Eukaryotic species use (cytosine-5) DNA methylation to facilitate phenotypic adaptation to their environments, which can include both the modulation of developmental and adaptive gene expression programs. Variations in the complement of cytosine methyltransferase enzymes have been interpreted to reflect multiple versions of a toolkit for phenotypic adaptation. During evolution, specific parts of this toolkit could have been contracted or expanded to facilitate specific requirements for genome regulation. We are using whole-genome bisulfite sequencing to investigate this hypothesis and to establish genome methylation maps of various model systems at single-base resolution. Our results define three groups of arthropod methylomes with fundamental differences that will be discussed in detail: The first group is defined by Drosophila and is characterized by the complete absence of recognizable DNA methylation patterns. The second group is defined by the honeybee and is characterized by the highly selective methylation of specific CpG residues. The third group is characterized by pervasive genome-wide methylation and we will present the marbled crayfish (Procambarus virginalis) as a novel model system to understand the relevance of DNA methylation for phenotypic variation.
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