Parenting influences many aspects of child development, including socio-emotional, cognitive, and behavioral outcomes. Yet most studies report only modest effect sizes. An increasingly likely... Show moreParenting influences many aspects of child development, including socio-emotional, cognitive, and behavioral outcomes. Yet most studies report only modest effect sizes. An increasingly likely explanation is that not all children are equally affected by environmental factors, including parenting. The differential susceptibility theory proposes that some children might be more susceptible to both positive and negative environmental influences, compared to other children. Such differences in susceptibility are thought to be due to genetic, temperamental, or physiological susceptibility factors. In the current thesis, we tested the theory of differential susceptibility of children to the effects of parenting in a large population-based cohort, the Generation R Study. Doing so, we went beyond common methods. First, we investigated differential susceptibility from a developmental perspective by including multiple measures over time. Second, we went beyond single-gene/polymorphisms in the investigation of gene-environment interplay by aggregating genetic variation in a set of dopamine genes. Third, we extended previous research on mild perinatal adversity as a susceptibility factor by examining its moderating role in the association between harsh parenting and hair cortisol levels, taking into account background factors that we demonstrated to be of influence on hair cortisol levels. Show less
The central theme of this PhD thesis is natural variation in the wing length of the predatory two-spot ladybird beetle, Adalia bipunctata. __Wingless__ individuals of this species occur... Show moreThe central theme of this PhD thesis is natural variation in the wing length of the predatory two-spot ladybird beetle, Adalia bipunctata. __Wingless__ individuals of this species occur occasionally. They possess truncated wing covers and flight wings and cannot fly, but the extent of the reduction is highly variable between individuals. At one hand, I take a multidisciplinary experimental approach to study the causes and consequences of this variation in an evolutionary context. Genetic and developmental studies show that it is regulated by several polymorphic genes, and results from gene-environment interactions affecting the growth of the larval wing discs. Studies on life-history traits and mating behaviour provide no evidence that winglessness is an adaptive trait in this ladybird. However, they reveal a function of the wing covers in survival and mating behaviour. On the other hand, I examine the use of wingless ladybirds in the biological control of aphids, since winged ladybirds are not effective when flying away soon after release. I show that wingless morphs have the potential to improve biocontrol efficacy. I then suggest that mass-rearing of this less fit morph could be improve by manipulation of the wing length. Altogether, this thesis interlinks the fields of fundamental (evolutionary) biology and applied biological control. Show less
The development of self-regulation is one of the major challenges of a child’s healthy development. In the current thesis, the contribution and interplay of parental and biological factors in... Show moreThe development of self-regulation is one of the major challenges of a child’s healthy development. In the current thesis, the contribution and interplay of parental and biological factors in the development of self-regulation in preschoolers are studied in a large population-based cohort, the Generation R Study. We found that attachment insecurity in infancy was related to higher levels of toddler active resistance during Clean-Up. Maternal negative discipline was related to lower levels of committed compliance in toddlers, and the association between maternal positive discipline and child committed compliance was moderated by the child’s COMT rs4680 genotype, indicating that the association was stronger in children with the Met/Met variant than for children with other COMT genotypes. Maternal family-related stress during pregnancy predicted lower levels of toddler committed compliance through lower levels of maternal positive discipline. Maternal sensitivity was associated with lower levels of executive function problems and lower levels of internalizing problems in preschool age. In children with a relatively short corpus callosum in infancy, higher levels of maternal positive discipline predicted lower levels of inhibition problems. Our studies demonstrate the role of various aspects of positive parenting and mother-child relationship quality in preschool children’s regulation of emotions and behavior. Show less
Wat bepaalt de kwaliteit van gehechtheid? In een grootschalig onderzoek, Generation R, zijn de stresshuishouding en enkele kandidaatgenen van de kinderen onderzocht, en het gedrag van de ouder. De... Show moreWat bepaalt de kwaliteit van gehechtheid? In een grootschalig onderzoek, Generation R, zijn de stresshuishouding en enkele kandidaatgenen van de kinderen onderzocht, en het gedrag van de ouder. De gehechtheidsrelatie is de relatie tussen een kind en een ouder (of andere stabiele verzorger) die in het eerste levensjaar wordt opgebouwd. Veilig gehechte kinderen gebruiken hun ouder als veilige haven van waar ze de omgeving verkennen. Onveilig gehechte kinderen hebben hier moeite mee; zij kunnen niet de juiste balans vinden tussen contact met de ouder en het verkennen van de omgeving. Dit onderzoek laat zien dat onveilig gehechte kinderen heftiger op stress reageren dan veilig gehechte kinderen. Wanneer er sprake was van depressie in het leven van de moeder, leidt dit tot een verdere toename van stress bij de onveilig gehechte kinderen. Hetzelfde gold voor onveilig gehechte kinderen met een risico-gen dat verantwoordelijk is voor een minder goede stressregulatie. Verder vonden we dat sensitief opvoedgedrag van moeder leidde tot meer veilige gehechtheid, maar alleen wanneer het kind een bepaalde variant van een gen droeg dat van belang is bij het omgaan met stress. De resultaten laten de kwetsbaarheid en stressgevoeligheid van onveilig gehechte kinderen zien. Daarnaast kunnen we op basis van de huidige resultaten zeggen dat insensitief opvoedgedrag, depressie van moeder en genetische risico’s een rol spelen bij onveilige gehechtheid. De ontwikkeling van gehechtheid is complex, en het resultaat van het samenspel tussen biologische aspecten en de opvoedingsomgeving. Daarop moet toekomstig onderzoek dan ook gericht zijn. Show less
The objective of the research described in this thesis was to demonstrate the role of gene-environment interactions in the emergence of individual differences in cocaine use. For this purpose we... Show moreThe objective of the research described in this thesis was to demonstrate the role of gene-environment interactions in the emergence of individual differences in cocaine use. For this purpose we used two inbred mouse strains, the C57Bl/6 (C57) and DBA/2 (DBA), which are known to differ in drug-intake and to be differentially sensitive to several stressors. We studied the impact of early life experiences (long-term influence) as well as a later life psychosocial stressor (short-term influence) on adult drug intake behavior in these two mouse strains. To study the impact of the early life environment, we manipulated the maternal environment of the mice by fostering them with non-related mother strains showing either high or low pup-oriented behaviour. The late life experience consisted of a short-lasting period of group housing in adulthood. Cocaine self-administration in mice with a C57 background was not affected by either changes in postnatal maternal environment or a short group housing experience in adulthood, while these same experiences did affect mice with a DBA background. As a first step towards the biological mechanisms underlying this gene-environment interaction we found that vasopressin was differentially regulated in the extended amygdala of the DBA mice. Show less
This thesis addressed the physiological impact of fear in 4- and 7-year-old children, induced by media and social fear-inducing tasks (the Trier Social Stress Test for Children). The main question... Show moreThis thesis addressed the physiological impact of fear in 4- and 7-year-old children, induced by media and social fear-inducing tasks (the Trier Social Stress Test for Children). The main question pertained to individual differences in physiological reactivity to fear-inducing stimuli. The possibly relevant factors of attachment security, the child’s temperamental fearfulness, and variations in the serotonin transporter gene (5-HTTLPR; long vs. short allele) were taken into account. Results showed that temperament, attachment, and genetic influences play significant and interactive roles in the expression of fear reactivity. A secure relationship affected the reactivity to media-induced fear stimuli in temperamentally more fearful children but not in less fearful children irrespective of children’s ages. This finding adds to the growing literature showing that children high in negative emotion are more susceptible to positive as well as negative rearing influences. Furthermore, we found evidence that reactivity to the social fear-inducing task was explained by a combination of variations in the serotonin transporter gene and attachment security. Children with a secure attachment representation and two long 5-HTT alleles showed the lowest levels of fear reactivity, indicating that physiological reactivity to a social fear-inducing task is a product of the child’s biology and environment. Show less
