network is divided into distinct subgroups or clusters. Theoretical modelling indicates that the modularity of a network will predict the rate of behavioural spread within a group, with higher modularity slowing the rate of spread and facilitating the establishment of local behavioural variants which can prelude local cultures. Despite prolific modelling approaches, empirical tests via manipulations of group structure remain scarce. We experimentally manipulated the modularity of populations of domestic fowl chicks, Gallus gallus domesticus, to affect the transmission of a novel foraging behaviour. We compared the spread of behaviour in populations with networks of high or low modularity against control populations where social transmission was prevented. We found the foraging behaviour to spread socially between individuals when the social transmission was permitted; however, modularity did not increase the speed of behavioural spread nor lead to the initial establishments of shared behavioural variants. This result suggests that factors in the social transmission process additional to the network structure may influence behavioural spread.

Elevated infant cortisol is necessary but not sufficient for transmission of environmental risk to infant social development: Cross-species evidence of mother-infant physiological social transmission

Environmental adversity increases child susceptibility to disrupted developmental outcomes, but the mechanisms by which adversity can shape development remain unclear. A translational cross-species approach was used to examine stress-mediated pathways by which poverty-related adversity can influence infant social development. Findings from a longitudinal sample of low-income mother-infant dyads indicated that infant cortisol (CORT) on its own did not mediate relations between early-life scarcity-adversity exposure and later infant behavior in a mother-child interaction task. However, maternal CORT through infant CORT served as a mediating pathway, even when controlling for parenting behavior. Findings using a rodent "scarcity-adversity" model indicated that pharmacologically blocking pup corticosterone (CORT, rodent equivalent to cortisol) in the presence of a stressed mother causally prevented social transmission of scarcity-adversity effects on pup social behavior. Furthermore, pharmacologically increasing pup CORT without the mother present was not sufficient to disrupt pup social behavior. Integration of our cross-species results suggests that elevated infant CORT may be necessary, but without elevated caregiver CORT, may not be sufficient in mediating the effects of environmental adversity on development. These findings underscore the importance of considering infant stress physiology in relation to the broader social context, including caregiver stress physiology, in research and interventional efforts.

Detecting and quantifying social transmission using network-based diffusion analysis

Although social learning capabilities are taxonomically widespread, demonstrating that freely interacting animals (whether wild or captive) rely on social learning has proved remarkably challenging. Network-based diffusion analysis (NBDA) offers a means for detecting social learning using observational data on freely interacting groups. Its core assumption is that if a target behaviour is socially transmitted, then its spread should follow the connections in a social network that reflects social learning opportunities. Here, we provide a comprehensive guide for using NBDA. We first introduce its underlying mathematical framework and present the types of questions that NBDA can address. We then guide researchers through the process of selecting an appropriate social network for their research question; determining which NBDA variant should be used; and incorporating other variables that may impact asocial and social learning. Finally, we discuss how to interpret an NBDA model's output and provide practical recommendations for model selection. Throughout, we highlight extensions to the basic NBDA framework, including incorporation of dynamic networks to capture changes in social relationships during a diffusion and using a multi-network NBDA to estimate information flow across multiple types of social relationship. Alongside this information, we provide worked examples and tutorials demonstrating how to perform analyses using the newly developed nbda package written in the R programming language.

Social Transmission and Buffering of Hippocampal Metaplasticity after Stress in Mice

In social animals, the behavioral and hormonal responses to stress can be transmitted from one individual to another through a social transmission process, and, conversely, social support ameliorates stress responses, a phenomenon referred to as social buffering. Metaplasticity represents activity-dependent synaptic changes that modulate the ability to elicit subsequent synaptic plasticity. Authentic stress can induce hippocampal metaplasticity, but whether transmitted stress has the same ability remains unknown. Here, using an acute restraint-tailshock stress paradigm, we report that both authentic and transmitted stress in adult male mice trigger metaplastic facilitation of long-term depression (LTD) induction at hippocampal CA1 synapses. Using LTD as a readout of persistent synaptic consequences of stress, our findings demonstrate that, in a male-male dyad, stress transmission happens in nearly half of naive partners and stress buffering occurs in approximately half of male stressed mice that closely interact with naive partners. By using a social-confrontation tube test to assess the dominant-subordinate relationship in a male-male dyad, we found that stressed subordinate mice are not buffered by naive dominant partners and that stress transmission is exhibited in ∼60% of dominant naive partners. Furthermore, the appearance of stress transmission correlates with more time spent in sniffing the anogenital area of stressed mice, and the appearance of stress buffering correlates with more time engaged in allogrooming from naive partners. Chemical ablation of the olfactory epithelium with dichlobenil or physical separation between social contacts diminishes stress transmission. Together, our data demonstrate that transmitted stress can elicit metaplastic facilitation of LTD induction as authentic stress.SIGNIFICANCE STATEMENT Social animals can acquire information about their environment through interactions with conspecifics. Stress can induce enduring changes in neural activity and synaptic function. Current studies are already unraveling the transmission and buffering of stress responses between individuals, but little is known about the relevant synaptic changes associated with social transmission and buffering of stress. Here, we show that authentic and transmitted stress can prime glutamatergic synapses onto hippocampal CA1 neurons to undergo long-term depression. This hippocampal metaplasticity is bufferable following social interactions with naive partners. Hierarchical status of naive partners strongly affects the social buffering effect on synaptic consequences of stress. This work provides novel insights into the conceptual framework for synaptic changes with social transmission and buffering of stress.

Detecting and quantifying social transmission using network-based diffusion analysis

Although social learning capabilities are taxonomically widespread, demonstrating that freely interacting animals (whether wild or captive) rely on social learning has proved remarkably challenging. Network-based diffusion analysis (NBDA) offers a means for detecting social learning using observational data on freely interacting groups. Its core assumption is that if a target behaviour is socially transmitted, then its spread should follow the connections in a social network that reflects social learning opportunities. Here, we provide a comprehensive guide for using NBDA. We first introduce its underlying mathematical framework and present the types of questions that NBDA can address. We then guide researchers through the process of selecting an appropriate social network for their research question; determining which NBDA variant should be used; and incorporating other variables that may impact asocial and social learning. Finally, we discuss how to interpret an NBDA model's output and provide practical recommendations for model selection. Throughout, we highlight extensions to the basic NBDA framework, including incorporation of dynamic networks to capture changes in social relationships during a diffusion and using a multi-network NBDA to estimate information flow across multiple types of social relationship. Alongside this information, we provide worked examples and tutorials demonstrating how to perform analyses using the newly developed nbda package written in the R programming language.

The optimal timing of teaching and learning across the life course

The evolutionary biologist W. D. Hamilton (Hamilton 1966 J. Theor. Biol.12, 12-45. (doi:10.1016/0022-5193(66)90184-6)) famously showed that the force of natural selection declines with age, and reaches zero by the age of reproductive cessation. However, in social species, the transfer of fitness-enhancing resources by postreproductive adults increases the value of survival to late ages. While most research has focused on intergenerational food transfers in social animals, here we consider the potential fitness benefits of information transfer, and investigate the ecological contexts where pedagogy is likely to occur. Although the evolution of teaching is an important topic in behavioural biology and in studies of human cultural evolution, few formal models of teaching exist. Here, we present a modelling framework for predicting the timing of both information transfer and learning across the life course, and find that under a broad range of conditions, optimal patterns of information transfer in a skills-intensive ecology often involve postreproductive aged teachers. We explore several implications among human subsistence populations, evaluating the cost of hunting pedagogy and the relationship between activity skill complexity and the timing of pedagogy for several subsistence activities. Long lifespan and extended juvenility that characterize the human life history likely evolved in the context of a skills-intensive ecological niche with multi-stage pedagogy and multigenerational cooperation. This article is part of the theme issue 'Life history and learning: how childhood, caregiving and old age shape cognition and culture in humans and other animals'.

Sex Bias in Gut Microbiome Transmission in Newly Paired Marmosets (Callithrix jacchus)

Social behavior can alter the microbiome composition via transmission among social partners, but there have been few controlled experimental studies of gut microbiome transmission among social partners in primates. We collected longitudinal fecal samples from eight unrelated male-female pairs of marmoset monkeys prior to pairing and for 8 weeks following pairing. We then sequenced 16S rRNA to characterize the changes in the gut microbiome that resulted from the pairing. Marmoset pairs had a higher similarity in gut microbiome communities after pairing than before pairing. We discovered sex differences in the degrees of change in gut microbiome communities following pairing. Specifically, the gut microbiome communities in males exhibited greater dissimilarity from the prepairing stage (baseline) than the gut microbiome communities in females. Conversely, females showed a gradual stabilization in the rate of the gut microbiome community turnover. Importantly, we found that the male fecal samples harbored more female-source gut microbes after pairing, especially early in pairing (paired test, P < 0.05), possibly linked to sex bias in the frequencies of social behavior. From this controlled study, we report for the first time that pair-living primates undergo significant changes in gut microbiome during pairing and that females transmit more microbes to their partners than males do. The potential biases influencing which microbes are transmitted on the basis of sex and whether they are due to sex biases in other behavioral or physiological features need to be widely investigated in other nonhuman primates and humans in the future.IMPORTANCE In this controlled study, we collected longitudinal fecal samples from 16 male and female marmoset monkeys for 2 weeks prior to and for 8 weeks after pairing in male-female dyads. We report for the first time that marmoset monkeys undergo significant changes to the gut microbiome following pairing and that these changes are sex-biased; i.e., females transmit more microbes to their social partners than males do. Marmosets exhibit pair bonding behavior such as spatial proximity, physical contact, and grooming, and sex biases in these behavioral patterns may contribute to the observed sex bias in social transmission of gut microbiomes.

Horses Failed to Learn from Humans by Observation

Animals can acquire new behavior through both individual and social learning. Several studies have investigated horses' ability to utilize inter-species (human demonstrator) social learning with conflicting results. In this study, we repeat a previous study, which found that horses had the ability to learn from observing humans performing an instrumental task, but we include a control for stimulus enhancement. One human demonstrator and thirty horses were included, and the horses were randomly assigned to one of three treatments: (A) full human demonstration, (B) partial human demonstration, and (C) no human demonstration. The task was for the horses to touch an object situated 1 m away from a feed box, to open this feed box, and thereby obtain a food reward. The success of each horse, the behavior directed towards the apparatus and the human, and behaviors indicative of frustration were observed. The results showed that horses observing a full and partial human demonstration were not more successful in solving the instrumental task than horses not observing any demonstration. Horses that did not solve the task expressed more box- and human-oriented behavior compared to successful horses, which may be an indication of motivation to solve the task and/or frustration from being unable to solve the task.

Household composition and the infant fecal microbiome: The INSPIRE study

OBJECTIVES

Establishment and development of the infant gastrointestinal microbiome (GIM) varies cross-culturally and is thought to be influenced by factors such as gestational age, birth mode, diet, and antibiotic exposure. However, there is little data as to how the composition of infants' households may play a role, particularly from a cross-cultural perspective. Here, we examined relationships between infant fecal microbiome (IFM) diversity/composition and infants' household size, number of siblings, and number of other household members.

MATERIALS AND METHODS

We analyzed 377 fecal samples from healthy, breastfeeding infants across 11 sites in eight different countries (Ethiopia, The Gambia, Ghana, Kenya, Peru, Spain, Sweden, and the United States). Fecal microbial community structure was determined by amplifying, sequencing, and classifying (to the genus level) the V1-V3 region of the bacterial 16S rRNA gene. Surveys administered to infants' mothers identified household members and composition.

RESULTS

Our results indicated that household composition (represented by the number of cohabitating siblings and other household members) did not have a measurable impact on the bacterial diversity, evenness, or richness of the IFM. However, we observed that variation in household composition categories did correspond to differential relative abundances of specific taxa, namely: Lactobacillus, Clostridium, Enterobacter, and Klebsiella.

DISCUSSION

This study, to our knowledge, is the largest cross-cultural study to date examining the association between household composition and the IFM. Our results indicate that the social environment of infants (represented here by the proxy of household composition) may influence the bacterial composition of the infant GIM, although the mechanism is unknown. A higher number and diversity of cohabitants and potential caregivers may facilitate social transmission of beneficial bacteria to the infant gastrointestinal tract, by way of shared environment or through direct physical and social contact between the maternal-infant dyad and other household members. These findings contribute to the discussion concerning ways by which infants are influenced by their social environments and add further dimensionality to the ongoing exploration of social transmission of gut microbiota and the "old friends" hypothesis.

Assortative Mating by an Obliquely Transmitted Local Cultural Trait Promotes Genetic Divergence: A Model

The effect of learned culture (e.g., birdsong dialects and human languages) on genetic divergence is unclear. Previous theoretical research suggests that because oblique learning allows phenotype transmission from individuals with no offspring to an unrelated individual in the next generation, the effect of sexual selection on the learned trait is masked. However, I propose that migration and spatially constrained learning can form statistical associations between cultural and genetic traits, which may allow selection on the cultural traits to indirectly affect the genetic traits. Here, I build a population genetic model that allows such statistical associations to form and find that sexual selection and divergent selection on the cultural trait can indeed help maintain genetic divergence through such statistical associations, while selection against genetic hybrids does not affect cultural trait divergence. Furthermore, I find that even when the cultural trait changes over time due to drift and mutation, it can still help maintain genetic divergence. These results suggest the role of obliquely transmitted traits in evolution may be underrated, and the lack of one-to-one associations between cultural and genetic traits may not be sufficient to disprove the role of culture in genetic divergence.

Understanding experiences of the self-harm of others: A qualitative exploration of the views of young people with complex mental health needs

As adolescent self-harm is a growing public health concern, more research is needed to identify potential risk factors. Studies have highlighted that exposure to the self-harm of others may be a risk factor associated with engagement in self-harm. However, research investigating young people's experiences of the self-harm of others has been limited. This qualitative study aimed to explore young people's experiences of the self-harm of others and interviewed a total of eight young people (five females and three males; aged between 13 and 18 years) resident at one of two adolescent mental health inpatient units in the North of England. The interviews were analysed using Interpretative Phenomenological Analysis and four themes were identified: 'Pre-admission exposure to self-harm', 'Exposure on the inside: An unpleasant environment', 'Helper vs helped' and 'Separation from the attention seekers: competing for authenticity'. Prevention efforts to reduce the social transmission and stigma surrounding self-harm among young people are discussed.

Social Learning in Horses-Fact or Fiction?

Prima facie, the acquisition of novel behaviors in animals through observation of conspecifics seems straightforward. There are, however, various mechanisms through which the behavior of animals can be altered from observing others. These mechanisms range from simple hard-wired contagious processes to genuine learning by observation, which differ fundamentally in cognitive complexity. They range from social facilitation and local enhancement to true social learning. The different learning mechanisms are the subject of this review, largely because research on learning by observation can be confounded by difficulties in interpretation owing to the looming possibility of associative learning infecting experimental results. While it is often assumed that horses are capable of acquiring new behavior through intra-species observation, research on social learning in horses includes a variety of studies some of which may overestimate the possession of higher mental abilities. Assuming such abilities in their absence can have welfare implications, e.g., isolating stereotypical horses on the assumption that these behaviors can be learned though observation by neighboring horses. This review summarizes the definitions and criteria for the various types of social transmission and social learning and reviews the current documentation for each type in horses with the aim of clarifying whether horses possess the ability to learn through true social learning. As social ungulates, horses evolved in open landscapes, exposed to predators and grazing most of the day. Being in close proximity to conspecifics may theoretically offer an opportunity to learn socially, however anti-predator vigilance and locating forage may not require the neural complexity of social learning. Given the significant energetic expense of brain tissue, it is likely that social facilitation and local enhancement may have been sufficient in the adaptation of equids to their niche. As a consequence, social learning abilities may be maladaptive in horses. Collectively, the review proposes a novel differentiation between social transmission (social facilitation, local, and stimulus enhancement) and social learning (goal emulation, imitation). Horses are undoubtedly sensitive to intra-species transfer of information but this transfer does not appear to satisfy the criteria for social learning, and thus there is no solid evidence for true social learning in horses.

Fear of predation shapes social network structure and the acquisition of foraging information in guppy shoals

Spatio-temporal variation in predation risk is predicted to select for plastic anti-predator responses, which may in turn impact the fine-scale social structure of prey groups and processes mediated by that structure. To test these predictions, we manipulated the ambient predation risk experienced by Trinidadian guppy (Poecilia reticulata) groups before quantifying their social networks and recording individual latencies to approach and solve a novel foraging task. High-risk conditions drove the formation of social networks that were more strongly assorted by body size than those exposed to low ambient risk and promoted longer durations of contact between preferred partners. Additionally, high background predation risk reduced the probability individuals would approach and solve a novel foraging task. Network-based diffusion analysis revealed that while social transmission of the task solution from knowledgeable to naive individuals occurred at a higher rate within low-risk groups, individuals in high-risk groups were particularly likely to investigate the task while shoaling with preferred social partners. Taken together, our results suggest that the structure and functional importance of prey social networks may partly depend on local predation pressure. Furthermore, by influencing individuals' access to information, fear of predation may impact decision-making in a potentially wide array of behavioural contexts.

The conceptual foundations of network-based diffusion analysis: choosing networks and interpreting results

Network-based diffusion analysis (NBDA) is a statistical technique for detecting the social transmission of behavioural innovations in groups of animals, including humans. The strength of social transmission is inferred from the extent to which the diffusion (spread) of the innovation follows a social network. NBDA can have two goals: (a) to establish whether social transmission is occurring and how strong its effects are; and/or (b) to establish the typical pathways of information transfer. The technique has been used in a range of taxa, including primates, cetaceans, birds and fish, using a range of different types of network. Here I investigate the conceptual underpinnings of NBDA, in order to establish the meaning of results using different networks. I develop a model of the social transmission process where each individual observation of the target behaviour affects the rate at which the observer learns that behaviour. I then establish how NBDAs using different networks relate to this underlying process, and thus how we can interpret the results of each. My analysis shows that a different network or networks are appropriate depending on the specific goal or goals of the study, and establishes how the parameter estimates yielded from an NBDA can be interpreted for different networks.This article is part of the themed issue 'Process and pattern in innovations from cells to societies'.

Pathways of information transmission among wild songbirds follow experimentally imposed changes in social foraging structure

Animals regularly use information from others to shape their decisions. Yet, determining how changes in social structure affect information flow and social learning strategies has remained challenging. We manipulated the social structure of a large community of wild songbirds by controlling which individuals could feed together at automated feeding stations (selective feeders). We then provided novel ephemeral food patches freely accessible to all birds and recorded the spread of this new information. We demonstrate that the discovery of new food patches followed the experimentally imposed social structure and that birds disproportionately learnt from those whom they could forage with at the selective feeders. The selective feeders reduced the number of conspecific information sources available and birds subsequently increased their use of information provided by heterospecifics. Our study demonstrates that changes to social systems carry over into pathways of information transfer and that individuals learn from tutors that provide relevant information in other contexts.

Kin-based cultural transmission of tool use in wild chimpanzees

Current research on animal culture has focused strongly on cataloging the diversity of socially transmitted behaviors and on the social learning mechanisms that sustain their spread. Comparably less is known about the persistence of cultural behavior following innovation in groups of wild animals. We present observational data and a field experiment designed to address this question in a wild chimpanzee community, capitalizing on a novel tool behavior, moss-sponging, which appeared naturally in the community in 2011. We found that, 3 years later, moss-sponging was still present in the individuals that acquired the behavior shortly after its emergence and that it had spread further, to other community members. Our field experiment suggests that this secondary radiation and consolidation of moss-sponging is the result of transmission through matrilines, in contrast to the previously documented association-based spread among the initial cohort. We conclude that the spread of cultural behavior in wild chimpanzees follows a sequential structure of initial proximity-based horizontal transmission followed by kin-based vertical transmission.

Epidemiological models to control the spread of information in marine mammals

Socially transmitted wildlife behaviours that create human-wildlife conflict are an emerging problem for conservation efforts, but also provide a unique opportunity to apply principles of infectious disease control to wildlife management. As an example, California sea lions (Zalophus californianus) have learned to exploit concentrations of migratory adult salmonids below the fish ladders at Bonneville Dam, impeding endangered salmonid recovery. Proliferation of this foraging behaviour in the sea lion population has resulted in a controversial culling programme of individual sea lions at the dam, but the impact of such culling remains unclear. To evaluate the effectiveness of current and alternative culling strategies, we used network-based diffusion analysis on a long-term dataset to demonstrate that social transmission is implicated in the increase in dam-foraging behaviour and then studied different culling strategies within an epidemiological model of the behavioural transmission data. We show that current levels of lethal control have substantially reduced the rate of social transmission, but failed to effectively reduce overall sea lion recruitment. Earlier implementation of culling could have substantially reduced the extent of behavioural transmission and, ultimately, resulted in fewer animals being culled. Epidemiological analyses offer a promising tool to understand and control socially transmissible behaviours.

Sociality and health: impacts of sociality on disease susceptibility and transmission in animal and human societies

This paper introduces a theme issue presenting the latest developments in research on the impacts of sociality on health and fitness. The articles that follow cover research on societies ranging from insects to humans. Variation in measures of fitness (i.e. survival and reproduction) has been linked to various aspects of sociality in humans and animals alike, and variability in individual health and condition has been recognized as a key mediator of these relationships. Viewed from a broad evolutionary perspective, the evolutionary transitions from a solitary lifestyle to group living have resulted in several new health-related costs and benefits of sociality. Social transmission of parasites within groups represents a major cost of group living, but some behavioural mechanisms, such as grooming, have evolved repeatedly to reduce this cost. Group living also has created novel costs in terms of altered susceptibility to infectious and non-infectious disease as a result of the unavoidable physiological consequences of social competition and integration, which are partly alleviated by social buffering in some vertebrates. Here, we define the relevant aspects of sociality, summarize their health-related costs and benefits, and discuss possible fitness measures in different study systems. Given the pervasive effects of social factors on health and fitness, we propose a synthesis of existing conceptual approaches in disease ecology, ecological immunology and behavioural neurosciences by adding sociality as a key factor, with the goal to generate a broader framework for organismal integration of health-related research.

Social network- and community-level influences on contraceptive use: evidence from rural Poland

The diffusion of 'modern' contraceptives-as a proxy for the spread of low-fertility norms-has long interested researchers wishing to understand global fertility decline. A fundamental question is how local cultural norms and other people's behaviour influence the probability of contraceptive use, independent of women's socioeconomic and life-history characteristics. However, few studies have combined data at individual, social network and community levels to simultaneously capture multiple levels of influence. Fewer still have tested if the same predictors matter for different contraceptive types. Here, we use new data from 22 high-fertility communities in Poland to compare predictors of the use of (i) any contraceptives-a proxy for the decision to control fertility-with those of (ii) 'artificial' contraceptives-a subset of more culturally taboo methods. We find that the contraceptive behaviour of friends and family is more influential than are women's own characteristics and that community level characteristics additionally influence contraceptive use. Highly educated neighbours accelerate women's contraceptive use overall, but not their artificial method use. Highly religious neighbours slow women's artificial method use, but not their contraceptive use overall. Our results highlight different dimensions of sociocultural influence on contraceptive diffusion and suggest that these may be more influential than are individual characteristics. A comparative multilevel framework is needed to understand these dynamics.

The amplification of risk in experimental diffusion chains

Understanding how people form and revise their perception of risk is central to designing efficient risk communication methods, eliciting risk awareness, and avoiding unnecessary anxiety among the public. However, public responses to hazardous events such as climate change, contagious outbreaks, and terrorist threats are complex and difficult-to-anticipate phenomena. Although many psychological factors influencing risk perception have been identified in the past, it remains unclear how perceptions of risk change when propagated from one person to another and what impact the repeated social transmission of perceived risk has at the population scale. Here, we study the social dynamics of risk perception by analyzing how messages detailing the benefits and harms of a controversial antibacterial agent undergo change when passed from one person to the next in 10-subject experimental diffusion chains. Our analyses show that when messages are propagated through the diffusion chains, they tend to become shorter, gradually inaccurate, and increasingly dissimilar between chains. In contrast, the perception of risk is propagated with higher fidelity due to participants manipulating messages to fit their preconceptions, thereby influencing the judgments of subsequent participants. Computer simulations implementing this simple influence mechanism show that small judgment biases tend to become more extreme, even when the injected message contradicts preconceived risk judgments. Our results provide quantitative insights into the social amplification of risk perception, and can help policy makers better anticipate and manage the public response to emerging threats.

Experimental evidence for the co-evolution of hominin tool-making teaching and language

Hominin reliance on Oldowan stone tools-which appear from 2.5 mya and are believed to have been socially transmitted-has been hypothesized to have led to the evolution of teaching and language. Here we present an experiment investigating the efficacy of transmission of Oldowan tool-making skills along chains of adult human participants (N=184) using five different transmission mechanisms. Across six measures, transmission improves with teaching, and particularly with language, but not with imitation or emulation. Our results support the hypothesis that hominin reliance on stone tool-making generated selection for teaching and language, and imply that (i) low-fidelity social transmission, such as imitation/emulation, may have contributed to the ~700,000 year stasis of the Oldowan technocomplex, and (ii) teaching or proto-language may have been pre-requisites for the appearance of Acheulean technology. This work supports a gradual evolution of language, with simple symbolic communication preceding behavioural modernity by hundreds of thousands of years.

The science of sharing and the sharing of science

Why do members of the public share some scientific findings and not others? What can scientists do to increase the chances that their findings will be shared widely among nonscientists? To address these questions, we integrate past research on the psychological drivers of interpersonal communication with a study examining the sharing of hundreds of recent scientific discoveries. Our findings offer insights into (i) how attributes of a discovery and the way it is described impact sharing, (ii) who generates discoveries that are likely to be shared, and (iii) which types of people are most likely to share scientific discoveries. The results described here, combined with a review of recent research on interpersonal communication, suggest how scientists can frame their work to increase its dissemination. They also provide insights about which audiences may be the best targets for the diffusion of scientific content.

Differential effects of dopamine receptor D1-type and D2-type antagonists and phase of the estrous cycle on social learning of food preferences, feeding, and social interactions in mice

The neurobiological bases of social learning, by which an animal can 'exploit the expertise of others' and avoid the disadvantages of individual learning, are only partially understood. We examined the involvement of the dopaminergic system in social learning by administering a dopamine D1-type receptor antagonist, SCH23390 (0.01, 0.05, and 0.1 mg/kg), or a D2-type receptor antagonist, raclopride (0.1, 0.3, and 0.6 mg/kg), to adult female mice prior to socially learning a food preference. We found that while SCH23390 dose-dependently inhibited social learning without affecting feeding behavior or the ability of mice to discriminate between differently flavored diets, raclopride had the opposite effects, inhibiting feeding but leaving social learning unaffected. We showed that food odor, alone or in a social context, was insufficient to induce a food preference, proving the specifically social nature of this paradigm. The estrous cycle also affected social learning, with mice in proestrus expressing the socially acquired food preference longer than estrous and diestrous mice. This suggests gonadal hormone involvement, which is consistent with known estrogenic regulation of female social behavior and estrogen receptor involvement in social learning. Furthermore, a detailed ethological analysis of the social interactions during which social learning occurs showed raclopride- and estrous phase-induced changes in agonistic behavior, which were not directly related to effects on social learning. Overall, these results suggest a differential involvement of the D1-type and D2-type receptors in the regulation of social learning, feeding, and agonistic behaviors that are likely mediated by different underlying states.

Social transmission of nectar-robbing behaviour in bumble-bees

Social transmission of acquired foraging techniques is rarely considered outside of a vertebrate context. Here, however, we show that nectar robbing by bumble-bees (Bombus terrestris)-an invertebrate behaviour of considerable ecological significance-has the potential to spread through a population at the accelerated rates typical of social transmission. Nectar robbing occurs when individuals either bite through the base of a flower to 'steal' nectar (primary robbing) or use robbing holes that others have made (secondary robbing). We found that experience of foraging from robbed flowers significantly promoted the development of primary robbing in previously legitimate foragers, thus implying that the acquisition of nectar robbing by one individual will facilitate its adoption in others. Our findings suggest that the positive feedback effects of social transmission may potentially play an ecologically important role in the relationship between plants and pollinators.

Combined lesions of hippocampus and subiculum Do not produce deficits in a nonspatial social olfactory memory task

Rats transmit information to each other about which foods are safe to eat. If a rat smells a food odor on the breath of another rat, it is subsequently more likely to eat that food than an alternative. Work by Galef et al. (1988) has shown that the observer rat forms an association between two olfactory stimuli on the breath of the demonstrator rat that has eaten the food, the food odor and carbon disulphide, which is normally present in the rat breath. Bunsey and Eichenbaum (1995) claimed that the hippocampus/subicular region is required for the long-term retention of this nonspatial form of associative memory on the basis that combined lesions of the hippocampus and subiculum produced a deficit, but lesions of either structure alone did not. We report here a failure to repeat this finding. Rats with either combined lesions of the hippocampus and subiculum or with amygdala lesions were tested on their ability to remember this association either immediately (testing short-term memory) or after a 24 hr delay (testing long-term memory). Neither lesion group exhibited significant memory deficits on this nonspatial associative task at either test interval. In contrast, a deficit was observed on a spatial memory task (forced-choice alternation t-maze) for animals with combined lesions of the hippocampus and subiculum. These results contradict the findings of Bunsey and Eichenbaum (1995) and support the idea that the hippocampus/subicular region is not required for this nonspatial associative memory.