Of pubs and platforms

This article argues for a more explicit concern with sociality in anthropology, illustrated through a study of one of the oldest English platforms for sociality: the English pub. Using an approach derived from the study of social media, the pub is analysed in terms of the balance between structural (mainly commercial) forces and agency (mainly the desire for particular kinds of sociality). Following an introduction to the English pub, the article considers how pubs exert control over which population they serve. The next section, shows how groups of people colonize pubs, regardless of the pub's intentions. This is followed by a discussion of the various responses by pubs to this colonization. The final section, ‘Scalable sociality’, demonstrates how these processes combine to produce a phenomenon called scalable sociality, which is also a definition of social media: a series of platforms that can be sited along various scales and parameters of sociality. This is important because a similar tension between, on the one hand, commercial or state forces and, on the other hand, the development of new forms of sociality is increasingly common within many topics studied by anthropologists.     

Evidence for coevolution of sociality and relative brain size in three orders of mammals

As the brain is responsible for managing an individual's behavioral response to its environment, we should expect that large relative brain size is an evolutionary response to cognitively challenging behaviors. The "social brain hypothesis" argues that maintaining group cohesion is cognitively demanding as individuals living in groups need to be able to resolve conflicts that impact on their ability to meet resource requirements. If sociality does impose cognitive demands, we expect changes in relative brain size and sociality to be coupled over evolutionary time. In this study, we analyze data on sociality and relative brain size for 206 species of ungulates, carnivores, and primates and provide, for the first time, evidence that changes in sociality and relative brain size are closely correlated over evolutionary time for all three mammalian orders. This suggests a process of coevolution and provides support for the social brain theory. However, differences between taxonomic orders in the stability of the transition between small-brained/nonsocial and large-brained/social imply that, although sociality is cognitively demanding, sociality and relative brain size can become decoupled in some cases. Carnivores seem to have been especially prone to this.     

The adaptive value of sociality in mammalian groups

According to behavioural ecology theory, sociality evolves when the net benefits of close association with conspecifics exceed the costs. The nature and relative magnitude of the benefits and costs of sociality are expected to vary across species and habitats. When sociality is favoured, animals may form groups that range from small pair-bonded units to huge aggregations. The size and composition of social groups have diverse effects on morphology and behaviour, ranging from the extent of sexual dimorphism to brain size, and the structure of social relationships. This general argument implies that sociality has fitness consequences for individuals. However, for most mammalian species, especially long-lived animals like primates, there are sizable gaps in the chain of evidence that links sociality and social bonds to fitness outcomes. These gaps reflect the difficulty of quantifying the cumulative effects of behavioural interactions on fitness and the lack of information about the nature of social relationships among individuals in most taxa. Here, I review what is known about the reproductive consequences of sociality for mammals.     

Energetic Benefits of Sociality Offset the Costs of Parasitism in a Cooperative Mammal

Sociality and particularly advanced forms of sociality such as cooperative breeding (living in permanent groups with reproductive division of labour) is relatively rare among vertebrates. A suggested constraint on the evolution of sociality is the elevated transmission rate of parasites between group members. Despite such apparent costs, sociality has evolved independently in a number of vertebrate taxa including humans. However, how the costs of parasitism are overcome in such cases remains uncertain. We evaluated the potential role of parasites in the evolution of sociality in a member of the African mole-rats, the only mammal family that exhibits the entire range of social systems from solitary to eusocial. Here we show that resting metabolic rates decrease whilst daily energy expenditure and energy stores (i.e. body fat) increase with group size in social Natal mole rats (Cryptomys hottentotus natalensis). Critically, larger groups also had reduced parasite abundance and infested individuals only showed measurable increases in energy metabolism at high parasite abundance. Thus, in some circumstances, sociality appears to provide energetic benefits that may be diverted into parasite defence. This mechanism is likely to be self-reinforcing and an important factor in the evolution of sociality.     

Towards an integrative model of sociality in caviomorph rodents

In the late 1990s and early 2000s it was recognized that behavioral ecologists needed to study the sociality of caviomorph rodents (New World hystricognaths) before generalizations about rodent sociality could be made. Researchers identified specific problems facing individuals interested in caviomorph sociality, including a lack of information on the proximate mechanisms of sociality, role of social environment in development, and geographical or intraspecific variation in social systems. Since then researchers have described the social systems of many previously understudied species, including some with broad geographical ranges. Researchers have done a good job of determining the role of social environments in development and identifying the costs and benefits of social living. However, relatively little is known about the proximate mechanisms of social behavior and fitness consequences, limiting progress toward the development of integrative (evolutionary-mechanistic) models for sociality. To develop integrative models behavioral ecologists studying caviomorph rodents must generate information on the fitness consequences of different types of social organization, brain mechanisms, and endocrine substrates of sociality. We review our current understanding and future directions for research in these conceptual areas. A greater understanding of disease ecology, particularly in species carrying Old World parasites, is needed before we can identify potential links between social phenotypes, mechanism, and fitness.     

食肉目动物的社会性及其进化起源的推测

在查阅大量文献的基础上,收集了有关食肉目动物的社会性行为方面的资料,我们推测食肉目动物的社会性进化主要有两条途径,第一条途径可能是食肉目动物为了适应在开阔栖息地捕食集群生活且活动性强的猎物,促进了以共同合作捕猎为目的的社会化群体的进化。第二条途径可能是食肉目动物依赖的食物资源分布均匀而丰富,个体间对食物资源的竞争很小,从而有助于动物集群以提高共同警戒御敌和合作哺幼的成效,促进了家族群为基础的社会性群体的进化。我们推测食肉目动物的社会性主要起源于家族群,在家族群的基础上加入一些其它家族群迁入的无亲缘的个体,使家族群进一步扩大。如果群体内全体成员共同合作捕猎、分享食物、警戒防御天敌、防卫领域、哺育和保护幼仔以及进行其它的社会性协作时,则初步形成具有社会性的群体。社群内个体进一步分工合作,最终进化出社会性。     

Cryptic plasticity underlies a major evolutionary transition

The origin of eusociality is often regarded as a change of macroevolutionary proportions [1, 2]. Its hallmark is a reproductive division of labor between the members of a society: some individuals ("helpers" or "workers") forfeit their own reproduction to rear offspring of others ("queens"). In the Hymenoptera (ants, bees, wasps), there have been many transitions in both directions between solitary nesting and sociality [2-5]. How have such transitions occurred? One possibility is that multiple transitions represent repeated evolutionary gains and losses of the traits underpinning sociality. A second possibility, however, is that once sociality has evolved, subsequent transitions represent selection at just one or a small number of loci controlling developmental switches between preexisting alternative phenotypes [2, 6]. We might then expect transitional populations that can express either sociality or solitary nesting, depending on environmental conditions. Here, we use field transplants to directly induce transitions in British and Irish populations of the sweat bee Halictus rubicundus. Individual variation in social phenotype was linked to time available for offspring production, and to the genetic benefits of sociality, suggesting that helping was not simply misplaced parental care [7]. We thereby demonstrate that sociality itself can be truly plastic in a hymenopteran.     

Phylogeography of the socially polymorphic sweat bee Halictus rubicundus (Hymenoptera: Halictidae)

The evolution of sociality in insects holds a central place in evolutionary theory. By examining the phylogenetic patterns of solitary and social behavior and how they correlate with ecological variables, we may identify factors important in the evolution of sociality. In this study, we investigated historical and biogeographical patterns of sociality in a socially polymorphic bee species (one that demonstrates both social and solitary nesting behavior). This unique system allows for a more powerful examination of evolutionary transitions in sociality than interspecific studies of obligately social and solitary species. We conducted a phylogenetic analysis among populations of the halictine bee Halictus rubicundus and then identified relationships among mitochondrial DNA sequence data, sociality, environmental conditions at the nesting site, and geographic location of populations of this species. Within North America, populations of H. rubicundus expressing social and solitary behavior belong to different genetic lineages. Sociality is also correlated with at least one environmental variable used in this study. Taken together, the results support the predictions for genetic control of sociality, but they are still consistent with social behavior at some level being determined by the environmental conditions at the nesting site.     

Evolution of culture-dependent discriminate sociality: a gene-culture coevolutionary model

Animals behave cooperatively towards certain conspecifics while being indifferent or even hostile to others. The distinction is made primarily according to kinship as predicted by the kin selection theory. With regards to humans, however, this is not always the case; in particular, humans sometimes exhibit a discriminate sociality on the basis of culturally transmitted traits, such as personal ornaments, languages, rituals, etc. This paper explores the possibility that the human faculty of cultural transmission and resultant cultural variation among individuals may have facilitated the evolution of discriminate sociality in humans. To this end, a gene-culture coevolutionary model is developed focusing on competition over control of resource as a context in which discriminate sociality may have evolved. Specifically, two types of culture-dependent discriminate sociality are considered: ingroup favouritism, with ingroup and outgroup being distinguished by the presence or absence of a cultural trait; and prestige hierarchies, with the prestige being conferred on the bearer of a cultural trait. The model specifies the conditions under which emergence and evolutionary stability of the two types of discriminate sociality are promoted by the presence of cultural variation among individuals.     

Sociality in New World hystricognath rodents is linked to predators and burrow digging

The importance of predation and burrow digging in explainingthe evolution of sociality is generally unclear. We focusedon New World hystricognath rodents to evaluate three key predictionsof the predation hypothesis. First, large-bodied surface-dwellingspecies will be more vulnerable because they are more detectable;thus sociality should be associated with body size. Second,surface-dwelling, diurnal species would be more vulnerable topredators than nocturnal species; thus sociality should be associatedwith the evolution of diurnality. Third, species living in openhabitats will be more vulnerable; thus sociality should evolvein species living in open habitats. Regarding the importanceof burrows, we tested if species that dig burrows can benefitfrom communal labor; thus, sociality should be associated withburrow digging. All traits had significant phylogenetic signal,thus comparative analyses should explicitly address this. Ina comparative analysis on independent contrasts we found thatsociality was correlated with body size (larger species weremore social), diurnality (diurnal species were more social),and burrowing (burrowing species were more social), but we foundno effect of overhead plant cover of habitat on sociality inhystricognath rodents. Somewhat different results were foundwhen we analyzed the raw data. Taken together, our results providesupport for a link between predation risk, burrow digging, andsociality in this group.     

Do sampling method and sample size affect basic measures of dolphin sociality?

Although the fission–fusion social patterns of bottlenose dolphins have been described, defining and measuring sociality is difficult. No study to date has investigated how much data are necessary to accurately depict social patterns in a fission–fusion species and whether this amount differs depending on the measure used. Using the long-term Shark Bay bottlenose dolphin study we examined four different measures of sociality for mothers and dependent calves ( n = 89). Our objectives were to determine (1) the amount of observation time necessary to accurately depict sociality using these measures, (2) correlations among these measures, and (3) if sampling method affects the validity of sociality measurements. A minimum of 10 h and 5 h of observations, respectively, were necessary to accurately capture calf associate numbers and percent time alone. A pairwise comparison of calf sociality measurements from focal and survey data found that calves spent from 0% to 70.2% of their time alone in focal data, but these same calves spent only 0%–7.7% alone in survey data. These findings indicate that (1) results differ depending on the type of sampling method and (2) the amount of observation time necessary to adequately capture individual variation differs depending on the measure of sociality.     

Ecological generalism facilitates the evolution of sociality in snapping shrimps

Evidence from insects and vertebrates suggests that cooperation may have enabled species to expand their niches, becoming ecological generalists and dominating the ecosystems in which they occur. Consistent with this idea, eusocial species of sponge‐dwelling Synalpheus shrimps from Belize are ecological generalists with a broader host breadth and higher abundance than non‐eusocial species. We evaluate whether sociality promotes ecological generalism (social conquest hypothesis) or whether ecological generalism facilitates the transition to sociality (social transition hypothesis) in 38 Synalpheus shrimp species. We find that sociality evolves primarily from host generalists, and almost exclusively so for transitions to eusociality. Additionally, sponge volume is more important for explaining social transitions towards communal breeding than to eusociality, suggesting that different ecological factors may influence the independent evolutionary origins of sociality in Synalpheus shrimps. Ultimately, our results are consistent with the social transition hypothesis and the idea that ecological generalism facilitates the transition to sociality.     

Sociality, glucocorticoids and direct fitness in the communally rearing rodent, Octodon degus

While ecological causes of sociality (or group living) have been identified, proximate mechanisms remain less clear. Recently, close connections between sociality, glucocorticoid hormones (cort) and fitness have been hypothesized. In particular, cort levels would reflect a balance between fitness benefits and costs of group living, and therefore baseline cort levels would vary with sociality in a way opposite to the covariation between sociality and fitness. However, since reproductive effort may become a major determinant of stress responses (i.e., the cort–adaptation hypothesis), cort levels might also be expected to vary with sociality in a way similar to the covariation between sociality and fitness. We tested these expectations during three years in a natural population of the communally rearing degu, Octodon degus. During each year we quantified group membership, measured fecal cortisol metabolites (a proxy of baseline cort levels under natural conditions), and estimated direct fitness. We recorded that direct fitness decreases with group size in these animals. Secondly, neither group size nor the number of females (two proxies of sociality) influenced mean (or coefficient of variation, CV) baseline cortisol levels of adult females. In contrast, cortisol increased with per capita number of offspring produced and offspring surviving to breeding age during two out of three years examined. Together, our results imply that variation in glucocorticoid hormones is more linked to reproductive challenge than to the costs of group living. Most generally, our study provided independent support to the cort–adaptation hypothesis, according to which reproductive effort is a major determinant, yet temporally variable, influence on cort–fitness covariation.     

Comparative analyses suggest that information transfer promoted sociality in male bats in the temperate zone

The evolution of sociality is a central theme in evolutionary biology. The vast majority of bats are social, which has been explained in terms of the benefits of communal breeding. However, the causes for segregated male groups remain unknown. In a comparative study, we tested whether diet and morphological adaptations to specific foraging styles, two factors known to influence the occurrence of information transfer, can predict male sociality. Our results suggest that the species most likely to benefit from information transfer--namely, those preying on ephemeral insects and with morphological adaptations to feeding in open habitat--are more likely to form male groups. Our findings also indicate that solitary life was the ancestral state of males and sociality evolved in several lineages. Beyond their significance for explaining the existence of male groups in bats, our findings highlight the importance of information transfer in the evolution of animal sociality.     

Patterns of interventions and the effect of coalitions and sociality on male fitness

In group living animals, especially among primates, there is consistent evidence that high-ranking males gain a higher reproductive output than low-ranking males. Primate studies have shown that male coalitions and sociality can impact male fitness; however, it remains unclear whether males could potentially increase their fitness by preferentially supporting and socializing with females. Here we investigate patterns of male interventions and the effect of coalitions and sociality on male fitness in rhesus macaques (Macaca mulatta) with particular focus on male-female interactions. We combined behavioural observations collected on Cayo Santiago with genetic data analysed for male reproductive output and relatedness. Our results revealed that the ten top-ranking males provided the majority of all male support observed. In contrast to other primates, male rhesus macaques mainly formed all-down coalitions suggesting that coalitions are less likely used to enhance male dominance. Males supporting females during and before their likely conception were not more likely to fertilize those females. We also found no evidence that males preferably support their offspring or other close kin. Interestingly, the most important predictor of male support was sociality, since opponents sharing a higher sociality index with a given male were more likely to be supported. Furthermore, a high sociality index of a given male-female dyad resulted in a higher probability of paternity. Overall, our results strengthen the evidence that sociality affects fitness in male primates, but also suggest that in species in which males queue for dominance, it is less likely that males derive fitness benefits from coalitions.     

Primate sociality in evolutionary context

Much work has been done to further our understanding of the mechanisms that underlie the diversity of primate social organizations, but none has addressed the limits to that diversity or the question of what causes species to either form or not form social networks. The fact that all living primates typically live in social networks makes it highly likely that the last common ancestor of living primates already lived in social networks, and that sociality formed an integral part of the adaptive nature of primate origins. A characterization of primate sociality within the wider mammalian context is therefore essential to further our understanding of the adaptive nature of primate origins. Here we determine correlates of sociality and nonsociality in rodents as a model to infer causes of sociality in primates. We found sociality to be most strongly associated with large-bodied arboreal species that include a significant portion of fruit in their diet. Fruits and other plant products, such as flowers, seeds, and young leaves, are patchily distributed in time and space and are therefore difficult to find. These food resources are, however, predictable and dependable when their location is known. Hence, membership in a social unit can maximize food exploitation if information on feeding sites is shared. Whether sociality evolved in the primate stem lineage or whether it was already present earlier in the evolution of Euarchontoglires remains uncertain, although tentative evidence points to the former scenario. In either case, frugivory is likely to have played an important role in maintaining the presence of a social lifestyle throughout primate evolution.     

Higher disease prevalence can induce greater sociality: a game theoretic coevolutionary model

There is growing evidence that communicable diseases constitute a strong selective force on the evolution of social systems. It has been suggested that infectious diseases may determine upper limits of host sociality by, for example, inducing territoriality or early juvenile dispersal. Here we use game theory to model the evolution of host sociality in the context of communicable diseases. Our model is then augmented with the evolution of virulence to determine coevolutionarily stable strategies of host sociality and pathogen virulence. In contrast to a controversial hypothesis by Ewald (1994), our analysis indicates that pathogens may become more virulent when contact rates are low, and their prevalence can ultimately induce greater sociality.     

Relaxed predation risk reduces but does not eliminate sociality in birds

Disentangling the relative contribution of predation avoidance and increased foraging efficiency in the evolution of sociality in animals has proven difficult given that the two types of benefits often operate concurrently. I identified different types of refuges from predation in birds related to morphological and ecological traits, providing an opportunity to examine concomitant changes in sociality over evolutionary times. Results of a matched-species comparative analysis indicated a reduction in the size of foraging or non-foraging groups but not complete disappearance under negligible predation risk. The results suggest that while predation avoidance is an important component in the evolution of sociality in birds, it is most probably not acting alone but rather in conjunction with other benefits such as increased foraging efficiency.     

Male and female brain evolution is subject to contrasting selection pressures in primates

The claim that differences in brain size across primate species has mainly been driven by the demands of sociality (the "social brain" hypothesis) is now widely accepted. Some of the evidence to support this comes from the fact that species that live in large social groups have larger brains, and in particular larger neocortices. Lindenfors and colleagues (BMC Biology 5:20) add significantly to our appreciation of this process by showing that there are striking differences between the two sexes in the social mechanisms and brain units involved. Female sociality (which is more affiliative) is related most closely to neocortex volume, but male sociality (which is more competitive and combative) is more closely related to subcortical units (notably those associated with emotional responses). Thus different brain units have responded to different selection pressures.     

Is sociality associated with high longevity in North American birds?

Sociality, as a life-history trait, should be associated with high longevity because complex sociality is characterized by reproductive suppression, delayed breeding, increased care and survival, and some of these traits select for high longevity. We studied the relationship between cooperative parental care (a proxy of complex sociality) and relative maximum lifespan in 257 North American bird species. After controlling for variation in maximum lifespan explained by body mass, sampling effort, latitude, mortality rate, migration distance and age at first reproduction, we found no significant effect of cooperative care on longevity in analyses of species-specific data or phylogenetically independent standardized linear contrasts. Thus, sociality itself is not associated with high longevity. Rather, longevity is correlated with increased body size, survival rate and age of first reproduction.