Changes of gene expression but not cytosine methylation are associated with plasticity of male parental care reflecting behavioural state, social context, and individual flexibility

Behaviour is often on the front line of plasticity in response to different environments. At the genetic level, behavioural changes are likely to be associated with changes of gene expression. Most studies to date have focused on gene expression differences associated with discrete behavioural states reflecting development or age-related changes, such as honey bee castes. However, more rapidly flexible behaviour is often observed in response to social context or simple individual variation. The differences in genetic influences for the different forms of plasticity are poorly understood. In this study we contrasted gene expression during male parental care of the burying beetle, Nicrophorus vespilloides, in a factorial design. Male N. vespilloides males typically do not provide care when females are present. However, male care is inducible by the removing female and has parental effects equivalent to female care. We used this experimental manipulation to isolate gene expression and cytosine methylation associated with differences of behavioural state, differences of social context, or differences of individual flexibility for expressing care. The greatest number of differentially expressed genes was associated with behavioural state, followed by differences of social contexts, and lastly differences of individual variation. DNA methylation has been hypothesized to regulate the transcriptional architecture that regulates behavioural transitions. We tested this hypothesis by quantifying differences of cytosine methylation that were associated with differences of behavioural state and individual flexibility. Changes of cytosine methylation were not associated with changes of gene expression. Our results suggest a hierarchical association between gene expression and the different sources of variation that influence behaviour, but that this process is not controlled by DNA methylation despite reflecting levels of plasticity in behaviour. Our results further suggest that the extent that a behaviour is transient plays an underappreciated role in determining the molecular mechanisms that underpin the behaviour.