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.

Dairy cattle have a high level of interaction with humans throughout their productive life. Welfare and productivity are affected if cows find these interactions aversive, so tests assessing fear of humans have been included in welfare assessment protocols. Practicality issues suggest that all animals on large farms cannot be tested. If a sub-sample is chosen, then animal factors affecting the response must be investigated. To assess the effect of age, 114 Holstein cows were tested at regular intervals across their productive lifetime. Animals were tested at 12-15 months of age, first breeding, prior to first calving, then at early, mid and late lactation for 1st and 2nd lactations and into their 3rd lactation. The test involved approaching each cow when standing in the passageway of the barn with sufficient space to retreat. Response was recorded on a 0-8 incremental scale, and several qualitative terms were scored using sliding scales from absence to full presence. There was a significant effect of age on response. Cows became more approachable with increasing age, up until the middle of the first lactation, with no further change beyond this stage. Cows became more at ease and less nervous with increasing age. Individual cow within-group rankings for tests at each stage showed correlation with rankings in the following stage. As this is a single-farm study, further research is necessary to assess interaction of factors such as housing, breed and quality of human handling on the long-term development of fear of humans. However, the results suggest that the age of the animal tested affects the response, and that animals of different age groups should be tested when a sub-sampling is required to assess welfare on large farms.

Merino ewes have been selected, over 18 generations, for calm (C) or nervous (N) temperament using using an arena test and an isolation box test. We investigated the relative contributions of genotype versus the post-partum behaviour of the dam on the temperament of the lambs using a cross-fostering procedure. Forty-eight multiparous calm and 52 nervous ewes were artificially inseminated with the semen of a sire of the same temperament. At birth, 32 lambs of a given temperament line were cross fostered to ewes from the other line (16 N × C, 16 C × N), 34 lambs were cross fostered to ewes from the same line (15 C × C, 19 N × N) and 30 lambs were left with their birth mother (15 C, 15 N), to control for the effect of cross fostering. The temperament of the progeny was assessed at two occasions, one week after birth by measuring locomotor activity during an open-field test and at weaning (16 weeks) by measuring locomotor activity during an arena test and agitation score measured during an isolation box test. There was a genotype effect but no maternal or fostering effect on the lamb temperament at one week. This may be because the maternal behaviour of the foster ewes did not differ considerably between the calm and nervous mothers during adoption or within the first week, post partum. Similarly, at weaning, only a genotype effect was found on the locomotor and agitation score. Therefore, it appears that temperament in Merino sheep is mainly determined by the genetic transmission of the trait across generations rather than behaviours learned from the mother.