Stronger Parental Than Temperature Effects on Methylation in Juvenile Brown Trout (<i>Salmo trutta</i>)

Epigenetic modifications, particularly DNA methylation, are increasingly recognized as mechanisms underlying phenotypic plasticity and potential mediators of transgenerational responses to environmental change. We investigated the persistence of early life temperature-induced DNA methylation changes and the role of parental life history in shaping methylation patterns in juvenile brown trout (<i>Salmo trutta</i>). Fertilized eggs from crosses of anadromous and resident trout were incubated under natural or elevated temperatures (by +3°C) until first feeding, after which all fish were reared under common conditions. Whole-genome bisulfite pooled sequencing was conducted on juveniles 10.5 months post-fertilization. We found weak and inconsistent evidence for persistent temperature-induced methylation changes, with little overlap among different parental cross types. In contrast, parental life history, particularly maternal origin, significantly influenced offspring methylation patterns. Maternally derived differences were more extensive than paternal effects and were enriched for genes related to metabolism, nervous system function, and digestion, suggesting potential adaptive relevance. These findings suggest a limited long-term impact of early-life thermal conditions on methylation and emphasize a stronger role of transgenerational epigenetic effects in brown trout. Given that climate change is expected to alter thermal regimes in future aquatic ecosystems, our results, along with other recent publications, suggest that parental environmental history may be a more significant driver of epigenetic variability than the temperature experienced during early life. Understanding such mechanisms is critical for predicting how populations may respond to ongoing and future climate change.