3. How would you find out if the cause of variation is genetic or environmental?
Answers
Explanation:
Abstract
The aim of this multi-informant twin study was to determine the relative role of genetic and environmental factors in explaining variation in trait resilience in adolescents. Participants were consenting families (N = 2,638 twins in 1,394 families), from seven national cohorts (age 12–18 years, both sexes) of monozygotic and dizygotic twins reared together. Questionnaire data on the adolescents’ Ego-resilience (ER89) was collected from mothers, fathers and twins, and analysed by means of multivariate genetic modelling. Variance in trait resilience was best represented in an ADE common pathways model with sex limitation. Variance in the latent psychometric resilience factor was largely explained by additive genetic factors (77% in boys, 70% in girls), with the remaining variance (23 and 30%) attributable to non-shared environmental factors. Additive genetic sources explained more than 50% of the informant specific variation in mothers and fathers scores. In twins, additive and non-additive genetic factors together explained 40% and non-shared environmental factor the remaining 60% of variation. In the mothers’ scores, the additive genetic effect was larger for boys than for girls. The non-additive genetic factor found in the twins’ self ratings was larger in boys than in girls. The remaining sex differences in the specific factors were small. Trait resilience is largely genetically determined. Estimates based on several informants rather than single informants approaches are recommended.
Keywords: Resilience, Adolescents, Twin study, Heritability, Multiple informants
Introduction
Many studies on human resilience have focused on how contextual factors may act as buffers against stressful life events and adversity (Cicchetti et al. 1993; Cowen et al. 1994; Hurd and Zimmerman 2010; Luthar 1991). However, it has also long been assumed that there must be a genetic component in human resilience against stress and adversity (Rutter 2003). Moderate to strong genetic effects have been reported in twin studies for several normal personality traits and competencies (Ganiban et al. 2008; Kandler et al. 2009; Koenig et al. 2008; Nes et al. 2006; Raevuori et al. 2007; Vernon et al. 2009) as well as in exceptional talents (Haworth et al. 2010; Vinkhuyzen et al. 2009) However, there are very few genetically informative studies on positive psychological personality traits related specifically to the reactivity to events.
Stein et al. (2009) recently reported a higher frequency of the homozygous ‘LL’ allele of the 5HTTLPR in a group of undergraduate students with high scores on trait resilience as measured by the Connor-Davidson Resilience Scale (CD-RISC) (Connor and Davidson 2003), but the authors duly emphasize the necessity of replication of this result. A Swedish twin study (Hansson et al. 2008) found moderate heritability estimates (h2 ranging between .24 and .49), and zero order shared environmental effects, on measures of well-being, negative and positive mental health. The authors related this to individual salutogenic factors and indirectly to trait resilience. Boardman et al. (2008) found h2 = 0.52 for men and h2 = 0.38 for women in a study of US adult twins, where resilience was indirectly defined as the residual variance in positive mood after adjusting for life stressors. Apart from these studies, we are not aware of other studies that have approached the study of resilience from a behaviour genetic perspective. Thus, the present state of knowledge in this field does not seem to differ much from that described by Shiner and Caspi (2003) almost 10 years ago: ‘Resilience researchers have called for increasing focus on the processes underlying resilience (ref.), and personality research should be an important part of future work in this area. It is curious, also, that genetic studies, which are so integral to research on vulnerability associations, have played such a minor role in research on resilience. From an evolutionary perspective genes are equally likely to protect against environmental insult as they are to create vulnerability to disease…’ (pp. 20).
Abstract
Background and Aims
Both environmental and genetic effects contribute to phenotypic variation within and among populations. Genetic differentiation of quantitative traits among populations has been shown in many species, yet it can also be accompanied by other genetic changes, such as divergence in phenotypic plasticity and in genetic variance. Sideroxylonal (a formylated phloroglucinol compound or FPC) is an important chemical defence in eucalypts. The effect of environmental variation on its production is a critical gap in our understanding of its genetics and evolution.
Methods
The stability of genetic variation in sideroxylonal was assessed within and among populations of Eucalyptus tricarpa in three replicated provenance/progeny trials. The covariance structure of the data was also modelled to test whether genetic variances were consistent among populations and Fain's test was applied for major gene effects.
Key Results
A significant genotype × environment interaction occurred at the level of population, and was related to temperature range and seasonality in source populations. Within-population genetic variation was not affected by genotype × environment effects or different sampling years. However, within-population genetic variance for sideroxylonal concentration differed significantly among source populations. Regression of family variance on family mean suggested that this trait is subject to major gene effects, which could explain the observed differences in genetic variances among populations.
Conclusions
These results highlight the importance of replicated common-garden experiments for understanding the genetic basis of population differences. Genotype × environment interactions are unlikely to impede evolution or responses to artificial selection on sideroxylonal, but the lack of genetic variation in some populations may be a constraint. The results are broadly consistent with localized selection on foliar defence and illustrate that differentiation in population means, whether due to selection or to drift, can be accompanied by changes in other characteristics, such as plasticity and genetic variance.
Keywords: Additive genetic variance, open-pollinated common-garden experiment, genotype × environment interaction, plasticity, Eucalyptus tricarpa, sideroxylonal, formylated phloroglucinol compounds (FPCs), chemical defence