by Molly Stephens
The molecular mechanisms underlying an animal’s “decision” to migrate are poorly understood, yet essential to unraveling the mystery of migration in many diverse species. Our new study, published as part of an upcoming Molecular Ecology special issue, ‘Epigenetic Studies in Ecology and Evolution,” offers a potential mechanism: epigenetics. Epigenetic modification, in this case DNA methylation, can alter the expression of genes without modifying the underlying DNA sequence. This type of regulation may provide an important link between external environmental migratory cues and the outward physical and behavioral appearance of a fish, producing rainbow trout (Oncorhynchus mykiss) individuals with one of two very different alternative life history strategies from the same population: smolts or residents (see figure at right).
To explore this potential link, we quantitatively measured genome-scale DNA methylation in fin tissue using a reduced representation bisulfite sequencing (mRRBS) technique on fish produced from crosses of non-migratory steelhead and migratory resident rainbow trout clonal lines. We found 57 differentially methylated regions between smolt and resident juveniles and identified several molecular categories of genes, including some with clear associations with migration, such as the circadian rhythm pathways.
This study provides the first evidence of a relationship between epigenetic variation and life history divergence associated with migration-related traits in any species and demonstrates the power of large-scale epigenotyping in ecological studies. For conservation purposes, resident and migratory rainbow trout are often managed separately based on their environmental and genetic variation. Careful consideration should also be given to the mechanisms by which these factors may interact to produce observable traits in this and other species.
Contact: Melinda Baerwald email@example.com
Reference: Melinda R. Baerwald, Mariah H. Meek, Molly R. Stephens, Raman P. Nagarajan, Alisha M. Goodbla, Katharine M.H. Tomalty, Gary H. Thorgaard, Bernie May, and Krista M. Nichols. 2015. “Migration-related phenotypic divergence is associated with epigenetic modifications in rainbow trout.” Molecular Ecology. doi:10.1111/mec.13231