Transcriptional variation among populations of salmon: The genetic architecture of local adaptation

Chinook salmon (Oncorhynchus tshawytscha) life history provides an excellent opportunity to study the molecular mechanisms of selective divergence. I analyzed gene transcription in Chinook salmon that were created in a replicated North Carolina II breeding design to estimate quantitative genetic parameters that contributed to among-population variation in gene expression. Following Fischer’s fundamental theorem, transcriptional variation of many genes was due to additive effects. However, a surprising number of genes exhibited non-additive genetic and maternal effects on transcription, and these effects may explain the high potential for rapid population-level evolution in salmon. Indeed, populations differed substantially in gene transcription. Pervasive non-additive gene expression raises concerns for conservation strategies that result in intraspecific hybridization. I document extensive amounts of reciprocal hybrid disagreement in gene transcription, indicative of breakdown of gene expression regulation complexes that are likely co-adapted. Anomalous hybrid gene transcription warrants caution for conservation strategies that employ mixing natural stocks.