DNA methylation patterns linked to salinity and geography in the American eel (Anguilla rostrata)

The panmictic American eel (Anguilla rostrata) displays a wide range of intraspecific phenotypic variation as well as geographical sex bias and differential recruitment. By definition, panmictic species lack genetic structure, thus local adaptation through genetic variation cannot explain the presence of intraspecific variation. As a result, the contrasting phenotypes observed in the American eel could be attributed to either spatially varying selection, phenotypic plasticity (often mediated through epigenetic changes), or the interaction of both processes. Here we explore, for the first time, the role of DNA methylation in acclimatization in a panmictic species, the American eel, as well as its association with salinity and geography in Northeastern Canada. Using whole genome bisulfite sequencing in 72 individuals, we found that DNA methylation patterns were associated with geography and to a lesser degree with salinity. We identified a genomic region with differential methylation associated with salinity that falls inside the SOCS2 gene, which has been previously linked to salinity differences in other fish species, as well as to metabolism and somatic growth regulation. This study advances our understanding of how panmictic species or populations with high gene flow acclimatize to variable environments in the absence of heritable genetic local adaptation.