Epigenetic Potential and Dispersal Propensity in a Free-Living Songbird: A Spatial and Temporal Approach

Natal dispersal is a key life history trait determining fitness and driving population dynamics, genetic structure, and species distributions. Despite existing evidence that not all phenotypes are equally likely to successfully establish in new areas, the mechanistic underpinnings of natal dispersal remain poorly understood. The propensity to disperse into a new environment can be favoured by a high degree of phenotypic plasticity, which facilitates local adaptation and may be achieved via epigenetic mechanisms, which modify gene expression and enable rapid phenotypic changes. Epigenetic processes occur in particular genomic regions-DNA methylation on CpG sites in vertebrates-and thus individual genomes may differ in their capacity to be modified epigenetically. This 'Epigenetic potential' (EP) may represent the range of phenotypic plasticity attainable by an individual and be a key determinant of successful settlement in novel areas. We investigated the association between EP-quantified as the number of genome-wide CpG variants-and natal dispersal propensity in a long-term study population of Pied flycatchers (Ficedula hypoleuca) monitored since colonisation of a new habitat 35 years ago. We tested this association at three levels, comparing EP between: (i) individuals dispersing between and within habitat patches; (ii) immigrants to the population and locally born individuals; and (iii) individuals from first (comprising colonisers or their direct descendants) and later generations of the population (consisting of locally born individuals, which did not show natal dispersal between habitat patches). Results show a significant, positive association between EP and dispersal propensity in comparisons (i)-only in females-and (iii), but not (ii). Furthermore, CpG variants were non-randomly distributed across the genome, suggesting species- and/or population-specific CpGs being more frequent in promoters and exons. Our findings point to EP playing a role in dispersal propensity at spatial and temporal scales, supporting the idea that epigenetically driven phenotypic plasticity facilitates dispersal and environmental coping in free-living birds.