Parental age is one aspect of the parental phenotype known to have consequences for aspects of offspring phenotype and fitness. Offspring from old parents have, for example, been found to have a reduced probability to recruit to the breeding population (e.g. Bouwhuis et al. 2009) or an altered (e.g. Bouwhuis et al. 2010) or reduced annual reproductive success or lifespan (Bouwhuis et al. 2015) after recruitment. The inheritance of epigenetic alterations to gene expression is a potential mechanistic explanation underlying parental effects in general, and of specific interest especially for species in which negative parental age effects on offspring have been found, despite parental care improving with age due to increased experience (e.g. Limmer & Becker 2009) or older parents being better at chick provisioning in general (e.g. Cansse et al. 2024). 

We obtained repeated blood samples from 17 breeding pairs and their offspring. These samples have undergone reduced representation bisulfite sequencing (RRBS) to characterise genome-wide DNA methylation profiles on the single nucleotide level. In addition, we have sequenced, de novo assembled and annotated a reference genome for the common tern (Meyer et al. 2023). With these data, we will be able to answer the following questions:

• do adult DNA methylation patterns change with age within individual common terns and does any within-individual change in adult DNA methylation pattern depend on sex?

• do offspring DNA methylation patterns resemble those of (one of) their parent(s) and do (sex-specific) offspring DNA methylation patterns predict offspring development or survival?