Similarity in temperament between mother and offspring rhesus monkeys: sex differences and the role of monoamine oxidase-a and serotonin transporter promoter polymorphism genotypes

Genetic polymorphisms in the serotonin, dopamine and opioid pathways influence social attention in rhesus macaques (Macaca mulatta)

Behaviour has a significant heritable component; however, unpicking the variants of interest in the neural circuits and molecular pathways that underpin these has proven difficult. Here, we present a comprehensive analysis of the relationship between known and new candidate genes from identified pathways and key behaviours for survival in 109 adult rhesus macaques (Macaca mulatta). Eight genes involved in emotion were analysed for variation at a total of nine loci. Genetic data were then correlated with cognitive and observational measures of behaviour associated with wellbeing and survival using MCMC-based Bayesian GLMM in R, to account for relatedness within the macaque population. For four loci the variants genotyped were length polymorphisms (SLC6A4 5-hydroxytryptamine transporter length-polymorphic repeat (5-HTTLPR), SLC6A4 STin polymorphism, Tryptophan 5-hydroxylase 2 (TPH2) and Monoamine oxidase A (MAOA)) whilst for the other five (5-hydroxytryptamine receptor 2A (HTR2A), Dopamine Receptor D4 (DRD4), Oxytocin receptor (OXTR), Arginine vasopressin receptor 1A (AVPR1a), Opioid receptor mu(μ) 1 (OPRM1)) SNPs were analysed. STin genotype, DRD4 haplotype and OXTR haplotype were significantly associated with the cognitive and observational measures of behaviour associated with wellbeing and survival. Genotype for 5-HTTLPR, STin and AVPR1a, and haplotype for HTR2A, DRD4 and OXTR were significantly associated with the duration of behaviours including fear and anxiety. Understanding the biological underpinnings of individual variation in negative emotion (e.g., fear and anxiety), together with their impact on social behaviour (e.g., social attention including vigilance for threat) has application for managing primate populations in the wild and captivity, as well as potential translational application for understanding of the genetic basis of emotions in humans.

Parental genetic contributions to neonatal temperament in a nonhuman primate (Macaca mulatta) model

Temperament is an individual's nature and is widely believed to have a heritable foundation. Few studies, however, have evaluated paternal and maternal contributions to the triadic dimensions of temperament. Rhesus monkeys are widely utilized to model genetic contributions to human development due to their close genetic-relatedness and common temperament structure, providing a powerful translational model for investigating paternal and maternal genetic influences on temperament. The temperament of rhesus monkey infants born to 19 different sires and 50 different dams was assessed during the first month of life by comparing the temperament of paternal or maternal half-siblings reared with their mothers in species-normative conditions or reared in a neonatal nursery. Factor scores from three dimensions of temperament were obtained (Orienting/Regulation, Negative Affectivity, and Surgency/Extraversion) and ANOVAs were used to assess genetic effects. For paternal half-siblings, results showed a statistically significant paternal contribution to Orienting/Regulation, Negative Affectivity, and Surgency/Extraversion factor scores. For maternal half-siblings, results showed a statistically significant contribution to Orienting/Regulation factor scores. When parsed by early rearing condition, results showed a paternal contribution Orienting/Regulation, Negative Affectivity, and Surgency/Extraversion scores for paternal half-siblings reared in the neonatal nursery, while there was only a paternal contribution to Surgency/Extraversion for paternal half-siblings reared by their mothers. There was only a maternal contribution to Orienting/Regulation for maternal half-siblings reared by their mothers. These results show that paternal and maternal contributions to temperament vary by environmental context, and that mothers may environmentally buffer their infants from paternal contributions to their temperament.

Early life maternal sociality predicts juvenile sociality in blue monkeys

Maternal effects are widespread in living organisms though little is known about whether they shape individual affiliative social behavior in primates. Further, it remains a question whether maternal effects on affiliative behavior differ by offspring sex, as they do in other physiological systems, especially in species with high levels of adult sexual dimorphism and divergence in social niches. We explored how direct and indirect experiences of maternal affiliative behavior during infancy predicted affiliative behavior approximately 1-6 years later during the juvenile period, using behavioral data from 41 wild blue monkey juveniles and their 29 mothers, and controlling for individual age, sex, and maternal rank. Female juveniles spent less time grooming with any partner and with peers the more maternal grooming they received during infancy, whereas males groomed more with any partner and with peers. Similarly, the more that mothers groomed with other adult females during subjects' infancy, female subjects played less with peers, and male subjects played more as juveniles. Further, this maternal effect on social behavior appears specific to early life, as the same aspects of mothers' sociality measured throughout subjects' development did not predict juvenile behavior. Overall, our results suggest that both direct and indirect experience of mother's affiliative behavior during infancy influence an individual's affiliation later in life that sexes respond differently to the maternal affiliation, and that the first year of life is a critical window.

Interindividual differences in neonatal sociality and emotionality predict juvenile social status in rhesus monkeys

In humans, socioeconomic status (SES) has profound outcomes on socio-emotional development and health. However, while much is known about the consequences of SES, little research has examined the predictors of SES due to the longitudinal nature of such studies. We sought to explore whether interindividual differences in neonatal sociality, temperament, and early social experiences predicted juvenile social status in rhesus monkeys (Macaca mulatta), as a proxy for SES in humans. We performed neonatal imitation tests in infants' first week of life and emotional reactivity assessments at 2 and 4 weeks of age. We examined whether these traits, as well as the rearing environment in the first 8 months of life (with the mother or with same-aged peers only) and maternal social status predicted juvenile (2-3 years old) social status following the formation of peer social groups at 8 months. We found that infants who exhibited higher rates of neonatal imitation and newborn emotional reactivity achieved higher social status as juveniles, as did infants who were reared with their mothers, compared to infants reared with peers. Maternal social status was only associated with juvenile status for infant dyads reared in the same maternal group, indicating that relative social relationships were transferred through social experience. These results suggest that neonatal imitation and emotional reactivity may reflect ingrained predispositions toward sociality that predict later outcomes, and that nonnormative social experiences can alter socio-developmental trajectories. Our results indicate that neonatal characteristics and early social experiences predict later social outcomes in adolescence, including gradients of social stratification.

Fetal iron deficiency and genotype influence emotionality in infant rhesus monkeys

BACKGROUND

Anemia during the third trimester of fetal development affects one-third of the pregnancies in the United States and has been associated with postnatal behavioral outcomes. This study examines how fetal iron deficiency (ID) interacts with the fetal monoamine oxidase A (MAOA) genotype. MAOA metabolizes monoamine neurotransmitters. MAOA polymorphisms in humans affect temperament and modify the influence of early adverse environments on later behavior.

OBJECTIVE

The aim of the study was to advance translation of developmental ID research in animal models by taking into account genetic factors that influence outcomes in human populations.

METHODS

Male infant rhesus monkeys 3-4 mo old born to mothers fed an ID (10 ppm iron) diet were compared with controls (100 ppm iron). Infant monkeys with high- or low-transcription rate MAOA polymorphisms were equally distributed between diet groups. Behavioral responses to a series of structured experiences were recorded during a 25-h separation of the infants from their mothers.

RESULTS

Infant monkeys with low-transcription MAOA polymorphisms more clearly demonstrated the following ID effects suggested in earlier studies: a 4% smaller head circumference, a 39% lower cortisol response to social separation, a 129% longer engagement with novel visual stimuli, and 33% lesser withdrawal in response to a human intruder. The high MAOA genotype ID monkeys demonstrated other ID effects: less withdrawal and emotionality after social separation and lower "fearful" ratings.

CONCLUSION

MAOA × ID interactions support the role of monoamine neurotransmitters in prenatal ID effects in rhesus monkeys and the potential involvement of common human polymorphisms in determining the pattern of neurobehavioral effects produced by inadequate prenatal nutrition.

Quantitative Genetics of Response to Novelty and Other Stimuli by Infant Rhesus Macaques (Macaca mulatta) Across Three Behavioral Assessments

Primate behavior is influenced by both heritable factors and environmental experience during development. Previous studies of rhesus macaques (Macaca mulatta) examined the effects of genetic variation on expressed behavior and related neurobiological traits (heritability and/or genetic association) using a variety of study designs. Most of these prior studies examined genetic effects on the behavior of adults or adolescent rhesus macaques, not in young macaques early in development. To assess environmental and additive genetic variation in behavioral reactivity and response to novelty among infants, we investigated a range of behavioral traits in a large number (N = 428) of pedigreed infants born and housed in large outdoor corrals at the Oregon National Primate Research Center (ONPRC). We recorded the behavior of each subject during a series of brief tests, involving exposure of each infant to a novel environment, to a social threat without the mother present, and to a novel environment with its mother present but sedated. We found significant heritability (h² ) for willingness to move away from the mother and explore a novel environment (h² = 0.25 ± 0.13; P = 0.003). The infants also exhibited a range of heritable behavioral reactions to separation stress or to threat when the mother was not present (h² = 0.23 ± 0.13-0.24 ± 0.15, P < 0.01). We observed no evidence of maternal environmental effects on these traits. Our results extend knowledge of genetic influences on temperament and reactivity in nonhuman primates by demonstrating that several measures of behavioral reactivity among infant rhesus macaques are heritable.

The emergence of personality in animals: the need for a developmental approach

Interest has been growing among behavioral biologists in individual differences in animal behavior of the kind that can be considered to reflect differences in personality. Once considered the exclusive domain of human psychology, biologists have found evidence for personality across a wide range of species, while behavioral ecologist and theoretical biologists recognize the likely evolutionary origins and contribution to fitness of such. However, until recently most work has concentrated on ultimate questions of fitness and thus on adult animals, with little attention given to proximate, developmental origins. This is now changing, as approaches to studying animal personality broaden and methodologies are developed enabling this to be studied across periods of near continuous and often rapid ontogenetic change. Debate continues, however, about the right methodologies to characterize the phenomenon and attempt to do so in a comparable manner across taxa that differ as widely in the expression of "personality" as insects and mammals. This makes it necessary to discuss this field in an interdisciplinary context among psychologists and biologists, and was the rational for a meeting on "The Emergence of Personality in Animals" held in May 2010 at the Center for Interdisciplinary Research (Zentrum für Interdisziplinäre Forschung; ZiF), Bielefeld, Germany. The diversity of topics, viewpoints and organisms covered and the excitement created by the ensuing discussions is reflected in the resulting collection of papers forming this special issue.