This study investigated the psychometric properties of the Highly Sensitive Child-Rating System (HSC-RS), the existence of sensitivity groups, and the characterization of sensitivity at behavioral, genetic, and physiological levels in 541 preschoolers (M(SD)age = 3.56(0.27); 45%male; 87%Caucasian). Temperament, genetic, cortisol, and electroencephalography asymmetry data were collected in subsamples (n = 94-476). Results showed a reliable observational measure of sensitivity. Confirmatory factor and latent class analysis supported a one-factor solution and three sensitivity groups, that are a low (23.3%), medium (54.2%), and a high (22.5%) sensitivity group. Hierarchical regression analyses showed moderate associations between HSC-RS and observed temperament traits (i.e., behavioral level). In addition, a small negative association between HSC-RS and a genome-wide association study polygenic risk score (GWAS PGS) for Attention Deficit Hyperactivity Disorder was found. No relations with candidate genes, other GWAS PGS phenotypes, and physiological measures were found. Implications of our findings and possible explanations for a lack of these associations are discussed.

This study investigated the role of temperament in oral language development in over 200 Mandarin and Cantonese speakers in the Growing Up in New Zealand pre-birth longitudinal cohort study. Mothers assessed infant temperament at nine months using a five-factor Infant Behaviour Questionnaire-Revised Very Short Form. They also reported on children’s vocabulary and word combinations at age two using adapted MacArthur-Bates Communicative Development Inventory short forms. Regression analyses were employed to examine unique links between infant temperament and language, respectively, controlling for demographic factors. Fear was associated with larger English vocabularies for English-Mandarin speakers and larger Cantonese vocabularies for Cantonese speakers. Orienting capacity was associated with more advanced word combinations for Mandarin speakers, whereas negative emotionality was associated with less advanced word combinations for Cantonese speakers. Positive affect/surgency was associated with more advanced word combinations for English-Cantonese speakers. This study revealed predictive patterns of infant temperament across Chinese-speaking children’s multiple languages.

The present study examined the longitudinal associations between three dimensions of temperament – activity, affect-extraversion, and task orientation – and childhood aggression. Using 131 monozygotic and 173 dizygotic (86 same-sex) twin pairs from the Louisville Twin Study, we elucidated the ages, from 6 to 36 months, at which each temperament dimension began to correlate with aggression at age 7. We employed latent growth modeling to show that developmental increases (i.e., slopes) in activity were positively associated with aggression, whereas increases in affect-extraversion and task orientation were negatively associated with aggression. Genetically informed models revealed that correlations between temperament and aggression were primarily explained by common genetic variance, with nonshared environmental variance accounting for a small proportion of each correlation by 36 months. Genetic variance explained the correlations of the slopes of activity and task orientation with aggression. Nonshared environmental variance accounted for almost half of the correlation between the slopes of affect-extraversion and aggression. Exploratory analyses revealed quantitative sex differences in each temperament-aggression association. By establishing which dimensions of temperament correlate with aggression, as well as when and how they do so, our work informs the development of future child and family interventions for children at highest risk of aggression.

Individual differences in sensitivity to context are posited to emerge early in development and to influence the effects of environmental exposures on a range of developmental outcomes. The goal of the current study was to examine the hypothesis that temperament characteristics and biological sex confer differential vulnerability to the effects of exposure to maternal depression on telomere length in early childhood. Telomere length has emerged as a potentially important biomarker of current and future health, with possible mechanistic involvement in the onset of various disease states. Participants comprised a community sample of children followed from infancy to age 3 years. Relative telomere length was assessed from DNA in saliva samples collected at infancy, 2 years, and 3 years. Maternal depressive symptoms and the child temperament traits of negative affectivity, surgency/extraversion, and regulation/effortful control were assessed via maternal report at each timepoint. Analyses revealed a 3-way interaction among surgency/extraversion, sex, and maternal depressive symptoms, such that higher surgency/extraversion was associated with shorter telomere length specifically among males exposed to elevated maternal depressive symptoms. These findings suggest that temperament and sex influence children’s susceptibility to the effects of maternal depression on telomere dynamics in early life.

How we are influenced by our environment is a fundamental question in developmental science. Theories and empirical research have claimed that some individuals are susceptible to environmental influences and others are much less susceptible. The present study addressed four questions: (1) Is environmental susceptibility a continuous or categorical construct? (2) Is environmental susceptibility unidimensional (i.e., domain general) or multidimensional (i.e., domain specific)? (3) Are there genetic contributions to individual differences in environmental susceptibility? (4) What are the temperamental characteristics of different environmental susceptibility patterns? We used child- and mother-report data from a sample of 11-year-old twins (N = 1,507) and applied a novel data-driven approach to assess an environmental susceptibility space, based on simultaneous associations between multiple environmental exposures (18 measures relating to parenting, parent, peer, and twin relationships) and developmental outcomes (10 measures relating to empathy, prosocial behavior, aggression, and self-esteem). The results suggest that the environmental susceptibility space we assessed is better conceptualized as continuous and multidimensional. Different children showed susceptibility to different contexts and variation in domain-general versus domain-specific patterns. A comparison of distances between monozygotic and dizygotic twins within the space demonstrated genetic contributions. Finally, susceptibility patterns could not be differentiated based on a specific temperament trait, but rather related to temperament profiles.

Prenatal maternal stress and mental health problems are known to increase risk for developmental psychopathology in offspring, yet pathways leading to risk or resiliency are poorly understood. In a quasi-experimental design, we prospectively examined associations between disaster-related prenatal stress, maternal mental health symptoms, and infant temperament outcomes. Mothers who were pregnant during Hurricane Harvey (N = 527) reported on objective hardships (e.g., loss of belongings or income, evacuation, home flooding) related to the storm and subsequent mental health symptoms (anxiety/depression, posttraumatic stress) across time. At a postpartum assessment, mothers reported on their infant’s temperament (negative affect, positive affect, orienting/regulatory capacity). Greater objective hardship indirectly predicted higher levels of infant orienting/regulatory capacity through its association with increased maternal posttraumatic stress symptoms. Greater objective hardship also indirectly predicted higher levels of infant negative affect through its association with increased maternal anxiety/depression symptoms across time. Our findings suggest a psychological mechanism linking prenatal stress with specific temperamental characteristics via maternal mental health symptoms. Findings point to the importance of high-quality assessment and mental health services for vulnerable women and young children.

Maternal antenatal anxiety is an emerging risk factor for child emotional development. Both sex and epigenetic mechanisms, such as DNA methylation, may contribute to the embedding of maternal distress into emotional outcomes. Here, we investigated sex-dependent patterns in the association between antenatal maternal trait anxiety, methylation of the brain-derived neurotrophic factor gene (BDNF DNAm), and infant negative emotionality (NE). Mother–infant dyads (N = 276) were recruited at delivery. Maternal trait anxiety, as a marker of antenatal chronic stress exposure, was assessed soon after delivery using the Stait-Trait Anxiety Inventory (STAI-Y). Infants’ BDNF DNAm at birth was assessed in 11 CpG sites in buccal cells whereas infants’ NE was assessed at 3 (N = 225) and 6 months (N = 189) using the Infant Behavior Questionnaire-Revised (IBQ-R). Hierarchical linear analyses showed that higher maternal antenatal anxiety was associated with greater 6-month-olds’ NE. Furthermore, maternal antenatal anxiety predicted greater infants’ BDNF DNAm in five CpG sites in males but not in females. Higher methylation at these sites was associated with greater 3-to-6-month NE increase, independently of infants’ sex. Maternal antenatal anxiety emerged as a risk factor for infant’s NE. BDNF DNAm might mediate this effect in males. These results may inform the development of strategies to promote mothers and infants’ emotional well-being.

For mother-infant health especially, the pandemic has brought multiple stressors inside a susceptible psychobiological system. We study the longitudinal associations between maternal prenatal and postpartum: (a) COVID-19 stressful events exposure, (b) pandemic psychological stress, and (c) mental health and infants’ negative affect. A sample of 643 Italian pregnant women completed a web-based survey from April 8th to May 4th, 2020 and a follow-up at 6 months after delivery. Maternal assessment covered prenatal and postpartum measures for: COVID-19 stressful events exposure, pandemic psychological stress, mental health symptoms (i.e., depression, anxiety, posttraumatic stress disorder) and postpartum, social support and report of infants’ negative affect. Maternal mental health symptoms during pregnancy, at the peak of pandemic, is longitudinally associated with infant negative affect, with postpartum mental health mediating this association. Also, maternal COVID-19 stressful events exposure in postpartum is associated with negative affect at 6 months mediated by postpartum mental health symptoms. Maternal pandemic psychological stress during pregnancy predicted mental health symptoms in postpartum. The study supports the association between pandemic-related maternal health across pregnancy and postpartum and offspring’s development (i.e., negative affect). It also puts the spotlight on mental health risk in women experiencing lockdown during pregnancy, especially when feeling high psychological stress in pregnancy or when directly exposed to COVID-19 stressful events postpartum.

It remains unclear how the COVID-19 pandemic has affected the mother–infant relationship and associations between maternal postpartum depression (PPD) and offspring temperament. This study examined the impact of the pandemic on these links and how maternal ratings of the mother–infant relationship mediated associations between PPD and infant temperament in a sample of treatment-seeking mothers in Ontario, Canada before and during the COVID-19 pandemic. Mothers with infants <12 months of age and Edinburgh Postnatal Depression Scale scores ≥10 enrolled in two separate randomized controlled trials of 1-day cognitive behavioral therapy-based workshops for PPD conducted before COVID-19 (n = 392) and during the pandemic (n = 403). Mothers reported on depressive symptomatology, infant temperament, and the mother–infant relationship. Maternal PPD was associated with more infant negative affectivity and mother–infant relationship difficulties. While associations between PPD and infant-focused anxiety were stronger during COVID-19, the pandemic did not otherwise affect associations between PPD and infant temperament. Mediation analyses suggested that aspects of the mother-infant relationship mediated associations between PPD and infant negative affectivity. Findings highlight the importance of detecting PPD and intervening to potentially improve outcomes for mothers and their children.

Individual differences in behaviour may be examined at two levels. First, individuals may differ in terms of frequencies, durations and/or patterning of particular measures of their behaviour. Second, individuals may differ in their temperament, ie in the way they react to environmental change and challenge. Individual differences in temperament are particularly relevant to animal welfare studies, for the welfare of an individual largely depends on whether it can cope with environmental challenge. Whereas the study of individual differences in behaviour at the first level may be achieved by using standard behavioural methods, the study of individual differences in temperament requires the use of more unusual methods, namely observers’ ratings and behavioural tests. Observers’ ratings provide information on subtle aspects of an individual's behaviour that could otherwise be overlooked. Behavioural tests facilitate comparisons between individuals in a more standardized way. It is suggested that both systems should be used together.

Taking individual differences into account when designing experiments may help reduce variability in studies on welfare issues and understanding the causes of individual differences in temperament may allow us to reduce the incidence of some welfare problems.

Animal welfare is a major issue in Europe, and the production of mink, Mustela vison, has also been under debate. One common method of solving animal welfare problems is to adapt the environment to fit the behavioural needs of the animals. In comparison with other forms of husbandry, the mink production environment has remained relatively unchanged over the years and provides for some of the most obvious needs of mink. Whether today's typical housing conditions adequately meet the welfare requirements of mink is currently a topic of discussion. An alternative approach to improving welfare is to modify the animals so that they are better adapted to farming conditions. In large-scale animal production, handling of the individual can be a sporadic event, making an animal's inherent characteristics for temperament and adaptability important factors to consider with respect to its resultant welfare.

In this review we present and discuss experiments on behavioural selection for temperament, and against undesirable behaviours, such as fur chewing, in mink. Fur chewing behaviour can be reduced by selection, apparently without any negative effects, whereas only a little is known about the nature and consequences of selecting against stereotypic behaviours. Long-term selection experiments have shown that it is possible to reduce fearfulness in farmed mink. Using a relatively simple test, it is possible for farmers to add behavioural measurements to their normal selection criteria and thereby improve the welfare of farmed mink.

Many breeds of companion animal have inherited disorders that may impair quality of life (QoL) to the extent that it is unkind to keep them alive. If we struggle to discern when this point is reached, why do we breed compromised, short-lived animals in the first place? If we struggle to judge when environmental conditions cause an unacceptable QoL, why not breed appropriately for modern environments? In breeding pedigree dogs, five major problems arise: (1) some breed standards and selection practices run counter to dog welfare; (2) insufficient selection pressure seems to be exerted on some traits that would improve animal well-being and produce dogs better suited to modern environments; (3) the incidence of certain inherited defects in some breeds is unacceptably high; (4) the dearth of registered animals of certain breeds in particular countries makes it extremely difficult for breeders to avoid mating close relatives; and (5) there may be financial disincentives for veterinarians to reduce the incidence of inherited diseases. Before we can judge when behavioural or morphological changes caused by selective breeding result in an unacceptable QoL, we have to know which are prevalent. This paper reviews progress in two Australian schemes to monitor trends in the prevalence of inherited disorders in dogs and to promote behavioural phenotypes likely to cope with contemporary domestic environments.