Stronger parental than temperature effects on methylation in juvenile brown trout (Salmo trutta)

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 (Salmo trutta). 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 highlight 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 temperature experienced during eary life. Understanding
such mechanisms is critical for predicting how populations may respond to
ongoing and future climate change.