Epigenetic Modifications Are Associated with Propensity to Migrate in Rainbow Trout

Although migration is a central life-history trait spanning all major branches of the animal kingdom, knowledge of the underlying molecular mechanisms regulating this trait remains limited. We are using the salmonid Oncorhynchus mykiss as a model to gain mechanistic insight into one migratory phenotype, the propensity to migrate. Given that gene x environment interactions and phenotypic plasticity are likely critical components to migratory divergence, epigenetic modifications (e.g., DNA methylation) may regulate gene expression and partially underlie migratory phenotypic diversity. An F2 family created by crossing steelhead (migratory) and rainbow trout (non-migratory) double haploid clonal lines was used to quantitatively measure genome-wide DNA methylation variation of skin tissue, which increases in reflectance prior to migration. Significant differential DNA methylation (hyper and hypo) was discovered when comparing juvenile steelhead and rainbow trout life-history types. Several of the differentially methylated regions are part of in silico-predicted CpG islands, suggesting epigenetic regulation of associated gene promoters leading to differential gene expression. This study provides the first empirical example of a relationship between epigenetic variation and alternative migratory behavior.