Sexual Differences in Chimpanzee Sociality

Scientists usually attribute sexual differences in sociality to sex-specific dispersal patterns and the availability of kin within the social group. In most primates, the dispersing sex, which has fewer kin around, is the less social sex. Chimpanzees fit well into the pattern, with highly social philopatric males and generally solitary dispersing females. However, researchers in West Africa have long suggested that female chimpanzees can be highly social. We investigated whether chimpanzees in the Taï Forest (Côte d’Ivoire) exhibit the expected sexual differences in 3 social parameters: dyadic association, party composition, and grooming interactions. Though we found a significant sexual difference in each of the 3 parameters, with males being more social than females, the actual values do not reveal striking differences between the sexes and do not support the notion of female chimpanzees as asocial: females had dyadic association indices comparable to mixed-sex dyads, spent ca. 82% of their time together with other adult chimpanzees, and had a comparable number of grooming partners. Further, female associations can be among the strongest bonds within the community, indicating that both sexes can have strongly favored association partners. The findings are in contrast to reports on East African chimpanzees, the females of which are mainly solitary and rarely interact with other females. Our results suggest that researchers cannot generally regard chimpanzee females as asocial and need to redefine models deriving patterns of sociality from dispersal patterns to integrate the possibility of high female sociality in male philopatric systems.     

ROGERS' PARADOX RECAST AND RESOLVED: POPULATION STRUCTURE AND THE EVOLUTION OF SOCIAL LEARNING STRATEGIES

We explore the evolution of reliance on social and asocial learning using a spatially explicit stochastic model. Our analysis considers the relative merits of four evolved strategies, two pure strategies (asocial and social learning) and two conditional strategies (the "critical social learner," which learns asocially only when copying fails, and the "conditional social learner," which copies only when asocial learning fails). We find that spatial structure generates outcomes that do not always conform to the finding of earlier theoretical analyses that social learning does not enhance average individual fitness at equilibrium (Rogers' paradox). Although we describe circumstances under which the strategy of pure social learning increases the average fitness of individuals, we find that spatial structure introduces a new paradox, which is that social learning can spread even when it decreases the average fitness of individuals below that of asocial learners. We also show that the critical social learner and conditional social learner both provide solutions to the aforementioned paradoxes, although we find some conditions in which pure (random) social learning out-competes both conditional strategies. Finally, we consider the relative merits of critical and conditional social learning under various conditions.     

Individual differences in learning behaviours in humans: Asocial exploration tendency does not predict reliance on social learning

A number of empirical studies have suggested that individual differences in asocial exploration tendencies in animals may be related to those in social information use. However, because the ‘exploration tendency’ in most previous studies has been measured without considering the information-gathering processes, it is yet hard to conclude that the animal asocial exploration strategies may be tied to social information use. Here, we studied human learning behaviour in both asocial and social two-armed bandit tasks. By fitting reinforcement learning models including asocial and/or social decision processes, we measured each individual's (1) asocial exploration tendency and (2) social information use. We found consistent individual differences in the exploration tendency in the asocial tasks. We also found substantive heterogeneity in the adopted learning strategies in the social task: Nearly one-third of participants used predominantly the copy-when-uncertain strategy, while the remaining two-thirds were most likely to have relied only on asocial learning. However, we found no significant individual association between the exploration frequency in the asocial task and the use of the social information in the social task. Our results suggest that the social learning strategies may be independent from the asocial exploration strategies in humans.     

A guide to choosing and implementing reference models for social network analysis

Analysing social networks is challenging. Key features of relational data require the use of non-standard statistical methods such as developing system-specific null, or reference, models that randomize one or more components of the observed data. Here we review a variety of randomization procedures that generate reference models for social network analysis. Reference models provide an expectation for hypothesis testing when analysing network data. We outline the key stages in producing an effective reference model and detail four approaches for generating reference distributions: permutation, resampling, sampling from a distribution, and generative models. We highlight when each type of approach would be appropriate and note potential pitfalls for researchers to avoid. Throughout, we illustrate our points with examples from a simulated social system. Our aim is to provide social network researchers with a deeper understanding of analytical approaches to enhance their confidence when tailoring reference models to specific research questions.     

The effect of social learning in a small population facing environmental change: an agent-based simulation

Learning is defined as behavioral modification due to experience, social or asocial. Social learning might be less costly than asocial learning and allow the rapid accumulation of learned traits across generations. However, the benefits of social learning in a small population of individuals relying on local interactions and experiencing environmental change are not well understood yet. In this study, we used agent-based simulations to address this issue by comparing the performance of social learning to asocial learning and innate behavior, in both a static and a changing environment. Learning was modeled using neural networks, and innate behavior was modeled using genetically coded behaviors. The performance of 10 mobile simulated agents was measured under three environmental scenarios: static, abrupt change and gradual change. We found that social learning allows for a better performance (in terms of survival) than asocial learning in static and abrupt-change scenarios. In contrast, when changes are gradual, social learning delays achieving the correct alternative, while asocial learning facilitates innovation; interestingly, a mixed population (social and asocial learners) performs the best.     

A Novel Method of Assessing Dominance Hierarchies Shows Nuance,Linearity and Stability in the Dinosaur Ant Dinoponera quadriceps

Many social species with relatively simple societies have dominance hierarchies of individuals, with dominant individuals achieving fitness and subordinate individuals either queuing to obtain fitness or achieving only indirect fitness by helping relatives. Assessing the dominance hierarchy in a social group is generally based upon observing dyadic interactions as and when they occur spontaneously within the whole‐group setting. However, this method can be very time‐consuming because many dyads interact only very rarely, necessitating either extremely long observation periods or many dyadic relationships being unresolved. Here, we report an alternative method using the queenless dinosaur ant Dinoponera quadriceps, which lives in colonies containing tens of individuals. We removed all individuals from their nest and observed the dominance behaviours expressed in isolated dyadic interactions for every pairwise combination of individuals. Individuals showed a classic dominance behaviour in this setting, and the rapid nature of the assay allowed us to observe every dyadic relationship on a weekly basis over 4 weeks. The dominance hierarchies based on these isolated dyadic interactions correlated well with those produced by the conventional method of colony observations. They showed the hierarchies to be highly linear and stable, and also revealed that dominance relationships may extend further down the hierarchy than previously thought. Although highly manipulative, the isolated dyadic interaction method works well and will likely make more feasible the study of other social species in which pairs of individuals can be isolated together.     

The evolution of social learning rules: Payoff-biased and frequency-dependent biased transmission

Humans and other animals do not use social learning indiscriminately, rather, natural selection has favoured the evolution of social learning rules that make selective use of social learning to acquire relevant information in a changing environment. We present a gene-culture coevolutionary analysis of a small selection of such rules (unbiased social learning, payoff-biased social learning and frequency-dependent biased social learning, including conformism and anti-conformism) in a population of asocial learners where the environment is subject to a constant probability of change to a novel state. We define conditions under which each rule evolves to a genetically polymorphic equilibrium. We find that payoff-biased social learning may evolve under high levels of environmental variation if the fitness benefit associated with the acquired behaviour is either high or low but not of intermediate value. In contrast, both conformist and anti-conformist biases can become fixed when environment variation is low, whereupon the mean fitness in the population is higher than for a population of asocial learners. Our examination of the population dynamics reveals stable limit cycles under conformist and anti-conformist biases and some highly complex dynamics including chaos. Anti-conformists can out-compete conformists when conditions favour a low equilibrium frequency of the learned behaviour. We conclude that evolution, punctuated by the repeated successful invasion of different social learning rules, should continuously favour a reduction in the equilibrium frequency of asocial learning, and propose that, among competing social learning rules, the dominant rule will be the one that can persist with the lowest frequency of asocial learning.     

An analysis of dyadic interactions of male Japanese monkeys (Macaca fuscata fuscata) in a cage-room observation

This is a laboratory observation (Home-cage and observation room) for individual and social behavior of four male Japanese monkeys. The monkeys were placed in a dyadic and trio situation with the purpose to investigate the relationships between aggressive and affinitive factors which regulated their social behaviour. Total amounts of attacks and receiving groom showed a consistent order for four monkeys through the pairwise conditions, which was presumed to indicate a dominance order. Grooming and mounting behavior, however, were influenced by the particular dyadic interactions, probably social attraction, rather than dominance order itself. The presence of the third animal facilitated such a social preference between animals positioned closely in the rank order as well as elicited aggression from the dominant animals.     

Experimental analysis of the nature of social context in captive groups of squirrel monkeys (Saimiri sciureus)

The nature of social context as a factor affecting grouping behavior is experimentally examined in captive groups of squirrel monkeys by recording the effects of systematic removal and return of individuals on the distributions of non-agonistic interactions and prolonged (huddle) contacts among the remaining group members. Observed changes in the distributions of these interactions among the remaining individuals are analyzed in terms of the age-sex class of the individual(s) removed, age-sex distributions of the individuals remaining, and the classes of dyadic relationships severed by the removals. Results indicate that, at least so far as these spacing-related behaviors are concerned, (1) the social environment does not act as a configurational whole on the grouping behavior of individuals, (2) the effect of social context on grouping behavior may be analyzed as the effects of specific dyadic relationships upon others, and (3) not all dyadic relationships significantly affect all others in a social group, i.e., not all of the social environment is relevant to the interactions between all pairs of individuals.     

Sexual and social stimuli elicit rapid and contrasting genomic responses

Sensory physiology has been shown to influence female mate choice, yet little is known about the mechanisms within the brain that regulate this critical behaviour. Here we examine preference behaviour of 58 female swordtails, Xiphophorus nigrensis, in four different social environments (attractive and unattractive males, females only, non-attractive males only and asocial conditions) followed by neural gene expression profiling. We used a brain-specific cDNA microarray to identify patterns of genomic response and candidate genes, followed by quantitative PCR (qPCR) examination of gene expression with variation in behaviour. Our microarray results revealed patterns of genomic response differing more between classes of social stimuli than between presence versus absence of stimuli. We identified suites of genes showing diametrically opposed patterns of expression: genes that are turned 'on' while females interact with attractive males are turned 'off' when interacting with other females, and vice versa. Our qPCR results identified significant predictive relationships between five candidate genes and specific mate choice behaviours (preference and receptivity) across females exposed to males, with no significant patterns identified in female or asocial conditions or with overall locomotor activity. The identification of stimulus- and behaviour-specific responses opens an exciting window into the molecular pathways associated with social behaviour and mechanisms that underlie sexual selection.     

Effects of fighting decisions on formation and structure of dominance hierarchies

The characteristics of complex social systems often cannot be predicted from exploring individual agonistic interactions in isolation. In a series of models, this study linked the decision-making processes that govern dyadic interactions with the emergent properties of hierarchical structures in social groups. Contrary to the intuitive expectation that resolution of ambiguities in fighting between closely matched opponents effectively promotes the formation of a social hierarchy, engagement in contests with opponents of dissimilar status lead to a faster emergence of hierarchical structures. The increased certainty of outcome in such asymmetric contests both reinforced the previously established dominance, and allowed for an indirect resolution of existing ambiguous relationships. High-return fights also resulted in a more rapid hierarchy formation, while escalating in fights decreased the costs of maintaining hierarchical relationships and increased their stability.     

Effects of fighting decisions on formation and structure of dominance hierarchies

The characteristics of complex social systems often cannot be predicted from exploring individual agonistic interactions in isolation. In a series of models, this study linked the decision-making processes that govern dyadic interactions with the emergent properties of hierarchical structures in social groups. Contrary to the intuitive expectation that resolution of ambiguities in fighting between closely matched opponents effectively promotes the formation of a social hierarchy, engagement in contests with opponents of dissimilar status lead to a faster emergence of hierarchical structures. The increased certainty of outcome in such asymmetric contests both reinforced the previously established dominance, and allowed for an indirect resolution of existing ambiguous relationships. High-return fights also resulted in a more rapid hierarchy formation, while escalating in fights decreased the costs of maintaining hierarchical relationships and increased their stability.     

Dyadic relationships in nesting males of the three-spined stickleback, Gasterosteus aculeatus

Multidimensional scaling analysis of nest site location, nesting interval, and aggressive and mating interactions revealed that male three-spined sticklebacks, Gasterosteus aculeatus, formed nesting clusters comprising five patterns of dyadic relationships. These patterns were defined by intervening variables such as size difference between the two males, nest site locations, synchronization of nesting cycles (egg presence in the nest), distance between two nests, and nest raiding behaviours. Several patterns of dyadic relationships were integrated among nesting males and their constellations indicated an expression of the social structure. Through an understanding the social structure, I described effects of social context or situations on individual reproductive success.     

Effects of fighting decisions on formation and structure of dominance hierarchies

The characteristics of complex social systems often cannot be predicted from exploring individual agonistic interactions in isolation. In a series of models, this study linked the decision-making processes that govern dyadic interactions with the emergent properties of hierarchical structures in social groups. Contrary to the intuitive expectation that resolution of ambiguities in fighting between closely matched opponents effectively promotes the formation of a social hierarchy, engagement in contests with opponents of dissimilar status lead to a faster emergence of hierarchical structures. The increased certainty of outcome in such asymmetric contests both reinforced the previously established dominance, and allowed for an indirect resolution of existing ambiguous relationships. High-return fights also resulted in a more rapid hierarchy formation, while escalating in fights decreased the costs of maintaining hierarchical relationships and increased their stability.     

The impact of environmental and social factors on learning abilities: a meta-analysis

Since the 1950s, researchers have examined how differences in the social and asocial environment affect learning in rats, mice, and, more recently, a variety of other species. Despite this large body of research, little has been done to synthesize these findings and to examine if social and asocial environmental factors have consistent effects on cognitive abilities, and if so, what aspects of these factors have greater or lesser impact. Here, we conducted a systematic review and meta-analysis examining how different external environmental features, including the social environment, impact learning (both speed of acquisition and performance). Using 531 mean-differences from 176 published articles across 27 species (with studies on rats and mice being most prominent) we conducted phylogenetically corrected mixed-effects models that reveal: (i) an average absolute effect size |d| = 0.55 and directional effect size d = 0.34; (ii) interventions manipulating the asocial environment result in larger effects than social interventions alone; and (iii) the length of the intervention is a significant predictor of effect size, with longer interventions resulting in larger effects. Additionally, much of the variation in effect size remained unexplained, possibly suggesting that species differ widely in how they are affected by environmental interventions due to varying ecological and evolutionary histories. Overall our results suggest that social and asocial environmental factors do significantly affect learning, but these effects are highly variable and perhaps not always as predicted. Most notably, the type (social or asocial) and length of interventions are important in determining the strength of the effect.     

Effects of fighting decisions on formation and structure of dominance hierarchies

The characteristics of complex social systems often cannot be predicted from exploring individual agonistic interactions in isolation. In a series of models, this study linked the decision-making processes that govern dyadic interactions with the emergent properties of hierarchical structures in social groups. Contrary to the intuitive expectation that resolution of ambiguities in fighting between closely matched opponents effectively promotes the formation of a social hierarchy, engagement in contests with opponents of dissimilar status lead to a faster emergence of hierarchical structures. The increased certainty of outcome in such asymmetric contests both reinforced the previously established dominance, and allowed for an indirect resolution of existing ambiguous relationships. High-return fights also resulted in a more rapid hierarchy formation, while escalating in fights decreased the costs of maintaining hierarchical relationships and increased their stability.     

Statistical analysis of the influence of conspecifics on the dispersal of a soil collembola

The evidence for dispersal activity among soil-living invertebrates comes mainly from observations of their movement on artificial substrates or of colonisation of defaunated soils in the field. In an attempt to elucidate the dispersal pattern of soil collembolans in the presence of conspecifics, statistical analyses were undertaken to describe and simulate the movement of groups of Onychiurus armatus released in trays of homogeneous soil. A chi(2) test was used to reject the null hypothesis that individuals moved independently of each other and uniformly in all directions. The mean radial distance moved (1-2 cm day(-1)) and the radial standard deviation varied temporally and with the density of conspecifics. To capture the interaction between the moving individuals, four dispersal models (pure diffusion, diffusion with drift interaction, drift interaction and synchronised diffusion, and drift interaction and behavioural mood), were formulated as stochastic differential equations. The parameters of the models were estimated by minimising the deviance between the observed replicates and replicates that were simulated using the models. The dynamics of movement were best described by modelling the drift interaction as dependent on whether individuals were in a social or an asocial mood.     

Aggression, grooming and group-level cooperation in white-faced capuchins (Cebus capucinus): insights from social networks

The form of animal social systems depends on the nature of agonistic and affiliative interactions. Social network theory provides tools for characterizing social structure that go beyond simple dyadic interactions and consider the group as a whole. We show three groups of capuchin monkeys from Barro Colorado Island, Panama, where there are strong connections between key aspects of aggression, grooming, and proximity networks, and, at least among females, those who incur risk to defend their group have particular "social personalities." Although there is no significant correlation for any of the network measures between giving and receiving aggression, suggesting that dominance relationships do not follow a simple hierarchy, strong correlations emerge for many measures between the aggression and grooming networks. At the local, but not global, scale, receiving aggression and giving grooming are strongly linked in all groups. Proximity shows no correlation with aggression at either the local or the global scale, suggesting that individuals neither seek out nor avoid aggressors. Yet, grooming has a global but not local connection to proximity. Extensive groomers who tend to direct their efforts at other extensive groomers also spend time in close proximity to many other individuals. These results indicate the important role that prosociality plays in shaping female social relationships. We also show that females who receive the least aggression, and thus pay low costs for group living, are most likely to participate in group defense. No consistent "social personality" traits characterize the males who invest in group defense.     

Knowledge and Perceptions of Macedonian Hunters and Herders: The Influence of Species Specific Ecology of Bears, Wolves, and Lynx

The fact that human—large carnivore relationships tend to be full of material and social conflicts raises applied questions concerning the origin of human perceptions linked to these animals and more theoretical questions concerning the link between identification and relational processes. This study, based on ethno-ethological surveys in the Republic of Macedonia (SE Europe), aims to show that the widely contrasting species specific behavioural characteristics of brown bears, wolves and Eurasian lynx influence local perceptions of these species through the nature and frequency of their interactions with humans. It appears that a high frequency of interactions allows the relational processes to dominate, leading people to modify their actions in response to the behaviour and ecology of the species. However, the fact that the virtual absence of interactions with lynx has not prevented the construction of a particular image of the species also highlights the complexity of the relationship between the level of interactions and people’s perception about animals.