Table of contents Chapter 1 General introduction Chapter 2 Genetic and phenotypic responses to genomic selection for timing of breeding in a wild songbird Chapter 3 Temperature has a causal and plastic effect on timing of breeding in a small songbird Chapter 4 Exploration of tissue-specific gene expression patterns underlying timing of breeding in contrasting temperature environments in a songbird Chapter 5 Fine-tuning of seasonal timing of breeding is regulated downstream in the underlying neuro-endocrine system in a small songbird Chapter 6 Exploring temporal changes in DNA methylation and RNA expression in a small songbird-correlations within and between tissues Chapter 7 General discussion References Summary Samenvatting Curriculum vitae List of publications Acknowledgements WIAS Training and Education Statement CHAPTER 1 General introduction Chapter 1 10 Evolution and natural selection Evolution, the process that leads to the formation of and change in biological systems in response to their environment, has shaped life since its beginning and continues to do so. All organisms, simple and complex, evolve over different scales in both time and space. In general, evolution is described and studied as two distinct hierarchical processes; macroevolution and micro-evolution. Macro-evolution refers to the origin of new morphological forms, species and divisions of the taxonomic hierarchy above the species level, together with the origin of complex adaptations, such as the eye (Reznick & Ricklefs 2009), but on which I will not dwell further. In contrast, micro-evolution refers to the processes of adaptive modifications (i.e. through alteration in allele frequencies in gene pools) within and among populations, propelled by mutation, migration, genetic drift and natural selection. The latter, put first into words by, independently, both Charles Darwin (1859) and Alfred Russel Wallace (1858), is usually defined as the consequence of three organismal properties: (1) variation among organisms of a population, (2) differential reproduction, and (3) traits that are important for survival or reproduction show heritability (Darwin 1859; Wallace 1858).
