Dyadic Encounters Research Articles

Tolerant mothers: aggression does not explain solitary living in the bush Karoo rat.

Many mammal species are thought to adopt solitary living owing to mothers becoming intolerant of adult offspring and the occurrence of social intolerance between adults. However, field studies on how solitary mammals interact are rare. Here we show that solitary living can occur without social intolerance. Over 3 years, we recorded interactions between free-living bush Karoo rats (Otomys unisulcatus) and conducted dyadic encounter experiments between kin and non-kin female neighbours, both in a neutral test arena and in field intruder experiments. Social interactions were rare (230/2062 observations), and they were aggressive in only 34% of cases. In dyadic encounters, mothers interacted amicably with young offspring. Aggression between mothers and offspring was almost absent. This mother-offspring relationship remained amicable even after adult offspring had dispersed. Aggression between neighbouring adult females was low in neutral arena tests, independent of kinship and season. However, in the field, females reacted more aggressively towards non-kin than kin intruders, especially during the breeding season. Tolerance between mothers and adult offspring indicates that aggression is not the mechanism leading to dispersal and solitary living. We found a solitary social system characterized by social tolerance, suggesting that dispersal and lack of social attraction rather than aggression can lead to solitary living.

A behavioral syndrome of competitiveness in a non-social rodent

Animals compete for limited resources such as food, mating partners, and territory. The outcome of this intraspecific competition should be determined by individual variation in behavioral traits, such as aggressiveness and dominance status. Consistent among-individual differences in behavior likely contribute to competitiveness and predispose individuals to acquire specific dominance ranks during parts of their adult life. Nevertheless, how dominance rank is correlated with animal personality traits remains largely unclear. In a first step towards better understanding these functional links, we studied trait integration into behavioral syndromes, using 26 captive male bank voles (Myodes glareolus). We repeatedly assessed boldness in an emergence test, exploration in an open-field test, aggressiveness in staged dyadic encounters, and the among-individual correlations between these behaviors. We further related these personality traits to dominance rank, from quantifying urine marking value (UMV), as marking in bank voles is related to dominance rank. We found repeatable variations in boldness, exploration, aggressiveness, and UMV, which were correlated at the among-individual level. Aggressiveness tended to be negatively correlated with body condition, a proxy for fitness. Thus, key personality traits and social rank are functionally integrated into a behavioral syndrome of intraspecific competitiveness. By joining social and non-social aspects of personality, our findings contribute to the ecological validation of personality traits and suggest how they contribute to higher-order component traits, such as dominance which directly affect fitness components.

It takes two to tango: a multidisciplinary bibliometric review across six decades of dyadic service encounter research

PurposeThe authors systematically review empirical dyadic service encounter research published in top-tier journals between 1972 and 2022.Design/methodology/approachThe authors employed bibliometric techniques, co-citation analysis and bibliographic coupling analysis to map schools of thought and research frontiers within the dyadic service encounter literature. In total, the authors analyzed 155 articles. To ensure inclusion of high-quality research, the authors screened articles from 139 journals with “4” or “4*” ratings on the 2021 Chartered Association of Business Schools (ABS) journal list, in addition to articles published in three service sector-specific journals: Journal of Service Management, Journal of Services Marketing and Journal of Service Theory and Practice.FindingsThe authors' co-citation analysis identified four distinct clusters within the dyadic service encounter literature: (1) shaping and explaining service encounters; (2) emotions in service work; (3) modeling, manipulating and measuring encounter service quality and (4) emotional labor and regulation in dyadic service encounters. Furthermore, the authors' bibliographic coupling analysis generated three research clusters: (1) service encounter characteristics; (2) emotions and emotional labor and (3) service encounter interaction content.Originality/valueThe authors' comprehensive review synthesizes knowledge, summarizing similarities among research clusters within the service encounter realm. Noteworthy are research clusters that clarify the emotion-based underpinnings and reciprocal nature of behaviors and emotions within dyadic encounters. By conducting complementary bibliometric analyses, the authors trace the evolution of the service encounter literature, providing an overview of the present state of dyadic service encounter research. These analyses offer valuable insights into the current landscape of the field, identifying future dyadic service encounter research opportunities.

The Goldilocks Principle: Balancing Familiarity and Novelty in the Selection of Play Partners in Groups of Juvenile Male Rats

Like many mammals, rats frequently engage in play fighting as juveniles, an activity that influences the development of socio-cognitive skills. Most studies that assess play are based on staged dyadic encounters, implying that some average quantity and quality of play are sufficient to produce these developmental effects. However, there are individual differences, with some rats not only preferring to play more, but also to have more physical contact than others. Given that rats have individual differences in play, it raises the possibility that rats might express these preferences when playing in groups. To determine whether rats form partner preferences, trials were conducted in which a focal rat was given the opportunity to play with three partners of varying familiarity. One partner was a cage mate, another was housed on the other side of a transparent and perforated divider and so familiar, but not a prior play partner, and the third was a stranger from another cage. A total of 36 focal rats, between 30-36 days of age, were tested and video recorded in 20-minute trials following 2.5 h of social isolation. Focal rats expressed a preference for neighbors over both strangers and cage mates, indicating that balancing between familiarity and novelty influences social play partner preferences. Mechanisms by which this preference might have been established, such as dominance relationships, weight differences, and congruency of play style, were investigated, but none were correlated with the preferences expressed. This group dynamics perspective provides a novel approach to studying play, and more generally, provides insights into social exploration and decision-making.

Cuticular hydrocarbon profiles in velvet ants (Hymenoptera: Mutillidae) are highly complex and do not chemically mimic their hosts

Although recognition using cuticular chemistry is important for host–parasite interactions within aculeate Hymenoptera, cuticular hydrocarbon (CHC) profiles of only a few host–parasite pairs were characterized and compared. One largely neglected family in this context is the Mutillidae (velvet ants), whose species are ectoparasitoids of bees and wasps. In our study, we characterized and compared the CHC profiles of five species of Mutillidae and seven host species. The CHC profile of velvet ants differed among species and included large proportions of n-alkanes and methyl-branched alkanes. Alkenes were much less abundant in the CHC profiles of three species of velvet ants compared with their hosts, while the other two species possess a much lower abundance of methyl-branched alkanes than their hosts. Both the number of peaks and compound diversity were generally higher in velvet ants compared with their hosts. Thus, CHC profiles of parasitoids did not show signs of mimicry when compared with their hosts. In dyadic encounters between one species of velvet ant and its host bee species, the parasitoid mainly avoided interacting, while aggression by the host was rare. Our results suggest that velvet ants did not evolve chemical mimicry, perhaps in accordance with their wide host spectrum which would limit chemical specialization. However, the reduction of alkenes in social bee-attacking species and the reduction of methyl-branched alkanes in social wasp-attacking species may favour host nest invasion, since these two CHC classes are known to be important in nestmate recognition for social bees and wasps, respectively. A larger, phylogeny-corrected comparison of Mutillidae and hosts may help clarifying the evolution of the CHC profile of these parasitoids.

Lack of Aggressive Behavior between Neonates of Little Brown Skinks (Scincella lateralis)

Nearly all studies of lizard behavior have been conducted on adults. Therefore, an important part of the lizard life cycle has been overlooked, the neonate stage. Lizards hatch at about the same time, briefly causing high density and increased chances that neonates engage in aggressive encounters. We studied the behavior of neonate Little Brown Skinks (Scincella lateralis) by staging a series of dyadic encounters between pairs of neonates in the laboratory. Two neonates were confined in an observation chamber on either side of a partition for 48 h. The partition was then removed, a single retreat was placed in the center of the observation chamber, and the behavior of the two neonates was recorded for 60 min. Neonate Little Brown Skinks almost never showed aggressive behaviors, such as biting and chasing, exhibited by adults. Neonates segregated themselves on opposite sides of the observation chamber when active on the surface, but frequently simultaneously occupied the retreat, something that almost never happens in adults. Limited data on species of skinks that form stable aggregations suggest that retreat sharing by neonates or juveniles may be common in members of the Scincidae.

Police discretion and the role of the ‘spotter’ within football crowd policing: risk assessment, engagement, legitimacy and de-escalation

ABSTRACT Discretion is a key feature of policing, yet its surrounding research has historically been heavily reliant upon exploring interpersonal or dyadic encounters between individual officers and members of the public. More recently, studies have explored how discretionary decisions by police officers impact upon and interact with group-level and organisational processes but few studies have explored the relevance of discretion to debates in the literature on public order policing. Correspondingly, there is to date only a limited body of research exploring the nature and dynamics of dialogue-based football-related public order policing. This study addresses these combined gaps by drawing upon data from interviews with specialist football officers, referred to as ‘spotters’ or Dedicated Football Officers, from five English police forces. Our analysis critiques the idea that these specialist roles revolve merely around the surveillance, categorisation and enforcement of fans who are considered to pose a risk to public order. We highlight how these officers understand their roles in terms of the use of discretion. We argue that in a complex intergroup environment officers utilise discretion to manage perceptions of their legitimacy among supporters. This ‘social capital’ in turn enhances their capacity to de-escalate and avoid disorder through the promotion of self-regulatory behaviour. We discuss the relevance of our study for theoretical approaches to understanding discretion and consider the implications of our analysis for developing a more formal dialogue-focused and discretion-based approach to football crowd policing in and beyond England and Wales.

Fighting cichlids: An integrated multimodal analysis to understand female and male aggression in Cichlasoma dimerus

Aggression has been historically linked to males and androgen levels and, even if females from different species also display aggressive behavior, female aggression is still widely understudied. The aim of the present work is to disentangle how sex differences in social plasticity can be explained by sex steroid hormone levels, gonadal state and/or morphometric characteristics. In this context, we performed intrasexual dyadic encounters to identify social plasticity after acquiring a winner or loser status in males and females of Cichlasoma dimerus. This integral analysis suggests that the reproductive and hormonal variables analyzed explain the behavioral variation among winner and loser males and females, and that there are significant differences between sexes and contest outcome when individual morphometric variables are excluded from the analysis. Interestingly, there are no sex differences in aggressive and submissive behaviors, and clustering into winners and losers is mainly explained by specific behavioral displays, such as bites, chases, approaches, passive copings, and escapes. Correlation heatmaps show a positive correlation between estradiol with aggression and a negative correlation with submission, suggesting estrogens may have a dual role regulating agonistic behavior. Finally, these results suggest that size difference can help to understand aggression in females but not in males, and that assessment of the opponent's body size is important to understand aggression also before the initiation of the contest in both sexes. Overall, this study constitutes an integral approach adding insights into the importance of reproductive and hormonal variables to understand social plasticity in males and females.

Characterizing group and individual engagement in intergroup encounters between small groups of ring-tailed lemurs (Lemur catta) on St. Catherines Island, USA.

Primate species exhibit considerable variation in behavior and outcomes during intergroup encounters (IGEs). Social group characteristics, like group size, and individual traits, such as sex, rank, and reproductive status, within those groups can influence both IGE engagement and outcomes. To better understand the impact of group heterogeneity on IGEs, we must examine individual strategies to elucidate individual costs and benefits of engaging in these interactions. Here, we present a descriptive study of the IGEs between two small social groups of ring-tailed lemurs (Lemur catta) on St. Catherines Island, GA, USA. We distinguish between dyadic and multiple-individual interactions between groups to compare collective and individual agonistic engagement. All encounters occurred when the East Road group (N = 7 individuals) traveled from the center of their home range to the boundary with Windmill group's (N = 5 individuals) home range, indicating that East Road might have been actively testing this boundary for access to food resources, sleeping trees, and mating opportunities. We also found notable individual variation in participation during IGEs. The daughters of the highest-ranking females were the most-engaged in dyadic intergroup and intragroup aggression, had high "win" rates during intergroup dyadic encounters, and engaged in intergroup multiple-individual interactions at high levels. These findings indicate that they might value their home range more as "potential alphas" compared to other group members. Dominant females were the most engaged in multiple-individual interactions, suggesting that they contribute heavily to collective action that might result in a gain or loss of access to resources. Finally, these two small groups might be equally matched despite the two-individual group size disparity due to individual free-riding strategies. Future research should focus on individual strategies during IGEs to characterize the complex decisions and trade-offs that influence participation.

Fighting ability, personality and melanin signalling in free-living Eurasian tree sparrows (Passer montanus).

BackgroundIndividuals’ access to resources is often decided during dyadic contests the outcome of which is determined by the fighting (or competitive) ability of the participants. Individuals’ fighting ability (termed also as resource-holding power or potential, RHP) is usually associated with individual features (e.g., sex, age, body size) and is also frequently signalled through various ornaments like the black throat patch (bib) in many birds. Individual personality is a behavioural attribute often linked to fighting ability as well. Based on earlier studies, however, the relationship between personality and fighting ability is far from being straightforward. While accounting for sex and body size, we studied whether exploratory behaviour, an aspect of personality, predicts fighting ability when competing for food during winter in free-living Eurasian tree sparrows (Passer montanus). We also investigated whether the bib can serve as a potential indicator of individual competitiveness in this species.MethodsWe captured adult tree sparrows, marked them with a unique combination of colour rings, and collected data about the individuals’ sex, body size, bib size and exploratory behaviour. Birds were then released and the agonistic behaviour of the marked individuals was recorded while foraging in groups on bird feeding platforms.ResultsThe probability of winning a fight, a proxy for fighting ability of individuals, was not related to exploratory behaviour, in either of the sexes. However, bib size was positively related to probability of winning in females, but not in males. Body size was not associated with probability of winning neither in males, nor in females.ConclusionsOur results suggest that, at least in tree sparrows, the outcome of dyadic encounters over food during the non-breeding period are not determined by the exploratory personality of individuals. However, our findings provide further support for a status signalling role of the black bib in tree sparrows, and hint for the first time that bib size might function as a status signal in females as well. Finally, our results do not confirm that body size could serve as an indicator of fighting ability (i.e., RHP) in this species.

Species recognition limits mating between hybridizing ant species.

Identifying mechanisms limiting hybridization is a central goal of speciation research. Here, we studied premating and postmating barriers to hybridization between two ant species, Formica selysi and Formica cinerea. These species hybridize in the Rhône valley in Switzerland, where they form a mosaic hybrid zone, with limited introgression from F. selysi into F. cinerea. There was no sign of temporal isolation between the two species in the production of queens and males. With choice experiments, we showed that queens and males strongly prefer to mate with conspecifics. Yet, we did not detect postmating barriers caused by genetic incompatibilities. Specifically, hybrids of all sexes and castes were found in the field and F1 hybrid workers did not show reduced viability compared to nonhybrid workers. To gain insights into the cues involved in species recognition, we analyzed the cuticular hydrocarbons (CHCs) of queens, males, and workers and staged dyadic encounters between workers. CHC profiles differed markedly between species, but were similar in F. cinerea and hybrids. Accordingly, workers also discriminated species, but they did not discriminate F. cinerea and hybrids. We discuss how the CHC‐based recognition system of ants may facilitate the establishment of premating barriers to hybridization, independent of hybridization costs.

Intersexual Agonism in Gray Langurs Reflects Male Dominance and Feeding Competition

Male-female agonism varies throughout the primate order with males often dominating females, especially in sexually dimorphic species. While intersexual agonism has been attributed to sexually coercive contexts, it can also occur for other reasons and intersexual dominance may be influenced by the adult sex ratio. If the proportion of males is high, certain males will regularly lose against other males. Loser-effects may then pave the way for some females to dominate these males, an effect that has been described in a few primate species. Here we investigated the frequency, general style, and context of agonism among gray langurs (Semnopithecus spp.). Data were collected at two study sites, at Jodhpur, India (one group), and at Ramnagar, Nepal (two groups). The adult sex ratio varied between 0.077 and 1.000 males to females. At both sites, data on agonistic interactions (aggression and submission) were collected in continuous focal animal and ad libitum sampling techniques during 1,945 contact hours (including 1,220 focal animal hours, total). Although aggression intensity was low, high directional consistency and the rare occurrence of counteraggression suggested a despotic dominance style, a likely prerequisite for dominance effects based on adult sex ratio. Aggression by females against males was very rare and mainly occurred in the defense of offspring. We found little evidence for partial female dominance regardless of adult sex ratio. In a few cases in which a female had a higher dominance index than a male, she did not dominate this male in dyadic encounters. Agonism by males directed at females occurred mainly in a feeding context while male policing and a sexual context were both rare. The latter was mostly restricted to females after they had harassed a sexual interaction or after they had behaved proceptively toward a male. Our study suggests that across species the effect of adult sex ratio on female dominance might be more variable than previously suggested. The fact that most agonism between males and females occurred over food identifies intersexual feeding competition as a new research avenue with potentially important consequences for existing ideas on the costs and benefits of group life and composition.

Electrocommunication signals and aggressive behavior vary among male morphs in an apteronotid fish, Compsaraia samueli.

Within-species variation in male morphology is common among vertebrates and is often characterized by dramatic differences in behavior and hormonal profiles. Males with divergent morphs also often use communication signals in a status-dependent way. Weakly electric knifefish are an excellent system for studying variation in male morphology and communication and its hormonal control. Knifefish transiently modulate the frequency of their electric organ discharge (EOD) during social encounters to produce chirps and rises. In the knifefish Compsaraia samueli, males vary extensively in jaw length. EODs and their modulations (chirps and rises) have never been investigated in this species, so it is unclear whether jaw length is related to the function of these signals. We used three behavioral assays to analyze EOD modulations in male C. samueli: (1) artificial playbacks, (2) relatively brief, live agonistic dyadic encounters, and (3) long-term overnight recordings. We also measured circulating levels of two androgens, 11-ketotestosterone and testosterone. Chirp structure varied within and across individuals in response to artificial playback, but was unrelated to jaw length. Males with longer jaws were more often dominant in dyadic interactions. Chirps and rises were correlated with and preceded attacks regardless of status, suggesting these signals function in aggression. In longer-term interactions, chirp rate declined after 1week of pairing, but was unrelated to male morphology. Levels of circulating androgens were low and not predictive of jaw length or EOD signal parameters. These results suggest that communication signals and variation in male morphology are linked to outcomes of non-breeding agonistic contests.

Inheritance of social dominance is associated with global sperm DNA methylation in inbred male mice.

Dominance relationships between males and their associated traits are usually heritable and have implications for sexual selection in animals. In particular, social dominance and its related male pheromones are heritable in inbred mice; thus, we wondered whether epigenetic changes due to altered levels of DNA methylation determine inheritance. Here, we used C57BL/6 male mice to establish a social dominance-subordination relationship through chronic dyadic encounters, and this relationship and pheromone covariation occurred in their offspring, indicative of heritability. Through transcriptome sequencing and whole-genome DNA methylation profiling of the sperm of both generations, we found that differential methylation of many genes was induced by social dominance-subordination in sires and could be passed on to the offspring. These methylated genes were mainly related to growth and development processes, neurodevelopment, and cellular transportation. The expression of the genes with similar functions in whole-genome methylation/bisulfite sequencing was also differentiated by social dominance-subordination, as revealed by RNA-seq. In particular, the gene Dennd1a, which regulates neural signaling, was differentially methylated and expressed in the sperm and medial prefrontal cortex in paired males before and after dominance-subordination establishment, suggesting the potential epigenetic control and inheritance of social dominance-related aggression. We suggest that social dominance might be passed on to male offspring through sperm DNA methylation and that the differences could potentially affect male competition in offspring by affecting the development of the nervous system.

‘Right, already brewing there’: Arriving to the staff breakroom and beginning interaction with a co-present colleague

This study investigates beginnings of dyadic encounters between acquainted persons in a ‘semi-public’ space, namely, staff breakrooms of Finnish work communities. Drawing on video data and using ethnomethodological conversation analysis as the method, we examine the coordinated vocal-bodily exchanges that participants carry out under close mutual monitoring as they establish co-presence and initiate interaction (through greetings and registerings) while also engaging in other, situated, break-relevant activities as part of an oriented-to, established routine of beginning, and being on, a break from work. We show how participants skillfully manage their simultaneous involvements in these activities, and how the specific vocal-bodily practices by which participants open their encounters in the breakroom index their orientation to each other as ‘familiars’ and to their encounters as highly routinized, recurring and ‘expected’ (rather than as ‘special’ or ‘not-everyday’) occurrences. Data are in Finnish with English translation.

Antenatal group consultations: Promoting wellbeing

Background: Most healthcare encounters take place in a dyadic encounter between a patient and healthcare practitioner, and improving dyadic communication has been the object of much health communication research. However, it seems that an alternative to the dyadic encounter – group consultations – may have distinct advantages for the promotion of patients’ wellbeing. Aim: This article focuses on antenatal group consultations (AGCs), where groups of pregnant women meet with one or more healthcare practitioners instead of meeting their midwife individually, and explores how the presence of other pregnant women in AGCs may promote wellbeing. Methods: Adopting a post-intentional phenomenological approach, we analysed the transcripts of 16 semi-structured interviews undertaken with pregnant women who attended AGCs in Denmark, focusing on their accounts of being with each other. Results: The presence of other pregnant women helped to generate trust, with the participants’ pregnant bodies symbolising their common situation. The presence of peers prompted feelings of identification and solidarity, generally decreased the women’s concerns, and normalised their experiences of pregnancy. Discussion and conclusion: This article develops understandings of how patients experience interpersonal healthcare encounters, and suggests the value of alternatives to the clinical dyad, such as group consultations, for promoting the wellbeing of other patient groups.

Factors associated with sniffing behaviors between walking dogs in public places

Although body sniffing is the most frequent canine interaction in public places, little is known about olfactory behaviors between walking dogs. The aim of this study was to examine the association of dog, human and behavior characteristics with the number of sniffing dogs within a dyad, with the initiation and termination of sniffing, with the first and last area sniffed on the recipient’s body and with the number of areas sniffed on the recipient’s body in walking dogs in public places. We observed 538 dyadic encounters between sexually intact dogs, each led by one owner. We randomly selected one dog from each of 538 dyads, yielding 486 focal dogs actively involved in sniffing for analysis. Interacting dogs were more likely to engage in mutual than single dog sniffing when the owners communicated with each other than when they did not. Dogs more likely initiated sniffing than not when a male dog encountered a female than vice versa. Dogs more likely sniffed the rear than the head as the first area on the recipient’s body when only one dog sniffed the other than when both dogs sniffed each other; and also when they initiated sniffing than when they did not. Dogs more likely sniffed more than one area than only one area on the recipient’s body when they sniffed the head or abdomen than the rear as the first area on the recipient’s body; when both dogs sniffed one another than when only one dog sniffed the other; and also when they initiated sniffing than when they did not. Dogs more likely sniffed the abdomen or rear than the head as the last area on the recipient’s body, when only one dog sniffed the other than when both dogs sniffed one another; and also when they sniffed more than one area on the recipient’s body than when they sniffed only one area. Dogs more likely terminated sniffing than not when an adult dog encountered a puppy than vice versa. In conclusion, dyadic sniffing behaviors between sexually intact dogs, each walking with one owner, were mainly associated with the owners’ communication, the number of sniffing dogs within a dyad, the dog’s sex and age and with the initiation of sniffing.

Provider–Recipient Dyadic Interactions: Impact of Service Quality on Customer Behaviours Using a Multi-Modelling Approach

Service-oriented industries now focus on capturing the encounter behaviours of both service providers and service recipients. It depends on the conditions of assessing the psychological needs of both parties in which the service provider provides services to the recipient and the recipient reciprocates service provider, in turn, to their services. Drawing from service encounter needs theory, this research has conducted two studies based on exploring the service provider–recipient dyadic encounter relationships between service quality and customer behaviours. By collecting data from 403 respondents from a broad range of service industries, study 1 found that service quality dimensions—reliability, responsiveness, assurance and empathy—were found to have a significant impact on customer satisfaction, but tangibility did not affect customer satisfaction. Interestingly, customer satisfaction is a psychological indicator of enhancing customer loyalty behaviours ( Zhang & Bloemer, 2008 ). So by surveying 361 respondents from different industries, study 2 was proposed to examine the notion that customer satisfaction mediates the relationship between service quality and customer loyalty behaviours—repurchase intention, word of mouth and willingness to pay more and to extend the literature of loyalty behaviours. Study 2 results show that there are significant mediating relationships between service quality and repurchase intention, words of mouth and willingness to pay more. Moreover, the research provides the guidelines, limitations and future directions.

Sociability, but not spatial memory, is correlated with regional brain volume variation in the striped mouse Rhabdomys spp.

Local environmental conditions associated with different geographic areas may elicit variations in behavioural responses in animals, leading to concomitant differences in functional brain region volumes. We investigated the behavioural correlates of hippocampus and amygdala volumes in three sister taxa of the murid rodent genus Rhabdomys, occurring in different environments. We used a Barnes maze to test spatial memory, dyadic encounters to test social behaviour, and histological brain sections to calculate hippocampus and amygdala volumes. Arid-occurring R. pumilio made fewer errors and had shorter latencies in locating the escape tunnel compared to moist grassland-occurring R. d. dilectus and R. d. chakae in two probe trials, 48 and 96 h after the last learning trial. R. pumilio was more amicable than the R. dilectus subspecies in intra-specific dyadic encounters. R. pumilio had larger hippocampus and amygdala volumes than the other species. Smaller amygdala volumes were correlated with longer latencies in females for probe trial 1, but males showed similar latencies regardless of taxon. Higher amicability scores were correlated with larger amygdala volumes in all taxa. Higher amicability scores were correlated with larger hippocampus volumes in R. pumilio and R. d. chakae but smaller hippocampus volumes in R. d. dilectus. Correlative relationships between spatial memory and amygdala volume appeared 48 h, but not 96 h, after the last learning trial. Local environmental conditions may influence spatial navigation, but social correlates drive regional brain size within cryptic striped mouse taxa.

Sharing Experiences in Infancy: From Primary Intersubjectivity to Shared Intentionality.

We contrast two theses that make different assumptions about the developmental onset of human-unique sociality. The primary intersubjectivity thesis (PIT) argues that humans relate to each other in distinct ways from the beginning of life, as is shown by newborns' participation in face-to-face encounters or “primary intersubjectivity.” According to this thesis, humans' innate relational capacity is the seedbed from which all subsequent social-emotional and social-cognitive developments continuously emerge. The shared intentionality thesis (SIT) states that human-unique forms of interaction develop at 9–12 months of age, when infants put their heads together with others in acts of object-focused joint attention and simple collaborative activities. According to this thesis, human-unique cognition emerges rapidly with the advent of mind-reading capacities that evolved specifically for the purpose of coordination. In this paper, we first contrast the two theses and then sketch the outlines of an account that unifies their strengths. This unified account endorses the PIT's recognition of the fundamental importance of primary intersubjectivity. Any act of sharing experiences is founded on the communicative capacity that is already displayed by young infants in primary intersubjectivity. At the same time, we question the PIT's interpretation that dyadic encounters have the triadic structure of joint attention. Lastly, we draw on empirical work on the development of joint attention, imitation, and social referencing that serves as evidence that primary intersubjectivity continuously unfolds into the capacity for triadic joint attention.