Grooming and the value of social relationships in cooperatively breeding meerkats

More allogrooming is followed by higher physiological stress in wild female baboons

Social bonds increase fitness in a range of mammals. One pathway by which social bonds may increase fitness is by reducing the exposure to physiological stress, i.e. glucocorticoid (GC) hormones, that can be detrimental to health and survival. This is achieved through downregulating hypothalamic-pituitary-adrenal (HPA)-axis activity. Indeed, long-term measures of social (grooming) bonds are often negatively correlated with HPA-axis activity. However, the proximate role of physical touch through allogrooming remains an open question in the sociality-health-fitness debate. Demonstrating the potential anxiolytic benefits of grooming in the wild is hindered by methodological limitations. Here, we match accelerometer-identified grooming in wild female chacma baboons (Papio ursinus) to non-invasive faecal GC metabolite concentrations (fGCs). Consistent with previous work, we found a negative (but statistically non-significant) overall relationship between individual averaged fGCs and grooming rates. However, when time-matching grooming to fGCs, we found that both more giving and receiving grooming were followed by higher fGCs. This upregulation of HPA-axis activity suggests that maintaining social bonds (and its ultimate fitness benefits) may come at a shorter-term physiological cost. This finding sheds new light on a ubiquitous social behaviour typically considered 'relaxing' and suggests that sociopositive contact can trigger physiological stress.

A marine cleaning mutualism provides new insights in biological market dynamics

Most mutually beneficial social interactions (cooperation within species, mutualism between species) involve some degree of partner choice. In an analogy to economic theory as applied to human trading practices, biological market theory (BMT) focuses on how partner choice affects payoff distributions among non-human traders. BMT has inspired a great diversity of research, including research on the mutualism between cleaner fish Labroides dimidiatus and other marine fish, their 'clients'. In this mutualism, clients have ectoparasites removed and cleaners obtain food in return. We use the available data on L. dimidiatus cleaner-client interactions to identify avenues for future expansion of BMT. We focus on three main topics, namely how partner quality interacts with supply-to-demand ratios to affect service quality, the role of threats and forms of forceful intervention, and the potential role of cognition. We consider it essential to identify the specifics of each biological market as a basis for the development of more sophisticated BMT models. This article is part of the theme issue 'Half a century of evolutionary games: a synthesis of theory, application and future directions'.

Quantifying allo-grooming in wild chacma baboons (Papio ursinus) using tri-axial acceleration data and machine learning

Quantification of activity budgets is pivotal for understanding how animals respond to changes in their environment. Social grooming is a key activity that underpins various social processes with consequences for health and fitness. Traditional methods use direct (focal) observations to calculate grooming rates, providing systematic but sparse data. Accelerometers, in contrast, can quantify activity budgets continuously but have not been used to quantify social grooming. We test whether grooming can be accurately identified using machine learning (random forest model) trained on labelled acceleration data from wild chacma baboons (Papio ursinus). We successfully identified giving and receiving grooming with high precision (81% and 91%) and recall (87% and 79%). Giving grooming was associated with a distinct rhythmical signal along the surge axis. Receiving grooming had similar acceleration signals to resting, and thus was more difficult to assign. We applied our machine learning model to n = 680 collar data days from n = 12 baboons and found that grooming rates obtained from accelerometers were significantly and positively correlated with direct observation rates for giving but not receiving grooming. The ability to collect continuous grooming data in wild populations will allow researchers to re-examine and expand upon long-standing questions regarding the formation and function of grooming bonds.

Effects of Mother’s Dominance Hierarchy on the Development of Social Relationships among Immature Tibetan Macaques

Simple Summary

In this study, we explored the role of females’ social ranks on social behaviors among immature Tibetan macaques (Macaca thibetana). The results suggest that females’ social ranks affected their offspring’s social play and grooming during the juvenile and adolescent periods, but not the infancy period. The present study provides new insight into understanding the effects of the female dominance hierarchy on the development of social relationships among immature offspring in nonhuman primates.

Abstract

During a relatively long period of growth, immature individuals rely on their mothers to obtain nutrition, and a good environment for learning social skills needed to cope with complex environments in adulthood. In this study, we collected the behavioral data of Tibetan macaques (Macaca thibetana) to investigate the effects of females’ social rank on the development of social relationships among their immature offspring from November to June 2021. The results show that there was no difference in the rate/type of social play and grooming among infants. However, among juveniles and adolescents, the higher their mother’s social rank, the higher the rate of social play they participated in, and the more aggressive play they engaged in. Immatures with high-ranking mothers initiated more social play among each other. A similar pattern of playmates was found among juveniles/adolescents with middle-ranking and low-ranking mothers. We also found that immatures preferred immatures with higher-ranking mothers as grooming mates and initiated more grooming with immatures with higher-ranking mothers than with those with lower-ranking mothers. Our study suggests that females’ social ranks affect the development of social relationships among their immature offspring. In despotic nonhuman primates, this indicates that the mother’s dominance hierarchy would directly or indirectly influence the processes of participating in social interactions and choosing partnerships among immature individuals with age (i.e., infancy, juvenile, and adolescent periods).

Distinct gene regulatory signatures of dominance rank and social bond strength in wild baboons

The social environment is a major determinant of morbidity, mortality and Darwinian fitness in social animals. Recent studies have begun to uncover the molecular processes associated with these relationships, but the degree to which they vary across different dimensions of the social environment remains unclear. Here, we draw on a long-term field study of wild baboons to compare the signatures of affiliative and competitive aspects of the social environment in white blood cell gene regulation, under both immune-stimulated and non-stimulated conditions. We find that the effects of dominance rank on gene expression are directionally opposite in males versus females, such that high-ranking males resemble low-ranking females, and vice versa. Among females, rank and social bond strength are both reflected in the activity of cellular metabolism and proliferation genes. However, while we observe pronounced rank-related differences in baseline immune gene activity, only bond strength predicts the fold-change response to immune (lipopolysaccharide) stimulation. Together, our results indicate that the directionality and magnitude of social effects on gene regulation depend on the aspect of the social environment under study. This heterogeneity may help explain why social environmental effects on health and longevity can also vary between measures. This article is part of the theme issue 'The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies'.

Do immigrant female bonobos prefer older resident females as important partners when integrating into a new group?

Intergroup transfer is a critical part of the life history of group-living species, with considerable variation in its timings and patterns among species. Immigrant female bonobos are documented to smoothly integrate into a new group through forming affiliative relationships with old, high-ranking resident females (Idani, Folia Primatol 57:83-95, 1991). However, only a few studies are available on immigration costs and strategies for female bonobos. Here, we compared social relationships of natal females (known to be 4.5-7.2 years old) and immigrant females (estimated to be 6.8-12.3 years old) from one bonobo group at Wamba in the Luo Scientific Reserve, Democratic Republic of the Congo. Similar to previous studies, resident females did not appear to spatially isolate immigrant females or act aggressively toward them. However, resident males were more frequently aggressive toward immigrant females than toward natal females. Both natal and immigrant females tended to groom high-ranking females more than middle- and low-ranking females, although immigrant females spent more time grooming unrelated females than natal females. Immigrant females did not exhibit rank-related partner preference for genito-genital rubbing and copulation. Although we did not control for age differences because of the small sample size, our results provide partial support for the hypothesis that old female bonobos are important partners for the successful integration of young females into an unfamiliar group. This strategy could explain why female bonobos disperse before reaching sexual maturity, which contrasts with the need for female chimpanzees to display sexual swellings and draw male interest as protection against aggression from resident females.

Trait-Based Vaccination of Individual Meerkats (Suricata suricatta) against Tuberculosis Provides Evidence to Support Targeted Disease Control

Simple Summary

There is evidence to show that, within a population, some individuals are more likely to spread infections than others. When trying to protect a population against infection, most strategies aim to vaccinate as many individuals as possible. However, vaccinating wildlife is difficult because individuals are difficult to find and capture. For wildlife therefore, the ideal strategy would involve targeting vaccinations at those individuals most likely to transmit infection, thus gaining maximum benefit from capturing a small number of individuals. Whilst this seems a very attractive solution, very few studies have attempted to provide evidence to support this theory. This study focuses on a population of meerkats with a history of tuberculosis. Previous work has suggested that socially dominant individuals are most likely to transmit infection, with subordinates most likely to become infected. Therefore, whilst some social groups were left untreated as a baseline, in others, either dominants or subordinates were vaccinated. All groups were monitored for two years, after which time the infection data was analysed. Groups in which vaccinations had been used showed reduced infection rates suggesting that the targeted approach had reduced transmission. A targeted approach may therefore offer an efficient option for vaccinating wildlife in the future.

Abstract

Individuals vary in their potential to acquire and transmit infections, but this fact is currently underexploited in disease control strategies. We trialled a trait-based vaccination strategy to reduce tuberculosis in free-living meerkats by targeting high-contact meerkats (socially dominant individuals) in one study arm, and high-susceptibility individuals (young subordinates) in a second arm. We monitored infection within vaccinated groups over two years comparing the results with untreated control groups. Being a member of a high-contact group had a protective effect on individuals’ survival times (Hazard Ratio = 0.5, 95% Confidence Interval, CI: 0.29–0.88, p = 0.02) compared to control groups. Over the study, odds of testing positive for tuberculosis increased more than five-fold in control groups (Odds Ratio = 5.40, 95% CI = 0.94–30.98, p = 0.058); however, no increases were observed in either of the treatment arms. Targeted disease control approaches, such as the one described in this study, allow for reduced numbers of interventions. Here, trait-based vaccination was associated with reduced infection rates and thus has the potential to offer more efficient alternatives to traditional mass-vaccination policies. Such improvements in efficiency warrant further study and could make infectious disease control more practically achievable in both animal (particularly wildlife) and human populations.

Foraging networks and social tolerance in a cooperatively breeding primate (Callithrix jacchus)

Within-group competition over food resources can be a major cost of social living. In the wild, foragers are confronted with social (e.g. hierarchical rank) and ecological (e.g. food availability and distribution) challenges that affect their foraging decisions and feeding success. Exhibiting prosocial behaviours, such as tolerance at feeding sites, can benefit group members by developing affiliative social relationships, enhancing access to resources and maximizing fitness. We examined social tolerance at feeding sites in Callithrix jacchus, a cooperatively breeding primate species. We investigated the set of social (rank, age and sex) and ecological (food availability) factors that influence the structure and dynamics of within-group foraging association networks. We designed and conducted an experimental field study of four wild groups of common marmosets in which we controlled food distribution (concentrated or scattered) and productivity (high, medium or low food rewards). Then, we used social network analyses to assess the number and strength of foraging associations among group members, their effects on individual food consumption, and whether recent experiences with conspecifics during foraging affected subsequent associations. Overall, common marmoset foraging association networks were cohesive, as group members jointly occupied feeding sites. The number and strength of associations varied depending on the ecological context. Associations were stronger during conditions in which food was concentrated at a single site. Individuals obtained greater access to food resources when sharing a feeding site with conspecifics, but once a food item was obtained, the forager moved to a nearby tree and consumed it away from others. Additionally, the strength of previous foraging associations and subsequent levels of social tolerance at feeding sites were positively related, a relationship compatible with the ability of memorizing associations over time and recalling the information in future decision-making. In sum, marmosets adjusted their partner choices and the strength of foraging associations in response to food availability. They exhibited increased social tolerance at feeding sites during conditions in which opportunities for contest competition were expected to be greatest. These cooperative breeding primates appear to mutually benefit by maintaining cohesive and strong affiliative relationships, and by increasing opportunities for coordinated behaviour and offspring survival.

Does the social network structure of wild animal populations differ from that of animals in captivity?

The social behaviour of wild animals living in groups leads to social networks with structures that produce group-level effects and position individuals within them with differential consequences for an individual's fitness. Social dynamics in captivity can differ greatly from those in wild conspecifics given the different constraints on social organization in wild populations, e.g. group size, predation pressure, distribution of resources (food, mates), which are all regulated by human carers in captive populations. The social networks of animals in zoos is expected to differ from those of free-living conspecifics. While many studies have described the social networks of a wide diversity of wild and captive animals, none has directly compared the networks of multiple groups of a single species both in the wild and in captivity. Meerkats, Suricata suricatta, are an excellent species to compare the social networks of wild and captive groups. We replicated the methods of Madden et al. (2009, 2011), who studied eight groups in the wild, in fifteen captive groups. We tested how network structures and individual positions in grooming, foraging competition and dominance networks differed between wild and captive groups. Groups of wild and captive meerkats differed in various aspects of their social network structure. Differences in the network may be due to individuals occupying different network positions and the difference in the number and strength of their connections to other individuals. This distinct way of interacting and associating could be a result of group specific attributes, such as group size, and/or the attributes of the donor and recipient, including sex, status or age. Critically, the differences may be explained by the dissimilar living environment that each encounters.

Do vampire bats groom others based on need?

Allogrooming provides a window into the social lives of many group-living mammals and birds. The fitness benefits of allogrooming are encouraged by proximate mechanisms that make it physiologically rewarding for both actors and receivers. However, receivers might not always benefit from allogrooming. Some allogrooming decisions might be the actor’s response to cues of the recipient’s need. Other decisions might only be caused by the actor’s motivational state. To test these ideas, we studied what triggers allogrooming in common vampire bats. In test 1, subjects that had experimentally disturbed and wetted fur were more likely to be allogroomed, even when controlling for increased self-grooming. In test 2, allogrooming rates were elevated not only by receiver self-grooming (a cue for receiver need) but also by the actor’s previous self-grooming. Both effects were significantly greater than the effect of self-grooming by third parties. Interestingly, we detected a negative interaction: the positive effect of receiver need on allogrooming was smaller when the actor was previously self-grooming. This is consistent with the hypothesis that there are “receiver-driven” allogrooming decisions, which are responses to recipient need, and “actor-driven” decisions, which are not. We predict that receiver-driven allogrooming will bestow greater benefits to recipients compared with actor-driven allogrooming.

Reproductive conflict resolution in cooperative breeders

Female infanticide is common in animal societies where groups comprise multiple co-breeding females. To reduce the risk that their offspring are killed, mothers can synchronize breeding and pool offspring, making it hard for females to avoid killing their own young. However, female reproductive conflict does not invariably result in reproductive synchrony, and we lack a general hypothesis explaining the variation in conflict resolution strategies seen across species. Here, we investigate the fitness consequences of birth timing relative to other females and the prevalence of birth synchrony in cooperatively breeding Kalahari meerkats (Suricata suricatta). We show that, although there would be substantial benefits to females in synchronizing births and reducing their risk of infanticide, birth synchrony is rare. Since precise breeding synchrony has evolved in a related species with similar infanticidal female reproductive conflict, its absence in meerkats requires an evolutionary explanation. We therefore explore the costs and benefits of synchronizing breeding in two theoretical models, each of which contrasts synchrony with an alternative reproductive strategy: (i) breeding opportunistically and accepting fitness losses to infanticide or (ii) suppressing the reproduction of others to prevent infanticide. Our models show that the costs of synchrony constrain its development if subordinates breed infrequently, and that selection instead favors the suppression of subordinate reproduction by the dominant and opportunistic reproduction by subordinates. Together, our results suggest that the resolution of reproductive conflict in animal societies is shaped by differential breeding propensities among female group members, leading to divergent conflict resolution strategies even in closely related species.

Animal Communication: Chit-Chat in Meerkats

Coordinated behaviors are the hallmark of animal societies. General mechanisms for the emergence of social group dynamics are still unknown. New research suggests that a vocal feedback loop explains the appearance of coordinated vocal exchanges in large groups of meerkats.

Mycorrhizal Markets, Firms, and Co-ops

The nutrient exchange mutualism between arbuscular mycorrhizal fungi (AMFs) and their host plants qualifies as a biological market, but several complications have hindered its appropriate use. First, fungal 'trading agents' are hard to identify because AMFs are potentially heterokaryotic, that is, they may contain large numbers of polymorphic nuclei. This means it is difficult to define and study a fungal 'individual' acting as an independent agent with a specific trading strategy. Second, because nutrient exchanges occur via communal structures (arbuscules), this temporarily reduces outbidding competition and transaction costs and hence resembles exchanges among divisions of firms, rather than traditional trade on markets. We discuss how fungal nuclei may coordinate their trading strategies, but nevertheless retain some independence, similar to human co-operatives (co-ops).

Temporal modification of social interactions in response to changing group demographics and offspring maturation in African lions (Panthera leo)

In group living animals, affiliative social interactions maintain cohesion between individuals. Involvement in these interactions is likely to differ between individuals, depending on their sex, age and life history stages. Here we investigated different social network measures to describe greeting interactions within two prides of captive-origin African lions (Panthera leo). We aimed to determine if the introduction of cubs to these prides altered the strength of greeting networks among female lions. We also tested if the strength of greeting interactions changed between the age classes as younger lions matured. We found that interactions amongst female lions decreased from the period before cubs were born (least square means [95% CIs] 15.3 [7.67-22.93]) compared to after their integration into a pride (5.63 [-1.99-13.26] χ²₁ = 210.03, p < 0.001). In contrast, greeting network strength increased as offspring matured, with adults directing more interactions towards younger lions from 30 months of age (12.89 [1.96-23.82]) compared to when offspring were cubs (-0.69 [-11.63--10.24] χ²₁₀ = 156.03, p < 0.001). We suggest that social interactions between age classes may mediate recruitment and dispersal in lion prides.

Intragroup social dynamics vary with the presence of neighbors in a cooperatively breeding fish

Conflict is an inherent part of social life in group-living species. Group members may mediate conflict through submissive and affiliative behaviors, which can reduce aggression, stabilize dominance hierarchies, and foster group cohesion. The frequency and resolution of within-group conflict may vary with the presence of neighboring groups. Neighbors can threaten the territory or resources of the whole group, promoting behaviors that foster within-group cohesion. However, neighbors may also foster conflict of interests among group members: opportunities for subordinate dispersal may alter conflict among dominants and subordinates while opportunities for extra-pair reproduction may increase conflict between mates. To understand how neighbors mediate within-group conflict in the cooperatively breeding fish Neolamprologus pulcher, we measured behavioral dynamics and social network structure in isolated groups, groups recently exposed to neighbors, and groups with established neighbors. Aggression and submission between the dominant male and female pair were high in isolated groups, but dominant aggression was directly primarily at subordinates when groups had neighbors. This suggests that neighbors attenuate conflict between mates and foster conflict between dominants and subordinates. Further, aggression and submission between similarly sized group members were most frequent when groups had neighbors, suggesting that neighbors induce rank-related conflict. We found relatively little change in within-group affiliative networks across treatments, suggesting that the presence of neighbors does not alter behaviors associated with promoting group cohesion. Collectively, these results provide some of the first empirical insights into the extent to which intragroup behavioral networks are mediated by intergroup interactions and the broader social context.

Biological markets in cooperative breeders: quantifying outside options

A major aim in evolutionary biology is to understand altruistic help and reproductive partitioning in cooperative societies, where subordinate helpers forego reproduction to rear dominant breeders' offspring. Traditional models of cooperation in these societies typically make a key assumption: that the only alternative to staying and helping is solitary breeding, an often unfeasible task. Using large-scale field experiments on paper wasps (Polistes dominula), we show that individuals have high-quality alternative nesting options available that offer fitness payoffs just as high as their actual chosen options, far exceeding payoffs from solitary breeding. Furthermore, joiners could not easily be replaced if they were removed experimentally, suggesting that it may be costly for dominants to reject them. Our results have implications for expected payoff distributions for cooperating individuals, and suggest that biological market theory, which incorporates partner choice and competition for partners, is necessary to understand helping behaviour in societies like that of P. dominula. Traditional models are likely to overestimate the incentive to stay and help, and therefore the amount of help provided, and may underestimate the size of reproductive concession required to retain subordinates. These findings are relevant for a wide range of cooperative breeders where there is dispersal between social groups.

Social and environmental factors affect tuberculosis related mortality in wild meerkats

Tuberculosis (TB) is an important and widespread disease of wildlife, livestock and humans world‐wide, but long‐term empirical datasets describing this condition are rare. A population of meerkats (Suricata suricatta) in South Africa's Kalahari Desert have been diagnosed with Mycobacterium suricattae, a novel strain of TB, causing fatal disease in this group‐living species.

This study aimed to find characteristics associated with clinical TB in meerkats. These characteristics could subsequently be used to identify ‘at‐risk’ animals within a population, and target these individuals for control measures.

We conducted a retrospective study based on a unique, long‐term life‐history dataset of over 2000 individually identified animals covering a 14‐year period after the first confirmatory diagnosis of TB in this population in 2001. Individual‐ and group‐level risk factors were analysed using time‐dependent Cox regression to examine their potential influence on the time to development of end‐stage TB.

Cases of disease involved 144 individuals in 27 of 73 social groups, across 12 of 14 years (an incidence rate of 3·78 cases/100 study years). At the individual level, increasing age had the greatest effect on risk of disease with a hazard ratio of 4·70 (95% CI: 1·92–11·53, P < 0·01) for meerkats aged 24–48 months, and a hazard ratio of 9·36 (3·34–26·25, P < 0·001) for animals aged over 48 months (both age categories compared with animals aged below 24 months). Previous group history of TB increased the hazard by a factor of 4·29 (2·00–9·17, P < 0·01), and an interaction was found between this variable and age. At a group level, immigrations of new group members in the previous year increased hazard by a factor of 3·00 (1·23–7·34, P = 0·016). There was weaker evidence of an environmental effect with a hazard ratio for a low rainfall (<200 mm) year of 2·28 (0·91–5·72, P = 0·079).

Our findings identify potential individual characteristics on which to base targeted control measures such as vaccination. Additional data on the dynamics of the infection status of individuals and how this changes over time would complement these findings by enhancing understanding of disease progression and transmission, and thus the implications of potential management measures.

Market forces influence helping behaviour in cooperatively breeding paper wasps

Biological market theory is potentially useful for understanding helping behaviour in animal societies. It predicts that competition for trading partners will affect the value of commodities exchanged. It has gained empirical support in cooperative breeders, where subordinates help dominant breeders in exchange for group membership, but so far without considering one crucial aspect: outside options. We find support for a biological market in paper wasps, Polistes dominula. We first show that females have a choice of cooperative partners. Second, by manipulating entire subpopulations in the field, we increase the supply of outside options for subordinates, freeing up suitable nesting spots and providing additional nesting partners. We predicted that by intensifying competition for help, our manipulation would force dominants to accept a lower price for group membership. As expected, subordinates reduce their foraging effort following our treatments. We conclude that to accurately predict the amount of help provided, social units cannot be viewed in isolation: the surrounding market must also be considered.

In cooperatively breeding species, subordinates help to raise the dominant breeders' offspring in return for benefits associated with group membership. Here, Grinsted and Field show that the amount of help provided by subordinate paper wasps depends on the availability of alternative nesting options, as predicted by biological market theory.

Associations and the role of affiliative, agonistic, and socio-sexual behaviors among common bottlenose dolphins (Tursiops truncatus)

Little is known about the specific behavioral exchanges that occur on a day-to-day basis between dyads of common bottlenose dolphins (Tursiops truncatus). This study assesses the proportion of time dyads spend in proximity (within ∼2m) and the proportion of time spent in affiliative, agonistic, or socio-sexual contexts within and between age/sex dolphin pairings to better understand their social relationships. Observations of bottlenose dolphins housed at the Roatan Institute of Marine Sciences provided 10.5h of underwater footage from which to examine association coefficients and inter-individual interactions. These data suggest similar patterns to previous studies on bottlenose dolphins: mother-calf dyads shared the highest coefficients of association, followed by male-male, female-female, and male-female dyads. Four classes of association coefficients were defined for the population including low, medium, medium-high and high. This study is the first to quantitatively assess association patterns concurrently with affiliative, agonistic, and socio-sexual behaviors for bottlenose dolphins. The predominant relationships were affiliative.

Brown spider monkeys (Ateles hybridus): a model for differentiating the role of social networks and physical contact on parasite transmission dynamics

Elevated risk of disease transmission is considered a major cost of sociality, although empirical evidence supporting this idea remains scant. Variation in spatial cohesion and the occurrence of social interactions may have profound implications for patterns of interindividual parasite transmission. We used a social network approach to shed light on the importance of different aspects of group-living (i.e. within-group associations versus physical contact) on patterns of parasitism in a neotropical primate, the brown spider monkey (Ateles hybridus), which exhibits a high degree of fission-fusion subgrouping. We used daily subgroup composition records to create a 'proximity' network, and built a separate 'contact' network using social interactions involving physical contact. In the proximity network, connectivity between individuals was homogeneous, whereas the contact network highlighted high between-individual variation in the extent to which animals had physical contact with others, which correlated with an individual's age and sex. The gastrointestinal parasite species richness of highly connected individuals was greater than that of less connected individuals in the contact network, but not in the proximity network. Our findings suggest that among brown spider monkeys, physical contact impacts the spread of several common parasites and supports the idea that pathogen transmission is one cost associated with social contact.

Social Grooming in Bats: Are Vampire Bats Exceptional?

Evidence for long-term cooperative relationships comes from several social birds and mammals. Vampire bats demonstrate cooperative social bonds, and like primates, they maintain these bonds through social grooming. It is unclear, however, to what extent vampires are special among bats in this regard. We compared social grooming rates of common vampire bats Desmodus rotundus and four other group-living bats, Artibeus jamaicensis, Carollia perspicillata, Eidolon helvum and Rousettus aegyptiacus, under the same captive conditions of fixed association and no ectoparasites. We conducted 13 focal sampling sessions for each combination of sex and species, for a total of 1560 presence/absence observations per species. We observed evidence for social grooming in all species, but social grooming rates were on average 14 times higher in vampire bats than in other species. Self-grooming rates did not differ. Vampire bats spent 3.7% of their awake time social grooming (95% CI = 1.5-6.3%), whereas bats of the other species spent 0.1-0.5% of their awake time social grooming. Together with past data, this result supports the hypothesis that the elevated social grooming rate in the vampire bat is an adaptive trait, linked to their social bonding and unique regurgitated food sharing behavior.

Evolution of microbial markets

Biological market theory has been used successfully to explain cooperative behavior in many animal species. Microbes also engage in cooperative behaviors, both with hosts and other microbes, that can be described in economic terms. However, a market approach is not traditionally used to analyze these interactions. Here, we extend the biological market framework to ask whether this theory is of use to evolutionary biologists studying microbes. We consider six economic strategies used by microbes to optimize their success in markets. We argue that an economic market framework is a useful tool to generate specific and interesting predictions about microbial interactions, including the evolution of partner discrimination, hoarding strategies, specialized versus diversified mutualistic services, and the role of spatial structures, such as flocks and consortia. There is untapped potential for studying the evolutionary dynamics of microbial systems. Market theory can help structure this potential by characterizing strategic investment of microbes across a diversity of conditions.

Head rubbing and licking reinforce social bonds in a group of captive African lions, Panthera leo

Many social animals have a species-specific repertoire of affiliative behaviours that characterise individualised relationships within a group. To date, however, quantitative studies on intragroup affiliative behaviours in social carnivores have been limited. Here, we investigated the social functions of the two most commonly observed affiliative behaviours in captive African lions (Panthera leo): head rubbing and licking. We conducted behavioural observations on a captive group of lions composed of 7 males and 14 females, and tested hypotheses regarding three social functions: tension reduction, social bonding, and social status expression. Disproportionately frequent male-male and female-to-male head rubbing was observed, while more than 95% of all licking interactions occurred in female-female dyads. In accordance with the social bond hypothesis, and in disagreement with the social status expression hypothesis, both head rubbing and licking interactions were reciprocal. After controlling for spatial association, the dyadic frequency of head rubbing was negatively correlated with age difference while licking was positively correlated with relatedness. Group reunion after daily separation did not affect the frequencies of the affiliative behaviours, which was in disagreement with the predictions from the tension reduction hypothesis. These results support the social bond hypothesis for the functions of head rubbing and licking. Different patterns of affiliative behaviour between the sexes may reflect differences in the relationship quality in each sex or the differential predisposition to licking due to its original function in offspring care.

Social systems and life-history characteristics of mongooses

The diversity of extant carnivores provides valuable opportunities for comparative research to illuminate general patterns of mammalian social evolution. Recent field studies on mongooses (Herpestidae), in particular, have generated detailed behavioural and demographic data allowing tests of assumptions and predictions of theories of social evolution. The first studies of the social systems of their closest relatives, the Malagasy Eupleridae, also have been initiated. The literature on mongooses was last reviewed over 25 years ago. In this review, we summarise the current state of knowledge on the social organisation, mating systems and social structure (especially competition and cooperation) of the two mongoose families. Our second aim is to evaluate the contributions of these studies to a better understanding of mammalian social evolution in general. Based on published reports or anecdotal information, we can classify 16 of the 34 species of Herpestidae as solitary and nine as group-living; there are insufficient data available for the remainder. There is a strong phylogenetic signal of sociality with permanent complex groups being limited to the genera Crossarchus, Helogale, Liberiictis, Mungos, and Suricata. Our review also indicates that studies of solitary and social mongooses have been conducted within different theoretical frameworks: whereas solitary species and transitions to gregariousness have been mainly investigated in relation to ecological determinants, the study of social patterns of highly social mongooses has instead been based on reproductive skew theory. In some group-living species, group size and composition were found to determine reproductive competition and cooperative breeding through group augmentation. Infanticide risk and inbreeding avoidance connect social organisation and social structure with reproductive tactics and life histories, but their specific impact on mongoose sociality is still difficult to evaluate. However, the level of reproductive skew in social mongooses is not only determined by the costs and benefits of suppressing each other's breeding attempts, but also influenced by resource abundance. Thus, dispersal, as a consequence of eviction, is also linked to the costs of co-breeding in the context of food competition. By linking these facts, we show that the socio-ecological model and reproductive skew theory share some determinants of social patterns. We also conclude that due to their long bio-geographical isolation and divergent selection pressures, future studies of the social systems of the Eupleridae will be of great value for the elucidation of general patterns in carnivore social evolution.

Market powers predict reciprocal grooming in golden snub-nosed monkeys (Rhinopithecus roxellana)

Social grooming is a common form of affiliative behavior in primates. Biological market theory suggests that grooming can be traded either for grooming or other social commodities and services. When no other services are exchanged, grooming is predicted to be approximately reciprocated within a dyad. In contrast, the amount of reciprocal grooming should decrease as other offered services increase. We studied grooming patterns between polygamous male and female in golden snub-nosed monkeys (Rhinopithecus roxellana) from the Qinling Mountains of central China and found that about 29.7% of grooming bouts were reciprocated. However, the durations of grooming bouts offered and returned was asymmetrical within dyads. In bisexual dyads, more grooming was initiated by females than males, which became more pronounced as the number of females per one-male unit increased. The rate of copulation per day for each female was positively correlated with the total duration of grooming time females invested in males.. Females without an infant (non-mothers) directed more grooming towards females with an infant (mothers) and were significantly more likely to be non-reciprocated. There was a significant negative relationship between non-mother and mother grooming duration and the rate of infants per female in each one-male unit. High-ranking females also received more grooming from low-ranking females than vice versa. The rate of food-related aggressive interactions was per day for low-ranking females was negatively correlated with the duration of grooming that low-ranking females gave to high-ranking females. Our results showed that grooming reciprocation in R. roxellana was discrepancy. This investment-reciprocity rate could be explained by the exchange of other social services in lieu of grooming.