Group-level signatures in bonobo sociality.

Humans show remarkable differences in social behaviour between families, groups, communities and cultures, whereas such group-level within-species variation in socio-behavioural propensities is typically overlooked in other species. Studies on intraspecific variation in animal social structures are needed to inform an evolutionary account of human sociality. Here, we study multiple independent bonobo populations ( = 6) in zoological settings to investigate if and how bonobos ( = 70) show group-specific signatures in sociality.

Qualitative Behavioural Assessment of bonobo emotional expressivity across observer groups and zoo housing environments.

Human evaluation of animal emotional expressivity can inform animal welfare. Qualitative Behavioural Assessment (QBA) has been applied to domesticated and some non-domesticated animals, but its use in primates is limited despite their emotional expressivity. We aimed to develop and apply a QBA for bonobos () through two consecutive studies.

Group-specific expressions of co-feeding tolerance in bonobos and chimpanzees preclude dichotomous species generalizations.

Bonobos are typically portrayed as more socially tolerant than chimpanzees, yet the current evidence supporting such a species-level categorization is equivocal. Here, we used validated group-level co-feeding assays to systematically test expressions of social tolerance in sixteen groups of zoo- and sanctuary-housed bonobos and chimpanzees. We found that co-feeding tolerance substantially overlaps between the species, thus precluding categorical inference at the species level.

Visually assessed body condition shows high heritability in a pedigreed great ape population.

Body condition, a measure for relative fat mass, is associated with primate health, fitness, and overall welfare. Body condition is often influenced by dietary factors, age, and/or sex, but several body condition measures (body weight, weight-to-height ratios, and so on) also show high heritability across primate species, indicating a role of genetic effects. Although different measures for body condition exist, many require direct handling of animals, which is invasive, time-consuming, and expensive, making them impractical in wild and captive settings.

Multi-group analysis of grooming network position in a highly social primate.

Individual variation in complex social behavioral traits, like primate grooming, can be influenced by the characteristics of the individual and those of its social group. To better grasp this complexity, social network analysis can be used to quantify direct and indirect grooming relationships. However, multi-group social network studies remain rare, despite their importance to disentangle individual from group-level trait effects on grooming strategies.

Vasopressin, and not oxytocin, receptor gene methylation is associated with individual differences in receptive joint attention in chimpanzees (Pan troglodytes).

Joint attention (JA) is an important milestone in human infant development and is predictive of the onset of language later in life. Clinically, it has been reported that children at risk for or with a diagnosis of autism spectrum disorder (ASD) perform more poorly on measures of JA compared to neurotypical controls. JA is not unique to humans but has also been reported in great apes and to a lesser extent in more distantly related monkeys.

Evaluating Self-Directed Behaviours and Their Association with Emotional Arousal across Two Cognitive Tasks in Bonobos ().

Self-directed behaviours (SDBs) are widely used as markers of emotional arousal in primates, and are commonly linked to negative arousal, or are used as indicators of stress or poor welfare. However, recent studies suggest that not all SDBs have the same function. Moreover, lateralisation in the production of these behaviours has been suggested to be associated with emotional processing.

Genetic determinants of individual variation in the superior temporal sulcus of chimpanzees (Pan troglodytes).

The superior temporal sulcus (STS) is a conserved fold that divides the middle and superior temporal gyri. In humans, there is considerable variation in the shape, folding pattern, lateralization, and depth of the STS that have been reported to be associated with social cognition and linguistic functions. We examined the role that genetic factors play on individual variation in STS morphology in chimpanzees.

Drivers of Dyadic Cofeeding Tolerance in : A Composite Measure Approach.

This study aimed to construct a composite model of Dyadic Cofeeding Tolerance (DCT) in zoo-housed bonobos and chimpanzees using a validated experimental cofeeding paradigm and to investigate whether components resulting from this model differ between the two species or vary with factors such as sex, age, kinship and social bond strength. Using dimension reduction analysis on five behavioral variables from the experimental paradigm (proximity, aggression, food transfers, negative food behavior, participation), we found a two-factor model: "Tolerant Cofeeding" and "Agonistic Cofeeding". To investigate the role of social bond quality on DCT components alongside species effects, we constructed and validated a novel relationship quality model for bonobos and chimpanzees combined, resulting in two factors: Relationship Value and Incompatibility.

Chimpanzee Extraversion scores vary with epigenetic modification of dopamine receptor gene D2 () and early rearing conditions.

Chimpanzees have consistent individual differences in behaviour, also referred to as personality. Similar to human personality structure, five dimensions are commonly found in chimpanzee studies that show evidence for convergent and predictive validity (Dominance, Openness, Extraversion, Agreeableness, and Reactivity/Undependability). These dimensions are to some extent heritable, indicating a genetic component that explains part of the variation in personality scores, but are also influenced by environmental factors, such as the early social rearing background of the individuals.

Adult bonobos show no prosociality in both prosocial choice task and group service paradigm.

Previous studies reported contrasting conclusions concerning bonobo prosociality, which are likely due to differences in the experimental design, the social dynamics among subjects and characteristics of the subjects themselves. Two hypotheses have been proposed to explain the occurrence of prosociality in animals: the cooperative breeding hypothesis and the self-domestication hypothesis. While the former predicts low levels of prosociality in bonobos because they are non-cooperative breeders, the latter predicts high levels of prosociality because self-domestication has been proposed to select for high levels of tolerance in this species.

Respiratory Disease Risk of Zoo-Housed Bonobos Is Associated with Sex and Betweenness Centrality in the Proximity Network.

Infectious diseases can be considered a threat to animal welfare and are commonly spread through both direct and indirect social interactions with conspecifics. This is especially true for species with complex social lives, like primates. While several studies have investigated the impact of sociality on disease risk in primates, only a handful have focused on respiratory disease, despite it being a major cause of morbidity and mortality in both wild and captive populations and thus an important threat to primate welfare.

Serotonin transporter (SERT) polymorphisms, personality and problem-solving in urban great tits.

Understanding underlying genetic variation can elucidate how diversity in behavioral phenotypes evolves and is maintained. Genes in the serotonergic signaling pathway, including the serotonin transporter gene (SERT), are candidates for affecting animal personality, cognition and fitness. In a model species, the great tit (Parus major), we reevaluated previous findings suggesting relationships between SERT polymorphisms, neophobia, exploratory behavior and fitness parameters, and performed a first test of the relationship between single nucleotide polymorphisms (SNPs) in SERT and problem-solving in birds.

Gray Matter Variation in the Posterior Superior Temporal Gyrus Is Associated with Polymorphisms in the Gene in Chimpanzees ().

Determining the impact that the gene has on primate brain morphology can provide insight into the evolution of human cognition and language systems. Here, we tested whether polymorphisms in in chimpanzees account for gray matter volumetric variation in brain regions implicated in language and communication (particularly within the posterior superior temporal gyrus and inferior frontal gyrus). First, we identified the nature and frequencies of single nucleotide variants (SNVs) in in a sample of unrelated chimpanzees ( spp.

The serotonin transporter gene and female personality variation in a free-living passerine.

Quantifying variation in behaviour-related genes provides insight into the evolutionary potential of repeatable among-individual variation in behaviour (i.e. personality).

Time-lag of urinary and salivary cortisol response after a psychological stressor in bonobos (Pan paniscus).

Cortisol is often measured as a marker for stress. Therefore, a profound validation of the time-lag between the stressor and the increase and peak in cortisol levels is needed. No study measured both the urinary and salivary cortisol time-lag after a psychological stressor.

The Pan social brain: An evolutionary history of neurochemical receptor genes and their potential impact on sociocognitive differences.

Humans have unique cognitive capacities that, compared with apes, are not only simply expressed as a higher level of general intelligence, but also as a quantitative difference in sociocognitive skills. Humans' closest living relatives, bonobos (Pan paniscus), and chimpanzees (Pan troglodytes), show key between-species differences in social cognition despite their close phylogenetic relatedness, with bonobos arguably showing greater similarities to humans. To better understand the evolution of these traits, we investigate the neurochemical mechanisms underlying sociocognitive skills by focusing on variation in genes encoding proteins with well-documented roles in mammalian social cognition: the receptors for vasopressin (AVPR1A), oxytocin (OXTR), serotonin (HTR1A), and dopamine (DRD2).

Age-associated epigenetic change in chimpanzees and humans.

Methylation levels have been shown to change with age at sites across the human genome. Change at some of these sites is so consistent across individuals that it can be used as an 'epigenetic clock' to predict an individual's chronological age to within a few years. Here, we examined how the pattern of epigenetic ageing in chimpanzees compares with humans.

Social culture in bonobos.

Van Leeuwen et al. found that two peculiar interactive behaviors (social scratching and groom slapping) transmitted socially through bonobo networks across six European zoos.

Bonobo personality predicts friendship.

In bonobos, strong bonds have been documented between unrelated females and between mothers and their adult sons, which can have important fitness benefits. Often age, sex or kinship similarity have been used to explain social bond strength variation. Recent studies in other species also stress the importance of personality, but this relationship remains to be investigated in bonobos.

Evolutionary divergence of neuroanatomical organization and related genes in chimpanzees and bonobos.

Given their close genetic relatedness to humans, bonobos (Pan paniscus) and chimpanzees (Pan troglodytes) offer an essential comparative framework for studying the evolution of uniquely human traits. These two species differ markedly in their socio-behavioral repertoires, which is reflected in neuroanatomical differences that have been reported in the literature. However, phylogenetic comparative methods have not yet been used to map the evolution of neuroanatomical traits in bonobos and chimpanzees, limiting our ability to understand which neural systems are derived in each species in relation to the last common ancestor of Pan (Pan-LCA).

Evolution of ASPM coding variation in apes and associations with brain structure in chimpanzees.

Studying genetic mechanisms underlying primate brain morphology can provide insight into the evolution of human brain structure and cognition. In humans, loss-of-function mutations in the gene coding for ASPM (Abnormal Spindle Microtubule Assembly) have been associated with primary microcephaly, which is defined by a significantly reduced brain volume, intellectual disability and delayed development. However, less is known about the effects of common ASPM variation in humans and other primates.

Serotonin Receptor 1A Variation Is Associated with Anxiety and Agonistic Behavior in Chimpanzees.

Serotonin is a neurotransmitter that plays an important role in regulating behavior and personality in humans and other mammals. Polymorphisms in genes coding for the serotonin receptor subtype 1A (HTR1A), the serotonin transporter (SLC6A4), and the serotonin degrading enzyme monoamine oxidase A (MAOA) are associated with anxiety, impulsivity, and neurotic personality in humans. In primates, previous research has largely focused on SLC6A4 and MAOA, with few studies investigating the role of HTR1A polymorphic variation on behavior.

Comparison of bonobo and chimpanzee brain microstructure reveals differences in socio-emotional circuits.

Despite being closely related, bonobos and chimpanzees exhibit several behavioral differences. For instance, studies indicate that chimpanzees are more aggressive, territorial, and risk-taking, while bonobos exhibit greater social tolerance and higher rates of socio-sexual interactions. To elucidate the potential neuroanatomical variation that accompanies these differences, we examined the microstructure of selected brain areas by quantifying the neuropil fraction, a measure of the relative tissue area occupied by structural elements of connectivity (e.