On the Genetics of Avian Personalities: mechanism and structure of behavioural strategies in the great tit (Parus major)

The need for evolutionary studies on quantitative traits that integrate genetics, development and fitness consequences is increasing. Due to the complexity, coherence and variability of behavioural traits, evolutionary biologists are therefore more and more attracted to the study of behaviour. The use of the model system of consistent individual differences in personality traits in the great tit provides a good foundation to do controlled experiments on the mechanisms underlying the variation in complex behavioural traits, and to make the step to functionality and evolution. The study presented in this thesis is part of a NWO program on the heritability, ontogeny and fitness consequences of personalities. The genetic background and the structure of the genetic mechanism that underlies the inheritance of these personality traits were investigated in this study. In our study on personality traits in the great tit we have been able to breed animals experimentally and to artificially select for our traits of interest. We show with two independent artificial selection experiments that a significant part of the phenotypic variation in early explorative behaviour (chapter 2) and in risk-taking behaviour (chapter 4) can be ascribed to variation in the genetic make-up of these traits. We found a difference in the realized heritability between the two traits (54% for early exploratory behaviour and 19% for risk-taking). Since risk-taking behaviour is measured in a later stadium of a birds life this difference could therefore be seen as an indication for the existence of learning effects in personality traits. With different methods we found different heritability estimates in our study. A possible cause for this variation in heritability estimates would be the existence of nonadditive or indirect genetic effects (IGEs) in the inheritance of these traits. The analyses of line crosses enabled us to separate the components of variation. The analysis (chapter 3) shows that besides a considerable amount of additive genetic variation also genetic dominance plays an important role in the structure of inheritance. Since we did not detect sex-dependent expression in this analysis, we can assume that differences between sexes that have been found are due to differences in selection pressures or interactions with the social environment (chapter 5), rather then a difference in expression of the same genes. Our analyses also showed that the part of the phenotypic variation that could be explained by heritable additive maternal effects was relatively low (7 %). In great tits, explorative behaviour showed to be phenotypically correlated with many other traits within the same context. Moreover, we measured two presumably independent traits (exploratory and risk-taking behaviour) and found that besides the phenotypic correlation, these traits were strongly genetically correlated (chapter 6). In this thesis we have shown that (i) personality traits have a clear genetic basis, that (ii) the structure of inheritance is not simply additive and that (iii) personality traits do not inherit independently of each other, and that (iv) therefore the genetic structure has to be taken into account when looking at the expected response to natural selection and past evolutionary forces. This has brought us a large step further in understanding the inheritance of complex behavioural traits in natural populations and will help building more realistic models in studying the evolution of complex traits and syndromes of traits. Moreover, with this study we provide the starting point for future research on more detailed questions on several levels, however without ignoring the development in other

Temporal changes in DNA methylation and RNA expression in a small song bird: within- and between-tissue comparisons

BackgroundDNA methylation is likely a key mechanism regulating changes in gene transcription in traits that show temporal fluctuations in response to environmental conditions. To understand the transcriptional role of DNA methylation we need simultaneous within-individual assessment of methylation changes and gene expression changes over time. Within-individual repeated sampling of tissues, which are essential for trait expression is, however, unfeasible (e.g. specific brain regions, liver and ovary for reproductive timing). Here, we explore to what extend between-individual changes in DNA methylation in a tissue accessible for repeated sampling (red blood cells (RBCs)) reflect such patterns in a tissue unavailable for repeated sampling (liver) and how these DNA methylation patterns are associated with gene expression in such inaccessible tissues (hypothalamus, ovary and liver). For this, 18 great tit (Parus major) females were sacrificed at three time points (n = 6 per time point) throughout the pre-laying and egg-laying period and their blood, hypothalamus, ovary and liver were sampled.ResultsWe simultaneously assessed DNA methylation changes (via reduced representation bisulfite sequencing) and changes in gene expression (via RNA-seq and qPCR) over time. In general, we found a positive correlation between changes in CpG site methylation in RBCs and liver across timepoints. For CpG sites in close proximity to the transcription start site, an increase in RBC methylation over time was associated with a decrease in the expression of the associated gene in the ovary. In contrast, no such association with gene expression was found for CpG site methylation within the gene body or the 10 kb up- and downstream regions adjacent to the gene body.ConclusionTemporal changes in DNA methylation are largely tissue-general, indicating that changes in RBC methylation can reflect changes in DNA methylation in other, often less accessible, tissues such as the liver in our case. However, associations between temporal changes in DNA methylation with changes in gene expression are mostly tissue- and genomic location-dependent. The observation that temporal changes in DNA methylation within RBCs can relate to changes in gene expression in less accessible tissues is important for a better understanding of how environmental conditions shape traits that temporally change in expression in wild populations