LAUSR

In recent years, the belief that the genetic code is the sole basis for biological inheritance has been challenged by the discovery of trans-generational epigenetic inheritance. Environmentally induced phenotypes can in this way persist for several generations, due to the transmission of molecular factors that determine how DNA is read and expressed (Jablonka and Raz 2009; Bonduriansky and Day 2009). Epigenetic regulation of gene expression is a common process that acts during the differentiation of somatic cells, as well as in response to environmental cues and stresses, and the passing on of these modulations to the offspring constitutes epigenetic inheritance. While the term ‘epigenetics’ (επ? [epi]+ genetics, which means ‘on top of/around of’ genetics) was first coined 76 years ago (Waddington 1942), the field has only recently gained an upsurge due to the emergence of modern sequencing methods (Verhoeven et al. 2016; Allis and Jenuwein 2016). These technological advances have highlighted the role and importance of a number of proximate mechanisms of epigenetic inheritance, including DNA methylation, histone modification and small RNA transmission. There is an overall lack in consistency with regards to the definition of epigenetic inheritance used, but here we adopt the broad definition of Burggren (2016) and consider trans-generational epigenetic inheritance as the non-genetic inheritance of a modified phenotype across generations, without focus on a specific mechanism. This definition enables us to concentrate on the evolutionary consequences of epigenetic inheritance. The focus of this special issue is broadly on the evolutionary forces selecting for epigenetic inheritance, its costs and importance for adaptation. In particular, we specifically highlight the effects of paternal trans-generational epigenetic inheritance, which until now have received comparatively little attention.